Re: [CAD_CAM_EDM_DRO] Sizing servo motors for BP size mill

Jon Anderson wrote:

> I am looking at possibly converting my Ahha mill to run brush servo
> motors using the Gecko 340 drives. Ball screws are .200 pitch, will run
> 2:1 belt reduction.
> Current stepper motors are older Sigma and I was told they are rated for
> 840 oz/in at 10 amps. They are presently running at 7.4 amps via
> Compumotor drivers.
>
> What in/lb range servo motors should I be looking for to offer a modest
> increase over what I have now?

Note that servo motors usually are rated in CONTINUOUS torque,
and can exceed this by a factor of 4 to 8 for short bursts. What you
want is a motor optimized for low speed and high torque. If you can
get the voltage at some speed rating for the motor and rated continuous
current, you can figure out the torque within rough limits because servo
motors are quite efficient. These specs are often listed on the motors.

Note also that steppers are rated at zero speed (holding torque) and
you never achieve that under motion. therefore, the torque specs
on the steppers seem excessive. I'm using a 1/8 Hp motor (100 W
continuous) rated at 1725 RPM. But, I am using a 4X value for peak
torque. i worked everything out to get 100 IPM and 1000 Lbs linear
force at the table, totally arbitrary numbers, but they work out pretty
well. See http://206.19.206.56/motor.htm for how I did the calculation.

> Also, a significant reason for looking into this is I do commercial
> work. When interpolating radii and holes, as well as shallow angle
> tapers, I get a visibly wavy cut. We're not taking much here. It's an
> aesthetics issue here, there are just classes of work where this is not
> acceptable and thus I lose out on the work.
> Will the Gecko drivers with a high resolution encoder improve upon this
> finish?

Yes, it should.

Jon