Idea was to have an ordinary radio receiver mounted on (my) instructor's transmitter, and use an Arduino (I used a 5V Pro Mini) to take the outputs from that receiver and convert them into the usual buddy-box format (CPPM). The receiver is bound to the student's transmitter, and then you can stand as far apart as you like!
You can use any brand of radio you like, and use 27 MHz, 35 MHz, 2.4 GHz or a mixture - receiver outputs (for connection to servos) and buddy box signals (save for using different connectors) have always been the same, for about forty years now!
Some other guys in the club want Futaba-compatible buddy connectors, so even though this student used Spektrum, I dusted off my old Futaba FF9 and lashed up a system using an Orange transmitter module in the FF9 and an Orange receiver to receive the signal from the Student's DX7.
That's a quick and dirty lash-up, of course, but I didn't have time to design and 3D-print a nice case to put the stuff in.
I could have used a CPPM receiver or an SBUS one, but using a plain dumb receiver has the advantage of making it easy to swap the received channels into the correct order, by simply swapping around the wires linking the receiver to the Arduino. This was definitely needed with the old FF9 transmitter. I didn't want to start swapping the servo connections around inside his plane, partly due to virus cares, but also so he won't have to swap them back again when he's ready to go solo. A bit of fiddling around with custom mixes allowed me to configure the Futaba transmitter to transmit in Spektrum channel order, but my old transmitter isn't smart enough to swap around the buddy box training lead channel order - so I did that by moving the wires where they plug into the receiver.
It all worked nicely, and we had a few successful flights.
For the Futaba project proper, I will use an SBUS receiver: for Futaba to Futaba there's no need to swap the channels around, and I expect the modern Futaba transmitters probably do have the option of trainer channel assignment anyway. The sbus-based system will be much smaller and neater because I can use a tiny SBUS only receiver and a smaller Arduino too. I'll post that project once I have it working.
Thanks to whichever admin/mod moved this to the correct Electronics Projects forum - I'd mistakenly posted it in the 3D printing projects forum.
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