Peter Carr W B3BQO 329 Lirlle A venue Rid1?wa y PA 15851 In the Stack - RICers, don't be grounded by control channel congestion! Put your ship on six! I • r < I ....~l , , > " , 1 '1 • ! ' , I Photo A. Transmitter case open with encoder board at bottom and bartery-cha rging jack at right. Four penfight cells of the ffight pack are at left, with the decoder at center and receiver at right. fight-cell trensmittet pack at upper left is held to the rear panel of the case with silicone rubber. Switches at the top of the uensmiuer case are sixth- and seventh-channel controls. They are lor dropping bombs or parachutes, operating retractable landing gear, or anything that does not need to be pro portionally controlled. S6 73 Magazine · April, 1981 T he m odel airpl ane contest is under way. Over a hundred pilots and their planes are gathered in the open meadow. At the p ilots' briefing, your radio control frequency is announced as being the most crowded. Th is means that in stead of select ing the time to fly when conditions are best, you must wait to be called to the flight l ine to fly . Only one RIC rig ca n be in ope ration at one time, or the resulting in terfer ence will cause the model to crash. W ith ten or more pilots on the same frequency as you, the rotation of the roster means a long wait between fl ights, and being hurried when your name is ca lled . The add itional pressure of being on a crowded frequency on top of the usua l " f irst flight nerve s " is unsettling and w ill not help you r scores. There ought to be a better w ay ! For ham s, there is a better wa y . While there are only seve n channels for RIC o peration in the 72-M HI band for no n-hams, there are fi ve chann el s from 50.100 to 50.500 MHz in the six-meter band. While these are not exclusively for RIC c perauon. th e ARRL and most ham gro ups througho ut the world have agreed to reserve them for rad iocontro l purposes. At a typical contest, there m ay be fo ur or five ham s fly ing, so the cr ow d ing on any pa rticular frequency w ill be very light. Now, in stead of having to wait to be ca lled up to fly, you can pick the best time and choose the fight conditions, not being bound by the frequency roster. W hile there are several factory-built radios on the six-meter band, most hams prefer to put together a kit. The best known of these is from Heathkit!', and this bran d is always well represented at the f lying field.
Ace RIC, lnc.. of Higginsvill e, Missouri, and Royal Electronics of Denver, Colorado, al so make rad io kits for the six-me te r band. While al l three fi rms offer so me flexibil ity in the choice of styles in components, Ace seemed to have the widest variety of gear at lower prices than the others. Since mo st RIC rigs operate o n the same basic principle, the choice of gear comes down to the specific use to which the rig will be put. For sma ll three-footwingspan models flown in small spaces suc h as school ya rds. the sma llest and lightest rig is best. For quarter-sc al e monsters weighing twenty-five pounds and spa nning nine or ten feet, the size and weight of the rig don't mean a th ing. It takes very powerful se rvos powered by large capacity batteries to move the ailerons or elevator on these biggies. The rad io in the photos is the seven-cha nnel kit from Ace RIC , with t he tran smitter hou sed in a Roya l Eleetronics case. In operation, the rig controls the plane like this: The pilot's th umbs rest on the two co ntro l stic ks on the transmitter. Each stick moves both forward and back as well as from side to side. The right stick controls the ailero ns (left/right) and the elevator (forward/back). The left stick co ntro ls the rudder (l eft/ri ght) and the motor speed (forward/back ). The remaining co ntrols are operated from switches and levers on the front and top of t he case-bo mb-dro p, la nding-gea r retract, and wing flaps . Each stick moves a potentiometer whi ch varies the width of a d igital pulse that becomes part of a pul se train. The pulse train has a clock pulse and seven data pulses, o ne for each contro l. The transmit carrier is turned on and off by the pul se width (A1 emissio n) set by the pulse train. In t he aircraft, demodulated pul ses come from the receiver, whic h is of standard supe rhe t design, to th e decoder board. Here, the clock pulse enables the circuitry to ro ute the first pul se after the clock to the elevator. the next pul se to the ailerons, and so on, un til all seven data pul ses are distributed to the proper se rvos . A se rvo is an e lectro n ic a lly-cont rolled electric motor. It moves an arm that is mechanically co nnected to whatever co ntro l on the plane yo u wish to control. When the data pul se enters the servo, it is compared to a n o n-board pulse-generator output which is co n trolled by a pot, physically positioned by the servo output arm. The on-board pulse is determined by where the arm is currently, while the data pulse from the ground indicates where the pilot wants the arm to be positioned. A difference between these two pulses produces an error, which causes the servo motor to rotate in the proper direction to move the arm/pot co mbination to red uce t he e rror. At zero error, t he motor sto ps a nd t he servo idles, waiting for a new positio n indication to be sent up from the ground via the pulse train. While the transmission method is digital pul se, the net effect on the plane is smoot h control, since the pulse-recurrence frequency is high enough to preclude stepping of the co ntro ls. In actual use, all th is highbrow theory is not important to the pilot and his plane. As the pilot thinks " let's do an axial right roll ," his thumb moves the transmitter's right stick to the right, and as the plane halfrolls to inverted, he pushes the stick forward for down e levato r, holding the nose up as the seco nd half of the • ,- • - -' ' 6 I • I • I • ,. I • • • • :1 I. • , • Photo B. Th e system buttoned up and ready to install in the aircra ft. A 6PD T switch (not shown] turns the airborne unit on and o ff. The receiver/decoder case is covered with thin foam rubber for protection. Th e servo at lo wer center is one o f fo ur in the basic system. Photo C. The rad io room o f a t yp ical powered aircraft. Re- ceiver/decoder and battery are both wrapped in one-inch foam to dampen vibration from the engine. The three servos control rudder. elevator. and motor speed. - 73 Magazine · April, 1981 57