Parallel Drives

[Zach_G]

So, why should I not take an 8 wire stepper motor, have it wired parallel except that each half of a phase goes to an Allegro 3977 so I effectively have a cheap 5 amp bipolar driver? I've not seen this done before so there's probably a reason, however I have seen this done with dc motors that have 4+ brushes.

[pminmo]

I'd have to ponder it some, but right of the top of my head, I don't think you can logocally sync two 3977's. While they would reset together, and it would make sense that the translator given the same logic inputs would stay in sync...

[Zach_G]

The pwm obviously won't stay synced and so bad things would definitely happen if two were paralleled on a phase sharing a common connection which is why this wouldn't work for 6 or 4 wire bipolars. However the phase sequencing better stay in sync between the two, otherwise people with xylotex drivers and all those other 3977 derived drivers have had steps stolen from them! Any problems that would result I imagine would be caused by out of phase chopping creating havoc on the physics of a stepper motor. Of such things I know little.

Anyone with a xylotex willing to see if they can run a larger size 8 wire stepper by paralleling 2 axis together? Make sure you know what you're doing though, I'd hate anyone to blow up their electronics.

[Zach_G]

A good test would be to take an axis running off of the a3977 and then separate the phases to two slaved drivers (set at half the current of the single driver) to run the same axis. If the system runs without decreased performance then it's possible to run 2 a3977's in parallel. Of course the stepper would need to have 8 wires running in bipolar parallel to begin with.

I'd perform said experiment myself if I had a3977 drives and my machine was built...

[pminmo]

If I get the time, I may slave two of my single axis boards together and give it a go, you have me curious.