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REMOTE CONTROL BY BOB YOUNG How to prevent damage to R/C transmitters & receivers This month, we will look at some of the problems asso­ciated with maintaining the modern R/C receiver &, in particu­lar, how to minimise damage when a crash occurs. Also, there is some very practical advice on how to avoid serious damage to the transmitter. Before moving on to receivers with their problems of high “G” forces together with dust and water ingress, I feel I should round off the transmitter articles with a bit of friendly advice. I said transmitters usually have a long and placid life but I should qualify that. I am reminded of a few incidents concerning transmitters, from my servicing experience. I once had a very irate customer in Melbourne return a valve transmitter it was just 25mm thick. What’s more, the valve was on the inside of the case when it left us and now the tip of the valve was sticking out of the front of the case. Add to this the fact that all of the control levers and switches were laying flat on the front of the case instead of sticking up in the air as is normal and I just knew that something was not normal. My first thought was in keeping with the serviceman’s men­tality that Lost transmitters are not uncommon & they are also stolen occasionally. Another common threat to transmitters is being left on the roof of a car & falling off during the trip home. (tuned reed) that I had just serviced and it was not working well at all. I can assure you, that on this occasion the set was working perfectly when it left our service department (I can hear mutterings about that’s what they all say) and when I opened the package, even I could tell that the transmitter was not at all well. For one thing, when it left us the transmitter was 100mm thick and now 42  Silicon Chip the customer had been fiddling again and trying me on. As it turned out, the package had fallen off the trolley at the airport and had been run over by a truck. I apologised men­tally to my customer. Another threat to the well-being of the transmitter, in this instance the plastic case of a transmitter, is leaving it in direct sunlight in a car; particularly if they are left on the back shelf. The temperatures in a locked car in summer are quite high and I have seen a few melted transmitter cases. Lost transmitters are not uncommon, being put down some­where and forgotten. Stolen transmitters raise their ugly heads on the odd occasion, although rarely on a flying field. I must say that I have never heard of stealing on a model field and there is valuable stuff lying about all over the place. Garage thefts seem to be the most common. One very common threat to transmitters is being left on the roof of a car and falling off during the trip home. Irate wives By far the greatest threat to the well-being of transmit­ ters however is irate wives and girl friends. Do not laugh, for there is nothing more vengeful than a woman scorned. Male modell­ers can get very carried away with their second love and wives, waiting hopefully in bed until two or three in the morning before falling asleep, tend to be a bit dirty in the morning. Now the most obvious object for revenge is the transmitter. The scorned woman sees her lover fondling this object of passion and often exacts a terrible reprisal. Beatings with a hammer are not uncommon. Trips out of a second floor (bedroom?) window are not unknown. Immersion in a hot, soapy bath has been encountered. So rounding up on the care and protection of the transmitter, if you are male and must indulge in foolish, insensitive and very dangerous behaviour, lock your transmitter away in a safe place. In case you think I am joking about TRANSFORMERS Fig.1: during a crash, sharp objects at the front of the aircraft can piece vulnerable components such as receiver PC boards & fuel tanks, while heavy objects towards the rear fly forwards to cause further damage. the foregoing, my own wife, on one occasion, exhibited such a reaction after a particu­larly insensitive period of frantic model building. This was quite early in our marriage and I came in one morning after a long building session to find my wife asleep in the spare room and one of my model fuselages tucked into bed in her place. I got the message. However, let’s get back to receivers. The modern receiver is a very reliable and robust unit. It has to be if it is to survive what modern modellers subject it to. With some model aircraft now capable of 200+ km/h, a crash can be devastating, with “G” forces measured in the 100s. Statistically, the most usual cause of failure in a receiv­er is crash damage. Even here, it is usually something sharp piercing the receiver case which causes the actual damage. Thus there is much that can be done to help the receiver survive even a high speed impact. Avoid crashes Rule one is to avoid crashes like the plague. This sounds like a ridiculous statement but you would be surprised how many flyers deliberately ignore this rule, largely out of impatience, but often out of a complete lack of understanding of the concept of preventative care. Therefore let us examine each aspect in turn. Firstly, why is it important to avoid crashes? Quite apart from the obvious cost involved in a crashed model, and this can run into many hundreds or even thousands of dollars, there are other factors involved, some technical, some psychological. To begin, learning to fly a model aircraft is a difficult and time consuming process. The ultimate success depends upon a large range of factors, which include aptitude, attitude, eye­sight and hearing. However, for most people the key factor is six consecutive weekends (or flying sessions). This is the prime reason for beginners to avoid crashing, as a crash will break the consecutive training sessions whilst repairs are in progress. During this time, what has been learned will be forgotten and the process of learning in this way can stretch out to several years (assuming that the modeller hasn’t given up in disgust). So keep that impatience in check and if you are learning, always have a spare model so that continuity can be maintained. For those who have already learned to fly, the break whilst repairing the model is not so serious, except psychologically. The important point is that during a crash, components can be stressed to close to the point of failure. This is particularly true of components such as crystals and IF coils which are not restrained inside their cans. Here we move to point two, the reason for the rule. Even a thorough check by a competent serviceman may miss these stressed components. Engine vibration and high “G” manoeuvres can then cause these stressed components to let go in flight, resulting in another crash and even more stressed components. This spiral of crash, stressed components, and crash again is devastating to model builders and is the prime cause of many leaving the hobby. So when I see a flyer adopt a “she’ll be right” attitude and launch an obviously sick model, I am horrified, for in my mind’s eye I see a chain of events which may ultimately cause TOROIDAL CONVENTIONAL POWER OUTPUT CURRENT INVERTER PLUG PACKS CHOKES DESIGN APPROVAL TO AS3108 MANUFACTURE 15VA to 7.5kVA – 100kVA Tortech Pty Ltd 24/31 Wentworth St, Greenacre 2190 Phone (02) 642 6003 Fax (02) 642 6127 APOLOGY We apologise that in the October issue of SILICON CHIP the Yaesu FRG 100 receive was incorrectly priced at $999. The correct price is $1199, an increase forced upon us by exchange rate fluctuations. We apologise for any inconvenience to customers. November 1993  43 Fig.2: crash damage to the receiver can be minimised by mounting it against a bulkhead with the PC board at right angles to the direction of flight. The components should be on the side facing away from the direction of travel that modeller to leave the hobby. Now we move on to the all-important aspects: prevention of the crash and prevention of damage in those crashes that cannot be prevented. In this section, most of the emphasis will be on aircraft, for these are the most difficult models in which to apply preven­tative measures. Preventative maintenance The success of all aspects of aviation has grown largely out of the concept of preventative maintenance and crash investi­ gation. You cannot stop and pull an aeroplane over to the side of the sky. Thus, you must work to see that all possible avenues for error are eliminated. You must work to ensure that the pilot is able to get the thing By far the most important and effective aspect of preven­tion is in the installation of the radio gear. The main point to keep in mind is what sort of forces are involved in a crash. Fig.1 shows some aspects of these forces. Note that the there are three major components of destruction to keep in mind. These are as follows: (1) Sharp objects in the front of the model. Due to inertia, all components will continue to move forward and thus will meet with considerable force any sharp object situated in the front. Things such as engine mounting beams and long bolts on nosewheel brack­ets are particularly destructive. They can pierce fuel tanks, battery packs and receivers and cause irreparable damage. “Engine mounting beams & long bolts on nosewheel brack­ets are particularly destructive. They can pierce fuel tanks, battery packs & receivers & cause irreparable damage”. safely on the ground if something does go wrong and finally investigate the crashes that do occur to find out what went wrong and close the loop in further preventative measures. The successful model flyer adopts exactly the same routine. It is no accident that some modellers are forever crashing, while some fly the same old model year after year. Without labouring the point then, prevention begins in the building process. Great care should be taken to ensure that the airframe is sound in construction and true in alignment. The choice of aircraft should be appropriate, so avoid the 4-engine super scale bomber or the 200km/h pylon racer as your first model. 44  Silicon Chip (2) Heavy components behind fragile components. At times, it is useful to mount the battery pack at the rear as a means of balancing the model. But remember that this will fly through the fuselage like a bullet in a crash. Any receiver or servos in its path are going to be subject to a hammering when they meet this panjandrum. (3) Bending stresses. Components standing at right angles to the line of flight will be subject to bending stresses and thus fracture or snap off completely in a crash. Receivers are very prone to this sort of problem. Minimising the damage Now let us examine ways to minimise this damage. Engine bearers these days are a little passe, as the radial mount has largely superseded them. They are still used by some modellers to spread the engine weight and vibration back into the fuselage. A good, solid beam mount is still one of the most effective ways of dissipating engine vibration. If you do use beams, make sure there is a 2.5mm plywood bulkhead butted against the beam ends. Cut off all the nosewheel mounting bolts flush with the nuts. Finally, check for any other protruding and sharp objects in front of the receiver and servos. Lightweight covers are often sufficient to deflect flying receiv­ers. There is little that can be done about heavy objects behind fragile ones. The best fix is to try to avoid this situation, ensure they are mounted firmly and perhaps provide a deflection plate between them. Again a plywood bulkhead suffices here. Nor can much be done to protect the servos but you can protect the receiver. Firstly, ensure that the receiver is mount­ed with the PC board at right angles to the direction of flight and the components are on the side facing away from the direction of travel – see Fig.2. Receiver protection A fair amount of protection can be provided for the receiver using a modern packaging foam. To do this, construct a self-contained housing which completely surrounds the receiver. Small, individual sheets of foam push­ ed down around the receiver are not going to help when the fuselage explodes on impact, sending the receiver flying through the air. On the other hand, a thick housing will stay with the receiver and allow it to bounce along the ground without damage (hopefully). This housing can be glued or wrapped in tape; the important point is that it stays intact on impact. Make sure that the receiver is mounted against a flat bulkhead with no protrusions and that the foam is not jammed in too tight; tightly packed foam will transmit engine vibration to the receiv­er components. Some compromise may be required here on the thick­ness of the foam. You may never have a crash (think positive), but you will certainly have engine vibration for the entire life of the model. Next month, we’ll cover the technical aspects of receiver servicing. SC