Re: [CAD_CAM_EDM_DRO]servo motors

Robert Campbell wrote:

>I have a question on servo motors.
>
>Do most servo motors require a belt drive reduction or are they set up for
>direct drive?
>
>

Motors with a lot of torque at low speed can be used direct-drive.
One of the DIS-advantages of this is that a good-quality zero-backlash
coupling that can handle motor torque and crash impact (when the
machine crashes, the inertia of the motor may subject the coupling to
an overload) can be quite expensive, making the belt and pulleys
look like a bargain. So, a 6000-RPM motor is definitely the
wrong one for a direct drive setup. A motor optimized for
peak power output in the 900 - 1800 RPM range is going to be
more suitable. Note that NEW cost of a 6000 RPM motor will
be a lot less than the same power output on a 900 RPM motor.
But, surplus, whatever the price you can get it for is what counts.
Direct-drive reel hub motors from big reel-type computer tape
drives are optimized for fairly low speed, so that's one good
source for this type of motor.

Figure out what rapid feed speeds you want on your machine,
multiply by the TPI of the screw, and you have screw RPM.
Do, for 120 IPM rapids, with a 5 TPI screw, the screw will have
to turn at only 600 RPM. If your motor delivers maximum power
at 1800 RPM, you will get better results with a 3:1 belt reduction
drive. If you use it direct, you'll never be able to develop more
than 1/3 the rated power output of the motor. But, that may be
enough - you have to run all the calculations to know.

Jon