Figure out why small movements & ends of movements make motors spazz

[dbenamy]

It seems the system doesn't handle small or slow movements well. The motors start buzzing. This doesn't happen every time but is easy to trigger by making a small movement in Printrun (0.1 or 1). Bigger movements work smoothly but then sometime do this at the end.

I think the big movements start out fast and slow down at the end at that's when this happens.

The controller may be trying to feed them too little current or in some way underpowering them for the small/slow move but they wind up not being to move at all.

Another hypothesis is that there are areas of movement with higher friction and if the motors happen to be trying to make a tiny move with no momentum over those areas, they stall.

When this happens, I click stop motors in Printrun and it stops.

Two obvious things to try are:

• Increase current limit - http://www.indigent-networks.com/pololu-drivers-current-limit-configuration/
• Calibrate step size (less likely to help but needs to be done anyway) - Calibrate stepper control (steps / mm) #4

[dbenamy]

The pololu data sheet says it "can deliver up to approximately 1 A per phase without a heat sink or forced air flow (it is rated for 2 A per coil with sufficient additional cooling)."

Our long axis motor data sheet is at http://www.xylotex.com/24H290-25-4B.pdf and says they're good for 2.5A per phase. It says they're only good for 5.5V. http://www.indigent-networks.com/pololu-drivers-current-limit-configuration/ says it's safe to overdrive the voltage as long as the current is within limits. Shrug.

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Our short axis & height motors are 57bygh317, specs at http://www.circuitspecialists.com/nema_23_stepping_motor_57bygh317.html. Max current is 2.5A.

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Unfortunately the vref test point on the pololu boards is half under the heatsink and hard to get to. Fortunately, we should be able to max out the current limit since our motors can handle 25% more current than the pololu max.

To do this we're going to need a fan blowing across the pololu heat sinks.

[dbenamy]

Oh, whoops. I can measure vref on the pot if I need it.

[dbenamy]

Hmm, I rotated the pots fully clockwise which put vref at it's max but don't see much different in the buzzing.

[dbenamy]

For future reference: vref is about 1.7V on the 3 pololu driver boards.

[dbenamy]

Hypotheses to investigate:

• Calibrate step size (less likely to help but needs to be done anyway) - Calibrate stepper control (steps / mm) #4
• Something's up with microstepping. Maybe the controller things the motors have more microsteps than they do?

It may not actually matter much. While it's cutting it'll be moving and may not happen, and when it's done cutting, we can send a stop motors command or power off the arduino which will stop the buzzing.

[dbenamy]

I set all 4 drivers' current limit pots to about 3/4 to reduce the risk of overheating since max didn't solve the problem.