Re: [CAD_CAM_EDM_DRO] Re: Max stepper motor speed - rpm

>--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Scott Riddle" <sariddle@l...>
>wrote:
>
>
>>Say I start with a Gecko drive that has a freq=200kHz and
>>it is a 10 micro step drive and the motor os 200 steps per rev. Would
>>it be 200,000/(200*10)= 100 revs per second. Times it by 60 to get
>>6,000 RPM. So the drive is capable. Now is the motor.
>>

No. Due mostly to iron losses, steppers cannot be run fast for very
long. They produce heat roughly proportional to speed. Somewhere around
2000 RPM on mid-size motors, the heat produced exceeds the motor's
heat dissipation capacity. Generally, smaller motors can spin a bit faster
than large motors.

>> Would you just
>>have to look at the speed torque curves and see for the desired torque
>>what speed you can run at? Is there some way to determine this if you
>>do not know the Mfg of the motor?
>>

With good drivers like the Gecko, you can get usable torque up to speeds
the motor
cannot survive for very long. At 6000 RPM, where the available torque will
be VERY small, the motor will self destruct in about 2-3 minutes.

>>
>>My main reason for this question is that I am thinking of buying a
>>stepper that puts out around 600 Oz-in torque and direct couple it to
>>my .200" pitch ball screw. This would give me good speed capabilities
>>when routing on wood. I am trying to avoid to have to add the extra
>>complexity of a belt system.
>>
>>

You can assume that it is impractical to run steppers much above 1500 RPM
on large motion control axes. I had a 150 Lb mini-mill with 16 TPI
leadscrews,
and direct-drove it with NEMA size 34 motors. I demoed it at the NAMES show
in 2003 running at 90 IPM. This required the motors to spin at 1440 RPM.
Only by using a hardware system to generate the smoothest trains of step
pulses
could I do this, and the motors got quite hot at this speed.

1500 RPM to a 5 TPI screw (.2" lead) is 300 IPM. 6000 RPM would produce
1200 IPM, but you won't do this with steppers. Do you really need to
move at
1200 IPM? This would cover 8 feet in 4.8 seconds.

Jon