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How do RC car/plane "servo motors" act as servos with only three leads and two w

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Beamin:
As far as I can tell  the little black box servos in rc stuff is just a way geared down motor with three leads NOT a servo or stepper motor. How do you stop it from spinning at a certain point , make a phase down the third wire that limits the turn when the signals cancel out?

beanflying:
The standard for these goes way back pre microcontrollers and traditionally relied on a Potentiometer for position sensing. The servo was sent a pulse that varies between 1 and 2mS which was 'normally' set at 1.5mS for center and the servo interpreted based on the feedback from the Pot and circuit. If the Pulse width doesn't agree with the Pot position then correct the angle by supplying positive or negative voltage to a DC motor to change it.

Some modern servos now use magnetic sensors for position and some run Micros internally to set end points, speed or rotation direction and a whole lot more.

There is plenty of info on controlling an R/C servo with an Arduino for example so grab a cheapy from evilbay or hobbyking and have a play  :)

Nerull:
I'm curious what you think a servo is and why hobby servos don't count.

It's a motor with position sensing and a closed loop control IC that drives the motor to the position received on the data wire. That's...what a servo is.

Servomotors and stepper motors are completely different things and often competing technologies.

Beamin:

--- Quote from: Nerull on February 15, 2020, 10:46:34 am ---I'm curious what you think a servo is and why hobby servos don't count.

It's a motor with position sensing and a closed loop control IC that drives the motor to the position received on the data wire. That's...what a servo is.

Servomotors and stepper motors are completely different things and often competing technologies.

--- End quote ---

I remember opening one up as a kid and just finding a motor inside no IC or positional sensor. I'm talking the 15.00$ motor that adjusts the steering or advances the throttle on the engine. Real simple device. Plus the receiver is a totally analog device that uses higher/lower tones to control it. Very simple too simple it seems to have a IC sending data back.

I shouldn't have said stepper motor, but I did read somewhere that stated the RC car servo motors weren't even servo motors too simple. The third wire measures resistance or something, cant find a good explanation of how they work.

beanflying:
Until very recently there was no data sent back. The servo is a contained box that works as I described above.

The early ones to reverse the direction of travel for example was done by flipping the motor wires and each side of the Pot as the radio Transmitters didn't have that functionality. This all predates IC's common use in consumer electronics.

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