Re:GeckoDrive 201 and Bridgeport Stepper Motors

Rick Dulas wrote:
<snipped>3a. The printed instructions point out that the module

>supply is 24-80vdc and the supply should be in the range of 4 to 10
>times the nominal stepper voltage to get good micro-stepping.

>The BMs operate at a nominal 56 volts which doesn't leave much
>headroom for the microstepping to happen. I ran the drive at 74vdc
>and found the performance on this Big Mutha' less than stellar.
>Rick Dulas

Rick,

Mariss may correct me, but microstepping is a function of the CURRENT
RATIOS between adjacent coils. Higher voltage just PUSHES this
current into the coils faster.

I believe you may be dealing with an internal(to the drive) time
constant which is set for typical 23/34 size steppers. This would
have the effect of trying to move the rotor to a new postion BEFORE
the current position is achieved. Net result would be loss of torque
and poor performance. ALSO, were the BM's hooked up (to the BP) when
testing? Steppers do better when they are driving something.
Otherwise the spring-damped system that is a stepmotor is out of
balance.

The 56 volts used in the bridgeport surely HAS ALREADY taken into
account the motor voltage rating. I don't believe your BP steppers
are nominally rated at 56volts, and therefore need to be driven at
224 to 560 volts for good performance!

Ballendo

P.S. Tim mentioned gecko may have drives optimized for 42 size
motors. This would probably correct the problem.