need help setting current limit (sanguinololu + pololus A4988

Hello,

I've just finished soldering the electronics, now I need to setup the current limit pot on the A4988, I'm wondering can I plug the A4988 onto the sanguinololu 1.3a and set it up that way? If so, where can I measure the current and do I need to plug in both ATX power and usb?
I went to the wiki and seems like I need to make some connections on a breadboard (which I don't have) or connect up manually, which could be messy.

I need a safe way to do this since my motor current spec is a bit lower than normal (0.8a 6v).
Thanks in advance.

bump

Set VREF to 0.32V on a genuine Pololu or 1.28V on a Stepstick. That gives a current of 0.8A. If the motor gets too hot reduce it.

You can measure VREF on the test point or on the wiper of the potentiometer.



Edited 1 time(s). Last edit at 02/08/2012 02:38PM by nophead.

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[www.hydraraptor.blogspot.com]

nophead Wrote:
-------------------------------------------------------
> Set VREF to 0.32V on a genuine Pololu or 1.28V on
> a Stepstick. That gives a current of 0.8A. If the
> motor gets too hot reduce it.
>
> You can measure VREF on the test point or on the
> wiper of the potentiometer.
>
> [lh4.googleusercontent.com]
> 5FdyLquI/AAAAAAAAF2U/Qm9xijmsHEI/s576/pololu.jpg

Thanks. I've made it work, all motors are turning fine, but some are turning in the opposite direction than what I expected, do I just swap the +/- wires?

Yes either put the motor plug on backwards or swap the first two wires.

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[www.hydraraptor.blogspot.com]

Thanks a lot, but I still have one more question. I'm very close to doing my first print, while I was testing the extruder motor, I was wondering how does sprinter know how fast to extrude if I use 3mm filament vs. 1.75mm ones. I thought there would be a define in the configuration.h, but could not find anything related to the filament thickness, so how do I tell it what's the correct extrudsion rate is?

The firmware doesn't need to know the diameter because it extrudes by length. The slicer has to know the diameter to calculate the length for the E codes.

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[www.hydraraptor.blogspot.com]

thanks so much, just downloaded slicer.

I connected A4988 to Stepper Motor: Unipolar/Bipolar, 200 Steps/Rev, 42x48mm, 4V, 1200mA
Vmm= 8.7V, Vdd = 6V. However my stepper motor refuses to move.
Any idea what is wrong.