A year and a half ago, when I started to fly with Multiplex, I was astounded by the range I got with the Profi 4000 with the 9 ch IPD receiver (this was before the 12 ch was available). When doing a Lee Demary full antenna length check, I got more than 3500 feet of range with turbine off and running (there was a farmer’s fence and no easy way of going further, so I stopped there). This was over a hill so I could not even see the plane and it was sitting on the ground, not up on a non-conducting table. I was jubilant! Almost a year ago, however, I put the same radio with the new 12 ch RX in my HotSpot. Suddenly I had seriously reduced range. I convinced myself that all was fine due to several factors, but in the back of my mind, I was always concerned that I had a problem. Well, as we say in the space launch bidness, I had “go fever”. I wanted to fly no matter what. This is what killed the seven crew members of the Challenger. I ignored the warnings and rationalized the issue in my head and flew anyway. Many many flights in fact. Last Sunday, in preparation for my first Isobar III flight today, I was installing the Multiplex Royal digital servos that I was gonna use on the flaps. I had programmed them to be capable of 180 deg. of throw. While making the linkages I happen to brush my hand against on of the flap servos. It was red hot! I felt the other, same thing. I was horrified. It turns out that when programming the servos to be capable of 180 degrees of movement (according to the MPX service dude they are capable of 200 deg., but of course you gotta pay attention to where the center is), it is possible to run out of room and hit an internal servo mechanical limit. That is exactly what I had done on the Isobar and previously on the HotSpot’s speed brake servo. I hooked up an amp meter to check the servo draw and each digital was drawing OVER 1.25 AMPS, CONTINUOSLY!!!! Suddenly it occurred to me. Was it possible that my crappy range with the Spot was due to the fact that this huge current draw on the speed brake servo was pulling down my entire system’s voltage (two 1400 mah 6.0 volt ElectroDynamics packs)? It was indeed. I fixed the problem by programming the servos to a bit less throw. Today, before the new Isobar’s initial flight, we did the Demary range check once again. I am happy to report that all was fine and, once again, I had the best ground range of any system (and I’ve owned the big two) out there. I am a very lucky dude that I did not wreck a plane due to this. From now on I will always check current draw on servos after installing them. I believe Andy Low at Electrodynamics has a set up that he sells to do exactly that (
http://www.electrodynam.com/ ), or just make one up as I did.