Homebrew PCBs

Robert Hedan wrote:
> Problem is now I have to reconsider a totally new driver circuit 'cause
> these are bipolar steppers.  Can I modify my schematic without TOO much
> trouble?  Or am I better using a new design?

IMHO steppers are a rather brute-force way to
address a limited set of applications.  If all
you need are simple open-loop indexed positioning,
minimal/moderate static holding torque for gratis,
but without much of a velocity/torque range,
steppers will fit the bill.

I'd spend some time looking at a DC motor approach
with shaft encoder positional feedback.  As a
back of the envelope estimate a 28TPI lead screw
combined with the optical encoder scavenged from
a $3 mouse can give you positional accuracy in
the 0.001" range.  Physical drive requirements
take the form of a simple H-bridge without the
gyrations needed by steppers.

You aren't likely to find anything off the shelf
to address the drive and closed loop control but
nearly any uC controller will due.  Direction and
velocity of the motor are proportional to the average
energy seen by the motor and is driven via PWM.
As with all but trivial stepper designs you'll need
to address velocity ramp up/down.  And if needed,
an algorithm to emulate static hold of the motor
position.  Though with a lead screw of sufficient
pitch and its inherent friction this may be
unneeded or at least trivial.

-- 
uhmgawa@...        www.gnu.org