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Setting current limits 4988 stepper drivers

Posted by SupraGuy 
Setting current limits 4988 stepper drivers
December 02, 2014 04:05PM
Okay, so I've got a Prusa i3 that I want to tune, and am wondering about current limits.

I found a recent post by user Plankton that seems very helpful in setting the 4988 driver current limits. The values that he posts seem to indicate a slightly higher limit for the Y axis (Makes sense as the Y axis usually carries the print bed with it in the designs that I've seen) than the X axis.

For the Z axis, since there are 2 motors, does this mean that the current is basically halved to each motor? I see that the current limits set in his post in this thread has a max close to that of the X axis. I don't know what build that is for sure, but for an i3 which uses 2 motors, I suppose that it may work because the Z axis has much more mechanical advantage with the threaded rod rather than the belt drive, but I don't know. Looks like the extruder motor is about the same, too.

Of course this is all assuming that the rest of this stuff turns out like I want...
Re: Setting current limits 4988 stepper drivers
December 03, 2014 05:22AM
I've got an OrdBot with Nema 17 motors.
my x and y steppers are set on about 0.36v. my z stepper running 2 motors with threaded rods is set on 0.72v.
Re: Setting current limits 4988 stepper drivers
December 03, 2014 06:38AM
It's a non sense to give values. Each motor needs it's own values. The formula is A*8*Ω(*%). Imagine you have a 1.5A motor, the resistence of the A4988 are 0.05Ω. So 1.5*8*0.005 = 0.6v ; with a 10% tolerance to avoid wiring looses = 0.66v. You should measure this amount of current between the variable resistor and the ground pin. Note you can be a little under this value if your printer stands it. This way your motors will be a bit less warm.

Collective intelligence emerges when a group of people work together effectively. Prusa i3 Folger (A lot of the parts are wrong, boring !)
Re: Setting current limits 4988 stepper drivers
December 03, 2014 11:53AM
Okay, I have the X, Y and Z axis all responding nicely, current settings all seem good. I had a minor issue with the wiring to my X axis motor, one pin wasn't making good contact, and the motor would switch directions randomly. Very weird.

Thanks for advise and info. I have the limiters set a touch below what the motors are rated for, should be safe, and that's a good place to start.
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