Most autopilots have the ability to read signals from a RC receiver and drive servos. For instance, in the case of ArduPilot, we read the current throttle setting when the autopilot is engaged (so we can maintain that setting, although we'll later nudge it up and down to maintain altitude) and we drive the rudder servo and ESC. In the case of BlimpDuino in RC mode, we read the throttle and left/right commands from the RC receiver and translate them into commands to the motor drivers (the vectoring thruster servo is connected straight to the receiver and doesn't have to go through the autopilot at all).
In Arduino, you read RC signals by using the PulseIn command, and you drive servos with the servo.write function added by the servo library. The problem is that PulseIn waits for the next pulse, and the more channels you're reading the more time your CPU is spent waiting. A good rule of thumb is that each PulseIn, without modification, takes about 30% of your CPU time, so you can see that about two channels is the max. However, the form of the function is pulseIn(pin, HIGH, timeout) and you can adjust "timeout" to minimize the waiting time and improve that effeciency. I've been playing around with 50000 (it's in microseconds), but your mileage may vary. Anybody having better luck with a different value?
Anyway, if you want to see how this works, here
is a simple demo that just reads two RC channels and mirrors the commands with two servos. It's just like regular RC, but it's all going through the Arduino (so it can take over and go into autonomous mode anytime you want). Just read the comments in the code and plug the RC channels and servos into the right pins in your dev board (a Decimila
--don't forget the breadboard
--work great). Here's a picture of my setup: