Brushless Servo Possibility?????

[crash80]

Hello all. Just to let everyone know, I am not savvy with electronics. I understand a little but not much. I love machining as it is my profession, and I love flying RC helicopters and airplanes. This is why I have pursued to build my own mini shop for my garage.

My question is would it be possible to build servos from any of the RC brushless motor world? Like I said I am not sure of how electronics work exactly, but I do know that a speed controller already designed for the brushless motor accepts inputs from a receiver for rpm control and controles the motor accordingly.

Now, would it be possible to put an encoder on the end of the motor, and build a similar controller that works off of the signal from the PC and the encoder.

I know that there are servos and controllers already out there, but I am just looking at possibilities. I have a bunch of motors as well as they can be bought for cheap from overseas. They might be limited on torque, but their RPM is so high, that I figured that a belt drive reduction would help the torque out.

Any thoughts and ideas would be greatly appreciated. I am just trying to figure how I want to go about this project and would like to get as much info as possible. I trying to learn the electrical side of the CNC. I can program and run them with my eyes closed, but building what I want in my garage is a different challenges.

Thanks,
T.J.

[ServoChris]

I am not familiar with RC brushless motors: Please keep that in mind, but here is a little information that may help. A Brushless servomotor - Some Call them AC servo's some call them DC brushless motors - I call them AC Servos - has magnets on the rotor. Unlike a regular 3 phase induction motor where speed is controlled by frequency of the elctricity fed to it, AC Servos are commutated. Commutatued means that a drive feeds DC voltage into the windings, in a specific sequence such that each coil creates a magnetic field that essentially drags the rotor through its rotation. What makes the process of commutation possible, is a feedback device which communicates the electrical position of the rotor inside the stator. Concievably you could modify these RC Brushless motors, and mount an encoder, resolver or other feedback device on one end. However if you wish to use an AC drive, No magnets on the rotors will stop your project dead in the water. The problem being that DC Voltage does nothing on the windings of an induction motor.

I don't know if that helps conceptually, but I'd be willing to answer more questions, if you care to expand.

Best, Chris

[dpuch]

http://www.aerodesign.de/peter/2001/...DY-BL_eng.html
has some info on a home made motor and speed control that is basically what is most used in the RC hobby. In this case an "outrunner" with the rotor on the outside for lower RPM and higher torque.

I would imagine you could adapt the motors for at least some CNC use. But I'd bet you would need different controllers to do it. Specifically stuff that handled low rpm positioning stuff.