Motors stutter when wired series

Using drv8255 vref tried all the way from 1 to max 2.5, motors were unreliable. Motors rated for 2a, 2.8v 59nm

That is very high. 0.7V is the typical starting point.

It started at .5 ish, then I bumped it up down and all over😀

Probably not your issue, but I had stutter when I had a bad connection in my series wiring. One wire had got pinched when crimping and was left an open.

Setting the pot to 0.7V gives about 1.4A which should run any reasonably stepper. Setting those to 1V is as high as you can go and still be stable if you have very good cooling fans directly on the drivers. 0.7 for the 2A should be very good. Set it there and start looking for other issues like abab vs aabb wiring or a loose connection.

Oddly, swapped out the steppers for some smaller ones and I’m having no issues now. Takes me several hours to wire a single axis because I’m slow. But thanks all!!

Edit. Board is running on a 24v 5amp power supply, maybe that factors in?

If you’re removing the stock connector from the motor when reworking the wrting, make sure you’re not intermixing the two stepper coils. That gets you buzzing and inconsistent directional movement.

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Yeah, going by colour, the data sheet showed which wires were for each coil. Maybe I fouled it up though it was definitely a gamble which direction it would go, different outcome on every jog

Wirring colors on steppers are notoriously inconsistent. One way to be certain is to check for the specified resistance with a meter. Another is to twist 2 motor wires together (while the motor is disconnected from anything else) and turn the shaft. When the shaft is harder to turn, those wires are the same coil.

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Will give that a go tomorrow, thanks😀

I had a lot of stutter/dither with my first lash-up.
Some was the gnd between motor supply 0v and Arduino 0v not as good as it might be, but mostly was due to my 12v supply (an apparently healthy (12.6v OC) 7Ah lead-acid battery) not cutting it. Since 8825 uses PWM to control current, result was a lot for high(ish) frequency noise on 12v side confusing internals of the 8825 (I have the luxury of a digital oscilloscope for debugging. Worth every cent.). Switch to Lab supply, and all became smooth and silent. (BTW, for same reason, don’t forget the big electrolytic on the 12v close to the 8825).

Turns out I’m just a crappy electrician, I think I exposed too much wire on one connection, and the extra wire got in the way of the latch that cold the crimped end into the connector, so one wire was pushing out and not connecting

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Glad you got it sorted out. I’m always most suspicious of my own “physical layer” work when stuff is hinky (an official technical term, according to my late father).


Very smart man

You by any chance a network engineer?

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Former IT professor, current IT problem manager.

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OSI 7-Layer Bean Dip, bay-bee! Good for describing/visualizing how data are moving around, horrible for describing actual devices/products…