Re: Max stepper motor speed - rpm

Thanks for the great info. No, I am not planning on running at 1200
IPM. I was just calculating what the Gecko's were capable of as a
drive using microstepping. I would be happy to cut in the 60-100 IPM
range. I will use your 1500 RPM as a good rule of thumb max. The 100
IPM I am looking at would only require 500 RPM. I hope that at this
speed I would not have a huge heating problem. I am looking at a Nema
34 640 Oz-in stepper for my X & Y axis and maybe a Nema 32 with 270
Oz-in for the Z. I would like to be able to do some light aluminum
cutting as well as the wood routing.

Thanks again...
Scott

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...> wrote:
>
> >--- 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