All rights reserved. We advise readers to check that all parts are still available before commencing any project.

Transcription

1 Copyright 2008, Wimborne Publishing Ltd (Sequoi House, 398 ingwood od, Ferndown, Dorset H22 9AU, UK) nd Techites Interctive Inc., (PO ox 857, Mdison, Albm 35758, USA) All rights reserved. The mterils nd wors contined within EPE Online which re mde vilble by Wimborne Publishing Ltd nd Techites Interctive Inc re copyrighted. Techites Interctive Inc nd Wimborne Publishing Ltd hve used their best efforts in prepring these mterils nd wors. However, Techites Interctive Inc nd Wimborne Publishing Ltd me no wrrnties of ny ind, expressed or implied, with regrd to the documenttion or dt contined herein, nd specificlly disclim, without limittion, ny implied wrrnties of merchntbility nd fitness for prticulr purpose. ecuse of possible vrinces in the qulity nd condition of mterils nd wormnship used by reders, EPE Online, its publishers nd gents disclim ny responsibility for the sfe nd proper functioning of reder constructed projects bsed on or from informtion published in these mterils nd wors. In no event shll Techites Interctive Inc or Wimborne Publishing Ltd be responsible or lible for ny loss of profit or ny other commercil dmges, including but not limited to specil, incidentl, consequentil, or ny other dmges in connection with or rising out of furnishing, performnce, or use of these mterils nd wors. EADES TECHNICAL ENQUIIES We re unble to offer ny dvice on the use, purchse, repir or modifiction of commercil equipment or the incorportion or modifiction of designs published in the mgzine. We regret tht we cnnot provide dt or nswer queries on rticles or projects tht re more thn five yers old. We re not ble to nswer technicl queries on the phone. POJECTS AND CICUITS All resonble precutions re ten to ensure tht the dvice nd dt given to reders is relible. We cnnot, however, gurntee it nd we cnnot ccept legl responsibility for it. A number of projects nd circuits published in EPE employ voltges tht cn be lethl. ou should not build, test, modify or renovte ny item of mins powered equipment unless you fully understnd the sfety spects involved nd you use n CD dptor. COMPONENT SUPPLIES We do not supply electronic components or its for building the projects fetured; these cn be supplied by dvertisers in our publiction Prcticl Everydy Electronics. Our web site is locted t We dvise reders to chec tht ll prts re still vilble before commencing ny project. To order you copy for only $18.95 for 12 issues go to

2 Constructionl Project FEEID GLIDE CONTOL MIKE ODEN An utomtic flight ttitude control system suitble for free flight model gliders I N order to muse his young nephew lst summer, the uthor mde number of model gliders, which were ten to the top of locl hill nd then lunched. The models were mde from bls wood nd were not powered in ny wy, except by grvity. Severl designs showed some promise, but mintining level flight with ny consistency ws problem. Promising designs were shelved becuse fter 20 metres they showed signs of losing stbility, preferring to roll over or stll with the occsionl crump of deforming bls wood. FLIGHT TIMES As their glides were observed, it seemed pprent tht it must be possible to incorporte n utomted flight control system, to give the designs t lest fighting chnce. Following number of prototypes, this rticle describes how to me nd instll into model glider low cost microcontrolled stbilistion system tht helps model gliders to fly little more stright nd level. Glider flight times hve been incresed from n verge of five to six seconds to over 15 seconds the limittion now being tht the uthor s locl hill is just not big enough! The rel power of Freebird is tht the flight correction lgorithm cn be modified by reprogrmming the PIC16F84A microcontroller, which hndles the ttitude detection nd flight correction, ll in rel time. FLIGHT PATH To encourge budding eronuticl engineers (young nd old) to te up this mid-summer mdness, n overview of ircrft flight dynmics nd some prcticl flying informtion hs lso been included. The design hs been ept simple, using low cost nd redily vilble components. For inexperienced model mers, glider cn be purchsed. During development, portble computer ws used in conjunction with the EPE Toolit M3 (Oct/Nov 01), to provide full in-the-field tuning of the softwre, but this is not essentil. FLIGHT THEO A full nlysis of how ircrft fly is complicted subject nd cnnot be fully detiled here. Further reding on the subject of erodynmics is given t the end of this rticle. In summry, for fixed wing ircrft to fly, it must be mde to move forwrd. The wings re designed to convert prt of the flling motion into forwrd motion. As the wings move forwrd they produce lift, which cts ginst the weight of the glider, effectively ming it lighter. The lighter glider in turn requires less forwrd speed so it settles into stble forwrd flight. The forces cting on glider in stble flight re shown in Fig.1. The min forces re: Lift force generted by the wings (upwrds) Weight of the glider nd control electronics (downwrds) Drg or retrdtion force s the glider tries to move through the ir (bcwrds) Propulsive force which for gliders is supplied by grvity (forwrds). In stble flight, the lift force is just less thn the weight force, (i.e. the model slowly descends) nd the thrust force is greter thn the drg force (i.e. the model moves slowly forwrd). The objective of glider designers is to mximise the distnce moved forwrd by the glider nd minimise the verticl distnce it flls. This is nown s the optiml glide-slope (refer to Fig.2) nd Freebird is iming to eep the glider within these operting prmeters t ll times. Incidentlly, this is lso guide to the slope of good hill to lunch from, s the glider should be ble to continully fll, yet mintin constnt height from the ground. So by the ddition of wings, the simple flling object is turned into gliding object. The next problem to solve is how to control the motion of the ircrft in threedimensionl spce. 636 Everydy Prcticl Electronics, September 2002

3 FLIGHT CONTOL Aircrft trvelling in spce cn move in the following wys (see Fig.3.): Pitch rottion bout n xis tht psses through the wings loos lie rising or lowering of the nose. To correct ltertions in pitch, the elevtors locted on the til surfces re djusted in unison (i.e. both elevtors up or both down). oll rottion through the centre line of the fuselge loos lie one wing rises, whilst the other flls. To correct ltertions in roll, the ilerons locted on the wings re djusted in opposition (i.e. one ileron moves up, whilst the other moves down). w rottion bout n xis perpendiculr to the fuselge. To correct ltertions in yw, the rudder locted on the til is djusted. When in flight, ll sorts of forces ct on the ircrft, so tht t given instnt ny combintion of these motions my be evident it relly is wonder tht hnd thrown model glider flies ny distnce t ll! So, the ide behind Freebird is to correct these motions before they become too extreme nd result in the ircrft crshing. THUST LIFT WEIGHT Fig.1. Forces cting on glider in stble flight. L H A computtionl system tht detects ttitude ltertions nd determines the correction necessry to restore norml flight. A servo system, tht cn move ircrft control surfces s directed by the ttitude computer. Usully, computtions re bsed upon generic informtion tht forms the bsis of n in-flight mthemticl model for tht prticulr type of ircrft. Also, specific informtion is dded tht reltes to tht flight i.e. ircrft weight nd locl wether conditions. Freebird does not crry out ny mthemticl computtions, but outputs predefined vlue of servo correction from loo-up tbles. Commercil detection systems me use of sophisticted detectors, including detectors sensitive to ccelertion, which results in more refined control. Although Freebird does not offer the sophistiction of commercil systems, it does incorporte ll of the elements detiled bove. DAG H GLIDE SLOPE = TAN ~ 6 TO 10 L HILL correction for this motion is derived from the mesurements ten from the pitch nd roll sensors. To ssist the setting up procedure, light emitting diodes (l.e.d.s), D1 to D4, re included in series with the tilt switch, nd re turned on when the respective switch closes. This corresponds to bout 10 degrees of tilt. Switches S5 to S8 re slide switches within 4-wy dul-in-line (d.i.l.) module. They llow different softwre routines or modes to be selected, s discussed presently, thereby ltering the correction chrcteristics of Freebird. The softwre cn be chnged without the removl of the PIC from the unit, by mens of in-circuit progrmming socet, SK1. Note tht this does not correspond to the pin rrngements used by John ecer in his numerous EPE projects. Fig.3. Aircrft ttitude nd surfces used to control movement. These help stbilise ginst the forces of pitch, roll nd yw. Fig.2. Optimum glide-slope. Objective is to mximise distnce moved forwrd nd minimise the verticl distnce it flls. FEEID DESIGN The design for Freebird ws loosely bsed upon commercil ircrft utopilot systems. Auto-pilots llow pilots to relx by flying the ircrft without ny humn intervention nd re normlly used in the mid-section of long flights where irspce is not crowded nd there is less need for the ircrew to lboriously mintin fixed heding nd level flight. Any utopilot requires the following systems to be present: An ttitude detection system. CICUIT DESCIPTION The complete circuit digrm for Freebird is shown in Fig.4. The hert of the system is the PIC16F84A microcontroller, running t 20MHz, s set by crystl X1. Tilt switches sense chnges in pitch (S1, S2) nd roll (S3, S4). They re rrnged in the sme plne, but offset with ech other t 90 degrees (see Fig.5). When perfectly level, the switches re rrnged to be off, which gives degree of ded bnd nd helps to reduce the sensitivity of the detection system. There is no sensor present to detect yw nd the FEEDACK COMPUTATION The softwre ssembly listing contins full description of the PIC s progrm opertion nd other detils, so just short summry is given here. The PIC undertes the following tss: 1. eds the mode switch nd executes the pproprite softwre module 2. Detects pitch or roll tilt, by mens of the tilt switches (ctive low) 3. Determines the pproprite servo(s) to move nd by how much 4. Determines if yw correction is required bsed upon roll nd pitch Everydy Prcticl Electronics, September

4 1 470Ω DOWN 2 470Ω D1 D2 D3 D4 UP 3 470Ω OLL LEFT 4 470Ω OLL IGHT S1 S2 S3 S4 D5 1N C2 15p X1 20MHz C1 15p 18 A1 17 A MCL 14 +VE 6 INT/ IC8 IC1 PIC16F84A OSC1/CLK IN 3 TOCKI/A4 1 A2 2 A3 15 OSC2/CLK OUT 13 DI0/7 12 CLK/6 GND 5 M1/7 M1/4 M1/3 DATA M3 AW +V 0V DATA M2 OLL +V 0V DATA M1 +V 0V M1/2 M M M M1/1 + C3 10µ C4 220n ESPONSE S8 OLL TAVEL S7 TAVEL S6 LOCK S5 1 SEE TEXT T1 T MCL 0V CLK DATA 5. Outputs corrective commnds to the roll, pitch nd yw servos Servo Loc, switch S5: When enbled, ll servos re loced in their current positions. This helps with lignment (sy, The min ctivities re crried out in (1) to (4) nd re rrnged to loop endlessly. checing zero, mximum up or down elevtor deflection on the ircrft). It lso The servo output module is clled by timer interrupt every 18ms nd this ensures llows the initil checing of l.e.d.s to be tht the servos receive their control informtion, irrespective of other ctivities crried out in comprtive quiet without the servos moving. going on t the time. Servo Trvel Pitch, switch S6: the trvel The min loop senses which, if ny, of of the pitch servo cn be incresed or the tilt switches re ctive. The combintion of tilt switch closures is used to decresed. When enbled, the servo rottion is ±60 degrees. When disbled the enter loo-up tbles which define the trvel in ech direction is hlved, i.e. bout pproprite degree of servo correction ±30 degrees. necessry. These vlues re plced into Servo Trvel oll, switch S7: s Pitch servo position register stores in rediness switch S6, but with respect to the roll for output when the servo interrupt is servo. executed. esponse, switch S8: when enbled The following modes re vilble in the (slow), the rte of trvel of the servo movement is pproximtely one second from softwre, nd re selected by switches S5 to S8: +60 degrees to 0 degrees. This sluggish response is better for flying on still, hot S5 S6 S7 S8 summer dys, or with lrger gliders. When Servo Loc Servo Trvel Servo Trvel esponse disbled (fst), the Pitch oll movement is speeded On enbled full full fst up to 0 5 seconds. This setting is useful Off disbled hlf hlf slow in gusty conditions where the glider must respond rpidly in order to mintin OLL SENSOS stbility. FOWAD Any mixture of the bove functions cn be selected. AFT SENSOS PIC T2 Fig.4. Complete circuit digrm for the Freebird Glider Control. TILT SWITCHES Fig.5. Attitude detection using tilt switches. Pitch S1/S2 nd roll S3/S4 re rrnged in the sme plne, but offset t 90 from ech group COMPONENTS esistors 1 to 4 5 M1 470W (4 off) 8-wy commoned pge s.i.l. resistor module All except M1 0 25W 5% crbon film or better. Cpcitors C1, C2 15p (or 10p) cermic (2 off) C3 10m rdil elect. 16V C4 220n cermic Semiconductors D1, D4 sub-min green l.e.d. (2 off) D2, D3 sub-min red l.e.d. (2 off) Approx. Cost Guidnce Only 15 excl. servos & btts. 638 Everydy Prcticl Electronics, September 2002 D5 IC1 See SHOP TALK 1N4148 signl diode PIC16F84A-20 preprogrmmed microcontroller (see text) Miscellneous M1 to M3 Servo motor (see text) (3 off) S1 to S4 Tilt switch (non-mercury type) (4 off) S5 to S8 4-wy d.i.l. on-off slide switch module T1 2-wy pin connector, mle, or 1mm terminl pins T2 4-wy pin connector, mle, or 1mm terminl pins X1 20MHz crystl Printed circuit bord, vilble from the EPE PC Service, code 367; bttery pc (see text); connecting wire; solder etc.

5 POWE SUPPL A supply of between bout 5V nd 6V is required to power the PIC nd servos. Power consumption pes t round 430mA with ll three servos in motion, but norml stedy stte consumption is round 45mA. To eep costs down, dry cells cn be used lthough rechrgeble cells such s Nicel Cdmium do help to reduce costs in the long run. The most importnt considertion here is weight. Use of four AA-size btteries is cceptble, weighing bout 170 grms, nd supplying bout 1 5V ech (totl 6V). The blnce of the glider is importnt nd the bttery pc will ply n importnt prt in the eventul setting up. S Model rdio control servos re used to control the ircrft s these re purpose built, lightweight, vilble t modest prices nd re designed to be instlled into model ircrft. dio control servos require position instruction every 18ms nd the PIC s interrupt routine is set to output this informtion, irrespective of wht other tss re being executed. The servo position instruction comprises 1ms strt pulse followed by commnd pulse vrying between zero nd 1ms. The servos re 3-wire units. The positive led connects to the power supply positive line, the erth connects to bttery negtive, nd the dt line to the pproprite PIC output. An nlysis ws not considered necessry with regrd to the vulnerbility of ech system to the overll stbility (nd therefore sfety) of the control system s it would be used in hobbyist setting nd not for commercil use. However, n irbre could be dded should the glider remin irborne for too long. eders nowledgeble in PIC progrm writing could esily modify the softwre to drive nother servo to control M1 M2 M3 OLL AW = ELLOW WIE = ED WIE = LUE WIE T1 S8 S7 S6 S5 POWE 0V +VE MCL 7 0V ON T2 D1 S4 M1 S2 S1 IC1 Completed printed circuit bord connected to single servo motor. Note the four ttitude tilt switches. it. A timer of up to 14 minutes durtion could be creted by counting the 18ms interrupts by mens of 16-bit counter. CONSTUCTION The printed circuit bord (p.c.b.) ssembly nd trc lyout detils re shown in Fig.6. This bord is vilble from the EPE PC Service, code 367. Assemble in your own preferred order, noting the direction of the diodes nd cpcitor C3. Use socet for the PIC. Identify the common led (it hs spot longside) on the s.i.l. resistor module nd position it s shown. Note tht p.c.b. holes 5 D2 1 D4 X1 4 Fig.6. Freebird printed circuit bord component lyout, wiring detils to servo motors nd full-size copper foil underside mster pttern. D3 S3 3 2 D5 C2 C1 + C3 C4 3. 0IN (76. 2mm) hve not been provided for the unused resistors in the module. The unrequired leds should be folded bc to llow the module to slot into the p.c.b. Instll the tilt switches with plenty of curvture in the leds this will me lter djustments esier. Me sure the d.i.l. switch is soldered in correctly (i.e. the switch should be closed when t the top of the bn, nd off t the bottom). After you hve fully checed the correctness of your soldering nd ssembly, nd confirmed tht the power supply is correctly woring, insert the preprogrmmed PIC into its socet, ensuring its correct orienttion. If you hve your own PIC progrmming fcility, such s the EPE Toolit MK3/TK3 progrmmer, the PIC could be progrmmed in situ. See this month s Shoptl pge for detils of obtining the softwre nd preprogrmmed PICs. Note tht the progrmming pinouts of the T1 connector do not correspond to the stndrd John ecer rrngement. Do not connect the servos to the p.c.b. until fter the following initil setting up. SETTING UP Plce the ssembled p.c.b. on flt tble nd ensure tht switch S5 (Servo Loc) is selected to disbled (i.e. ll servos unloced). Physiclly djust the verticl ngle of the tilt switches until ll the l.e.d.s re just out. ise the free end of the bent over tilt switch to turn it on erlier, lower to turn it off lter. To chec the Pitch setting, rise the rer of the bord by pproximtely 10mm until tilt switch S1 nd l.e.d. D1 just turn on. eturn Everydy Prcticl Electronics, September IN (40. 7mm)

6 ELEVATO UDDE AILEON Fig.7. Generl rrngement of servos within the glider. UDDE the bord to horizontl nd then rise its front by bout 10mm, to chec switch S2 nd l.e.d. D2. To chec the oll setting, lift the left edge of the bord (i.e. bn to the right) nd chec tilt switch S4 until l.e.d. D4 just lights. epet for left bning. Connect up the yw servo. Chec tht this servo responds to right nd left roll. Then connect up the Pitch nd oll servos (omit the roll servo if desired see lter). Mr ech servo with lbels stting Elevtor (pitch, A2), Aileron (roll, A3) nd udder (yw, A4). Chec tht ll of the mode slide switches (S5 to S8) operte correctly. Freebird is now redy for instlltion into glider. WINGS AND THINGS More experienced model mers my wish to build their own glider specificlly for the job. For those new to flying free flight model gliders, purchsing prtilly completed model is recommended, which only requires minor dditions for completion. For the novice, the subject of model gliders nd how to fly them is quite extensive, but with little ptience, n enquiring mind nd will to tiner, there is no reson why resonbly good glider, with dequte flight chrcteristics cnnot be built. Joining club will be of gret benefit to the novice. With the prototype instlltion, using NiCd bttery pc nd three servos, the weights were s follows: ttery pc 150gms Freebird p.c.b. 30gms Servos 150gms (totl) Adding little for linges, nuts nd bolts, the totl pylod weight ws bout 350gms. The servos used for initil tests were fr hevier thn necessry nd were lter replced with micro servos, reducing the weight by 80gms. FEEID ELEVATO AILEON SEO (WING MOUNTED) AILEON The glider requires to not only lift itself, but lso the pylod, plus little for luc. It ll gets little complicted now nd you re best dvised to s your locl model hobby store to recommend glider. Tell them you need something suitble for novice to build, the pylod will be 350gms, with low wing loding. For good stbility, loo to cquire glider with double dihedrl wing. Fix the wings to the fuselge using severl lrge overlpping rubber bnds. This helps to bsorb the shoc when lnding on wing, which is common event, lthough it is reduced s Freebird becomes more tuned. ON ALANCE The model must blnce correctly in the pitch nd roll xes. The blnce point for pitch should be one-qurter to one-third of the width of the wing bc from the leding edge. Position btteries or dummy weight to obtin this blnce point. Chec tht the model blnces lso in the roll xis, by supporting ech end of the fuselge centre line with pins. Chec to see which direction the glider rolls. Use PVC tpe or some cots of dope (model pint) on one wing s counterweights to correct s much s possible, lthough perfect blnce in this xis is not relly possible. Note tht Freebird is not sophisticted enough to enble poorly constructed nd set-up glider to fly, but it will extend the flight of resonbly well set-up glider. When selecting glider, remember to chec tht the wings re detchble nd tht ll the vrious prts will go through cr door. Access to the p.c.b. will be necessry to llow different softwre modules to be selected vi the d.i.l. switch. This normlly will require the wings to be ten off. If you intend to crry out in the field progrmming, chec tht smll hole cn be mde in the fuselge for the progrmming connector. The first objective should be to obtin good understnding of free flight glider by ming series of flights with the glider loded up with equivlent weight of btteries nd servos. Lern how to note the wether conditions, how to chec the blnce, nd how to lunch. Finlly, lern how to note ech flight nd the correction(s) (me only one t time) necessry to slowly improve the flight time. reges nd how to fix them on the hills will become second nture! INSTALLATION The flight of the glider is corrected by mens of moving rudder, ilerons nd elevtors in exctly the sme wy tht full size ircrft re controlled, see Fig.7. The servos connect to the control surfces by mens of thin push rods or owden cble most good model shops will stoc such items. The direction of trvel of the servos is importnt to note, but more on tht lter. With the bttery instlled in the nose of the glider, the servos re ll mounted in the fuselge, usully somewhere under the wing so tht the glider blnces, when held by the wing tips. The ileron servo is mounted in the wing nd this cn be little tricy for those new to model glider construction. The servo linges should be rrnged to deflect ech ileron in the opposite direction (i.e. left up, right down), but they should both return to neutrl. To ese this problem, it is possible to fly Freebird using only two servos (elevtor nd rudder) lthough correction of roll is not s effective. Ech control surfce will require different degree of movement to djust the flight of the glider, but surprisingly smll chnge cn hve significnt effect. Normlly, the control surfce needs to only move bout 10 degrees bove or below the horizontl to hve n effect on flight ttitude. The surfce re of the control nd the speed of flight lso hve n impct upon the mount of trvel necessry. Me use of the servo loc mode to view the trvel distnces nd chec the neutrl point of ech surfce is exctly in the centre of trvel. Add smll offsets in the looup tbles to correct minor errors, or djust the trvel t 640 Everydy Prcticl Electronics, September 2002 ATTE Positioning of the circuit bord, servos nd bttery (nose cone) in the fuselge sections.

7 the servo rm. Also, most servo rms cn be removed nd repositioned to extend the rnge of convenient positions. TAVEL Note the direction of trvel of ech servo nd chec tht the movement will lter the control surfce in the correct direction. If the direction of trvel is incorrect, swp to the other side of the servo control rm, or rotte the servo 180 degrees in the ircrft, or chnge the linge to the control surfce. Ensure tht ll of the movements re correct, before instlling the servos, s ming chnges fter instlltion in the glider is difficult nd time wsting. Ensure tht some djustment cn be mde to the servo trvel (normlly done with smll brss threded screw connected to the servo drive disc, gin vilble from model shops). If PIC progrmmer is vilble then simply djust the zero point in the loo-up tble. Position the bttery unit into the front of the glider. The glider should blnce when held by the wing one-third of the wy from the leding edge chec this nd djust the bttery pc s necessry. Locte the bttery pc with bls wood nd sponge to ct s shoc bsorber. Connect up push rods or cbles to the control surfces. Instll the p.c.b. (tilt switch S2 points ft (til)) in the fuselge, under the wings nd on the floor of the glider. Chec tht ccess to the progrmming socet is cler. Chec tht with the wings level nd the fuselge level ll l.e.d.s re off redjust s necessry. If the servos re moving ll the time, then they cn be loced using slide switch S5. Locte nd bolt the p.c.b. into the glider nd use hot-melt gun to finlly fix the tilt switches onto the PC. It my be necessry to hot-glue ny connectors, s the uthor hs sometimes found them disconnected fter forceful lndings. SOFTWAE TECHNICALITIES The softwre is written with simplicity nd the expecttion is tht it will prompt experimenttion, modifiction nd improvement. The core of the softwre is centred round the PIC TM0 timer. This is set to interrupt the minline every 13ms thus ensuring tht the servos re serviced with their control pulses irrespective of the other things going on. The interrupt code outputs to ech servo 1ms strt pulse followed commnd pulse of between 1ms nd 2ms durtion. When the progrm is not executing n interrupt, it is constrined to constntly execute the minline loop. The minline undertes three tss: l. red mode switches nd execute the pproprite softwre module 2. red tilt switches 3. clculte required position of ll servos nd lod the demnd vrible, in rediness for the interrupt to output it. Three vribles define servo demnd: servop pitch servo position servor roll servo position servoy yw servo position Flight correction tble for Pitch: Flight Attitude Sensor vlues corrective elevtor D1 U1 servop vlue degrees Level flight deg pitch down up elevtor 10 deg pitch up down elevtor Inverted flight 0 0 n/ n/ Flight correction tble for oll: Flight Attitude Sensor Vlues Corrective Aileron L1 1 servop vlue degrees Level flight roll left right ileron 10 roll right left ileron Inverted flight 0 0 n/ 0 n/ Flight correction tble for w: Flight Attitude Sensor Vlues Corrective udder L1 D1 1 U1 servoy vlue degrees level flight centre 10 roll left, only right 10 roll right, only left 10 roll left, pitch down right 10 roll right, pitch down left 10 roll left, pitch up right 10 roll right, pitch up left Inverted flight centre Error Error A servo position is determined by the vlue plced in ny of the vribles bove. Five positions for the pitch servo re given below. The current servo position is held in the vrible servpc nd is used where slower rte of movement hs been selected. Servop (deciml) Servo degrees The rte of trvel of the servos cn be djusted by mens of the mode switch. The demnd position is subtrcted from the current position to give n error vlue nd the servo is instructed to move in the direction so s to reduce the error to zero. Freebird cn operte fourth (uxiliry) servo. This could be used to operte ir bres, fter period of time for exmple. As sid erlier, one wy to devise timer could be to use the 18ms interrupt to increment 16-bit counter. This would give timed periods in excess of 15 minutes. It is possible for Freebird to detect inverted flight, but correction of this extreme sitution hs not been implemented. New nd experimentl code cn be progrmmed into the PIC either t home, or on the hillside nd then tried out. The mode switches cn be reprogrmmed for this ts if required. The ttitude sensors re defined s: Pitch: U1 forwrd sensor (senses 10 pitch up) D1 ft sensor (senses 10 pitch down) oll: L1 right sensor (senses 10 roll left) 1 left sensor (senses 10 roll right) w: not present (computed response) FLING Te cre when selecting the lunch site. Avoid crowded res nd plces where the glider might stry into trffic. Me sure tht ccess to the site hs been pproved nd preferbly fly with club. The following list of equipment tht cn be put into rucsc my be useful for the independent flyer. Notepd nd pen Smll selection of ls nd glue Tissue pper, dope, clener nd brush (for covering holes in the tissue covering) Selection of trimming weights (nuts nd bolts) Spre set of btteries Pliers, screwdriver ubber-bnds PVC Duct Tpe Sunglsses, blnet, sndwiches, fls of coffee! Choose sight with 180 degree unobstructed field of view (i.e. no trees, styles or fences etc) combined with good slope of bout 30 or 40 per cent. For initil glide testing, try to find field with long grss this mes good cushion. For the first flight, unloc the servos nd set pitch nd roll to mximum trvel nd response rte to fst. Tilt the glider nd chec tht ech control surfce moves in the correct direction. echec the glider blnce, under the wing tips. Lunch the glider into wind whenever possible. Try to void gusty conditions t first. Do not lunch the glider upwrds this will result in stll. Wht the glider initilly requires is irspeed, so lunch the glider horizontlly. It will initilly drop quicly until irspeed is gined nd then it will then slow down nd settle into stble flight. As soon s possible note wht the glider does. If it pitches up nd stlls, set little more down elevtor. Te your time in between flights thin bout wht hppened. Trce the flight pth with your hnd to reinforce the complexities in your mind Everydy Prcticl Electronics, September

8 Using spirit level to chec fuselge blnce. wht needs to be corrected? It cn be severl motions combined try correcting one motion or problem t time. Chec the blnce every time the glider is prepred for lunch. FLIGHT PLAN Note tht flying gliders tht hve pronounced flight durtion requires fliers to give extr considertion to sfety. Keep models to wing spn of less then 90cm. Avoid flying ner rods where cr drivers might be distrcted or in crowded prs. If you find field, gin permission from the frmer or owner these re smll considertions nd dhering to them will enble gliders to be enjoyed by everyone. Try to join your locl model flying club, where you will find welth of experience nd tlented people, dded to the fct you should be covered by club flying insurnce policy. Under no circumstnces should Freebird be used in power models of ny sort. e wre tht bd lndings nd vrious forms of breges re nturl prt of experimenting with free flying models nd these should be seen s n inevitble prt of investigting flying mchines, rther thn mjor ctstrophe. Ptch them up nd get them bc into the ir. If you thin tht seeing your model with broen wing on the first flight might tempt you to jump off the hill in despir, then this pstime is not for you. The best of luc to those of you tht Using severl cots of dope (model pint) to counterblnce wings. SQUIES MODEL & CAFT TOOLS ANTEX SOLDEING STATIONS ANTEX 660TC might be tempted to build Freebird nd venture out onto the hills this summer. 6 eferences sic Aeronutics for Modellers, Alsdir Sutherlnd, Trplet Publictions ISN Designing Model Aircrft, Peter Miller, Trplet Publictions ISN ritish Model Flying Assocition: ll sorts of informtion bout clubs etc. dio Controlled Soring: www. csoring.com gliders, ger, events. Trplet Publictions: Quiet Flight gliding nd electric flight mgzines, designing nd building ircrft. ANTEX 690SD * Temperture control rnge C` * Temperture control rnge C * Thumb wheel potentiometer control * Digitl redout temperture control * 50 Wtt Iron Included (25W Optionl Extr) * 50 Wtt sttic dissptive iron included * Wide rnge of spre bits (0.5mm - 6.0mm * Wide rnge of spre bits (0.5mm - 6.0mm) Norml Price Now Norml Price Now Post Free to UK ddresses. Post Free to UK ddresses. Post, Telephone or Fx your orders to:- Squires, 100 London od, ognor egis, West Sussex, PO21 1DD Tel Fx OU 600 PAGE POST FEE MAIL ODE CATALOGUE IS AVAILALE FEE OF CHAGE TO ADDESS IN THE UK - OVESEAS CATALOGUE FEE, POSTAGE CHAGED AT COST TO CEDIT CAD Shop Open Mondy - Fridy, 9-5 Sturdy 642 Everydy Prcticl Electronics, September 2002