Re: Two related questions, Sherlines and Steppers

> That is a common misconception. You would not change the inductance
> one iota; you would only halve the resistance.

Interesting .. certainly in the case of general purpose inductors,
of the sort from my old tube days, paralleling inductors cuts the inductance.

> Using a current source instead of the motor winding resistance may
> help some but it will be at the expense of considerable heating in
> the current source pass transistor. Also mind the fact the motor also
> is a dandy 2:1 step-up autotransformer as well; at 75VDC your phase
> transistors will see 150VDC or more.

Well, in such a design, SOMETHING has to get hot. Frankly, I prefer
hot semiconductors to hot resistors, as most of my power semis have some
means of being heatsinked, while none of my power resistors do.

I understand the "transformer" issue, and hence my suggestion to use
transistors from a switching power supply .. they're often rated at 400v
or greater.


Turns out the point is moot. I DID rewire the motor, which is to say, I
brought all 8 leads out. From there, it was simply trial and error to
determine windings and phase, using a 297/298 driver.

Run in half step mode and direct drive to the Sherline leadscrew, I should get
a pretty reliable 15 IPM, based upon my thumb and forefinger "squeeze" test.
That should be quite fast enough.


But if not, it might be kinda fun to build a CC source unipolar driver using
a pretty high voltage and then see what happens ... OR ... any word on the
G298 ? As in price and availability ?


Anyway, thanks for all the time ! It's been a fun afternoon. <G>


Alan


--

Alan Rothenbush | The Spartans do not ask the number of the
Academic Computing Services | enemy, only where they are.
Simon Fraser University |
Burnaby, B.C., Canada | Agix of Sparta