Lemon RX. Stabilizer PLUS 7-Channel Receiver. Reference Guide

Transcription

1 Lemon RX Stabilizer PLUS 7-Channel Receiver Reference Guide Contents An Introduction to the Lemon Stabilizer PLUS...1 Using the Lemon StabPLUS...3 Capability with Various Transmitters... 3 Optional Ways to Use the StabPLUS... 4 Transmitter and DIP Switch Setup... 5 Receiver and Servo Power Supply... 6 Dual Rates and Expo in the Transmitter... 7 Installation...7 Orientation of the Receiver Unit... 7 Mounting... 9 Minimizing Vibration... 9 Setting up Stabilization Stabilizer Response and Direction Gain Adjustments Setting Stabilizer Gain Pots Optimizing Gain Autolevel Gain Master Gain Control Resetting the Stabilizer Resetting Stabilizer Level Resetting Stick Neutrals Initial Test Flying with Autolevel mode Controlling the Way it Works Selecting the Operational Method Selecting the Mode How Mode Control Works Changing Mode Order and Autolevel Setting Mode Change and the Toggle Gesture Using a Two-Position Switch to Control Stabilization Startup Binding Stabilizer Condition after a Rebind Failsafe Options Understanding the Three Different Calibrations" Why the Gyros Need Occasional Recalibration What the LEDs Mean... 23

2 Further Options Stabilizer Always-ON Hardware Reset Mixing Mixing and the Lemon Stabilized Receiver WARNING: Flaperons and Aileron Differential Stabilizer Modes: Gyro vs. Autolevel Appendices Appendix 1: Diversity and RSSI Appendix 2: Range Checking Appendix 3: Versions of the Lemon StabPLUS Receiver Appendix 4: Using the StabPLUS with a DX6i Appendix 5: Using an Open Source Transmitter (Taranis, 9XR, etc.) Appendix 6: Throttle Drift in Autolevel Mode StabPLUS Ref Guide v.1b.doc ii

3 Lemon Rx Stabilizer PLUS A DSMX compatible Receiver with Integrated Stabilizer Identification of components An Introduction to the Lemon Stabilizer PLUS The Lemon 7-channel Stabilizer PLUS (referred to from now on as the StabPLUS) is a versatile integrated, full range, DSMX compatible receiver and stabilizer, primarily intended for electric models, but suitable for use with some IC (fuel-powered) models too. It is a development of the original Lemon Stabilizer with some additional features, including an Autolevel mode, but does not replace it. The Lemon philosophy is that the StabPLUS should be simple to set up without using any PC, smart phone or programming box for configuration. In the words of the CEO, It is designed for the flier who does not want to spend time with a graphical interface for various settings but just wants to enjoy flying at the field, using a screw driver to set just about anything easily and quickly. I also think that too much autonomous capability would make the plane become an FPV for aerial photos. Just not fun to fly. The Lemon StabPLUS is very small and light. Despite its low cost, it offers both high quality and high performance. The Lemon StabPLUS is available with dual diversity antennas for enhanced reliability of the radio link. StabPLUS Ref Guide v.1b.doc 1

4 The StabPLUS automatically switches from DSMX to DSM2 and so will work with most Spektrum technology transmitters, including the basic DX4e and DX5e units and the popular DX6i, as well as computer transmitters such as DX6, DX7s, DX8 (both versions) and DX9 and the JR9303/9503. It can also work with open source transmitters such as Taranis and Turnigy 9XR using an add-on DSM2 or DSMXcompatible module, although not all available modules necessarily work correctly. 1 Organization of the Instructions For basic step-by-step guidance in setting up and using the Lemon StabPLUS, go to the Essential Instructions, available at: This Reference Guide is intended to provide additional material on installing, using and understanding the StabPLUS, as well as optimizing the reliability of the radio link. Because it is a reference guide it may include some repetition of material in different sections. For simplicity, a first reading should skip over the footnotes which provide clarifications or explanations of exceptions and special cases. Do come back and reread them however as there may be some important information for particular situations. These documents are prepared by jj604 (John) and Daedalus66 (Nigel). We have worked closely with the people at Lemon RX but are not paid by, or associated with, the manufacturer. The Lemon 7 channel StabPLUS combines the ease of use and performance of the regular Lemon Rx 7- Channel Stabilizer with enhanced features that give greater flexibility and security of operation. In addition to the three internal gyros, which allow normal Gyro (rate) stabilization, the PLUS adds three accelerometers, which make it possible to sense the direction of down and therefore enable automatic leveling. 2 The StabPLUS has three possible operating modes, depending on the capability of your transmitter: OFF (no stabilization) Gyro (rate stabilization) Autolevel (self-level plus limited bank and pitch) In addition, Autolevel mode has two settings: Beginner (very restricted roll and pitch angles) and Advanced (much greater maximum angles). The StabPLUS provides built-in mixing capability for elevon (delta) and V-tail, and supports dual ailerons on separate channels. Note, however, that flaperons and aileron differential cannot be used when in Autolevel mode. 3 The StabPLUS is available with two types of antenna: a single short antenna, which is suitable for most line-of-sight flying, or twin diversity antennas to provide even greater radio link reliability. Top-pin and end-pin options are available in the twin antenna diversity version. The single antenna version is available only in top-pin configuration. 1 In particular the Spektrum DM8 and DM9 modules and some versions of the OrangeRX transmitter module are known not to work reliably with this receiver. Always range test any particular combination before flight. 2 You will sometimes see the regular Lemon Stabilizer called (confusingly) a 3-axis and the StabPLUS a 6-axis stabilizer. The stabilizer only corrects in the three flight axes no matter how many gyros/accelerometers it has. 3 See page 27. StabPLUS Ref Guide v.1b.doc 2

5 The StabPLUS has been designed to be as easy as possible to use and to serve as a drop-in replacement with added Autolevel functionality for the original seven channel Lemon Stabilizer. Don t think of the StabPLUS as a low cost Spektrum SAFE system. While it has some of the features of the SAFE approach, the StabPLUS should be seen as an excellent rate stabilizer with some additional limited Autolevel functionality. The integration of a proven DSMX receiver and well-optimized stabilizer satisfies one main design aim of simple installation in electric powered models. At a minimum, the StabPLUS uses the four flight 4 control channels (TAER), plus channel 5 (Gear) for control of stabilizer mode. The maximum capability of the StabPLUS, with an eight or more channel transmitter and in Always-ON configuration, is to use channels 1 to 7 for flight control, flaps, landing gear, etc. and have in-flight adjustable stabilizer gain on channel 8. 5 Using the Lemon StabPLUS Capability with Various Transmitters The minimum number of transmitted channels required in order to use the stabilizer with a conventionally configured, electric-powered, three-axis plane without any additional features like retracts or flaps is five. That covers the four flight channels: Throttle (channel 1), Aileron (channel 2), Elevator (channel 3) and Rudder (channel 4); plus Gear (channel 5) to switch the stabilizer on and off in flight. All full range Spektrum transmitters have at least five controllable channels and thus can be used with the Lemon stabilizer. 6 The computer transmitters offer the following possibilities. With a DX6i, DX6 or DX6e, Aux1 (channel 6) can be used to control one of three main possibilities: Retracts, or Flaps, or A second aileron servo (as in a dual aileron setup). A DX7 or DX7s enables the use of Aux2 (channel 7); thus a 7-channel transmitter enables any two of the above three possibilities. A DX8 or higher transmitter enables internal use of Aux3 (channel 8), giving Master Gain control. It does not provide an additional free channel. Note that no amount of transmitter mixing can change the receiver s use of channel 5 (commonly labeled Gear) or channel 8 (commonly labeled Aux3). These channels are committed within the receiver to stabilizer Mode and Master Gain respectively. You can on some transmitters adjust which switches, knobs or sliders control those channels, or you may be able to use mixes from other channels for this purpose, but these channel assignments within the receiver cannot be altered. 4 The StabPLUS is designed for aileron control, but some people report using it successfully in three channel models (Rudder, Elevator, Throttle) by plugging the rudder servo into the aileron channel. 5 The Stabilizer PLUS has user pre-set failsafe (which the original Stabilizer lacks) and so is suitable for use with internal combustion (fuel) powered models. If you intend to use it in an IC model (gas or glow), please read Minimizing Vibration on page 9. 6 Gear (channel 5) is operated by the ACT/Aux switch on a DX4e and the Ch 5 switch on a DX5e. StabPLUS Ref Guide v.1b.doc 3

6 It follows from all this that you cannot on a conventional powered model have Stabilizer Mode control plus all three of: dual ailerons and independent flaps and independent gear, even with an 8-channel transmitter. There are simply not enough channels available in the Lemon receiver. The exception to all this is that the StabPLUS provides an Always-ON capability, which allows the stabilization to be turned on (either Gyro or Autolevel) permanently. This frees up channel 5 for other uses, such as retractable landing gear but loses the in-flight OFF switch. To summarize, practical arrangements for a powered plane, using a seven or more channel transmitter and a StabPLUS receiver with channel 5 for in-flight mode control include: A single Aileron servo (or two servos on a Y-cable) on Ail (channel 2), with Flaps on Aux1 (channel 6) and Retracts on Aux 2 (channel 7); Separate Aileron servos on Ail (channel 2) and Aux1 (channel 6), with Retracts OR flaps on Aux 2 (channel 7); this arrangement would allow use of the flaperon function in Rate mode. Using Always-ON makes one more channel available. So you can have separate Aileron servos on Ail (channel 2) and Aux1 (channel 6), with Flaps on Aux 2 (channel 7) and retracts on Gear (channel 5). Optional Ways to Use the StabPLUS The StabPLUS can be set up to operate in three different ways. The options are: 1. With stabilization turned permanently OFF. It then acts as a normal 7 channel non-stabilized receiver. This option is set when the white DIP switches J4 and J5 are both Off. 2. With stabilization mode switched by channel 5. This is the most common way and leaves 6 channels available for flight controls. Channel 5 output is unavailable for most practical purposes. This is the most likely way to use the StabPLUS. 3. With stabilization turned permanently ON. Using the Always-ON setting, Channel 5 is available and is commonly used for Gear. However the stabilization mode cannot be changed, nor can stabilization be turned off in flight. 7 The table below provides a detailed chart of the various combinations of control functions available with transmitters that have different capability. Channel 1 Thr 2 Ail 3 Ele 4 Rud 5 Gear 6 Aux1 7 Aux2 8 Aux3 Pins None Stab OFF Throttle Ail/RAL Elevator Rudder Gear Aux1/LAL Bind/Aux2 Stab ON Throttle Ail/RAL Elevator Rudder (Mode) * Aux1/LAL Bind/Aux2 (Gain) Always-ON Throttle Ail/RAL Elevator Rudder Gear Aux1/LAL Bind/Aux2 (Gain) * Although the channel 5 (Gear) signal appears on these pins, it is not useful as it changes with the mode command (unless the StabPLUS is set to Always-ON or stabilization is disabled by setting J4 and J5 to off). 7 If you have an eight channel or better transmitter you can reduce Master Gain to zero (or very low), which effectively shuts stabilization off. See Master Gain Control on page 12. StabPLUS Ref Guide v.1b.doc 4

7 Transmitter and DIP Switch Setup Lemon Stabilizer PLUS Receiver Reference Guide The transmitter channel setup, as well as DIP switch settings and wing type, are shown below for all supported configurations. Check that the servos and ESC are in the appropriate slots on the receiver. Because it is used internally by the receiver to turn stabilization on/off, normally the Gear slot (channel 5) will be empty. This is indicated by the XXX in the lists below. Set switches J4, J5 and J6 on the receiver as indicated below. For recent Spektrum transmitters, set the Aircraft Type menu as shown. In all cases, including V-tail, the tail type is Normal. Note that mixing for elevons or V-tail is ALWAYS done in the stabilizer; the transmitter MUST NOT be programmed for elevons or V-tail. Transmitter and Switch Configurations Conventional controls with single aileron servo or two aileron servos with a Y-cable: Channels: 1 THR, 2 AIL, 3 ELE, 4 RUD, 5 XXX. Switches: J4 ON, J 5 ON, J6 OFF. Wing type: Normal. Conventional controls with aileron servos on separate channels: Channels: 1 THR, 2 R-AIL, 3 ELE, 4 RUD, 5 XXX, 6 L-AIL. Switches: J4 ON, J 5 ON, J6 ON. Wing type: Dual Ail. 8 Elevon (Delta wing) control configuration: Channels: 1 THR, 2 R-ELEV, 3 L-ELEV, 4 RUD 9, 5 XXX. Switches: J4 ON, J 5 OFF, J6 OFF. Wing type: Normal (NOT Delta). V-tail control (single aileron servo or Y-cable): Channels: 1 THR, 2 AIL, 3 R-TAIL, 4 L-TAIL, 5 XXX. Switches: J4 OFF, J 5 ON, J6 OFF. Wing type: Normal. Tail type: Normal (NOT V) V-tail control (separate aileron servos): Channels: 1 THR, 2 R-AIL, 3 R-TAIL, 4 L-TAIL, 5 XXX, 6 L-AIL. Switches: J4 OFF, J 5 ON, J6 ON. Wing type: Dual Ail or Flaperon. 8 Tail type: Normal (NOT V). Important safety warning: Leave the motor unconnected or remove the propeller when testing or programming. Electric models can bite! 8 Flaperon wing type can also be used, BUT read the important WARNING on page 27 before activating a Flaperon configuration. 9 Only used if the model has a separate vertical rudder. StabPLUS Ref Guide v.1b.doc 5

8 Lemon Stabilizer PLUS Receiver Reference Guide This table pulls the information together for easy reference: Summary of Settings for Various Control Configurations Wing Type Channel Assignments Model Type * 6 7** Conventional (one ail channel) Thr Ail Ele Rud Mode?? Conventional (two ail channels) Thr RAil Ele Rud Mode LAil? Elevon/ Delta Wing Thr RElev LElev Rud Mode?? V-Tail (one ail channel) Thr Ail RTail LTail Mode?? V-Tail (two ail channels) Thr RAil RTail LTail Mode LAil? 8*** Master Gain Master Gain Master Gain Master Gain Master Gain Stabilizer Switches J4 J5 J6 Normal X Dual Ail Normal X X Normal X X Dual Ail X? indicates available for any function (such as Gear or Flaps). * If the StabPLUS is set to Always-ON, channel 5 (Gear) becomes available for other functions. ** Use of Channel 7 (Aux2) requires a transmitter with more than six channels such as a DX7/8/9. *** Channel 8 (Aux3) is internally wired for Master Gain and is not usable for any other function. Receiver and Servo Power Supply The Lemon StabPLUS has a supply Voltage Range of V. A standard 5V or 6V BEC, or a 4 or 5 cell NiMH pack are common power sources. A 2S LiFe receiver pack is also suitable (7.2V). A 2S LiPo pack, however, is NOT suitable, as it can reach 8.4V when fully charged. Power supply in all stabilizer installations is more critical than for an unstabilized receiver, as the stabilizer works the servos more frequently and harder than a human pilot does. But for an autolevelling stabilizer like the StabPLUS reliable power is even more important than for a simple rate stabilizer (like the regular Lemon). The reason is that if the autolevelling stabilizer loses power for any significant time it will go through an initialization routine. You will have no control during this time. The StabPLUS has a very high tolerance for short power drops (brown outs) but if they exceed about a second it will restart itself and be out of action for up to 20 seconds. Lemon recommend using a stand-alone BEC, or ESC with integral BEC, that has 50% more current capacity than is required in a non-stabilized setup. In practice BECs commonly come in 3A and 5A sizes. For smaller park flier planes an integrated or separate 3A BEC will normally do fine; a switching-type is preferable to a linear one. In larger planes a separate 5A switching BEC is probably good insurance. In some cases an even larger BEC may be advisable depending on the servos size and load. StabPLUS Ref Guide v.1b.doc 6

9 Dual Rates and Expo in the Transmitter Dual Rate adjusts the amount of response of the control surface to transmitter inputs. Many transmitters allow use of triple rates for more variety in adjustment of control throw. At 100% setting of D/R, the throw is as set in the Travel menu under Servo Setup in recent Spektrum transmitters. D/R enables the rate to be reduced for smoother control. A good starting point for D/R is to set High Rate at 100% and Low Rate at 65-75% for each axis. 10 Expo works with D/R to change the control response from linear to an S-curve, flattened around neutral and steeper as the stick approaches the ends of its travel. In effect, on Spektrum transmitters positive expo gives a lower control rate around neutral and progressively higher rates at bigger stick movements. A typical Expo value of 20-30% softens response around neutral and can make smooth flying easier. Stabilization settings also affect the response of the model to the transmitter sticks, typically reducing sensitivity with an expo-like effect. To achieve your preferred response, you may need to adjust your rates and expo once you find out how the model reacts. Note that for OFF and Gyro modes, the dual rate and expo settings determine stick response but don t affect how the stabilization works. That is entirely done within the stabilizer. Things are different in Autolevel, in that aileron and elevator control throw, together with the setting of Autolevel to Beginner or Advanced, directly determine the maximum angles of bank and pitch possible. Consequently, for optimum control, 100% rate and no expo is normally used in Autolevel mode. Installation Orientation of the Receiver Unit The stabilizer must be installed with the pins toward the tail of the aircraft and aligned with the centerline but four orientations are available Upright with DIP switches pointing to sky. Inverted with DIP switches pointing to ground. Vertical with DIP switches pointing to left or right of the aircraft. The most common arrangement is to mount the stabilizer level and upright, aligned with the centerline of the fuselage, with the connector pins toward the tail. The StabPLUS autosenses its orientation if you do an initial calibration toggle gesture and will work properly if rotated 90 on the roll axis. This means that you can fasten it to the flat side of a profile aircraft. A common arrangement that also presents no problems is mounting the stabilizer upside down for access from the bottom of the model. It should not however be rotated so that the pins are facing forward. The stabilizer has not been tested for operation this way If using a DX4e, DX5e or DXe, the built-in D/R function gives rates of 100% (Position 0) and 75% (position 1). 11 Some users with difficult installation issues have reported success when mounting the stabilizer with pins forward. Lemon advise that this may work satisfactorily but they have not tested it under all conditions and therefore they do not recommend it. StabPLUS Ref Guide v.1b.doc 7

10 Not only must the stabilizer be correctly oriented in the model but it is also influenced by the actual positioning. It is a good idea to place a stabilizer that contains accelerometers like this one does as close to the CG of the plane as is reasonably practical. Although a good principle, in practice people have found that stabilizers such as the Lemon PLUS still work quite effectively when placed some distance from the CG although sensitivity and precision may be affected a little. During the initialization process, the accelerometers determine the direction of maximum gravitational force and identify that as Down. This is then recorded as the Z axis of the stabilizer. Whenever auto leveling is engaged the stabilizer attempts to control the aircraft so that the current down direction aligns with the Z axis. It really only needs to know which axis is the Z axis and the direction of the current gravity force in able to do this. The effect is to bring the stabilizer back to the same orientation it was when it was initialized and with the X and Y axes level. It depends for accuracy on the stabilizer being correctly mounted in the aircraft. If the stabilizer is misaligned during installation then the aircraft will fly in a misaligned way. The pitch/roll offset calibration process on page 13 will correct for this by setting an offset that the stabilizer remembers until the power is removed. The plane has to be held level during this initialization. What does this mean in practice? The stabilizer only needs to know which direction is down and establishes this from the direction of earth s gravity sensed by the inbuilt accelerometers. It then knows where the Z axis should point (up and down) when auto leveling is initiated. When that happens it manages the control outputs to attempt to make the bottom of the stabilizer level. That is, the stabilizer will control the plane such that the circuit board (or the bottom of the case) will be normal to the gravity vector. Normal as used here is a mathematical term meaning a line that is at right angles to a flat surface. Because of this it is important to place the stabilizer flat in the plane. To emphasize, unlike some other auto leveling stabilizers, if you do not do a deliberate toggle, level flight attitude is NOT set by default as the attitude of the plane at power on but by the alignment of the stabilizer in the airframe. This makes it simpler and fairly foolproof but only if you mount the stabilizer level. The pitch/roll offset calibration process can be done during the 9 seconds of Indicator 1 flashing and will set an offset that the stabilizer remembers, even when the power is removed However this all assumes the 3 flight control sticks are at standard neutral with no trim. If the sticks are deflected or trim is applied in Auto level mode, the stabilizer thinks you want to pitch or roll the plane and will move the controls to respond in the correct direction. What it will try and do is make the z axis line up with gravity PLUS some deflection angle set by the sticks. Clearly if you apply trim to make the plane fly StabPLUS Ref Guide v.1b.doc 8

11 level with the stabilizer off, then you switch it to auto level, the stabilizer will attempt to change the pitch or roll angle because it thinks you want to initiate that response. To accommodate this, the stabilizer is able to reset what it thinks is stick neutral if you do a toggle of channel 5 at any time. In practice what this means is you can trim the plane to fly as you want it, then do a toggle of the channel 5 switch. This tells the stabilizer to treat the current trim and/or stick position as neutral stick. The setting will remain until you toggle again and is not reset at power on. This toggle reset avoids having to mechanically adjust a model to fly precisely level when the trims and sub trims are set at zero. Lemon recommends that you do this when the plane has landed back on the ground and is stationary. It is possible to do a trim toggle in flight but results may sometimes be unpredictable. HINT Don t get too caught up in this. Lemon have tried to make everything as simple as possible. Provided you install the stabilizer flat in the plane with its case aligned with level flight direction, and avoid excessive transmitter trim or sub trim, a level reset is often not needed. Only Auto level is affected anyway, not Gyro (Rate) stabilization. If you do see significant climb/dive or roll when you switch to Autolevel mode, it may be a sign that your model has too much transmitter trim; you should correct for this by doing a trim reset toggle or even better by adjusting the controls mechanically if possible. Mounting All stabilizers must be protected from vibration and shock, yet attached securely enough to follow the movements of the model and cannot come loose. The double-sided mounting tape provided with the Lemon StabPLUS offers the simplest solution. Use it to attach the receiver in the appropriate attitude to a flat surface in the model. Make sure the surface is clean, the attachment is secure and the receiver case is not touching any part of the model. Good quality servo-mounting tape or 3M (Scotch) Permanent Outdoor Mounting Tape is also suitable for this purpose. Do not use the common indoor white foam mounting tapes. Mounting with adhesive tape can make subsequent removal of the unit difficult. Accordingly, Velcro type tape can be used. Cover the whole bottom of the receiver with the fuzzy (loop) side of the material. Use a patch of the hook-side material at least as big as the case to avoid the possibility of the stabilizer wobbling. Check to make sure the stabilizer is firmly attached as if not the stabilizer will be trying to level itself and not the model in Auto level mode. Be careful when removing the receiver, as the case is only held together by two small screws and two friction pegs. To provide reinforcement, you may wish to apply transparent tape to the case sides. These methods are suitable for electric-powered models, but may not provide sufficient isolation in the harsher environment of a fuel-powered (IC) model. Minimizing Vibration Autolevel stabilizers are particularly susceptible to vibration. It is therefore very important, even for an electric model with a properly mounted receiver, to eliminate sources of vibration. Balance the propeller and check for any out-of-true running of the motor shaft or bearings. A well-balanced electric model should show no noticeable vibration in any part of its speed range. StabPLUS Ref Guide v.1b.doc 9

12 Internal combustion (IC) engines are however vibration generators and there is little you can do to stop that. Be aware that flight stabilizers can be adversely affected by regular significant vibration and there is no simple single solution. The StabPLUS has been designed with additional vibration rejection software and should perform better than some other stabilizers but there is no guaranteed straightforward solution that fits all cases. People have had success using the anti-vibration mounts sold for FPV cameras and with various DIY solutions which normally rely on a mounting tray suspended by rubber bands from the vibrating airframe. Addition of weight to the tray to lower its resonant frequency can help but the calculation of such a solution is not straightforward. The best advice for anyone wanting to use the StabPLUS in an IC powered aircraft is to try it and see but make sure you can turn stabilization off in a hurry. You may be fortunate and find there is no issue or you may not. Vibration problems normally show themselves as erratic control behavior or by a constant drift from the set Autolevel attitude, sometimes after a stable period. Setting up Stabilization Stabilizer Response and Direction The starting point for stabilizer adjustment is with the three onboard gain adjustment pots set at 12 o clock (straight up). If Master Gain (channel 8) is available, set it in middle position; check the transmitter s Monitor screen to make sure Master Gain is at 0%, corresponding to a Gain of 1x. The diagram shows how the surfaces should respond to movement of the model about each axis. It is easier to see this in Auto level mode. When the model is rolled to the right, the right aileron should go down and the left aileron up to resist the displacement. Likewise, when the model pitches nose-down, the elevator should go up to compensate. And when it yaws nose-right, the rudder should go left. However the rudder will only pulse then return to neutral. It does not stay deflected. In Gyro mode, the stabilizer only applies a brief pulse of correction in all three axes. The stabilizer knows nothing about the position and attitude of the model, it just responds to momentary outside disturbances. This is ideal for making the model fly more smoothly, much like a bigger and heavier plane, and does not unduly limit the pilot s ability to control the model. By contrast, Autolevel mode introduces a quite different style of control in the pitch and roll axes. In Auto level mode the sticks directly control the attitude of the plane not the deflection of the control StabPLUS Ref Guide v.1b.doc 10

13 surfaces. The stabilizer decides how much surface deflection to give in order to achieve the commanded attitude. The result is that if the sticks are neutral and you deflect the model and hold it at a tilt or roll angle, the elevator or ailerons will deflect and stay deflected. The stabilizer is waiting for the plane to level out before restoring the surfaces to zero deflection. If you find it hard to see the surface movement, temporarily increase the gain by turning the pots fully clockwise or try putting your finger on the hinge line. It is very easy to tell the direction by feel. THIS NEXT THING IS VITALLY IMPORTANT: If stabilization moves the surfaces the wrong way (i.e., to increase the disturbance) your model will be uncontrollable in flight (until you switch off stabilization)! To correct this, change the appropriate switch: J1 (aileron), J2 (elevator) or J3 (rudder). Just as experienced RC pilots check stick directions before the first flight of the day, so a pilot using a stabilizer should check that the surfaces move correctly in response to a disturbance. Gain Adjustments Setting Stabilizer Gain Pots Gain is normally set in Gyro mode to achieve maximum stabilization short of causing oscillation at higher speeds. It is recommended in the Essential Instructions to set the three gain pots at about the 12 o clock position as a good starting point for many models, but this could show some oscillation at high speeds. You may prefer 10 o clock as a more conservative starting point that will still produce noticeable stabilization. For most models, at least one or two gain settings will need to be increased or decreased during flight testing to achieve optimum stabilization. Many models fly with gains between 10 o clock and 2 o clock but some may require minimum gain (< 8 o clock) and some maximum gain (> 4 o clock) on a particular channel. There is no hard rule and gains can only be fine-tuned by observing the behavior of the model at various speeds during flight testing. The StabPLUS gain settings usually need to be higher to achieve a given level of stabilization than those of the regular Lemon Stabilizer. Optimizing Gain To optimize the individual gain settings, it s necessary to perform a couple of test flights in Gyro mode. This will involve landings to adjust each pot on the receiver, followed by retesting in flight, but the basic job can be done relatively quickly. It s a good idea to keep notes. If you have an eight or more channel transmitter, Master Gain can be used to assist the process. If you encountered oscillation on any axis during the initial flight, turn down the gain a little for that axis. Then go through the following steps: StabPLUS Ref Guide v.1b.doc 11

14 Lemon Stabilizer PLUS Receiver Reference Guide Increase the Rudder pot setting by about two hours. Take off with stabilization OFF. Turn ON at a safe height with the model in level flight. Watch for oscillation on the yaw axis ( tail wag ). Do a shallow dive to pick up speed and again watch for oscillation. Land and adjust the rudder pot as required. If there was no oscillation, even when diving, turn the pot up further. If there was oscillation, turn the pot down a bit. Take off and retest. You re aiming to set the pot fairly close to the maximum gain that doesn t produce oscillation in any normal flying. So if necessary, repeat until you encounter oscillation or reach the maximum. When satisfied with the rudder gain setting, repeat the process for the elevator setting. Finally follow the same procedure to set the aileron gain pot. Note that aileron is often the most sensitive control, so increase gain in moderate steps. Many people find that on typical models the rudder gain can be quite high (or even full) while aileron and elevator end up somewhere in the range of 9 o clock to 2 o clock, but the settings vary with factors such as model design, flight speed and control setup. If you have Master Gain available, you can greatly speed up the process of setting individual gains. In the air, advance the channel 8 (Aux3) control gradually until you observe oscillation on an axis. Note which axis, land and turn down the gain on the corresponding pot. Repeat until all three axes are set so that with the Master Gain at midpoint, there is no oscillation. Turning up Master Gain to 2 or 3 o clock should start to show signs of oscillation. HINT: It s best to do the initial setup and tuning in fairly calm conditions to avoid confusing stabilizerinduced oscillation with buffeting caused by turbulence. Once you have things adjusted, test the effectiveness of stabilization by flying in windier weather, turning Gyro stabilization on and off. You should see a noticeable improvement in smoothness with Gyro stabilization turned on. Autolevel Gain Normally, setting the gain level for Gyro mode as described above should ensure a satisfactory gain level for Autolevel mode. When you switch to Autolevel you may see what appears to be intermittent oscillation even at lower speeds. The model rolls for example and then seems to bounce back slightly. This is characteristic sometimes of Autolevel operation, and is not a problem. Master Gain Control If the transmitter has eight channels or more, then Master Gain is available on Aux3 (channel 8) and controls the overall gain of the stabilizer system. If not, Master Gain is automatically set to 1. The Master Gain function multiplies the setting of the individual gain pots by a factor that can range from 0 to 2. In other words, with Master Gain turned full up the gain setting of each individual axis will be roughly doubled. If turned full down, there will be little or no stabilization on any axis, regardless of the setting of the pots. For Master Gain to be useful it is best controlled by a knob, slider or lever on the transmitter. On a DX8G2, for example, the Right Knob is used (labeled RKnb in Channel Assign). StabPLUS Ref Guide v.1b.doc 12

15 To check operation, make sure Gyro or Autolevel stabilization is ON (green ON or red/green alternating). Look at the Monitor screen on the transmitter to make sure the value is going from -100% to 100% when you turn the control through its full range. You can use channel reverse to change the direction of operation of the knob/slider/lever controlling the Aux 3 channel. Most people intuitively think of clockwise as increase for a knob and upwards as increase for a slider or lever. Understanding Master Gain Think of the three stabilized channels as the three inputs of a three-channel audio mixer. The on-board rotary controls or pots (potentiometers) are like the three individual volume controls. The Master Gain is the overall volume control. It modifies the levels of all three channels, turning them up or down together. The individual gain values are multiplied by the value of the Master Gain, controlled by Aux3 (channel 8). With the Master Gain in the center (channel 8 = 0%) the gain value is 1 and the individual gain values set by the pots are unaffected. If channel 8 is at -100%, Master Gain is very low and the individual gains become very small. If channel 8 is at +100%, the Master Gain is nearly 2x and the individual gains have almost twice their usual effect. To turn the stabilizer completely off with Master Gain, travel for the low end of channel 8 must be set to -150%. This is important if you are using a Mix on channel 8 to turn the stabilization function completely off. Likewise, to get the maximum Master gain value of 2x, channel 8 must be at 150%. In practice many people initially set channel 8 at 0% (middle position) so that the Master Gain multiplier is 1x, then they adjust the individual gains to give good stabilization without any oscillation. Master Gain can greatly help in this process and can subsequently be used to turn the overall gain up or down to suit changing flight conditions. Resetting the Stabilizer Resetting Stabilizer Level There are two reasons for performing a Level Reset : either you have mounted the StabPLUS upside down, on its side or not quite level in the model, or you need to reset the stabilizer s sense of level in order to correct its flight attitude. It s a good idea to do a level reset any time the model displays any strange behavior. Note that Level Reset is mainly about Autolevel behavior. It does, however, serve to inform the stabilizer, quite literally, which way is up, so is also necessary for Gyro mode use if the stabilizer is mounted on edge or upside down. The Essential Instructions provide step-by-step details on the process, but in essence it is as follows. The fundamental element you need to master is the Toggle Gesture : StabPLUS Ref Guide v.1b.doc 13

16 Toggle Gesture Move the Stabilizer Mode switch on your transmitter back and forth as quickly as possible through its full range for 2-3 seconds. This procedure applies to both 2- and 3-position switches. At a minimum the stabilizer needs to see six changes of switch position (see diagram) within 2 seconds, but a few more changes are desirable to guarantee a successful reset. 3-position 2-position Assuming that the receiver was previously bound, power up the transmitter. Apply power to the receiver and note that the Green/Blue LEDs next to the pushbutton will be flashing for about 8-9 seconds. Within this period complete the Toggle Gesture (above). If the stabilizer alignment is within +/- 20 degrees of absolute level, the current position of the model will be used as level flight. Successful level calibration will be indicated by the green LED light next to the header pins flashing four times at the end of the 9 second period. The stabilizer will then leave level calibration mode and enter whatever normal operation mode is set by the Mode switch (channel 5). If alignment is NOT within +/-20 degree tolerance (the stabilizer is installed with a large angle offset from the reference axis in either pitch or roll) or significant movement occurred in the calibration period, the red LED light next to the header pins will flash twice to indicate failure. You can attempt to calibrate the unit any time within the 9 seconds period by toggling the switch again. If no calibration is carried out, or calibration fails after 9 seconds, then 0 degree offset with the reference axis will be used. That is, if no previous toggle has been done, the stabilizer will assume that its case is upright (i.e., with label on top). This is fine for a stabilizer mounted flat on the floor, right side up, but can be catastrophic for an inverted or a side mounted one! If you are using anything other than the default level and flat in the model installation, make sure you get the 4 green LED flashes at some stage before leaving the ground. Resetting Stick Neutrals To ensure optimum stabilizer performance, after any major adjustment of the trims or subtrims you should use the toggle gesture (as defined above) to reset the stabilizer's values for the stick neutral positions. This is an entirely separate process from resetting level and can be done at any time after the stabilizer has completed its initialization. During the reset, the aileron, elevator and rudder sticks and the corresponding trims must not be moved. With the transmitter and receiver ON, and leaving the sticks and trims untouched, move the Stabilizer Mode (Gear) switch as quickly as possible back and forth for at least 2 seconds. The StabPLUS performs best, especially in Autolevel mode, when trim and subtrim settings are kept to a minimum. Where possible, use mechanical adjustments to eliminate the need for large trim offsets, then reset the stick neutrals as described above. StabPLUS Ref Guide v.1b.doc 14

17 A Practical Note on Stick Centring (resetting stick neutrals) Do not get over-concerned about stick centering and calibration. The last known good value will be used even after a power cycle. So the next time when you go to the field with the same plane, just turn on the transmitter and StabPLUS. The old values will be used until the next toggling. Under some circumstances, however, such as when trim or subtrim have been set to extremes, the stabilizer may have difficulty identifying level correctly and require a neutral reset. Initial Test Flying with Autolevel mode For initial test flights, after the 9 second calibration period is completed and before taking off, starting in the OFF position, perform a toggle gesture with the Mode switch to store the neutral positions of the controls, as described above. This toggle should be done before each flight if any of the trims and/or subtrims are far from zero. This is particularly important if you will be using the Autolevel mode. 12 Check that the stabilizer is turned OFF. Take off and fly around, adjusting trim as necessary. Make sure the model flies properly without stabilization. If you make major trim adjustments, land and do a toggle to enable the stabilizer to store the new neutral positions. At a safe height, use the Mode switch to turn the stabilizer ON in Auto level mode. If the model rolls, dives or turns suddenly, at least one of the gyro direction switches (J1, J2, J3) is incorrectly set. Switch OFF the stabilizer immediately! Land and fix. Likewise if you encounter major oscillation, land and reduce gain in the axis/axes involved. Assuming the model does nothing scary, continue flying to explore the action of the stabilizer. Do a shallow dive to pick up speed and watch for oscillation on one or more axes. If it happens, just throttle back and slow down. Oscillation is quite different from control surface flutter and is generally not destructive. Notice how the model handles with the stabilizer turned on. It will be much less responsive in the pitch and roll axes and the response will be quite different. In Auto level the amount of deflection of the Aileron and Elevator sticks control the attitude of the plane with respect to the ground not the amount of deflection of the control surfaces. There is a detailed explanation starting on page 28 which you should read if you are unfamiliar with Autolevel stabilization. Experiment with dual rate settings. Turn stabilization off and on to get familiar with its effects. Controlling the Way it Works Selecting the Operational Method The StabPLUS can be set up to operate in three different ways: 1. With stabilization mode switched by channel 5. This is the most common way and leaves six channels available for flight controls. Channel 5 output is unavailable for all practical purposes since its output always operates in lock-step with the stabilizer mode selection. This is the normal default operation as long as either or both of DIP switches J4, J5 is ON. 12 After the first toggle when setting up, and if little trim/subtrim is used, this step can be omitted if you use Gyro mode. However in Autolevel mode any offset from stick center after trimming a plane s servo without neutralizing it will cause the stabilizer to shift the plane s roll or pitch angle and it will not fly level. StabPLUS Ref Guide v.1b.doc 15

18 2. With stabilization turned on permanently using the Always-ON option. Channel 5 then becomes available and is commonly used for retractable landing gear. Using this option, the stabilization mode is fixed on either Gyro or Autolevel, and this cannot be changed in flight. Nor can stabilization be turned OFF (although with an eight-channel transmitter the same effect can be obtained by reducing Master Gain to zero, that is -150%). 3. With stabilization deactivated by setting DIP switches J4, J5 and J6 all to OFF. The StabPLUS then acts as a normal seven channel non-stabilized receiver. There will be no stabilization and no internal mixing within the receiver. The Always-ON option is selected by re-binding the stabilizer, waiting for the initialization sequence to finish, and then setting the Mode switch to either Autolevel (Indicator 2 Red/Green LED alternating flashes) or Gyro (rate) mode (Indicator 2 Green LED ON). Now press and hold the button until the Indicator 1 Blue LED is ON solidly, signaling that the stabilizer is Always-ON in either Autolevel or Gyro mode (as selected during setup). The channel 5 (Gear) output will no longer have any effect on stabilizer mode and can be used as a normal servo or retract input. The channel 5 switch, however, can still be used to do the toggle gesture to reset level or stick neutrals. Remove the bind plug and power cycle the unit. Selecting the Mode Stabilizer Off: The stabilizer can be turned off permanently and used as a standard 7 channel nonstabilized DSMX compatible receiver (by setting the on-board DIP switches), OR, if stabilization is active, the stabilization function can be turned off in-flight using channel 5 as a control. Gyro (Rate) Mode: In this mode the PLUS functions exactly like the regular Stabilizer, providing rate stabilization that smooths out flying for fixed wing models, even in windy and turbulent conditions. A switch moving channel 5 to 0% turns rate stabilization on. If channel 8 (Aux3) is available on the transmitter, Master Gain can be adjusted in the air to change the overall response sensitivity of the stabilizer. It modifies the gains set by the three pots on the stabilizer (Aileron, Elevator, Rudder). Autolevel Mode: The PLUS can be set up to maintain the model in a level attitude, allowing the pilot to steer it with rudder and/or aileron and control climb and descent rate with elevator and/or throttle. This mode is intended for beginners needing some assistance, for assistance in landing during gusty conditions, and for people flying FPV who want to concentrate on the imagery. Note that Autolevel acts to keep the plane level. It does not know how to maintain a fixed height, as the stabilizer does not contain an altimeter. In this mode, the Stabilizer adjusts aileron and elevator control the plane s flight attitude directly, keeping it level unless otherwise commanded. Stick deflection angle will directly adjust the bank/pitch angle of the plane up to a fixed limit. The Rudder remains unaffected and will move normally according to stick movement but with the addition of Rate stabilization. The Stabilizer has no control of throttle. Throttle stick movement controls power to the motor as usual. StabPLUS Ref Guide v.1b.doc 16

19 How Mode Control Works This table shows the relationship between the percentage value (switch position) of channel 5 (Gear) and stabilizer mode for default and alternate orders. Gear Channel Value Switch Position Position 0 36% to 100% and beyond Default Mode Order (OFF/Gyro/Autolevel) Alternative Mode Order (OFF/Autolevel/Gyro) Function LED Indicator 2 Function LED Indicator 2 OFF Red and Green OFF Red and Green Position 1 35% to -35% Gyro Green only Autolevel Red/Green alternating Position 2-36% to -100% and beyond Autolevel Red/Green alternating Gyro Green only Gyro means basic rate stabilization. The stabilizer will provide an opposite but momentary reaction of the control surfaces if the plane is disturbed. This is the same functionality as the original 7-channel stabilizer. Auto level means that the stabilizer will attempt to bring the plane to an orientation flying straight and level and will maintain that while the sticks are in neutral. The plane is heavily stabilized and this mode is suitable for beginners or FPV imaging. Changing Mode Order and Autolevel Setting With a bind plug inserted across the top (signal) pins of channels 4, 5, and 6 and the receiver powered up, the StabPLUS displays the current state of these two settings. The transmitter is not required. The StabPLUS uses the blue/green Indicator 1 lights to display the Stabilization Mode Order: Default order: OFF/Gyro/Autolevel Indicator 1 green flashing Alternate order: OFF/Autolevel/Gyro Indicator 1 blue flashing The Stabilizer uses the red/green Indicator 2 lights to signal the Autolevel setting: Beginner setting limits the model to gentle bank and pitch angles Indicator 2 Green flashing Advanced setting gives the pilot a greater degree of control Indicator 2 Red flashing. StabPLUS Ref Guide v.1b.doc 17

20 To change one or both of the settings, press the receiver button: for more than 1 second to change the Stabilization Mode Order. for less than 1 second to change the Autolevel mode. When the desired changes have been made, power OFF the receiver and remove the bind plug. The settings will be retained even when the receiver is powered off. Mode Change and the Toggle Gesture The stabilizer monitors the position of channel 5 and notes any mode changes. It counts as a change when the value of channel 5 changes from the previous value. It does not matter what the actual values are, but if the number of changes add up to 6 within any 2 second interval it is regarded as a toggle. It is only the number of changes that matter. For example: 100% to 0% to -100% on a three-way switch is two changes. Flipping back the other way is two more. So one-and a half back and forth cycles gets you the necessary minimum of six changes. On a two-way switch, one movement is one change. So to get six changes, you have to flip three full back and forth cycles. Basically the stabilizer counts the number of any changes on the gear channel in comparison to the last known value. If there are six changes within 2 seconds, a toggle will be triggered. Be aware of this if using a three-position switch for control. Moving from Off to Rate to Autolevel, then immediately back again causes no problem since that is four transitions. But moving Off/Rate/Autolevel and back twice within 2 seconds could unintentionally initiate a trim reset toggle in flight. Using a Two-Position Switch to Control Stabilization The ability to set Mode Order facilitates use of the StabPLUS with transmitters lacking a three-position switch to control channel 5 (Gear). By choosing the appropriate Mode Order, the StabPLUS can be set to use the two position Gear switch to provide access to either Gyro mode or Autolevel mode, but not both. Spektrum transmitters with only a two-position channel 5 switch include older examples of the DX4e and DX5e. A two-position switch normally provides 100%/-100% output with no middle position. Thus in the default Mode Order (OFF/Gyro/Autolevel), the switch will select OFF or Autolevel, while Gyro mode will not be available. Changing the Mode Order to OFF/Autolevel/Gyro will allow the switch to select OFF or Gyro. StabPLUS Ref Guide v.1b.doc 18

21 Startup Lemon Stabilizer PLUS Receiver Reference Guide Assuming a correctly bound receiver and transmitter is on and connected, this is the sequence of events after the power is applied. LEDs Action What s happening STEP 1 Indicator 2 shows rapid green flash for about 1 second Indicator 2 shows rapid red flash for about 1 second STEP 2 Indicator 1 shows slower rapid green/blue flash for about 9 seconds Indicator 2 shows rapid green flashing for about 1 second Indicator 2 shows rapid red flashing for about 1 second STEP 3 After about 9 seconds. Any time after 9 seconds OPTIONS After binding with bind plug still in. After binding with bind plug still in. Model is stationary. Model has been moved. Do Nothing OR Perform Toggle Gesture OR OR Indicator 2 shows the mode status of the stabilizer: Red+Green solid = OFF Green solid = Gyro (rate) Green/Red flash = Autolevel Perform Neutral Reset Toggle Short press (<1s) sets failsafe to current stick/switch positions. Long Press (>1s) sets Stabilizer to Always-ON mode Gyros are internally calibrating. Internal calibration failed and previous calibration value is used. 13 The stabilizer defaults all offsets to zero and uses the previous orientation information. The stabilizer will attempt to level the case or use the previous level setting. Stabilizer stores all offsets for the current model position. Orientation information is refreshed. The stabilizer will attempt to level the model. Offset and orientation are valid. Offset and/or orientation are not valid. 14 DO NOT USE IN THIS CONDITION Stabilizer is ready for flight. Current transmitter trims are reset to neutral on the stabilizer. The values are stored until the next Neutral Reset toggle. Indicator 1 green ON = Pre-set failsafe Indicator 1 green OFF = No pulse on signal loss Indicator 1 blue = Always-ON (Channel 5 Gear output available for toggling) 13 The gyro calibration is very stable over long periods of time, so this is normally not a problem. 14 This can be caused if the stabilizer is mounted at an angle of more than 20 degrees from horizontal/vertical. StabPLUS Ref Guide v.1b.doc 19

22 Binding Lemon Stabilizer PLUS Receiver Reference Guide See the Essential Instructions for basic information on binding the StabPLUS. Here are a few additional points. Binding is the process of locking the receiver so that it ignores any other transmitters and is the first step in setting up any receiver. It is most easily done on the bench, rather than in the model. Ensure that the transmitter and receiver are separated by 3-6ft/1-2m for binding or the transmitter may swamp the receiver. The Lemon stabilizer has good sensitivity and occasionally it may be necessary to have as much as 10ft/3m separation to achieve binding, especially in an area of WiFi activity or close to a large metallic object, such as a furnace. Generally you should only need to bind once, unless you change transmitters. After binding, normal linkup should not require more than 2-3 feet/1m of separation. The power source for binding can be: A receiver pack battery ( v); or A stand-alone BEC (battery eliminator circuit); or The throttle connection from an electronic speed control (ESC) with built-in BEC. If using a speed controller as the power source, and it is installed in a model, make sure the motor is unplugged or the propeller is removed for safety. Binding can be done with or without servos. Servos plugged in the wrong way round may prevent binding, so check this if you have difficulty. If the receiver LEDs don t flash rapidly to indicate bind mode, you have a problem (such as a reversed connector). Don t go any further until you identify the issue and get rapid flashing. On some transmitters entering bind mode requires holding the Bind or Trainer button/switch while powering up. Others require opening a menu to enable bind mode. Newer Spektrum transmitters can be put into bind mode by holding the button (Switch I) while turning on the power switch. The bind process continues until the receiver internal Red LED stops flashing. 15 A solid green or green and red light on Indicator 2 also indicates a successful bind. Some transmitters will display on-screen (and/or announce) the type of bind (DSMX/DSM2) and the frame rate (e.g., 22 milliseconds ). If a successful bind is not achieved, remove power from the receiver and transmitter and repeat the whole process with the transmitter at a greater distance (e.g., 2 or even 3m). Avoid trying to bind in close proximity to large metal objects such as chain link fences, vehicles or a furnace. A nearby WiFi transmitter (e.g., a wireless modem) can also block binding. When binding is complete, don t forget to remove the bind plug. If it is left in place it will prevent the receiver from linking with the transmitter and require a re-bind. If you didn t have servos connected while binding, plug in one or more now to channel 2, 3 or 4. Turn the transmitter back on, then apply power to the receiver. Check that the receiver is operating properly and 15 Transmitters and modules that use a button or switch for binding vary. Some may require it to be held to the end of the process, while others will not complete until it is released. Releasing when the flashing changes works in most cases. StabPLUS Ref Guide v.1b.doc 20

23 that servos respond to the transmitter controls. Check the operation of the channel 5 Mode switch. Look it the Monitor screen on the transmitter if you have any doubt about how the channels are responding. Stabilizer Condition after a Rebind In summary, when you bind the StabPLUS the X, Y, Z installation offset will be assumed to be 0 degrees. In other words, the level offsets are reset to zero. The receiver is assumed to be placed flat on the floor of an aircraft at its normal level flight attitude. The aileron, elevator, rudder stick neutral position (as set by trim and sub-trim values) will be considered as 0%. Any fail-safe settings already made will not be affected. Failsafe Options The Lemon StabPLUS, unlike its predecessor but like most other Lemon receivers, has a Pre-set Failsafe option in addition to the default No-Pulse Failsafe. No-Pulse Failsafe No-Pulse failsafe requires no action on the part of the user. If the receiver loses signal for more than about a second, it shuts down pulses on all channels. This normally causes the speed control on an electric model to go to 0% power to the motor. The servos on other channels are left in the positions set by the last good command. No action is needed by the user, except to ensure that Pre-set failsafe is not turned on (indicator 1 Green light is not lit). No-Pulse Failsafe works well within its limitations. The speed control must default to shutting down the motor if it gets no pulses; modern ESCs do this but it should be tested. No-Pulse failsafe is not acceptable for use with IC (fuel powered) models. Pre-set Failsafe This option causes all channels to go to a preset position on loss of transmitter signal. For example, with a glider you may choose to set failsafe with a small rudder offset to keep the model circling and perhaps with Crow braking to guarantee a rapid but safe descent. Some clubs and model insurance policies may have requirements that failsafe on fixed wing models must make the throttle go to zero, and in most cases this is a wise choice. To enable Pre-set failsafe, the receiver must be re-bound. After the receiver has finished initializing, but with the bind plug still in place, the transmitter sticks and switches are moved to the desired mode or positions. A brief press (<1S) on the button will set failsafe, as indicated by the Indicator 1 Green light. If you get a blue light you have held the button down too long and have entered Always-ON mode. Hold it down again till the blue LED goes out. The failsafe setting is stored and will not change until you deliberately do so. Even if you rebind the receiver, the previously stored Pre-set values of failsafe are retained. Be very careful if you shift the receiver to a different model that you cancel any Pre-set failsafe and reset appropriately. StabPLUS Ref Guide v.1b.doc 21

24 Understanding the Three Different Calibrations" Calibration of the gyros themselves The gyros are very stable but over time they will gradually drift. Eventually there will be a significant offset of the servo position when switching between Off and Rate stabilization. For this reason the StabPLUS is designed so that it tries to calibrate the gyros internally every time when it is powered on. 16 The first thing it does after power on, or after binding completes if the bind plug is in place, is to attempt this gyro calibration. Unsuccessful calibration is normally due to movement during the 1-2 second window before the blue/green Indicator 1 is flashing. Because of the stability of the circuits, unsuccessful calibration is not normally an issue but after a few months it will need to be calibrated at some point. Over a period of a few months of flying a particular plane it is expected there will be at least one chance that the calibration will be made successfully because the plane is sufficiently stationary. However for the worst-case scenario, if you are in the habit of moving planes during the initial power on when you plug in the flight pack, then the gyro will never have a chance to calibrate. So it is recommended to ensure a deliberate gyro calibration at power on with absolutely no movement of the plane during start up every now and then. If you make a practice of always leaving the model stationary during the 1-2 second startup window, the problem will never arise. Calibration of level attitude This happens after gyro calibration. A) If you do nothing to a stabilizer that has just been rebound, the stabilizer calibrates itself to make the current bottom face of the case level with the ground regardless of the orientation or angle it is mounted at and assumes 0 degree installation offset. If you switch to Autolevel in flight, the stabilizer will act on the control surfaces to level itself. If the stabilizer is carefully installed with its fore/aft axis along the level flight direction of the plane this may work perfectly well. B) However you may find that the plane does not fly level enough because the stabilizer is not exactly along the axes or the plane requires some up or down angle to fly level. You also have to perform the following if it is not mounted in the default flat and level orientation. If during the 9 seconds that the green/blue Indicator 1 LEDs are flashing you do a toggle, then the stabilizer makes the calibration with respect to the plane. That is - the position the plane is in becomes level flight. If you switch to Autolevel in flight, the stabilizer will act on the control surfaces to level the plane. It also sets the orientation memory. During this calibration Indicator 2 stays red. At the end of the 9 second window, Indicator 2 close to the header pins will show 4 green flashes if calibration was successful or red flashes if calibration is not achieved. The red flash is normally due to a huge movement during the calibration period or a stabilizer that is mounted at an extreme angle and you need to repeat the process. If the stabilizer exceeds its detectable range with an installation offset of more than 20 degree from level, this will cause failure of this calibration. Do not leave the ground if you do a toggle and the green Indicator flash is not achieved! NOTE that the offset correction is saved when power is removed. It is not necessary to do a level calibration by toggling every time you power up the stabilizer. If you do not, then the previous leveling and stabilizer orientation (upright/inverted/sideways) will be used. 16 The automatic mechanism of the StabPLUS contrasts with the manual process used by the regular Lemon Stabilizer, involving opening the case (v.3) or using two bind plugs (v.4 and 4.5). StabPLUS Ref Guide v.1b.doc 22

25 Calibration for trim offset Lemon Stabilizer PLUS Receiver Reference Guide This applies a correction of any trims to neutral for the stabilizer so it doesn't think trim is an actual stick deflection. This is done with a toggle at any time after the first 9 seconds when the receiver is receiving a transmitted signal and is able to control the servos. It is saved when power is removed so does not have to be done again for that model if you do not change flight trim. Why the Gyros Need Occasional Recalibration The stabilizer senses motion through tiny solid state gyros and accelerometers. The gyros perform the same function as the old fashioned spinning wheel gyroscopes: they resist any attempt to move them and the force of the resulting resistance can be measured, amplified and used to control the servos. Instead of a spinning mechanical wheel, the MPU-3050 Motion Processing Unit sensor in the StabPLUS uses tiny solid state elements that vibrate about 30,000 times a second. The gyros can sense an angular rate of up to +/-2000 /sec for a full range output. They are so small that they can withstand a shock of 10,000g! They are extremely accurate and stable. Over a long time however the circuits in the MPU can drift and it is sensible to recalibrate them occasionally. Unlike with the original Lemon stabilizer, the user no longer needs to manually perform gyro calibration. This is done automatically during power on and the whole process takes about 1.2 seconds. If no vibration is detected during power on, the gyro offset value will be automatically updated, indicated by the green LED in Indicator 2 flashing twice. If vibration is detected during power on, the stored calibration value will be used. This will be signaled by the red LED flashing twice. What the LEDs Mean The StabPLUS has three sets of LEDs: Indicator 1, the blue/green ones near the pushbutton, Indicator 2, the red/green ones on the top near the connectors, and a red one on the back of the PC board, inside the case. This single internal LED can normally be ignored as it is basically just to show that the receiver is connected to the transmitter. There is one exception: when using a transmitter on DSM2 this LED can flash a brownout warning to indicate momentary power loss. Basic Light Signals Indicator 2 and Internal Lights Status LEDs Transmitter Receiver Stabilizer Green LED Red LED Internal LED Normal Operation Binding OFF ON - X X X ON ON OFF ON ON Autolevel Alternating ON ON Gyro X DSM2 only Brownout 17 Flashing BIND MODE Rapid Flash Rapid Flash Rapid Flash BIND MODE BINDING Flashing Flashing Slow Flash BIND MODE BOUND ON 17 The Brownout warning will be triggered if you turn a DSM2 receiver off and back on again without also power cycling the transmitter. StabPLUS Ref Guide v.1b.doc 23

26 Bottom line: Lemon Stabilizer PLUS Receiver Reference Guide A properly bound, active stabilizer in Rate (Gyro) mode will show a solid Green external LED. In Autolevel mode the alternating Green and Red LEDs will show. Both LEDs will come on when you turn the stabilizer OFF using the gear channel or the DIP switches. Other Light Signals Indicator 1 and 2 Lights Function Stick Centring (toggle after initialization) Pre-set Failsafe ON Stabilizer Always-ON Gyro calibration: 1 st second of power cycle Awaiting toggle for pitch/roll/stabilizer orientation calibration after power cycle and gyro calibration (max. wait = ~9sec) Accepted toggle. Calibration in progress for pitch/ roll/ stabilizer orientation LED Indications Mode Red/Green rapid flash very briefly Indicator 1: Green ON No light indicates No-Pulse failsafe Indicator 1: Blue ON Mode indicator: Green flashes twice = OK Red flashes twice = fail. Indicator 1: Green/Blue slow flashing Mode indicator: Red ON for ~4 seconds, followed by green flashes for successful calibration, red flashes for fail Further Options Stabilizer Always-ON During the bind process you can set the stabilizer to be permanently on. Set the three-position switch for Autolevel (Indicator 2 Red/Green LED alternating) or Gyro mode (Indicator 2 Green LED ON) as desired. Press and hold the button until Indicator 1 blue LED is on. Blue LED on means the stabilizer is always on in either auto-level or gyro mode. Channel 5 will no longer have any effect on stabilizer mode and is available for retracts or similar. You should choose whether you want Gyro or Auto level mode using the channel 5 switch before you select Always-on (since you cannot then change it). However the toggle gesture for both Orientation/Autolevel offset and Trim offset will still work in Always-on mode. Remove bind plug and power cycle the unit. If a suitable transmitter is used, Master Gain on channel 8 can be used to effectively turn OFF the stabilizer if required. To set a transmitter with only a two-position switch on channel 5 (Gear) to Always-ON, you first need to ensure that Mode Order is set correctly. For Gyro mode Always-ON, select OFF/AL/Gyro as the order; for Autolevel select OFF/Gyro/AL as the order. StabPLUS Ref Guide v.1b.doc 24

27 Hardware Reset Lemon Stabilizer PLUS Receiver Reference Guide To reset the StabPLUS to factory default settings, insert a bind plug on the signal pins of channels 2, 3, and 4, as shown in the picture. Note that channel 2 (Aileron) is the third set of pins from the left. The ESC, BEC or battery is connected to channel 1 (Throttle) as usual (or to other available channel pins). The transmitter is not required. When power is applied briefly, the lights on the receiver will blink in sequence, indicating that all internal settings have been returned to default. This includes any stabilizer offsets, orientation settings, failsafe presets, mode order changes, etc. To complete the reset, you may wish to set the stabilizer pots back to the 12 o clock position and return all DIP switches to OFF, but this is not required. A good practice if you encounter unexpected behavior from the stabilizer is to perform a hardware reset, followed by rebinding of the receiver. Then start afresh with stabilizer settings. Mixing Mixing and the Lemon Stabilized Receiver The Essential Instructions should give you the information you need to set up elevon or V-tail mixing with the Lemon StabPLUS. The purpose of this section is to explain further how all this works. This section does not apply if DIP switches 4 and 5 are off as the StabPLUS then operates exactly like a normal 7 channel unstabilized receiver and all mixing needs to be done at the transmitter. The key point to understand is that the Lemon stabilizer only recognizes and corrects for movement in the three standard flight axes (shown in the diagram on page 8). Consequently, the stabilizer expects the transmitter to provide the conventional pure inputs: roll (aileron), pitch (elevator) and yaw (rudder). Any processing (mixing) needed to turn these inputs into servo commands for a non-standard control arrangement such as elevon or V-tail MUST take place in the stabilizer itself, NOT in the transmitter. By contrast, even when stabilization is active, flaperon and other types of mixing take place in the transmitter. What is mixing? In a simple control setup, each axis has a dedicated control surface (or pair of surfaces in the case of aileron). Each axis is controlled by a separate channel passed from the transmitter through the receiver (and its integrated stabilizer) and onward to the servo that moves the control surface. For the Lemon receivers, channels 2, 3 and 4 are used, respectively, for the three basic flight surface controls, aileron, elevator and rudder. Mixing is the process of combining transmitter inputs to provide the servo output(s) required for control. For many purposes, the mixing is done in the transmitter. For example, throttle can be mixed to elevator so that as power is increased, a small amount of down is added to the elevator signal in order to counter the model s tendency to climb. Another common mix couples aileron and rudder to aid in coordinating turns. The important thing about such mixes for our purposes is that they don t affect the basic StabPLUS Ref Guide v.1b.doc 25

28 arrangement of allocating one channel to each control axis or function. Consequently, they still provide the separate inputs required by the stabilizer. However they DO affect behavior in Autolevel mode since Autolevel reacts to any change in the position of the aileron and elevator channels as a command to change the attitude of the plane and a Throttle->Elevator mix for example will do just that. The V-tail and elevon mixes we are concerned with here are different in that they involve two separate and independently driven control surfaces working together to provide a single aerodynamic function. For example, a pair of elevons must work in unison to produce pitch and in opposition to generate roll. To achieve this, the mixing MUST be done on board, since the stabilizer cannot interpret inputs in the form of mixed control commands; it only understands roll, pitch and yaw. Any V-tail or elevon mixing in the transmitter must therefore be disabled. Flaperon is another case where two inputs (aileron and flap) are involved, but only one is a primary flight control, so here the mixing is done in the transmitter. Let s take a look specifically at how these three types of control setup are dealt with in relation to the Lemon StabPLUS. DIP switches are the six small white slide switches on the receiver, which are numbered and referred to by Lemon as J1 to J6. V Tail In this arrangement, the functions of elevator and rudder are managed by tail control surfaces that move up or down together for pitch, right or left together for yaw. Right rudder is achieved by the left surface moving UP and the right surface moving DOWN. In the transmitter tail type (if available) is set to Normal (not V-tail); this ensures that separate (not mixed) elevator and rudder signals are sent to the stabilizer. In the receiver, DIP switch J4 (Delta) is OFF and DIP switch J5 (V-tail) is ON, thus activating on-board mixing. The setting of DIP switch J6 depends on the aileron configuration. The right and left tail servos are normally plugged into channels 3 (elevator) and 4 (rudder) respectively. Elevon / Delta Wing This arrangement is generally used for a tailless aircraft, such as a flying wing or delta, in which the wing control surfaces (elevons) are used to control both pitch (elevator) and roll (aileron). The elevons move up or down together for pitch and in opposite directions for roll. Right roll is achieved by the left elevon moving DOWN and the right elevon moving UP. In the transmitter, Wing Type is set to Normal (not Delta). In the receiver, DIP switch J4 (Delta) is ON to activate mixing. DIP switches J5 (V-tail) and J6 (flaperon) are OFF. The right and left elevon servos are conventionally plugged into channels 2 (aileron) and 3 (elevator) respectively, but it is often necessary to interchange the servo connections to achieve correct control directions. Flaperons (dual aileron servos on separate channels) The flaperon arrangement enables the ailerons not only to move in the usual opposite directions to produce roll, but also to move together downward to produce flap action (and possibly upward to produce spoiler action), thus controlling lift and drag. This dual function capability requires that each aileron servo have its own channel: normally channel 2 for right aileron (RAil) and channel 6 for left aileron (LAil). The stabilizer (with J6 ON) passes the control inputs sent by the transmitter through to the two aileron channels. The inputs can include not only StabPLUS Ref Guide v.1b.doc 26

29 flaperon mixing but also differential aileron (more up than down to compensate for adverse aileron drag). Unlike V-tail and Elevon, where the mixing happens in the stabilizer, aileron/flaperon mixing takes place in the transmitter. For the stabilizer to apply corrections to both ailerons in response to wind gusts, etc., switch J6 must be ON. (If it is OFF, only the right aileron (CH2) will have stabilizer action.) In the transmitter, Wing Type should be set to Flaperon, as appropriate. If flaperon is used, then Flap mixing may be applied; this usually includes mixing to the elevator channel to compensate for the pitch effects of flap action. Also, differential aileron can be applied if required. In the receiver, DIP switch J6 (flaperon) is ON to enable stabilization on the second aileron channel. DIP switches J4 and J5 are ON (except for a model with a V-tail, when J4 must be OFF). The right and left aileron servos are plugged into channels 2 and 6 respectively. NOTE: You MUST NOT use either Flaperons or Aileron Differential when Auto level mode is active; see the warning below. Reversing Control and Stabilization Directions with Mixing After setting any mixing is set up for V-Tail, Elevons and Flaperons, the direction of response of the control surfaces to the transmitter inputs must be checked and corrected as necessary. To avoid distracting control surface motions, stabilizer action should be turned OFF with the Mode switch (channel 5/Gear) during this process (mixing is not affected by turning off the mode switch). Note that to achieve the correct control directions, it may be necessary not only to use channel reversing in the transmitter but also to interchange the plugs of the two servos involved in the control mixing. For example, if both V-tail surfaces move sideways when the elevator stick is moved, interchange the plugs in channels 3 and 4. Then if necessary, use channel reverse in the transmitter to adjust the direction of motion of the two surfaces. When all control settings and mixing are completed, and the control directions are correct, the direction of the stabilizer s response to a flight disturbance must be set for each axis. Checking must be done with the stabilizer turned ON and in accordance with the instructions provided earlier (see page 7). To change the direction of response for an axis, use the appropriate DIP switch: J1 (aileron), J2 (elevator) or J3 (rudder). WARNING: Flaperons and Aileron Differential Autolevel mode on the StabPLUS is intended to help you stay within safe limits or recover from difficult situations. This means, however, that it must limit the pilot's degree of control and restrict certain options. In particular, Autolevel is incompatible with the use of either Flaperons or Aileron Differential. These advanced features, found on most programmable Spektrum transmitters, are only available when dual aileron servos are driven by separate channels. Here s why they can't be used with Autolevel: When activated, the flaperon function causes the servos to lower or raise both ailerons, thus giving a flap or spoiler effect. This action represents a significant shift in the neutral settings of the two aileron channels. The stabilizer, however, in Autolevel mode may interpret this shift as a command to roll the model. Thus, selecting Autolevel while flaperons are deployed may cause the model to bank or even roll inverted. Hence, flaperons must NOT be deployed when the stabilizer is in Autolevel mode. StabPLUS Ref Guide v.1b.doc 27

30 Likewise, Aileron Differential causes the two servos to travel different amounts. For example, in a right turn, positive differential will cause the right aileron to go UP more than the left aileron goes DOWN. This can conflict with the efforts of Autolevel to apply roll correction. Consequently, the message is: Don't use either Flaperons or Aileron Differential while the StabPLUS is in Autolevel mode. Solutions Flaperons can be used when the StabPLUS is in OFF or Gyro mode, but be sure you don t accidentally select Autolevel at the same time. The safest approach is to disable either flaperons or Autolevel. There s no problem using two servos on separate channels in Dual Aileron Wing Type, or a Y-cable to drive both servos off the Aileron channel in Normal Wing Type. It s when the Wing Type is set to Flaperons that you need to take great care. If you do choose to use flaperons with the StabPLUS, we have on RCGroups provided mixes for the DX8 and for more recent Spektrum transmitters that ensure that Autolevel mode can t be selected when flaperons are active. For details on these mixes, go to Post #4 of The Official Lemon Instructions thread: Although the way Autolevel mode works in the Lemon StabPLUS is not compatible with Aileron Differential, you might want to program your transmitter to allow use of differential when the Stabilizer is set to OFF or Gyro mode. To do this in a modern Spektrum transmitter, use the same three-position switch to select Differential as you use for Stabilizer Mode; simply ensure that the differential amount corresponding to the Autolevel switch position is set to 0%. In the default setup of the StabPLUS, Position 0 corresponds to OFF and Position 1 to Gyro mode. The differential values for these positions can be set according to your preferences. The differential for Position 0 (Autolevel) must, however, be set to 0%. Note that even with differential set to 0%, Autolevel provides Gyro-type stabilization on the yaw axis, thus helping to ensure coordinated turns. In addition, you might want to program your transmitter to provide a small amount of aileron-to-rudder mixing, either full time or only when in in Autolevel mode. Finally, old-fashioned mechanical aileron differential is very effective and is generally easy to incorporate by offsetting either the servo arms or the aileron control horns. Stabilizer Modes: Gyro vs. Autolevel Although Gyro (Rate) and Autolevel both stabilize the model, they operate in quite different ways and result in totally different control responses. Gyro mode responds to a disturbance of the plane by giving a pulse of opposite control surface movement. It works by sensing the angular motion 18 about one or more of the three flight axes. If the model is moving in a straight line with no change in direction, the stabilizer does nothing. But if a gust hits the plane and lifts one wing, the stabilizer immediately applies opposite aileron to counteract the roll. The aggressiveness of the response (the amount of aileron deflection) is determined by the gain on the roll axis and the violence of the disturbance. That gain is a product of the setting of the stabilizer's 18 Technically, the Motion Processing Unit (MPU-3050) measures the angular rate in degrees/second, which is an angular velocity, but it may be easier to think of the stabilizer reacting to an angular acceleration. Acceleration is just the rate of change of velocity. StabPLUS Ref Guide v.1b.doc 28

31 Aileron pot (which has a value of 1 at midpoint) multiplied by the Master Gain value set by channel 8 (which is 1 if channel 8 is not available). 19 If the gains on the three axes are correctly set, the effect is to damp out external disturbances caused by turbulence due to wind, gusts and thermal activity. The stabilizer acts as though it has increased the inertia of the plane. Many pilots describe Gyro mode as like flying a much bigger and steadier model. However, if the gains are set too high, the stabilizer applies too much correction and the end result is an oscillation back and forth rather than damping of the disturbance. Autolevel mode works quite differently. In this mode, if the inputs from the sticks are neutral, the stabilizer constantly tries to return itself to a level position. If it's correctly installed and adjusted, and you don't touch the sticks, it will try to keep the model flying in a straight line with wings level. Given a suitable throttle setting, this results in more or less level flight. This diagram we saw earlier shows the three flight axes. In Autolevel mode, with no stick input, the stabilizer keeps the Z axis aligned with the downward direction of gravity. So if the model pitches up or down or rolls from side to side, the stabilizer will automatically correct by leveling the model. If a gust hits the model, the stabilizer will immediately return the model to level attitude, no matter the strength of the original disturbance. The stabilizer in this mode does not attempt to hold the heading of the model, but simply applies Gyro (rate) stabilization to the rudder to damp out directional disturbances in the yaw axis. So what happens if you deflect a stick in Autolevel mode? The stabilizer adjusts the ailerons and/or elevator to move the model away from level to a new bank/pitch attitude that is determined by the stick deflection. As long as you hold the stick with a constant deflection, the stabilizer works to maintain that attitude. As soon as you release the sticks to neutral, the stabilizer returns the model to level flight. Of course, there is no exact correspondence between stick deflection and model s attitude. The stick commands a response which is proportional to its angle, but the proportionality varies with two main factors. First, the sticks on most transmitters are physically limited to between 30 and 40 degrees of deflection on each side of neutral, but we want to have the option of commanding steeper angles of bank and pitch for greater maneuverability. To this end, the Autolevel function of the stabilizer has two settings, Beginner giving very restricted bank and pitch angles and Advanced allowing steeper angles and thus greater maneuverability. As well, the servo travel volume (end point) settings of the transmitter for aileron and elevator directly adjust the maximum angles that can be commanded If there is no channel 8 on the transmitter, Master Gain defaults to a constant multiplier of 1.0x. 20 In addition, the gain settings on the stabilizer (and Master Gain, if available) will affect the ratio of stick-to-model movement, up to the maximum limit. Hence, the maximum bank angle is slightly affected by the gain setting, and there may be variation of a few degrees from the exact 30/45 or 50/75 numbers. StabPLUS Ref Guide v.1b.doc 29

32 To be specific, Autolevel Beginner mode limits the bank and pitch angles of the model to about 30 maximum with the transmitter set to 100% servo throw. If you increase the servo throw to 150% in the servo travel menu, the maximum bank/pitch angle will increase to about 45. In Advanced mode, full stick deflection produces a maximum bank/pitch angle of about 50 for 100% and 75 for 150% servo limits. To summarize how the Lemon StabPLUS in Autolevel mode functions: Roll (aileron): Stick input directly controls the roll angle (bank) of the model. The roll angle is proportional to the stick deflection. Pitch (elevator): Stick input directly controls the pitch angle of the model. The pitch angle is proportional to the stick deflection. Yaw (rudder): Autolevel mode does not apply to the rudder channel. Instead when Autolevel is selected, the rudder is stabilized in Gyro mode, reacting to angular disturbances while responding to control inputs in the usual way. The individual channel gains (and master gain if available) do NOT significantly affect the maximum bank and pitch angles. However they do affect the speed with which the stabilizer responds and the ratio of the response angle with respect to the stick deflection up to the maximum value. High gains will give more rapid response and a greater model angle for a given stick deflection, up to the maximum available. In roll and pitch, there may be a progressive movement with the model rapidly following the first deflection then gradually reaching the final position. The critical difference between Gyro mode and Autolevel mode. Essentially a stabilizer in Gyro mode does not alter the way in which the control surfaces affect the flight behavior of the model except to damp its reactions, particularly to external disturbances. The control surfaces work exactly as they do in a real aircraft. If you push the stick to one side and hold it the plane will roll and continue to do so until you neutralize the control. To roll out of the turn, you have to apply opposite aileron. Gyro mode, like flying without stabilization, is as though you put yourself in the cockpit and make the aircraft your frame of reference. Autolevel stabilization on the other hand adjusts the plane s orientation with respect to an absolute down direction. If you deflect the stick by a certain amount and keep it there, the plane simply goes to the commanded attitude and holds it. With Autolevel it s as though you are on the ground and the frame of reference is the earth. And that is exactly how it is for RC pilots, as we are on the ground. For beginners in particular, Autolevel can be a great help, giving them a chance to sort out their reactions and deal, for example, with apparently reversed control directions when the model is flying toward them. This is vital for those who lack the assistance of an instructor; as it can save the pilot from disorientation that too often result in a crash. The more you fly and less you crash, the quicker you can become a good pilot. It also helps greatly during landing, where you are trying to keep the model in a constant relationship with the ground. Autolevel is also popular with FPV (first person view) pilots who let the stabilizer take control and fly the plane straight and level while they concentrate on shooting an image. Thus Autolevel mode is much like steering the plane around the sky. Let the sticks go and the model will always attempt to return to flying straight and level. StabPLUS Ref Guide v.1b.doc 30

33 By contrast, Gyro stabilization does make the model easier to fly, but only in the sense that it smooths out the response and helps the model resist disturbances. Gyro stabilization is very like normal unstabilized RC flying but much smoother particularly in windy conditions. The stabilizer when in Gyro mode is designed to do its job while minimizing interference with normal control. To achieve this, the amount of correction (stabilizer gain) is automatically reduced for large stick excursions. This is because the stabilizer will see your large intended movement as a significant disturbance and will attempt to correct it strongly. It only senses the model moving and does not know whether it was an intended movement or an unintended one. The balance between onboard stabilization and transmitter control is a compromise, as there is always some stabilizing effect whenever the stabilizer is active. Consequently, for maximum response to stick inputs, you can set the Stabilizer Mode switch to OFF. In practice the Gyro mode does just what most people need most of the time smoothing out flight while leaving the pilot fully in control. Autolevel reduces control response, offering useful options but at the expense of some degree of pilot control. In particular, Autolevel is good for beginners, or for FPV pilots who want to concentrate on imaging, but it does restrict the flight envelope. The Beginner setting in Autolevel is particularly restrictive, so if you want to improve your piloting skills you should move off it as soon as you have the confidence. Experienced flight instructors generally encourage students to shift to Autolevel Advanced mode and then to Gyro stabilization as early as possible so that they learn to control the plane instinctively using normal surface deflections. StabPLUS Ref Guide v.1b.doc 31

34 Appendices Appendix 1: Diversity and RSSI The principles There is quite a bit of confusion about the purpose and significance of diversity antennas and the meaning of Received Signal Strength Indication (RSSI). 21 Some of this is compounded by expert advice from modelers who grew up in the era of dedicated frequency AM or FM receivers who may not be familiar with modern 2.4GHz Spread Spectrum R/C systems such as DSMX. All common RF control systems work by propagating a high frequency electromagnetic signal from a transmitter to a receiver. If the transmitter antenna is reasonably well tuned to the frequency of the signal, an electromagnetic wave is generated that can propagate through space to generate matching voltage variations in an antenna connected to a sensitive receiver. This is the fundamental basis of all common RF communication. One simple way to measure the strength of the signal is to measure the voltage appearing at some point near the antenna in the receiver. Some popular RC systems including FrSky and the Lemon telemetry systems, display an RSSI value (Received Signal Strength Indication). The RSSI used in model control systems may vary between systems and according to how it is measured. Nevertheless, for a given system, RSSI is a useful measure of the signal received at your model. We ll refer to this as Signal Strength. However, what really matters is not the absolute signal strength but the signal/noise ratio. Optimizing the signal/noise ratio and minimizing any interference from other sources or multipath reception is important for signal integrity but there s more to 2.4GHz spread spectrum radio than this. Our 2.4 RC signal is not an analog modulated RF carrier signal but a digitally encoded one. And it is spread across the frequency band not concentrated at a single frequency. In a spread spectrum system, a pseudorandom number (PN) sequence is used to randomize the signal in the air. Only the receiver having the exact same pseudo-random sequence and synchronous timing can decode and retrieve the original signal. Because the control data is encoded into digital numbers and transmitted over a range of frequencies spread over the 2.4 GHz band, then as far as the receiver is concerned the correct data is either there or it is not there is no half-way house of a poor signal. The receiver does not rely solely on the strength of the transmitted signal (although that is still important) but on its ability to recognize the correct encoded data from the accumulation of signals it sees. It is perfectly normal for the strength of a particular signal to be less than the noise level on the band yet for an unambiguous data stream to be detected. As one expert described it, It's like hearing a whisper at a heavy metal concert. A good analogy is conversation at a fairly rowdy party. Imagine you and your partner are having an intimate conversation. When you are standing face to face you can each make out every word. But if you start moving further and further apart, communication becomes more difficult. When you get to a certain distance, you have to face the other person and concentrate intently on what they are saying in order to avoid serious 21 The StabPLUS does not display an RSSI value on the transmitter as it does not support telemetry. However the term is commonly used to describe the actual signal strength at the receiver. StabPLUS Ref Guide v.1b.doc 32

35 misunderstandings. In radio terms your antennas have to be optimally aligned for maximum signal transfer and maximum noise rejection. No matter how hard you try to concentrate, as you move still farther apart the surrounding babble eventually overwhelms any attempt to understand your partner and everything becomes unintelligible. The signal gets lost in the noise. However what if you and your partner are the only English speakers at a noisy party of Mandarin-speaking Chinese? You will be able to understand your partner at a greater distance this time because you are the only two in the room with a particular data encoding system (English) while the background noise uses a different system (Mandarin). This is so even though everyone is using the same medium, audio speech. With different coding, you can separate the meaningful conversation from meaningless background even if the background is louder. Only a receiver able to properly decode the transmitted signal gets a clear data stream with unambiguous information. The various proprietary systems used in RC (DSM2 and DSMX are just two examples) all work on the same principle, varying in the way the frequencies are used and distributed. Let s call this Data Integrity. Data integrity is important because in digital systems what finally matters is simply whether a valid data packet is received or not. Different systems have their own ways of reporting on signal strength and data integrity. Spektrum systems do not report an RSSI value at all. They use three different measures of data integrity. Firstly, antenna fades (A). These apply to a specific antenna and represent the loss of a small chunk of information. They are often fairly frequent it s normal to have as many as antenna fades on any one of the antennas during a flight. This is a measure of signal strength, which contributes to data integrity. Secondly the system reports on frame loss (F). This means simultaneous antenna fades on all attached receivers. It represents the loss of a valid data frame, so is a measure of data integrity. If the RF link is performing optimally, frame losses per flight should be less than 20. Finally they will report on holds (H) a hold occurs when 45 contiguous (one right after the other) frame losses occur. This is a serious loss of data frames over an extended period of about one second. Any holds are a matter of concern. Lemon systems do not report on any of these three values but all of the above helps define what we are striving for and to understand what we need to do to optimize the control link. The reporting of RSSI is only an indication of the reliability of the signal link. In the end it is data integrity that is the critical thing. In a sense the receiver doesn t care about how the signal got there, only if the data is accurate and uncorrupted. We need to maximize the RF transmission link between transmitter and receiver AND ensure the receiver receives a continuous flow of valid data packets. We maximize the signal strength by optimizing the location and direction of an antenna. This provides the best or strongest signal between the transmitter and receiver. We optimize the likelihood of receiving valid data packets by adding diversity switching to the antenna system, ensuring that the receiver has multiple sources of data. With a diversity switch, the encoding match between the transmitter and receiver allows the receiver to only hear the data it's looking for. If it doesn t see it, then it will use the other antenna although the precise logic behind the antenna switching algorithm is generally a proprietary secret of the vendor. (Some Lemon receivers achieve diversity by adding a satellite receiver to provide another data source, and some can use both a satellite and dual diversity antennas, for a total of up to four data sources.) StabPLUS Ref Guide v.1b.doc 33

36 It is important to emphasize that the receiver does not look for the best or strongest signal among those available to it. Data is either valid or not and the receiver simply looks for a data from a valid source. Any one will do and no special decision is needed. With our RC systems we do not attempt to measure the error rate and correct any errors; there are not enough extra bits sent to unscramble a faulty reception. We just wait, since we are sending it again shortly. Statistically, it's likely to arrive just fine the next time. If it doesn't, there's always another in just a few milliseconds. The Practical Implications Lemon receivers including the StabPLUS are all described as full range. While absolute or theoretical range is not affected by the use of dual antennas (or satellite receivers), adding diversity should help to ensure that there is always at least one antenna capable of delivering data within that range. Of course, this assumes that the installation is done correctly, and that the antennas are placed in favorable locations, with the active portions well separated and in different alignments. The diversity StabPLUS has two active antenna wires (the last 32mm with outer sheath stripped off) connected to a switch that selects between them. Commonly you will see this described as selecting the stronger available signal but this is not strictly true. The receiver will continue to use one antenna as long as valid data is being received. If valid data packets cease it will switch antennas very quickly and use the other. The switch will occur within 300mS and no control signal is lost during the switching period. Some receivers (including many Lemon standard receivers and the original Stabilizer which is still sold) also have a connector to allow the use of a satellite for additional signal robustness. A satellite does not increase the maximum possible range. Rather, as a separate stand-alone receiver it increases the probability that a reliable signal will be obtained no matter the orientation of the model. The satellite may also have a diversity twin antenna system identical to the receiver. The main receiver will read its own data and that from the satellite. It doesn t care where it comes from since the data signals are identical. As long as one is there it will function correctly. Note that if the satellite has diversity antennas there are four separate antenna sources for the receiver/satellite combination. The effect is that the receiver may be using data received by any one of them depending on the orientation of the model. The antennas we use for radio control radiate (and receive) in all directions, but the signal is much weaker off the ends of the antenna (the active portion of the cable) than "broadside" to it. Think of an ancient naval battle where the ships had very little firepower fore and aft because most of their cannon were pointed out the sides. To achieve the most reliable possible link to the model, therefore, what we want to avoid are situations in which the transmitter and receiver antennas are end-on to each other. For the transmitter, the advice to the pilot is simple: don't point the antenna at the model. For the receiver, things are more complicated because the model is constantly changing its orientation in relation to the transmitter. A single receiver antenna will inevitably be pointed at the transmitter some of the time. This is where diversity comes in. If the receiver has two active antennas positioned at right angles to each other, they can never both be pointed at the transmitter simultaneously. The receiver has an excellent chance that valid data will be available from at least one of the two. StabPLUS Ref Guide v.1b.doc 34

37 Diversity improves the reliability of the RF link in other ways. If the two receiver antennas are well separated, at least one should have a clear view of the transmitter, minimizing the risk of signal blanking. As well, with antennas at right angles one of them should be roughly parallel to the transmitter antenna, thus aligning polarization for a stronger signal. Conductive materials such as foil coverings, batteries, metal components and carbon fiber can absorb and shield the incoming radio signal. 2.4GHz systems have a very short wave length and are susceptible to this. Receiver aerials need to be placed so that this effect is minimized. What all this means for the installation of the receiver is simple. Make sure its antenna is not close to conductive stuff like battery, wiring and carbon fiber. If it has twin antenna, ensure the two antennas are separated as far as practical from each other and keep the active portions (the last 30mm/1.2 inches or so) reasonably straight and at right angles to each other. In a case where the model has a large flat conductive area, such as carbon fiber or metallic covering. The antenna should be then mounted perpendicular to the conductive surface. To avoid an unwanted reflection/coupling effect, never place the antenna close and parallel to any wire or conducting surface. This is even more important than the angle between the two diversity antennas. Just think of the signal as a light ray and the conductive object as a mirror. Types of Lemon antenna The correct length for the short simple wire 2.4GHz antenna found on the single antenna version of the StabPLUS is 29mm. This is slightly shorter than theoretical ¼ wavelength of 31.25mm due to the coupling effect for an omnidirectional ¼ wave antenna. Note that the actual length can vary a bit for other brand receivers, which may be as short as 27mm. The dual diversity antenna versions have slightly longer active ends due to attenuation by the coax cable portion. When positioning the antenna, it is the thin exposed active end that is critical. Last word Don't get paranoid. The installation doesn't have to be perfect to support an adequately strong RF link. Our modern receivers do a remarkably good job of picking up the signal, even with just a simple single antenna, so diversity can be thought of as extra security for when the going gets tough. StabPLUS Ref Guide v.1b.doc 35

38 Appendix 2: Range Checking To verify a new installation or to check radio operation before the first flight of the day, use the Range Test function on your transmitter. This temporarily attenuates transmitter power, reducing range by a factor of about 30. With Spektrum transmitters, full control at 30 paces in Range Test mode indicates ample range for normal visual flying (the distance is now specified as 30m or about 33yds). Normally the receiver will show considerably more range than this, but the important thing for safe flying is that it meet this basic go/no go standard. Range varies with the square of output power. To double the range, the transmitter requires four times the power(2 squared). This explains the large reduction in power needed for the Range Test. The power is cut not by 30X but by 30X squared, or a factor of about 900. So if the transmitter puts out 100mw (milliwatts) at full power, in range check mode its output is cut to a little over 0.1mw. There are two kinds of range test you should do: one-time testing of a new installation to discover any problems of antenna location, etc. and routine checks at the beginning of each flying session to verify that everything is working correctly. The first needs to be thorough, but the second can be very quick. The key point about testing is that range is not an absolute value for a given receiver but can vary considerably, depending on such factors as the alignment of the transmitter and receiver antennas, whether the receiver antennas are blocked ( shadowed ) from some directions by the battery or other conductive parts of the model, and proximity to the ground or metal objects like cars and trucks. Your aim in initial testing is to ensure that not only is there satisfactory range in one direction, but that there are no dead spots or directions in which range is considerably reduced. What you do is to set up the model off the ground on a wooden stand in the middle of an open area. Then, with the transmitter in range test mode, go out about 30m and walk around the model, moving one of the controls deliberately, every second or two. What you re looking for is loss of control on the channel you are moving (or any sign of twitching on the controls that should be steady). While doing this, deliberately keep the end of the transmitter antenna pointed at the model to ensure a worst case scenario (not necessary for recent Spektrum transmitters with dual diversity antennas). You should get no indication of signal loss at any point in your circumnavigation of the model at 30m. If you do, it s time to take a close look at the installation. If you have a single antenna StabPLUS, ask yourself whether the antenna is clear of wiring, ESC, battery, etc. Often the best way to mount such a receiver is against the fuselage side with the antenna poking out. With a dual diversity receiver, the tips of the antennas should be well separated and at 90 degrees, and again not blocked by conductive stuff. Rearrange the installation and try again until you get essentially no signal loss. This is normally not difficult to achieve, but occasionally you ll discover a problem and thereby prevent an accident. You may want to continue out in one direction, still in range test mode, to find out what sort of range your transmitter/receiver combination can achieve. Don t be surprised if you get 50 to 100m or more. But the important thing is reliable performance at 30m, which translates to nearly 1km at full power. The purpose of a routine range test when you arrive at the field is simply to establish that things are working properly. For example, a common failure mode is for the transmitter antenna cable to be damaged, drastically reducing output, or for the receiver to suffer damage in a crash. For the test, just go out 30m, switch to Range Test mode, and move one control repeatedly so you can see that it s responding properly. That s enough to tell you that the RF link is functioning correctly. StabPLUS Ref Guide v.1b.doc 36

39 Appendix 3: Versions of the Lemon StabPLUS Receiver Version 1 of the Lemon Stabilizer PLUS shipped in early January Visually, the Stabilizer PLUS is very similar to its predecessor, the Lemon Stabilizer. It is packaged in the same case, as the photos show. Identifying features include a push button for setting options (including failsafe) and an additional pair of LED indicator lights. The PLUS can also be distinguished by the lack of a satellite receiver connector. The obvious differences are highlighted in yellow in the photos. StabPLUS Ref Guide v.1b.doc 37