stepper motion not smooth

I've yet to receive the hardware, so I'm testing my freshly soldered Sanguinololu 1.3a board and 1.8 degree NEMA17 steppers.

First off, I sorted out why they wouldn't perform in reverse... needed to short the endstop leads for each axis.

Now, the first couple of turns are steady - but when I tell something like X to travel +100 it will go smoothly for the first 60% and then will momentarily pause at times as it completes the entire cycle. Not sure why this is happening.

I'm imagining it could be one of these things:

1) Not enough power on the PC power supply (230max, +12V @7A)
2) wrong setting for axis_steps_per_unit[] in Sprinter firmware
3) need to tweak the pots on the Pololu A4988 drivers
4) Pololu's getting too hot (heatsinks are on the way)
5) or possibly signal interference? Sometimes I get something that looks like cross-talk (ie. the Y axis will stutter in place when the Z is moving)

Any ideas?

Edited 1 time(s). Last edit at 07/25/2011 11:13PM by TheCase.

You may be trying to go faster than your stepper can turn. Which firmware are you using and what are the speeds you are trying to achieve?

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I'm using the latest Sprinter firmware.

My testing (in pronterface) was initially set to 3000 mm/min for the first tests. I moved it down to 300 mm/min and I still get the same results: the first 100mm of move command is smooth, subsequent moves have stutter.

This only seems to affect X and Y. Z moves smooth as butter.

If the Pololus get too hot, turn down motor current. While these pots should always be adjusted, people usually simply forget to do so.

Turn the pot all to the left. Then turn it to the right in tiny steps. After each step find out wether the motor has enough tourque, i.e. move the carriage all the way up and down. If you just get away without step losses, turn another 1/8 to the right and you're done.

Quote

You may be trying to go faster than your stepper can turn.

In such a case, the stepper motor will stop entirely and just hum without moving.

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Traumflug Wrote:
-------------------------------------------------------
> If the Pololus get too hot, turn down motor
> current. While these pots should always be
> adjusted, people usually simply forget to do so.
>
> Turn the pot all to the left. Then turn it to the
> right in tiny steps. After each step find out
> wether the motor has enough tourque, i.e. move the
> carriage all the way up and down. If you just get
> away without step losses, turn another 1/8 to the
> right and you're done.
>

Awesome. In all my reading, I've seen no mention of tuning the pots on the drivers.

It looks like the drivers shipped with the pots turned all the way up. I've turned them all the way down and maybe up a 1/4 turn for my testing. Much better results, and the drivers are cool to the touch.

Excellent advice. Thank you!

> You may be trying to go faster than your stepper
> can turn.
>
> In such a case, the stepper motor will stop
> entirely and just hum without moving.

Edited 3 time(s). Last edit at 07/26/2011 12:10AM by TheCase.