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RADIO CONTROL BY BOB YOUNG The philosophy of R/C transmitter programming This month we will look at some of the principles in­volved in the programming of the modern R/C transmitter. We discuss the use of memories and initial R/C model setup for best flying response. In the course of my radio service work I spend a lot of time listening to tales of woe from concerned or frustrated customers, so much so that, like doctors, you begin to feel that the only people (or R/C systems) in the world are those who are unwell. This can be depressing at times and it must be a real prob­lem for doctors. However, in my work as an R/C system designer, I find these tales very important because I can do something to help and I have used the information gathered to great effect in recent years. The work we did on third-order intermodulation came out of the endless murmurings and hand wringing that surfaced in the lead-up to the MAAA Frequency Subcommittee conference in Sun­bury, Vic. The very popular AM versus FM articles, which are now being picked up by overseas magazines, arose from a South Austra­lian reader’s letter. This poor fellow was under intense pressure from the technocrats in his club who were telling him to get rid of his “inferior” AM equipment and buy the new all-singing, all-dancing FM gear. The transmitter intermodulation articles came to light as a result of the uncertainties that triggered the reluctance of the clubs to accept the earlier issue Keyboards and my subsequent investigations to arrive at the 76  Silicon Chip truth of the matter. As a result, the new highly modified Issue 4 Keyboard has gained wide accept­ance amongst those previously reluctant clubs and is thus alle­viating the worries about transmitter intermodulation for clubs across Australia. Because I was prepared to listen to the worries, inves­tigate and report on what I saw as the truth, those SILICON CHIP articles have completely transformed the way things are being done in clubs all around Australia. There is renewed interest in 29MHz operation; AM no longer carries the stigma imposed by the FM sales hype; 3rd order intermodulation interference (3OI) is a thing of the past in most clubs and transmitter intermodulation is now well understood. However, in the words of one member of the trade, the transmitter intermodulation articles “created a storm” and there are now opposing points of view circulating in the R/C movement. Some members of the trade are not too happy about those articles because they have shifted the emphasis to dual-conver­sion receivers for operation on 36MHz and those in the trade not supplying dual-conversion 36MHz receivers are walking around with noses severely out of joint. At the top of the list of these trade members is Bob Young of Silvertone Electronics, who does not yet have a dual-conversion Rx in his range. This is interesting because it is being whispered in cer­tain quarters that Bob Young of SILICON CHIP fame is pushing the Tx intermodulation line to help Silvertone sales. Wearing two hats is a trying process at times. Programming Now let’s get onto the main theme of programming transmit­ters. There are a wide range of people engaged in R/C activities. Some just need a toy to play with for a few hours to take their mind off work or home pressures. Others, like the dedicated inter­national level contest modeller, need the very best that technolo­gy can provide for that competitive edge. In the middle is a vast array of wants and needs. Sadly, modern mass-production and marketing techniques tend to constrain development so that the needs of the many tend to be forced along lines dictated by the needs of the few. Such is the case in modern transmitter development and now the beginner and sports flier is faced with a choice of the computerised monster more suited for the international competitor or nothing. It was to bridge this gap that I designed the Mk.22 trans­mitter which we have covered in past columns. Unfortunately, whilst that transmitter fulfilled the necessary technical role, the high cost of manufacture in this country has lifted it out of the beginners’ price bracket. Having listened and established that there is much unhappi­ n ess regarding the programming of the Fig.1: servo error should be minimised by transmitting the maximum number of steps available and using the mechanical linkages to reduce the control surface travel. This also stiffens the linkage in regards to control flutter. Fig.2: An off-centre servo will give unequal throw about neutral and will call for less than ideal settings in the transmitter. modern computer radio, let us see what can be done to ease some of the burden. This month we will look at the fundamental principles of programming transmit­ters and some of the common complaints associated with this programming. As programming begins with the model design, we will start from the very beginning. Crook manuals The single most common complaint that I receive is that the instruction manuals are almost incomprehensible. Add this to the fact that the programs are now so complex and it’s not hard to understand why so many people are completely overwhelmed by the whole business. One customer told me that he had flattened the Tx battery three times just trying to program exponential control into his elevators. Another told me that she had locked out all functions except basic 4-channel operation. The poor quality of the factory manuals has driven several people to completely rewrite the manuals for some systems, so have a look at what is available in the model shops for your system. There is an excellent manual written in good English by Don Edberg for the Futaba Super-7 system, for example. Not only does it show how to program in easy logical steps but also gives the theoreti­cal and practical reasons for using each of the programming functions. There is no doubt that the computerised encoder is by far the best method of encoding and a virtual must for the serious competitive modeller. However, in trying to make the transmitter all things for all people, the manufacturers have completely lost the plot in regard to a simple transmitter for the beginner and sports flier. So let us look at some of the fundamentals in order to simplify programming for these two groups. Model memory One of the very interesting developments in the computer encoder is that of model memory. This allows each program to be stored in a separate memory so that the program may be recalled when needed. This has opened new avenues for the contest flier in that multiple configurations of a single model may be stored in sepa­rate memories and changed in flight. Thus, an F3B model may be configured for towline launch, cruise, en­durance, speed or landing (crow), all at the touch of a button or flick of a switch. This is pretty powerful stuff considering that six to eight servos may be involved with multiple point mixing on most of these servos. Programming such a model takes years of experience and requires an excellent knowledge of aerodynamics combined with a very sound grasp of the ramifications of swapping between programs. At the club level, a more mundane use of model memory is to be found. This is the process of storing the flight trims for each model so that when each model is flown that program is called up ready for use. This program may also store such infor­mation as direction of rotation of the servos, channel alloca­tion, servo travel length and mixing ratios. Now it is immediately apparent that there is great danger here for the absent-minded or the modeller who is less than fully aware of the value of preflight checking. What if the model is flown with the wrong program loaded? Controls may be reversed, mixed incorrectly or worse still, allocated to different channels. Anyone who has ever taken off with the ailerons reversed can attest to what happens next. I have done it in my early days but God alone would know how you would cope with a channel wrongly allocated. Horror stories abound in all clubs of models flown with the wrong programs in place and there is absolutely no excuse, for if the correct preflight checks had been carried out the error would have been found on the ground. I am not a great fan of model memory for this type of application. At the height of my contest flying career, long before model memories were invented, I flew aerobatic, helicopter and pylon models all from the one transmitter and on the same day. I even refused to use “dual rate” because I believed that flying was pure instinct and to learn to use two sets of control responses only complicated the learning process and diminished the final performance. I could also have used as many transmitters as I needed (after all I did manufacture the things) but again I wanted that one transmitter to be a part of me. I wanted no variations in stick angles, stick movement, spring pressures, switch placement or transmitter weight or feel. I wanted August 1997  77 Radio Control – continued every hour of practice to reinforce my familiarity with that one transmitter. And it worked. I won many a contest against some of Australia’s best fliers of those days. Setting up the model The secret of my success was all in the setting up of the model. Now there are certain fundamentals which are currently being ignored at club level due to the fact that computer trans­mitters permit sloppy practices which are not in the best inter­est of peak performance of any model. The techno-junkie will revel in the flexibility of the computer encoders. Rudder too sensitive? No problem; just dial in a 50% reduction in servo travel. Elevator operating in the re­ verse direction? No worries; just flip it with servo reverse. And that is how the program stays for the rest of the life of the model. The next model is set up just as casually with travel directions flipped, etc and the stage is set for a possible calam­ity. The astute modeller will look at the setting-up process from the design of the model onwards, with a view to maximising performance, reliability and safety from the very outset. This astute modeller will realise that dialling out 50% of the servo travel at the transmitter end will immediately double the ampli­fier minimum impulse and servo gear slop errors at the servo end, reducing control accuracy in flight and possibly exposing the model to control flutter. Our diligent modeller will instead aim at minimising servo error by employing the maximum number of steps available in the transmitter and using the mechanical linkages to reduce the control surface travel (see Fig.1). This also stiffens the link­age in regards to control flutter. What our thinking modeller will do is use the transmitter to quickly establish the correct control throws on the field by using the electronic adjustments and then, when he arrives home, transfer these adjustments into the mechanical linkages, paying particular attention to setting all transmitter trim controls to neutral, setting servo arms to 90° and reset­ting the transmitter for maximum data transfer. 78  Silicon Chip If your model flies with control surfaces and/or servos off centre, badly balanced controls and more control throw than is necessary, then it is not correctly trimmed and you will never be able to execute manoeuvres properly. An off-centre servo will give unequal throw about neutral (see Fig.2) and again call for less than ideal settings in the trans­mitter. Of course, this can be very useful for maintaining maximum resolution in the transmitter under certain conditions but to leave it because of laziness is wrong. Certainly small variations can be accommodated without loss of system integrity but the opera­tive word is “small”, if you care about top performance. Our thinking modeller will also realise that one day he or she is bound to make a mistake. Thus, he will always attempt to design each model so that servo reversing is not necessary, at least on all flying controls. Suddenly, our astute modeller realises that, in the event of the wrong program being loaded, he has sidestepped a potential accident as a result of attention to good practice and that perhaps he does not need model memory anyway. Thus, we have now greatly reduced the number of programming steps required to set up any one model. Certainly this is the case for most sports fliers and great care should be exercised in not allowing yourself to fall into the trap of the quick and dirty fix. Programming makes it very easy to slip into sloppy habits. Yes, it is more tedious and yes it appears to negate the major advantage of the computer radio but long term success is measured largely in the degree of fi­nesse that one applies to his trade. Allied to the foregoing is the problem of using dual rate to cut down on excessive control throw. Again, the end result is to increase the servo inaccuracy. The most impressive fliers that I have seen are those that let the aircraft fly itself, interfer­ing with the controls only when necessary. Dr Ralph Godkin showed me this back in the early 1960s with the most stunningly impres­sive display of low flying I have ever witnessed – and on reeds (not proportional) to boot. Most modellers tend to use far too much control throw with the result that the flight looks jerky and out of control. This particularly applies to beginners and makes learning just that much more difficult. Instead, the controls should be adjusted so that maximum throw is set to give the desired result. For example, we were required to complete three rolls in five seconds in our aerobatic schedule. In fact I found that I could get away with three rolls in six seconds without loss of points, so my maximum aileron throw was set to give this result. Likewise, full elevator gave the minimum loop diameter called for and so on. Sure, square corners in the manoeuvres complicated things a little but there are aerodynamic ways around this. As a result of this philosophy I extracted the maximum accuracy from the R/C system combined with the maximum rigidity of the control surfaces. Smooth flying Consequently people always remarked on how smooth my flying was and how crisp the exits from the manoeuvre were. The problem arose when other people wanted to fly my models. On several occasions, very experienced aerobatic pilots nearly crashed my models because the controls were so soft that they did not have enough control throw to complete the manoeuvre they had started. I refused to permit people to fly my models from that point on. Beginners need a little more control throw than this be­ cause very soft controls call for the pilot to be in absolute control of all situations. Too much control throw will make the aircraft twitchy and difficult to control and greatly increase learning times. Striking the correct balance is the important point and it is here that a good instructor is crucial. Thus the golden rule in programming your transmitter is to always look well ahead and plan every step with that one ultimate result fixed firmly in your mind – that is, to maximise every aspect of the model’s performance in order to make you the most competent, impressive to watch and safety conscious pilot in your club. Next month we will look at the step-by-step details of proSC gramming.