Re: Re: Two related questions, Sherlines and Steppers

Mariss;

Thanks for the reply.

Given your guesstimate of 30 oz-in, I may elect to not use any reduction
pulleys, which should help the speed. The table only has 3 inches or so of
travel, so these small numbers are less troubling than first appears.

I could run it unipolar with a genuine constant current source on the top
end ( as opposed to an R/L drive ). I should have some LM783s around .. good
for 75 volts and a single resistor turns them into a CC source. I'd just have
to find some high voltage driver transistors .. out of an off-line switching
power supply, perhaps.

But it would seem to me that if wired in bipolar mode, I'd cut the inductance
in half. With a suitable drive, that should get me double the speed and twice
the holding power ( more or less ) as in unipolar mode. I understand that
reality might well rear its ugly head, but this SHOULD be an improvement, no ?

And that being the case, any thoughts on how would I rewire the motor ?

Alan

> Speed certainly won't be an issue with those motors because there
> won't be any particularly with a 4:1 reduction.
>
> What you have there are some size 17 motors, probably about 30 in-oz
> in holding torque. I'm guessing you have a 20TPI leadscrew so you can
> calculate "push" in lbs as being 2pi * 20TPI * 4 * 30 in-oz /16 or
> 942 lbs (neglecting screw efficiency). The problem will be speed; at
> 24VDC those motors may manage 3 revs per second at best. Figuring 80
> revs per inch (TPI * reduction ratio of 4:1) you will get 3/80 inches
> per second or 2.25" per minute.
>
> There isn't much point in rewiring the motors because you will still
> have way to much inductance to make it worthwhile to run them with a
> switching type drive.
>
> You may wish to think about re-motoring with higher current motors.
> If you insist on running them anyway, plan on using an R/L drive.
>
> Mariss

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Alan Rothenbush | The Spartans do not ask the number of the
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