RE: 3 speed controls with 4 channel radio
You have several options. One would be to use separate ESCs for the two outer motors, and a simple on/off for the third. Most times that third motor is just for speed, right? The third motor can be turned on/off with a simple servo arrangement. I can't think of a more simple way of doing it. From there, it just depends on how complicated and expensive you want to make it.
- 'Doc