Hi all,

I am doing research to someday build my own plane, or to take an existing old plane and put new guts (motor, ESC, receiver, servos) into it. It seems that usually, most brands of servos work with most brands of receivers and if everything is sized the same (e.g., if it's all "micro" stuff), even the connectors will fit. But is that true? If it is true, is there a name for the standard or protocol by which receivers and servos work together?

Thanks,

-Tom

It's called "PWM" or Pulse Width Modulation. The TX sends out a train of pulses, one for each channel. The length of time each pulse takes determines the direction and amount a specific servo will turn. The RX feeds that information to each servo - usually individually via the 3rd wire going to each servo.
Servos vary sometimes as to how they interpret the pulse length. Most use a length of 1500 uS (microseconds) as "go to center". Some may use 1520 uS, which may result in the arm not really being centered at neutral if the rest of the system assumes it will be 1500. That can be adjusted for on the transmitter, except perhaps for the very cheap "toy" ones.
A longer time for the pulse tells the servo to go one way, a shorter to rotate the other. The exact amount over or under tells it "how far".

Some manufacturers have a version known as "SBUS, "PPM", or other. Rather than each servo using it's own wire from the receiver, there is just one going from servo to servo to servo. In that case, a servo has to "know" which signal it is hearing is meant for it and not one of the others. Usually an ID number that is sent with the PWM value. For servos, the scheme has not really caught on, so there aren't many choices, and they have to be specific to the scheme used by that radio manufacturer. However, it is a great way to hook up flight controllers or other items that need to know all the time what all the controls are commanding, without having to have a mess of separate wires from the receiver.

In the end, if the receiver has more than 1 3-wire connector on it, and the servo has a 3 wire plug that fits (commonly known as "Futaba" or "JR" connectors), it will work. You can even mix and match servo sizes - really big with "micro", etc.

Note that there are also "HV" (High Voltage) servos that achieve much higher power and speeds, intended to be used with LiPo batteries. They will work in non-HV systems, but not near as well and would be a waste of money. Putting a "regular" servo in a high voltage system is just asking for it to burn up pretty quickly. Most ESC's feed "normal" voltages (4.8-6) to the rest of the system, so "regular" servos are perfect. But it is something to verify when selecting one.

Thank you tedsander !