Dolly - Stepper motors not working

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DavideTampellini
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Joined: Mon Mar 19, 2018 6:49 pm

Dolly - Stepper motors not working

Post by DavideTampellini » Mon Mar 19, 2018 7:43 pm

Hello everyone,

I'm trying to build Dolly, but I'm having some issues with stepper motors.
Once powered, they have enough torque to hold still (I have to push very hard to move them by hand), but as soon as I manually send some gcode to the board, nothing happens.
Or better, I hear them buzzing, but they don't move. If I push them by hand, they move.
I already tried switching drivers and even different ones (still A4988 model), but no joy.
I thought some over belt tension was involved, so I tried with Z axis. I unscrew the couplers, so they could rotate freely.
Again, same issue: I can feel the resistance when they home still, but only buzzing instead of moving.
I even fiddled around with the potentiometers, but the picky thing different was the torque applied while stopped.
Any suggestions? Am I missing anything?

The only thing left could be the checking the correct coupling of wires and coils, but they sounds a hell of test...

Stefan
Posts: 223
Joined: Thu Jun 15, 2017 12:46 am

Re: Dolly - Stepper motors not working

Post by Stefan » Tue Mar 20, 2018 1:38 am

Hi Davide,

Sounds like you may have your wires in the wrong order, especially if none of them are moving on their own. Pick one (I'd suggest your x or y axis) and examine the order of the wires. Usually, the black and green are adjacent and the red and blue are adjacent, but your mileage may vary depending on your board and your harnesses. Don't push them by hand too hard, as the voltage generated by the motors (acting as generators) could blow out your drivers.

Send pics!

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DavideTampellini
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Joined: Mon Mar 19, 2018 6:49 pm

Re: Dolly - Stepper motors not working

Post by DavideTampellini » Tue Mar 20, 2018 10:19 am

Ok, this morning I did some homework.
Wires were already in the right order (black + green and red + blue), but just to be sure I checked the resistance with the multi-meter.
I check both directly on motor pin and after the wire, just to be sure there were no faults in the wires.
They read the correct values, so wiring was ok.

But while playing around with Pronterface, I saw this weird behavior:
https://youtu.be/2W8v_rUACS0

I'm doing increments by 10mm using Pronterface interface (you can hear me clicking). As you can see, sometimes it moves correctly, other times it simply goes nuts and perform a several full rotations. This only happens when I apply a very small increment: if I send a large movement request (ie return to 0, like I did at the end of the video), the motor simply buzzs and does nothing.
Honestly I'm out of ideas... Could it be the cheap RAMPS being faulty?

Stefan
Posts: 223
Joined: Thu Jun 15, 2017 12:46 am

Re: Dolly - Stepper motors not working

Post by Stefan » Wed Mar 21, 2018 12:39 am

Did you put in the jumpers on the RAMPS underneath the driver? Also, it may be possible that one of your pairs of wires may need to be flipped as polarity matters.

What have you set for your step settings in the config?

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DavideTampellini
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Re: Dolly - Stepper motors not working

Post by DavideTampellini » Wed Mar 21, 2018 5:07 pm

Did you put in the jumpers on the RAMPS underneath the driver?
uhm... ehm... sure!
* searches the Trash Bin frantically *

Once again, the problem was between the chair and the keyboard :D
Well, at least now I'm very skilled in testing and debugging stepper motors

Thanks for the help!

Stefan
Posts: 223
Joined: Thu Jun 15, 2017 12:46 am

Re: Dolly - Stepper motors not working

Post by Stefan » Wed Mar 21, 2018 8:11 pm

Glad it worked!

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