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stepper motor question

Posted by jaques 
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jaques
stepper motor question
October 28, 2014 02:02PM
What happens when a stepper motor doesnt get enough current?
I suspect my chinese PSU is not powerful as it claims to be, as during printing my led lights flash and fan speed slows down.

Will not enough current cause the motors to not run at all, or run at slower speed?
I have this artifact on my prints wich happens when the motor stops (powers off? ) and starts again (to rotate the other angle) and I suspect this might be the issue.
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Srek
Re: stepper motor question
October 28, 2014 02:18PM
It will loose steps, resulting in it vibrating but not turning.

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jaques
Re: stepper motor question
October 28, 2014 02:20PM
Thanks. Can less current result in it starting to turn later in time than it should have?

Edited 1 time(s). Last edit at 10/28/2014 02:21PM by jaques.
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Srek
Re: stepper motor question
October 28, 2014 04:18PM
No, stepper motor motions are directly controlled per step. They either move, or loose the step, no delay possible.
If the psu is insufficient you might get a voltage drop that messes up the electronics. The dimming of lights and the fan outages indicate that as well. Get a more pwerful psu

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jaques
Re: stepper motor question
October 28, 2014 04:26PM
Thank you for the help.
Well if less powerful PSU might cause it to lose a step (or few steps?), that sounds like it might cause the problem I'm having.
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Srek
Re: stepper motor question
October 29, 2014 04:07AM
Lost steps can have other reasons as well, wrong current adjustment, to much mechanical resistance, but the other symptoms you describe point to the PSU imo.

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jaques
Re: stepper motor question
October 29, 2014 06:18AM
Thanks for the info.

This is the problem I'm having:
here's a video showing the extruder printing circle and a close up of the y motor at the same time.
[www.youtube.com]


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Srek
Re: stepper motor question
October 29, 2014 06:38AM
Sorry, i can't see anything wrong with the motors here, you would hear and see a loss of steps quite clearly.

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kimented_
Re: stepper motor question
October 29, 2014 08:01AM
Hello Jaques,
your print is good. If you want to verify your power supply, use a volmeter and take a look at its voltage during a print. You should be able to adjust the voltage a bit with a screw on your power supply.
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jaques
Re: stepper motor question
October 29, 2014 11:33AM
This is how it is printing right now:


basically like this


I've tested and adjusted the stepper chips while the printer is on, but not while printing. The support page of Solidoodle says to aim for 1 Volt for each motor chip, which I've done.
Completely out of ideas what else might be the problem.

Edited 1 time(s). Last edit at 10/29/2014 11:33AM by jaques.
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Andrew Smith
Re: stepper motor question
October 29, 2014 11:37AM
Thats backlash, not skipped steps. The motors are moving correctly, but the mechanics are not responding instantly when the direction changes.It could be a loose belt, or the pulley slipping on the motor shaft, or any play in the system.
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Srek
Re: stepper motor question
October 29, 2014 11:59AM
What Andrew said. Missing steps would result in parts of the circle being offset

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jaques
Re: stepper motor question
October 31, 2014 04:31AM
Quote
Srek
What Andrew said. Missing steps would result in parts of the circle being offset
Arent these offsets?


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justcurious
Re: stepper motor question
October 31, 2014 05:33AM
Try to exchange X-cables with Y-cables, if problem stays you may have a mechanical problem and if it follows you may suspect your drivers.
You could also try to make a sawtooth based model with fast turns amd make your conclusions.
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Srek
Re: stepper motor question
October 31, 2014 09:59AM
They look like it, but since the innermost an last printed circle does not show it, it is not a result of a loss of steps. Backlash is more probable.

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Andrew Smith
Re: stepper motor question
October 31, 2014 10:53AM
Both offsets are close to where the print head changed direction on Y, so I'm guessing that they were caused when the printer approached from below the circle to start, and ended by approaching the start point from above. Theres no offset on the innermost circle because that was started on the lower right, where the head was moving upwards on both the approach and the print moves.

Anyway, the proper test for skipped steps is to check layer alignment, if there's a problem it will be very apparent on a printed part.
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