Re: Stepper performance

Chris,

Good evening. You would benefit from increasing your power supply
voltage. You will double your speed with a 48VDC supply.

Alternately you may wish to decrease your reduction or possibly go
1:1. Calculations show you are getting 3,768 lbs of "push" with your
current setup (neglecting leadscrew efficiency).

Lbs = (2pi times 300 oz-in times 32TPI) / 16

Going 1:1 you would still have 942 lbs of push while your speed would
increase to 32 IPM @ 24VDC or 64 IPM @ 48VDC.

Finally, you may wish to check if something isn't to tight or
binding; the motor as configured now should be able to attain much
higher speed (500 to 1,000 RPM) under a light load.

Mariss

--- In CAD_CAM_EDM_DRO@y..., ccs@m... wrote:
>
> I've temporarily mounted an older (but new-in-box) 4.4v 3.5A 300
ozin
> NEMA 34 stepper to the 8 tpi leadscrew on my 9" lathe with 4:1 belt
> reduction. Drive is a G210 running off 25 volts with the motor
wired
> half-coil. It certainly works and will make the cuts I need,
however
> rapids leave much to be desired at only around 8 ipm for reliable
> operation (ie, that's over two minutes to traverse the 18" working
> length of the lathe) This isn't the end of the world as the fact
that
> I'm driving the leadscrew via the halfnuts means I can easily
> reposition the carriage manually, but it would be nice to run
faster.
>
> The most obvious suspect is the low power supply voltage, which was
> set by having a transformer that could only be wired up in
> increments of 25 volts and an older cross slide drive that was
limited
> to 40 something volts. I just aquired a torroid with 24 volt AC
> secondary which I believe will yield about 34 VDC. Switching both
> drives to this may help, or maybe I'll leave the gecko on the
present
> supply, but rewired for 50 volts (75v on an unregulated supply
strikes
> me as pushing it too close?)
>
> Another possibility is the 4:1 reduction. I did that because the
> inefficiency of the acme leadscrew coupled with all the drag in the
> rack and pinion of the carriage was quite a hefty load. 8 IPM with
> 4*8tpi=32 revs per inch works out to 256 rpm. Would I do better to
> change the reduction so that the motor stays in its better torque
> range?
>
> I was trying to decide if one could learn anything about the
> performance of a stepper/drive system by looking at the waveform
with
> a scope. In full stepping mode, it would seem that chopping duty
> cycle would approach 100% as the reactance approaches the limit of
the
> supply voltage.
>
> To ease the friction loads I'm probably also going to add
> needle-roller thrust bearings to the leadscrew mount, and hanging a
> cheap ballscrew on the back of the bed is within possibility -
> especially as it would save wear on the leadscrew.
>
> Chris