RC servo hack for CNC use?

Hi
Has anyone ever hacked an RC servo for use with CNC?

If you take an RC servo and remove the stop block from the output shaft and
replace the feedback pot with a resistor network. The servo will always
think that it is on the mid point. It would then be possible to control the
servo direction and speed from a micro controller with PWM.

Add a quad encoder to the servo or lead screw and the same micro controller
can count the encoder output and know when the servo has moved a
predetermined amount. Now feed the micro controller with step / dir signals
and it moves the servo (with PWM) in the required direction until the
encoder counts the predetermined ticks. The servo uses very little power
when in a 'neutral' state and actively resists external forces.

A standard RC servo has about 5kg/cm torque = 69 ounce/inch (if my math is
right)
A standard RC servo moves 0.22 seconds per 60 degree travel = 90.9 RPM
At 10 TPI that would make for 9.09 IPM - a bit slow?

Please give me your thoughts on where you would mount the encoder and
whether you think that it would be able to handle higher currents (around
2A). Or any other feedback would be great.

Regards
Coert


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