Construction of unmanned aerial vehicle based on remote controls models, open source autopilot projects and commercial off-the-shelf equipment.

Transcription

1 UAV Project Construction of unmanned aerial vehicle based on remote controls models, open source autopilot projects and commercial off-the-shelf equipment. von Olav Strehl

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3 Abstract

4 Contents Table of contents List of figures List of tables List of abbreviations I III IV V 1 Background Airframe Fixed wing aircraft Helicopter Quadrocopter Hexacopter Octacopter VTOL fixed wing aircraft Engines and power output Power Propeller and thrust How to choose the right prop Balancing of the prop Props for Quadro-, Hexa- and Octocopters Remote control Signal modulation Telemetry AdruPilot - Autopilot Suite Autopilot hardware DR PixHawk board Additional Information Additional components Autopilot software Mission Planner APM Planner Ardupilot APM Copter Autopilots in Detail PID Controller Additional Components FTDI Cable (USB to Serial) Telemetry Data Link Radio Configuration Flashing the firmware of the 3DR Radios FPV Gimbal Frequency usage in Germany ISM-Band Video transmission in Germany Own projects DR DIY Y I

5 2.1.1 Components Setup and Instalation Mechanical Software Remote control setup Changed receiver output to SUM Channel set up Flight mode switch (CH5) Failsafe First Flight First improvements Power supply for additional components Navigation Light Installation of a telemetry module Video Transmitting and recording Measured Data Lesson learned First Mission (Flight in Auto Mode) Experience of the first mission Second improvements Fine tuning Improved power distribution board for 12 and 5 V On-board Computer Video streaming via Wlan Mav-Link via Wlan Stereoscopic imaging Bibliography 30 II

6 List of Figures 0.1 Pulse position modulation VI 0.2 Pulse width modulation VI 1.1 Propeller and pitch FTDI cable pinouts DR Radio air module connected to the PC via a FTDI cable Latency measured with different FPV cameras This figure shows the step necessary to set up switch 8 and control 9 to switch between all 6 flight modes This Figure shows the assignment of the flight modes to the switch positions within APM-Planner Ground mount for testing First flight performed at January Improved wiring of the power distribution board Homebuilt power regulation and distribution board for 12 and 5 Volt DR DIY Y6 with mounted telemetry system Analysis of telemetry radio signal noise and strength - Broken remote transmitter Analysis of telemetry radio signal noise and strength - Working radios Basic gear needed for video transmission Improvised camera mount used for the first test flight Impressions from the first test flight with video transmissions Display of the video and remote data during flight Gimbal setup with APM Planner Homebuilt 2 Axis Gimbal First on-board video recording Planning of the first mission with APM Planner Track of the first mission displayed in APM Planner III

7 List of Tables 1.1 Comparison of the APM vs. the PixHawk auto pilot board Flight mode settings with 2 and 3 way switch IV

8 List of abbreviations BEC - Battery Eliminator Circuit A Battery Element Circuit is a power supply unit which is often used in remote control vehicles to supply the receiver with energy out of the drive / flight battery. This makes it unnecessary to use an extra receiver battery. Most modern ESC have an integrated BEC unit, which delivers a 5 voltage current. CW - Clock Wise rotation direction CCW - Counter Clock Wise rotation direction Drone ESC - Electronic Speed Control An electronic speed control or ESC is an electronic circuit with the purpose to vary an electric motor s speed, its direction and possibly also to act as a dynamic brake. ESCs are often used on electrically powered radio controlled models, with the variety most often used for brushless motors essentially providing an electronically generated three-phase electric power low voltage source of energy for the motor. FPV - First Person View also known as remote-person view (RPV), or simply video piloting, is a method used to control a radio-controlled vehicle from the driver or pilot s view point. Most commonly it is used to pilot a radio-controlled aircraft or other type of unmanned aerial vehicle (UAV). The vehicle is either driven or piloted remotely from a first-person perspective via an onboard camera, fed wirelessly to video fpv goggles or a video monitor. Gimbal is a pivoted support that allows the rotation of an object about a single axis. A set of three gimbals, one mounted on the other with orthogonal pivot axes, may be used to allow an object mounted on the innermost gimbal to remain independent of the rotation of its support. I2C (Inter-Integrated Circuit) is a multi-master, multi-slave, single-ended, serial computer bus invented by Philips Semiconductor. It is typically used for attaching lower-speed peripheral ICs to processors and microcontrollers. Lidar - light detection and ranging MAV Link - Micro Air Vehicle Link is a protocol for communicating with small unmanned vehicle. It is designed as a header-only message marshalling library. MAVLink was first released early 2009 by Lorenz Meier under LGPL license.[1] PID-Controller - proportional integral derivative controller is a control loop feedback mechanism (controller) commonly used in industrial control systems. PPM - pulse position modulation Pulse position modulation is a width spread method to transmit values of several control functions via a digital signal. The signal consists out of a package with n+1 impulse, whereby n is the number of the transmitted control functions. [2] V

9 Figure 0.1: Pulse position modulation [2] In this diagram a pulse position modulated signal is displayed. PWM - pulse width modulation Pulse width modulation (Pulsweitenmodulation) is a simple process to transmit analogue signals with a digital amplitude. Therefore the width of the pulse dose represent the amplitude of the signal. For remote controls this is used as standardized signal between receiver and servos. [3] Figure 0.2: Pulse width modulation [3] In this diagram a pulse width modulated signal is displayed. Servo position from top to bottom: neutral, left, right. RC - remote controlled RC stands for remote controlled or radio controlled. revs - revolution per minute SF Prop - Slow Flyer Propeller SFP Prop - Slow Flyer Propeller Pusher SLAM - Simultaneous Localization and Mapping In robotic mapping, simultaneous localization and mapping (SLAM) is the computational problem of constructing or updating a map of an unknown environment while simultaneously keeping track of an agent s location within it. UAV - unmanned area vehicle VTOL - vertical take off and landing VI

10 1 Background 1.1 Airframe All kind of airframes from single fixed wing aircraft to octacopters can be used for building an UAV. In this section some common types will be introduced Fixed wing aircraft Fixed wing aircraft s are using wings to generate lift caused by the vehicle s forward airspeed and the shape of the wings. The advantage of fixed wing aircraft is there good fuel efficiency, which makes them interesting for missions where long flight times or a large operation range is required. Many kind of fixed wing RC aircraft s are available on the market. Many of them could be considered to be used as an UAV platform. The key-points to choose one of them as UAV platform are the payload which they can carry, good mounting positions for cameras and sensors and enough space to mount the electronic and additional batteries without moving the center of gravity outside the safe envelop Helicopter A helicopter produces lift and thrust by rotors. This allows the helicopter to take off and land vertically, to hover and to fly forward, backward, and laterally. Classical helicopters are equipped with a single main rotor to provide lift and thrust and an anti-torque tail rotor. Classical helicopter can are at least this much stable that they can be controlled by humans without using any electronic stabilization system. The main disadvantages of the classical helicopters against multicopters is the complexity in its mechanic and higher vibrations Quadrocopter Like the name enunciate a Quadrocopter is a rotorcraft with four props. The typical Quadrocopters do consists out of a frame with 4 evenly spread arms with an prop at the end of each arm Hexacopter A Hexacopter is equiped with 6 engine and props. Hexacopter are available with two different arrangements of the props. One arrangement is called Y6, which means that the frame is Y shaped with 2 props at each arm. Therefore one prop is facing downward and one upward. For the other arrangement the frame is equipped with 6 arms with one prop at the end of each arm. The big advantage of a Hexacopter against a Quadrocopter is that a Hexacopter is theoretical still able to fly when one engine/prop is lost. Anyway, if the take-off weight is to high or a partly broken prop causes to much vibration which confuses the sensors a Hexacopter might crash also after the lost of one prop/engine. 1

11 1.1.5 Octacopter The idea behind an Octacopter is to get even more redundancy if one engine/pro fails. Octacopter are also available in two configuration. One based on 4 arms and 2 props at each arm (one facing down, one up) or with 8 arms VTOL fixed wing aircraft Vertical takeoff and landing aircraft combines the advantages of rotorcraft and fixed wing aircraft. They have a better endurance and range than rotorcrafts but they also can land and takeoff at one spot. 2

12 1.2 Engines and power output Within this section some thoughts about the power system of an UAV are undertaken. For the here describes UAV only brushless electric motors with lithium polymer battery are considered Power For most engines the maximum amps as well as the number of cells are provided. The power input which an engine can handle can be calculated using the following formula: P = U I Lithium polymer batteries have a maximum current of 4,2 Volts per cell. The minimum voltage is 3.0 Volts per cell. If we calculate carefully we use 3.3 Volts per cell like suggested in [4]. To have a bare first reference point how much power will be needed performance per kg take-off weight can be used like suggested in [4]. There the following guidelines are suggested: For fixed wing planes: Ground take-off: 80 Watt/kg Simple acrobatic flight: 160 Watt/kg Motor glider: 180 Watt/kg Slow flying oldtimer: Watt/kg Dynamic acrobatic flight: Watt/kg Pylon: Watt/kg Hotliner: Watt/kg For helicopters: For multicopters: 1.3 Propeller and thrust The performance per take off weight gives only a estimation how the UAV will perform. A more detailed performance estimation can be done by taking the propeller within the calculation. Actually the selection of the right propeller has a big influence of the performance. The most propellers are defined by 2 values. The first value is the diameter and the second values is the pitch. The pitch defines the theoretical distance in axial direction which the prop would travel through the air during one turn. This distance is only a theoretical distance because off the compressibility of the air. Some propellers are denoted in inch and some are metric. Mostly the inch values are marked with quotes. A 9 x 7" propeller for example has a diameter of 9" and pitch of 7". Thereby 1" = 2.54 cm How to choose the right prop The following rule of thumbs suggested by [5] can be used to find the right propeller: When the diameter of the propeller is increased, the number of revolution can be decreases to achieve the same thrust. Less revs mostly mean a better efficiency and less noise. 3

13 If the diameter is increased by 1" and pitch decreased by 1" the revs of the engine roughly stay the same. A propeller with a low pitch does give more thrust when the airspeed is low. A width propeller does deliver more thrust then a small one when the airspeed is low. A 3 blade propeller does always have less thrust with lower airspeeds than a 2 blade propeller. With higher airspeeds the 3 blades wins performance. If a 2 blade propeller should be replaced by a 3 blade propeller the diameter of the 3 blade can be chosen 1" less than the 3 blade prop, so they revs roughly stays the same. Props from different with same dimension can very within their behaviour because of different blade shapes and blade endings Balancing of the prop To avoid vibration which can harm the UAV and mess up the values from the sensors it is important to balance all props as good as possible. //TODO Props for Quadro-, Hexa- and Octocopters For Quadro-, Hexa- and Octocopters propellers for slow flyers are often used, because a high amount of thrust at low airspeeds is needed. The "slow fly" props have a thin, wide blade and are quite flexible. The blade flexibility means that they won t break as easily on a prop-strikes but on the other side they also "open up" in pitch (reduce the pitch, or flatten out) at higher RPM. The slow flyer props are available as puller (SF) and pushers (SFP). 4

14 Figure 1.1: Propeller and pitch [5] The blue line demonstrates the pitch, that is the distance which the propeller would travel during one turn without slip. The red line shows the real travelled distance taking the slip into account. 5

15 1.4 Remote control There are many remote controls on the market. The most remote controls currently available are operating on the 2.4GhZ band. Whereby older remote controls are operating on 27, 35, or 40 MHz Signal modulation Telemetry Modern remote controls are available with a telemetry system, which means that a two way communication between sender and receiver is established. 6

16 1.5 AdruPilot - Autopilot Suite Adrupilot is an open source autopilot suite which contains hardware and software for all kind of UAV applications (rotorcraft, airplanes or ground vehicles). Further information can be found on the projects website [6] In the following sections some of its component are introduced. All components are Dronecode supported projects. The goal of Dronecode is to bring existing and future open source projects under a non-profit structure together. Further information can be found under [7] Autopilot hardware 3DR PixHawk board The PixHawk board is an advanced autopilot for building UAVs, based on the PX4 open-hardware project. Its predecessor is the APM Board, which is only supported until the Coopter Version 3.2.1, which means that many features are not available for the APM. A comparision between the PixHawk and APM can be found in table 1.1. Category APM PixHawk Processor 8bit Atmega MHz 32bit ARM Cortex M4-168 MHz Memory 8KB RAM, 256KB 256KB RAM, 2MB Flash Flash Sensors MPU6000 Acc/gyro, L3GD20 16bit Gyro, MS561101Ba03 Baro, LSD303D 14bit Acc/- Exterman compass mag, MPU6000 Acc/- (APM 2.6) Gyro, MS55611 Baro Latest supported APM Copter Latest Version Firmware Extra Features Redundant power supply, Redundant sensors, SD card for storage, new features (i.e. Extended Kalman Filter in Software Table 1.1: Comparison of the APM vs. the PixHawk auto pilot board Additional Information The Pixhawk (FMUv2) single board flight controller is based on the the original PX4 system which consists of the PX4 FMUv1 and various piggyback boards needed for I/O operations. Additional components GPS and compass kit 3DR ublox This module does provide a digital compass and a GPS module. In older version the compass was included within the Pixhawk module, which had the disadvantages that often interferences occurred. Now the compass can by mounted away from sources of interference. I2C Splitter The I2C splitter is needed to connect several I2C module to the Pixhawk board. 7

17 Power distribution module The power distribution board is useful for all electric powered UAV with more than 1 engines. Comfortable power distribution boards does not only provide the ESC with powers from the battery, they also split the control signals to the ESC and provide power from a BEC to the servo rail of the Pixhawk board. Power module from 3DR The power module does supply the Pixhawk auto pilot board with power and with current and voltage measurement from the LiPo flight battery. It can be used with a LiPo battery up to 4S. connectors Autopilot software Mission Planner The Mission Planner is only available under windows and provides functionality to install, update and initialize the autopilot board as well as mission planning and mission surveillance via a telemetry system. Because of the Windows only availability mission planar is not further evaluated here. APM Planner The APM Planner has the similar propose as the Mission Planner but it is available for Windows, Linux and MacOs. For achieving of the cross platform functionality it is build based on the Qt framework. For the projects described within the following section the APM Planner source code was cloned form git and build form source. Ardupilot APM Copter APM Copter is a full-featured, open-source multicopter UAV controller software. Copter is capable of the full range of flight requirements from fast paced FPV racing to smooth aerial photography to fully autonomous complex missions. [8] 1.6 Autopilots in Detail In this section it is tried to provide some background how a autopilot works PID Controller 8

18 1.7 Additional Components FTDI Cable (USB to Serial) The FTDI cable is a USB to Serial (Transistor-Transistor-Logic (TTL) level) converter which allows for a simple way to connect TTL interface devices to USB. The FTDI cable is designed around an FT232RQ, which is housed in a USB A connector. The other side of the cable is terminated with a 6-pin connector with the following pinout: RTS (Request To Send), RX (Receive), TX (Transmit), 5V, CTS (Clear to send) and GND (ground). Figure 1.2: FTDI cable pinouts Telemetry Data Link The PixHawk auto pilot allows to connect an additional telemetry radio to provide a data link connection to the ground station independent from the USB connection. As communication the MAVLink protocol is used. To easiest way to implement this connection is to use the 3DR Radio. The radio uses open source firmware which has been specially designed to work well with MAVLink packets and which is integrated in the Mission Planner, APM-Planer, Copter, Rover and Plane. See [9] The 3DR-Radio is available in 900MHz or 433MHz in the v2 variant and can transmit with a power up to 100mW (20db). The frequency and transmit power must be chosen accordingly to the local laws. An disadvantage of the 3DR radio is that the connection can easily be hijacked because no encryption is used. If somebody knows what he is doing he can take control of the UAV using MAVLink via 3DR radio. Radio Configuration Flashing the firmware of the 3DR Radios The 3DR radio ground module can be flashed directly via the USB port within the "Initial Setup" section of the APM planner. The Baud rate therefore must be set to The air module can also be flashed with APM planner but a FTDI (See Section 1.7.1) must be used to connect it to the USB port. Therefore the FTDI cable is connected to the air module as shown in Figure 1.3 and the baud rate must be set to

19 Figure 1.3: 3DR Radio air module connected to the PC via a FTDI cable This images shows the 3DR radio air module connected to a FTDI cable. Notice that RTS and CTS are not connected, and that the green TX cable coming from the radio must be connected to the orange TX cable on the FTDI cable FPV First Person View means that a video from a camera mounted on the UAV is transmitted to the operator and the UAV is flown based on this video. In Germany it is only legal to fly a UAV within the sight of the operator, so FPV can legaly only be done within sight of the operator and when video goggles are used with an additional spotter. However transmitting a life video to the ground station allows many interesting activities like having a preview for video capture. As minimum equipment for FPV a camera, a video transmitter, a video receiver and some kind of display device is needed. Mostly analogue video transmission is used because it is said to provide a lower latency. When a 2.4GHz remote control is used for flying the only frequencies which can be legal used are within the 5.8GHz band (See Section 1.8). Regarding the latency issue, also the cameras are causing some reasonable latency. An interesting test was done by [10]. The latency of different cameras, who are popular for FPV and video capturing, where compared against each other. Therefore the complete latency from capture to display (including analogue video transmitting) where measured. The results are displayed within Figure

20 Figure 1.4: Latency measured with different FPV cameras This graph shows the total measured latency from capture to display of different cameras which are popular for FPV. The video captured from the camera is transmitted via analogue radio and displayed on a screen. The measurement was done by [10]. A disadvantage of analogue video transmitting is that only a limited video resolution can be transmitted. So Videos in the 1080p or the 720p format can t be transmitted as analogue signal because of the limitation of the available bandwidth Gimbal A Gimbal is a pivoted support that allows the rotation of an object about a single axis. A set of three gimbals, one mounted on the other with orthogonal pivot axes, may be used to allow an object mounted on the innermost gimbal to remain independent of the rotation of its support. To capture more stable and images a camera can be mounted on an electronic stabilized gimbal. This allows the camera to stay a steady position independent of the the orientation of the UAV. Most modern flight control boards like the PixHawk provide additional PWM outputs to control a servo driven Gimbal. More advanced Gimbals are driven by brushless Gimbal motors and an extra controller. These Gimbal allows faster and smoother responses but on the other the are more expensive and an extra controller is needed. 11

21 1.8 Frequency usage in Germany As seen in the predeceasing sections different types of radio connections are needed for the communication between the ground station / operator and the UAV. To avoid interferences between the different connections the frequencies must be spread over different frequencies band. Although the legal issue, like frequencies and tx power restrictions must be taken into account ISM-Band The ISM-Band (Industrial, Scientific and Medical Band) is reserved internationally for the use for industrial, scientific and medical purposes other than telecommunications. Within the ISM Band different frequency ranges are available. Here only the ones which are interesting for UAV operations are introduced. In Germany the following frequencies ranges are open for usage for industrial, scientific, medical and home application (See [11]): 9 khz bis 10 khz khz bis 13,567 khz khz bis khz MHz bis 40,70 MHz 150 MHz 433,05 MHz bis 434,79 MHz 2400 MHz bis 2500 MHz 5725 MHz bis 5875 MHz 24,00 bis 24,25 MHz Video transmission in Germany In Germany video transmission can be accomblishe within the 5,8 GHz band with 25 mw or within the 2.4 GHz band with 10 mw. If a remote control within the 2.4 GHz band is used the video should not be transmitted within the same frequency range. Within the 5.8 GHz band only the frequency range between 5725 MHz and 5875 MHz is allowed. These channels are mainly within the B band. [12] Usage example: 433,05-434,79 MHz for telemetry via 3DR-Radio: Frequency range from MHz to MHz, 10 mw TX power ,5 MHz for remote control with 100 mw TX power MHz for video transmission with 25 mw 12

22 2 Own projects 2.1 3DR DIY Y After considering building the airframe by myself or building an VTOL air-plane based UAV the do it yourself Y from 3D robotics was chosen due to complexity and time reasons Components The kit contains the following components: Airframe Electronic speed controller Engines and props I2C splitter Pixhawk autopilot board Power Distribution board Power Module Following additional components are used: Battery LiPo 4S 6000mAh PPM Encoder The RC receiver delivers 8 PWM signals, these have to be encoded to one PPM signal for the PixHawk board. This module is only needed if the receiver can not be switches to PPM sum signal output. RC Receiver Graupner GR-16 HoTT A modern 8 channel receiver working on the 2.4GHz band with telemetry module. This receiver is able to output the control signals as a PPM sum signal APM Planner - Version 2.0(9) Open Source Software to set up, calibrate, plan and execute missions. APM Copter - Version Flight Control Software installed on the PixHawk controller via APM Planner Setup and Instalation Mechanical The assembly was done according to the manual //todo(add to appendix). Here are some extension to the assembly steps which are not described in detail. Software APM Planer was Downloaded from in the Version APM planner was also used to flash the adrucopter software on the PixHawk4 control board. 13

23 2.1.3 Remote control setup Changed receiver output to SUM 08 To connect the Graupner GR-16 HoTT receiver direct to the PixHawk flight controller the receiver output must be changed from PWM (one channel for each servo) to a PPM sum signal which is provided at servo port with the highest number (8 when a GR-16 is used). This can be done using the telemetrie menu available in the Graupner remote control. Channel set up The following adjustment have to be performed for correct channel mapping between the Graupner receiver and the PixHawk flight controller: Under servo adjustment channel 1 till 4 must be reversed Under transmitter output the following channels must be mapped to the following outputs 2 -> 1 3 -> 2 1 -> 4 4 -> 4 Flight mode switch (CH5) The AdruCopter software running on the PixHawk flight controller allows to predefine 6 different flight modes. The active flight mode can be chosen via CH5 of the remote control. The Graupner mx-20 transmitter does only provide 3 way and 2 way switches, so a 2 way switch and a 3 way switch have to be combined via a free blender to be able to select one of all 6 flight modes. In the following set-up example switch number 8 and control 9 is used. The steps therefore are explained in Figure

24 Figure 2.1: This figure shows the step necessary to set up switch 8 and control 9 to switch between all 6 flight modes. After setup of the remote control the flight mode where assigned as followed: Flight mode 1 -> Stabilize Flight mode 2 -> Alt Hold Flight mode 3 -> Loiter Flight mode 4 -> Pos Hold 15

25 Flight mode 5 -> Auto Flight mode 6 -> RTL (Return to Land) A screen-shot of the APM Planner flight mode assignment page is displayed within 2.2. Figure 2.2: This Figure shows the assignment of the flight modes to the switch positions within APM- Planner. Failsafe To ensure a controlled behaviour when the remote control connection is lost fail safe behaviour should be defined for the remote control. By default the last received position is hold for each channel, which could easily cause the model to get into an uncontrollable state when the signal is lost First Flight To perform a check up of the basic functions with connected engines and flight battery a ground mount was created. (See 2.3.) This makes it possible to check the spinning direction of the propellers, the reaction on control inputs, the reaction on attitude changes and for harmful vibration caused by bad balanced props in a safe way. 16

26 Figure 2.3: Ground mount for testing Prior the first the flight a mount for the hexacopter was created to perform engine test in a safe way. After everything was configured the first flight was performed without any problems. (See 2.4) 17

27 Figure 2.4: First flight performed at January

28 2.1.5 First improvements After the basic functionality were verified in the first flights additional components were added to the Hexacopter. Power supply for additional components To supply additional equipment with electrical power an additional cable was soldered to the battery cables on the power distribution board. Via this cable the full battery voltage is provided. Otherwise only 5V from the servo rail of the PixHawk board would be available. Within the same step the wiring of the ESC, engines, Power Distribution Board, Power Module was rearranged. 2.5 Figure 2.5: Improved wiring of the power distribution board The hardest part during the assembly of the drone is to fit the power distribution board, the power model, the ESCs and the wiring into the frame. This pictures shows one way to order the wiring and how the modules can be mounted. In the middle of the power distribution the additional wires added for the power supply can be seen. Because of the need for 12V (LED Lights, Video Transmitter) and 5V (Mobius Camera) a simple voltage regulation and power distribution board was constructed. For voltage regulation a L78S05CV and a L78S12CV fixed positive single output standard regulators are used together with 4 capacitors. For easy connection of the consumers 4 12V and 4 5V plugs are provided. The drawback of the standard regulators is their bad level of efficiency. Event with the low voltage consumption of the Mobius (250mA) and of the video transmitter (200mA) and the LEDs a heat sink is needed to keep the voltage regulators within an acceptable temperature range. The board itself mounted on the hexacopter can be seen within Figure

29 Figure 2.6: Homebuilt power regulation and distribution board for 12 and 5 Volt Navigation Light When in air it is hard to determine the orientation of the Hexacopter, so Navigation Lights where added to arms. Therefore three coloured 12 V LED light strips where used. The strips are self adhesive and the color can be chosen between green, red and blue and all combinations of them. For navigation lights the colors for the arms where chosen according to the colors used in aviation (left = red, right = green) with an additional blue light for the tail arm. Installation of a telemetry module The telemetry system from 3DR Robotic Version 1 using the 433 MHz frequency band was mounted on the front side of the hexacopter. The frequency and output power was adjusted to the legal limitations and the SSID of the radio was changed to avoid possible conflicts with other 3DR telemetry users. All the radio where performed within the setting section of the APM planner. A image of the Y6 with the telemetry module mounted is displayed within Figure

30 Figure 2.7: 3DR DIY Y6 with mounted telemetry system In a first test it was detected that that the communication via the does work, but only when the laptop is really close to the hexacopter. After double checking of the settings the logfiles, which are created by APM planner, where analysed using the graphs tool included in APM planner. In Figure 2.8 the remote and ground signal strength as well as the remote and the ground noise are diagrammed. In the diagram it can be seen that the signal strength at the ground station is much lower than the signal strength at the remote station. Which leads to the assumption that there is a problem with the transmitter at the remote station. After exchanging of the antennas the situation stays unchanged so that the assumption was taken that there is a problem with the transmitter of the remote station. Figure 2.8: Analysis of telemetry radio signal noise and strength - Broken remote transmitter This Figure shows the signal strength received on the ground, the signal strength received on the hexacopter, the noise measured on the ground and the noise measured at the hexacopter. The diagram was created with the graph tool provided by mission planner. 21

31 After the transmitting problem was detected it was first tried to flash a new firmware on the radio using the APM planner and a USB to R232 (FTDI) cable. See Section But the firmware update did not brought any improvements. Finally a new telemetry radio set was ordered. After installation the remote signal, ground signal, remote noise and the ground noise where measured again. In Figure 2.9 it is displayed that the remote and the ground signal strength are now almost the same. Figure 2.9: Analysis of telemetry radio signal noise and strength - Working radios This Figure shows the signal strength received on the ground, the signal strength received on the hexacopter, the noise measured on the ground and the noise measured at the hexacopter. It can be seen that the signal strength at the ground and the remote stations are almost the same. Video Transmitting and recording Different aspects have to be taken into effect when it comes to video transmission and video recording. For activities like FPV flying the video should be available at the ground station with a low latency and a good reliability and range. For video recording or later video processing a good quality with an high video resolution is needed. Taking all this into effect makes the selection of an appropriate camera and a video transmitter an complicated task. For the first experiments the decision was taken to use a camera with recording capability and an analogue video output. The video is transmitted via an analogue video transmitter / receiver combination operating on the 5.8GHz B band. As camera the Mobius action cam was chosen because of its capability to record videos on a SD card and to provide an analogue video output in PAL or NTSC simultaneously. Also the Mobius action cam is with a weight of 42g lighter and the GoPro Hero. The equipment used for the first experiments is shown within Figure

32 Figure 2.10: Basic gear needed for video transmission For the first tests flight the camera was mounted on a board attached at the front of the hexacopter shown in Figure Figure 2.11: Improvised camera mount used for the first test flight 23

33 Figure 2.12: Impressions from the first test flight with video transmissions Figure 2.13: Display of the video and remote data during flight This screen-shot was taken during the first flight with installed video equipment. To provide more stable videos and to allow remote controlled changed off the camera view point a simple, RC servo driven two axis Gimbal was constructed. For control of the servos the PixHawk port has additional PWM outputs, the settings for stabilization, end position and used remote control channels can easily be set up using the APM Planner software. The Gimbal set up in APM Planner is shown in Figure 2.14 and the Gimbal itself in figure 24

34 Figure 2.14: Gimbal setup with APM Planner This screen-shot displays how comfortable the gimbal can be set up using APM planner. Figure 2.15: Homebuilt 2 Axis Gimbal This pictures shows the homebuilt to axis gimbal. On flight 3 and 4 no videos where recorded on the Mobius camera. At first the power supply to the camera and the camera configuration where checked, but now error where found there. On the forums in can be read that the Mobius does not work with all kind of SD cards. At first the 16 GB SD card from Intenso, which was used first, was reformat within the camera. After the reformat some short video sequence could be captured but not reliable. After that a new 32GB SanDisk Ultra SD card with 80MBit/s was ordered. With this card the video recording works without any problems. In Figure 2.16 a screen-shot from the first recorded on board video is shown. 25

35 Figure 2.16: First on-board video recording. On flight 5 finally a first on-board video could be recorded with the Mobius. Measured Data 3DR Y6 Takeoff weight with basic RC equipment and 4S 6000 mah Lipo: 1960g 3DR Y6 Takeoff weight as described above and 4S 6000 mah Lipo: 2280g Bias current with active video transmission, video recording, 3DR Radio and lights 1030 ma Hover current 26A Max measured current 34A Flight time 12:30 min Lesson learned Video recording problems with Intenso SD Card -> fixed by using SanDisk 32 GB Ultra SD Card with 80 MBit/s Interference problems caused by the Mobius camera causes a high noise on the 3DR radio air station. High latency from camera to display on the PC via video grabber (240ms - 300ms). Low efficiency of the Linear Voltage regulators used to power camera, servos, video transmitter and lights leads to a High temperature of Linear voltage regulator and a unnecessary power consumption. The Gimbal causes vibration when the roll axis is adjusted, which leads to a unsteady video. It seems like the Micro Servo used for the roll axis stabilisation runs to rough and the mounting of the camera is to unstable First Mission (Flight in Auto Mode) On flight number 8 the first mission in auto mode was performed. For testing a less frequented wide open area was chosen. The mission was preplanned within APM planner and than uploaded to the flight controller. A screen shot of the planned mission can be seen within Figure

36 Figure 2.17: Planning of the first mission with APM Planner. In Figure 2.18 the recorded track of the first mission and the planned mission can be seen. At the end of track some "free flight" was done, which tracks are also displayed. Also some render errors can be seen, within APM Planner under Ubuntu some screen elements seem not be repainted properly. Figure 2.18: Track of the first mission displayed in APM Planner. Experience of the first mission The flight was performed with the default settings of the PixHawk. At the day a strong west-wind was present. The legs from waypoint 1 to 3 where performed with the desired ground-speed of 5m/sec, but on the way back the ground-speed was much less due to the headwind. So it seems that some settings have to be adjusted in future to allow better headwind performance. 27

37 2.1.7 Second improvements Fine tuning Auto-mode Tuning: To achieve a better agility the following values are used for Waypoint Navigation: Speed: 800 cm/s Radius: 100 cm Speed up: 300 cm/s Speed down: 150 cm/s Loiter speed: 800 cm/s To achieve a better usability when switching between flight modes loiter and pos hold where changed as followed: Flight mode 1 -> Stabilize Flight mode 2 -> Alt Hold Flight mode 3 -> Pos Hold Flight mode 4 -> Loiter Flight mode 5 -> Auto Flight mode 6 -> RTL (Return to Land) With a 2 way and a 3 way switch the flight modes can be set as described within Table way switch pos 3 way switch pos Flight mode 0 0 Stabilize 0 1 Alt Hold 0 2 Pos Hold 1 0 Loiter 1 1 Auto 1 2 RTL Table 2.1: Flight mode settings with 2 and 3 way switch Improved power distribution board for 12 and 5 V Due to the bad efficiency of the Linear Voltage regulator the home-made power distribution board for 12 and 5 V is redesigned. Therefore the Linear Voltage Regulator are replaced with Step-Down Voltage regulators from Pololu. For 12 V D24V6F12 with a maximum continuously current of 600 ma is used and for 5 V the D15V35F5S3 with a maximum continuously current of 3,5 A is used. 12 V is needed for powering of the 12 V video transmitter and the LED lights. For the lights have a current drain of 180 ma and the video transmitter of 200 ma, so enough reserve is provided. 5 V is needed for powering of the Mobius camera, the servos for the Gimbal and for an planned on board computer and Wlan connection. So in regard to the extension plan are larger board was chosen. On-board Computer As onboard computer a Raspberry Pi should be used. Just a few days age the Raspberry Pi 3 started to become available. 28

38 Video streaming via Wlan Mav-Link via Wlan Stereoscopic imaging 29

39 3 Bibliography [1] Wikipedia, Wiki - MAV-Link, [Online]. Available: [2] RC-Network-PPM, RC-Network PPM, [Online]. Available: index.php/ppm [3] RC-Network-PWM, RC-Network PWM, [Online]. Available: index.php/pwm [4] M. Trauernicht, Wie suche ich den richtigen Brushless Motor für mein Flugzeug aus? pp. 1 14, [Online]. Available: Brushless-Motoren-Markus-Trauernicht.pdf [5] S. Thurnherr, Wissenswertes über Propeller, [Online]. Available: wordpress.com/2011/07/28/wissenswertes-uber-propeller/ [6] Adru Pilot, Adru Pilot Autopilot Suite, [Online]. Available: [7] Dronecode, Dronecode, [Online]. Available: [8] Adru Copter, Adru Copter. [Online]. Available: [9] Adrupilot, 3-DR Radio, [Online]. Available: common-3dr-radio-version-2/ [10] Painless360, FPV Camera Latency - Testing and comparison (Mobius, 808#16, GoPro and FatShark). [Online]. Available: //painless360.webs.com/ [11] Bundesnetzagentur, Funkanwendungen auf den ISM-Bändern. [Online]. Available: http: //emf3.bundesnetzagentur.de/pdf/ism-bnetza.pdf [12] Walkera, FPV in Germany, [Online]. Available: fpv-reichweite-und-verbotene-sachen/ 30