Controlling a Nema 17 with DRV8825 for Octobouncer project

Other Hardware Motors, Mechanics, Power and CNC
1

Hi everyone,

I am currently building an Octobouncer. I have four Nema 17 17HS08-1004S stepper motors. Each one is controlled by a DRV8825. Each motor moves a mechanical arm composed by two PVC bars. The mechanical arms hold the platform, built with methacrylate.
The structure of the Octobouncer is built with light materials, so the motors should have enough power to move the structure individually.

I have tested a single motor moving a single small PVC bar and it does well, but when I attach the PVC bar to the whole structure, it cannot move it.

I did another test with the single PVC bar hitting an obstacle while it spins. When the PVC bar hits the obstacle, instead of keeping with the spin, the motor stops and the bar falls to the ground.

Does anybody know why does this happens?

Thank you in advance.

2

Use a multimeter and a small screwdriver to tune the potentiometer on the DRV8825. Target:

VREF = 0.5V → ≈ 1A per phase (safe for your motor)
Use this formula:
Current_Limit = VREF × 2 for DRV8825

Make sure to cool the driver (heatsink + airflow) if going beyond 1A.

3

If @ahsrabrifat suggestion does not work it appears you overestimated the output capabilities of the motors. You will either have to lighten the load or use bigger motors or possibly a combination of both.

4

Set Vref to a certain voltage before any motor is connected.
Setting it to draw a certain current might not work as you think it does.
Pololu has a good tutorial. Check if your driver has the same value sense resistors.
Leo..

5

Hi, @octobouncer_02
Welcome to the forum.

https://forum.arduino.cc/t/how-to-get-the-best-out-of-this-forum

What is your power supply?

Can you please post a copy of your circuit, a picture of a hand drawn circuit in jpg, png?
Hand drawn and photographed is perfectly acceptable.
Please include ALL hardware, power supplies, component names and pin labels.

Thanks.. Tom.... :smiley: :+1: :coffee: :australia:

6

A12volt supply would be absolute minimum. A 24volt supply would be preferred for faster accelleration.
Leo..

7

That works for Pololu brand DRV8825s with 0.1Ω current sense resistors but other brands may have different resistors.

See formula on page 12 of datasheet.
https://www.ti.com/lit/ds/symlink/drv8825.pdf

8

All right, I'll try this.

9

Try what...
Setting Vref on the drivers should be the first thing you do, before connecting the motors. 0.5volt, assuming the sense resistors on the drivers are 0.1 Ohm.

We asked about your motor power supply (voltage and current), which you didn't answer yet. And which stepper library are you using, regarding accelleration.
Leo..

10

I am using the following power supply:

With 12V DC and 5-7 A.

I am using the AccelStepper library.

I used the following scheme to connect the drivers with the motors and the Arduino.

image
image655×359 53.4 KB

I have followed this website to build the electric circuit.

I have connected the M1 pin only, so I am doing 1/4 step.

11

The stated torque of your motor is only valid using full steps! What happens when you use full steps?

12

Allright, thank you for the advice. I'll try working with full steps.