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### Topic: 6 Stepper Motors, A4988, Power, help beginner! (Read 217 times)previous topic - next topic

#### lyhui

##### Aug 13, 2018, 08:26 pmLast Edit: Aug 13, 2018, 09:55 pm by lyhui Reason: display images without having to download
Hi!
First and foremost i'm a huge beginner when it comes to electronics and have a little experience with arduino.. Therefore i'm sorry if i'm very vague and clueless. Please be easy on me.

For my project i am using an arduino uno, can be changed if necessary. I want to control 6 nema17 stepper motors (12v, 0.4amps, 26ncm) individually using a a4988 driver for each of them. They will be used to pull strings, not a steady weight but pulling an elastic fabric with the weight ~ 1kg, by a wheel (2cm radius) attached to the motors shaft, so it should be 2kg.

Right now i want to test one motor using the attached diagram. To do that i need to adjust the current limit of the a4988. I tried following pololu's tutorial on setting the current limit using the formula VREF=8⋅IMAX⋅RCS that i got from pololus website. Depending on the driver model Rcs will be 68 mΩ or 50 mΩ but my a4988 isnt from pololu so i just used 68 mΩ for testing first, resulting in Vref= 8*0.4*68 = 217.6 mV. (i couldnt find details on the Rcs on mine, what should i do? but i also saw another formula IMAX = VREF x 2.5 so it'd be 0.4/2.5 = 0.16V) When i tried setting the current limit with the potentiometer onboard, i only got a range from ~ 3.07 - 4.30 V. I can't go any lower, what am i doing wrong here?

Also i found this 12 VDC 5 A adapter, will it be enough for this? I believe i should connect the motors in parallel, so the voltage will 12V for all and amps will be added, so 0.4 A *6 = 2.4 A. Then 5 A should be sufficient, right? I want to plug it in directly to the arduino but i saw that some had problems with 12V. I believe it was because they were unregulated power sources, so as long as its regulated it should be fine, right? How can i know whether mine is regulated or not? Furthermore i read that to maximize the stepper motors performance a higher voltage would be better. Would it be wiser to use more than 12V and connect it externally with a dc barrel jack adapter?

I'd be greatful for any help

a4988 longruner
https://www.amazon.de/gp/product/B071P41ZBW/ref=oh_aui_detailpage_o00_s01?ie=UTF8&psc=1

nema17 longruner
https://www.amazon.de/gp/product/B071P6JPF9/ref=oh_aui_detailpage_o00_s01?ie=UTF8&psc=1

#### Robin2

#1
##### Aug 13, 2018, 09:21 pm
Follow the Pololu advice for setting the current limit, and for connections to the A4988 stepper drivers.

Stepper Motor Basics
Simple Stepper Code

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

#### MarkT

#2
##### Aug 14, 2018, 11:59 am
You should be able to read the shunt resistor value from the resistor directly - surface mount
resistors usually have this printed on - usually black with white text.  The manufacturers of
surface mount capacitors are much less helpful for some reason I've never been able to fathom
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

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