First of all this is a personal project that I took on partly because I
don't have much experience controlling motors and want to broaden my
horizons a bit. With that said.......

I'm driving 12V unipolar steppers with a 12V supply and am a little
disappointed at the performance - namely speed wise. I can get the torque
needed but only with low step rates. After putting together and playijng
with my own FET driver, I tried the Allegro 5804 chips, which is what I am
using now. They made the cotroller code and hardware simple for pennies. An
Allegro engineer then talked me into checking out their bipolar
microstepping chopper chips, which I will do - but not before I get more out
of the unipolars & 5804's. (or is this a waste of time?)

I understand that the voltage across the motor can be increased up to a
published limit as long as I add ballast to limit the current. I did a
simple test with some resistors and a supply I had on hand, but it seemed
that with the current at like levels, the performance was approximately the
same.

Thomson/Airpax recommends L/4R - This sounds like 4X the voltage to me. What
about a 2R setup?

Allegro suggests using zeners at a V a bit less than the supply level to
help dump the BEMF quickly. That would mean the diodes would need to be
rated for the full motor current, I would think....

I guess my question is if I should bother with any/all of this, or scrap the
uipolar design and move on to the bipolar chopper chips? If I only knew how
much improvement to expect by raising the voltage and adding the
zeners......Also, I don't think I can beat the under $10 cost of the new
closed loop chips with my own chopper design.....
Anyone feel like sharing any clues to help keep me from bad decisions? - I
really do not enjoy working with motors (yet) and obviously have much to
learn. Perhaps with more experience they will grow on me.

TIA,
Chris

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