# Is stepstick a drop in for pololu?

Posted by sodonnell
 Is stepstick a drop in for pololu? August 20, 2014 12:24AM Registered: 8 years ago Posts: 53
Hey guys,
So I blew one of my pololu's because I'm an idiot and bought a stepstick to replace it because I wanted it fast. The one I bought is a stepstick A4988. Will I need to change anything for my step per mm calculation? Also is it still .4vref to output a max of 1A? I really dont want to blow this one too.

Thanks
 Re: Is stepstick a drop in for pololu? August 20, 2014 02:17AM Registered: 10 years ago Posts: 1,592
You may need to go to 0.8v with a stepstick - your motors will tell you!
No need to change steps/mm.

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Waitaki 3D Printer
 Re: Is stepstick a drop in for pololu? August 20, 2014 09:18AM Registered: 8 years ago Posts: 53
Thanks waitaki,

With a Pololu sense resistance being .05 ohms and the stepstick being .2 ohms wouldnt it be higher then .8v? Or is there some variable I am missing?
 Re: Is stepstick a drop in for pololu? August 20, 2014 10:38AM Registered: 9 years ago Posts: 869
Quote
sodonnell
Thanks waitaki,

With a Pololu sense resistance being .05 ohms and the stepstick being .2 ohms wouldnt it be higher then .8v? Or is there some variable I am missing?

A = VREF / (8 * RS), or rearranged, VREF = A * 8 * RS where RS is the sense resistor.

If with a Pololu your VREF was .4v and it had a .05 ohm resistor, your current was 1 amps. 1 amps * 8 * .2 ohms = 1.6 volts. This presumes that you have a StepStick that is built off of the reference design that uses a 10k trim pot and a 20k resistor for R1.
 Re: Is stepstick a drop in for pololu? August 20, 2014 10:50AM Registered: 12 years ago Posts: 7,616
Quote
cdru
This presumes that you have a StepStick that is built off of the reference design

Exactly. It's more than a neglibile "if" and another reason why I recommend to adjust these trimpots not by reference voltage, but by actual torque requirements of the printer. In other words, just crank them up until your axes move fine.

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