current required to drive steppers

[Bill Schwanitz]

So, I've been having some fun with tuning/tweaking on my printer. Aside from a few things being a little off dimensionally, things are going well.

What kind of current should I look to push to drive the steppers? I had taken one direction initially which was to set the trim pots down to the lowest setting and then push it up slowly until the motor was moving the axis, then just added a bit. I was more interested in keeping the steppers from getting too warm and also reducing competition for current between the heated bed/steppers and hot end on the ramps board which is limited to 5 and 11 amps ( bed is 11, hot end/steppers are on the 5 )

I have been getting these weird skips on the y axis during prints. What I initially thought was belt slipping or possibly due to friction on the pillow block bushing I'm using on the Y axis ( https://www.lulzbot.com/products/pillow-block-bushing ). I had replaced the belt, added silicone lubricant and neither seemed to work. I was getting skipping just randomly and totally screwing up the prints.

I've switched controllers now and am using the azteeg x5 mini which is a smoothie based firmware. I now have much finer grained access to the trim pot as it is digital ( was the x5 or a rambo board, goal was getting to easier tuning of the current ). My last print I kicked the current to the Y stepper from 1 to 1.5 amps, no skipping... Does this make any sense? Was I just not giving enough current to the steppers - can that cause these skips?

[Larry Knopp]

Yes.
;)
At least, most likely.
If you search the RepRap forums, there are exhaustive discussions about this.

The "tl:dr"...

Dial stepper current up progressively until until it is too much, then back off just a tiny bit until it isn't too much.
Monitor your motors and drivers temps to be sure they aren't burning up, add cooling if necessary, or back current off a tiny bit more.

Your PSU and electronics are - should be - more than capable of handling and distributing the load.

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[Bill Schwanitz]

Larry,

Yea I have *plenty* of power ( 25 amps @ 12v dc ) so power is not a problem. Hell the fuze is only 20A on the controller ;)

I'll run another print later tonight with the current lowered. Is there any empirical way to determine the current needed for the steppers? I imagine looking at the specs for the individual steppers is necessary here?

As I understand it the heat is just wasted power to the stepper. So, my previous tuning was more of the minimal approach. maybe too minimal? ;)

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[Bill Schwanitz]

Ok, brought the current from 1.5 => 1.2 and the steppers are between 117 and 122 ( extruder at 122 ) F

I don't have a reading from the other day but they don't feel as hot.

[Larry Knopp]

Yep.
Without knowing the specific steppers you have, it's only a guessing game.

This is exactly why there are so many discussions in the RepRap forums on the subject...  so many different motors out there.

It sounds like you're definitely dialing it in better.

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