Stepstick with 2A steppers

Hello,
I'm building my first RepRap. My setup at this point is:
N1728D63 steppers (2A, 2.8V)
RAMPS 1.4
Stepstick steppers.
Sprinter firmware
Pronterface

A bit of background on the motor choice- previously, I had helped to build DIY CNC plasma cutter, and too weak steppers caused a lot of headache later, so I decided that it *should* be better that motors have more torque than required rather than being topped out.

However, when I finished the wiring, motors acted strange- they vibrate around the same spot. I have double checked the calculations of steps/mm in firmware, tried to adjust the pot, and keep the speed down in pronterface, but I have not managed to run it as I'd like.

So, I started to investigate my hardware...

When I ordered Stepsticks, I was under impression that they are able to handle 2 amps per phase, but the more I read about this the more it seems to me that stepsticks are only able to handle ~1 amp by design (not talking about heat dissipation here).
Is that correct? (my sources: [forums.reprap.org] and [forums.reprap.org]).

If it is- could that be the cause my steppers are not turning properly?

Would Pololu drivers fix the problem, and would I be able to cool them down using active cooling, with the standard heatsinks?


Kind Regards,
Reinis

Quote

Would Pololu drivers fix the problem

Both use the exactly same driver chip, so, no, moving from StepSticks to Pololus won't solve anything. In my experience, StepSticks stay a bit cooler, due to a better heat dissipation design, so they can handle a bit more current with the same heatsink/fan combination.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

I think stepsticks limit the current to 1A by the choice of sense resistors and max vref, so yes you can get more current from a Pololu if you can cool it well enough.

1A would be plenty enough current to turn a 2A motor with no load.

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[www.hydraraptor.blogspot.com]

Thank you for replies. nophead, by the way parts you printed for me are excellent

I had came to similar conclusions when I took the pulley off from the motor (i.e. no load)- the issue I'm experiencing is because of wiring or electronics issues. When there is no load, the motor acts a bit different- it spins in random direction and is easily stopped by hand. From what I've read on similar issues, one phase might not be working correctly.

I performed the following steps to troubleshoot this problem:
1) Measured vref, calculated the current according to vref/(8*0.2) which came out to be about 1 amp.
2) Measured resistance across each pair of coils, checked that there are no shorts in motor wiring- it was a bit inconsistent with specs (1.8Ohm in my case, 1.4Ohm in datasheet of the motor), but there were no shorts, and the error might as well come from cheap multimeter.
3) Tried increasing delay between steps in firmware- no effect.
4) Monitored direction pin with multimeter- got steady 5v in one direction, and steady 0v in other.
5) Tried running the motor without one of the phases. In one case it acted exactly the same- rotating in random direction. In other case there was barely noticable vibration when running the motor, and it produced no holding torque at all- I was able to turn the motor by hand easily.
6) I now have 2 stepsticks left (one was dead-on-arrival- the board didn't even power on, fried another one by inserting the other way around), so I tried the other stepstick. With the other one, motor vibrated in static position and there was no change when I tried to run it.

Due to my lack of experience with electronics I'm unable to pinpoint where exactly is the problem in my setup. Maybe someone has some suggestions, what else should I try?

2) You need to short the meter probes first to get the resistance of its leads and then subtract that from the readings. Typically the meter leads are about 0.2R.

5) So it looks like one coil is not working. If you swap the coils over you should be able to tell if it is the motor or the stepstick outputs. Since the resistance is correct it looks like the stepstick output is faulty.

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[www.hydraraptor.blogspot.com]

The cause of this problem was indeed a bad batch of Stepsticks. Pololus I just received work just fine with no other changes in wiring or software.