I am upgrading from a 12V power supply to a 24V power supply on my RUMBA system, and have a 24V E3D and heated bed. I use Repetier, and have tested the hot end and heated bed at 24V, no issues. I have Pololu A4988 motor drivers, and when I attempt to move any of the motors (X,Y, Z, E), I get erratic motor behavior, not at all what I expected. I suspect I am hitting some sort of current limit with the pololus. Is there some method I should follow to recalibrate these pololus to be able to power them with 24V? I know their input voltage range is 8-35V - it just seems like something isn't set right.

Thoughts/help?

Thanks,
Rob

Okay, update on the troubleshooting for this problem. First, some info:

1) The motors and wiring on this printer (Mendel90 config) have worked with a Sanguinololu 12V system previously.
2) The motors and wiring have never been tried with a RUMBA configured with 12V instead of 24V.

Given #2, I swapped out power supplies to see if 12V has the same behavior. It does - which means to me it has nothing to do with voltage, and make be a wiring issue (like many of these symptoms indicate).
I will also check the Marlin firmware configuration.h file to determine if the right board is selected.

Before I checked this, I did check current limiting Vref on the A4988s, and they all read 0.8v - which (x2.5) equates to a 2A current limit on each. Seems okay, but let me know if you disagree.

Thanks!
Rob

Next update....
The wiring was okay - I think.
I adjusted the max acceleration and jerk values in the Marlin firmware downward, and now the motors seem to operate normally - in one direction. They still only move a little in the opposite direction! I have never seen this kind of problem before.
Rob

The one-way behavior was due to some error (not yet determined) with the endstops. Taking the endstops off the board, the motion behavior is normal. So, looks like the main culprit was setting acceleration values in the firmware!

Hey, Thanks for posting your updates.

So, which driver would you recommend for RUMBA ? I only have the A4988 from my old ramps board and I would prefer to reuse them. I think i would need a new hot end though, but apart from that do I need to get anything different for the 24V PSU ?

Please point me to your firmware changes as well, I hav not played with PWM settings for 24v

Edited 1 time(s). Last edit at 03/30/2016 10:26PM by warankarp.

Quote
rtrahms
Before I checked this, I did check current limiting Vref on the A4988s, and they all read 0.8v - which (x2.5) equates to a 2A current limit on each. Seems okay, but let me know if you disagree.

2A is WAY too much for those little plug-in drivers, because they have nothing like enough PCB area to remove the heat from the chip. The chips will be going into thermal shutdown, resulting in the erratic movement you observe. Try 1A.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

how to set the stepper current ? should that be done on firmware or on the board with the stepper screws ?

Like all current boards with plug-in drivers, RUMBA doesn't support software-settable stepper motor current, so you have to adjust the pots on the driver boards.

Edited 1 time(s). Last edit at 04/01/2016 03:54AM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].