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Deezal
09-12-2018, 09:36 AM
Hi guys!

Hope you can help me out with something.
Im currently building a self-balancing robot as a hobby.

So I'm using 2 stepper motors (nema17) along with a motor driver each (drv8825) for my project. The rated current of the stepper is 1.3A and the max operating current of the driver is 2A.


The motor driver has a pot that allows you to change the current limit. Current limit = V * 2. So if I want 1A, then I have to set the pot to 0.5V.


When I connect my power supply to one motor, it runs smoothly. However, when both motors are connected to the supply, one starts to hum and moves very slow and the other continues to move at a decent speed that I require. Please can you help me out.

GhengisDhon
09-13-2018, 10:58 PM
What current is your power supply rate for? Maybe your pulling down your power supply running 2 motors.

jwatte
09-13-2018, 11:48 PM
Maybe the power supply is not filtered well, and trying to run two motors (with PWM?) will make it oscillate? What is the power supply?

Maybe the signals driving the second motor aren't actually behaving the way you expect? Do you have an oscilloscope to check them with?

Deezal
09-26-2018, 02:30 AM
Hi there! Yes I was pulling down my power supply running 2 motors. But I have sorted this issue.
Thanks

Deezal
09-26-2018, 02:36 AM
So I need an onboard power source for my robot. When I used my power supply, I had it set at 12V, 1.3A.

I would like to use LiPo batteries.
I need 12V for my stepper motors. I have a step-down voltage regulator that currently steps down the 12V to 5V for my Arduino Uno and MPU-6050 IMU.

Please help me out :confused:

jwatte
09-26-2018, 09:19 PM
You don't actually need exactly 12V. Typically you can go down a little bit (as long as you have power margin) and you can go up a fair bit (as long as you can reduce heat by using PWM in drive, or don't drive too hard.)

A 3S LiPo battery of sufficient size to give you whatever lifetime you need would be fine. I don't know how heavy your bot is -- anything from 800 mAh to 3000 mAh might be reasonable, depending on how much you need and want to carry. 3S LiPo charges up to 12.8V, have a nominal voltage of 11.1V, and should not be discharged below 9.6V.
You could go 4S (16.8V, 14.8V, 12.8V respectively) or, perhaps, 4S LiFePo instead, which charges to 14.8V, is nominal at 12.8V, and should not discharge below 10.8V.

Make sure to use a proper LiPo charger to not set the battery on fire. Also, you'll want a battery with a 10C or more discharge current capacity -- most RC car and plane batteries will work for this, but some watch/TV/phone bank batteries might not.
If you need a small and light battery, here's something: https://hobbyking.com/en_us/turnigy-nano-tech-850mah-3s-30c-lipo-pack-jst.html