Re: [CAD_CAM_EDM_DRO] RC servo hack for CNC use?

Why bother? An RC servo is a PWM position input rather than step and
direction. It moves to a position determined by the width of the input
pulse. Yes if you disconnect the pot then as soon as it receives an input it
will run full speed one or the other way trying to get back to the correct
position. It may have a reasonable looking torque ouput but at very low
speed and hence has very little power.

Na forget it. Try a step motor and controller or dc servo motor and
controller.

Regards Peter

----- Original Message -----
From: "Van Der Sandt Coert" <vandersandtc@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Friday, November 15, 2002 8:44 AM
Subject: [CAD_CAM_EDM_DRO] 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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