24V Stepper Motor Driver

[BURevisfan]

Good evening all!

I have a project where I'm trying to retrofit some controls using an arduino based controller.

I have three existing stepper motors that I'm trying to control. The big problem right now is that they're 24V steppers. I tried using the V2 Stepper Shield and driving them at 12V but as I expected I've lost all of the torque on them.

Does anyone have any experience with a driver board for 24V steppers? or any suggestions?

I've looked a little at the CNC controller units but they're not really what I'm looking for.

[rpiloverbd]

Hello, have you tried Big Easy driver?
https://www.sparkfun.com/products/12859

[adafruit_support_bill]

Voltage is only one part of a motor specification - and arguably the least important one. To match a driver to a stepper we'd need to know at least the phase resistance and current rating of the windings. If you post a link to the electrical specs for your motors we can take a look.

https://learn.adafruit.com/all-about-st ... he-stepper

[BURevisfan]

I wish I could find a link to the specs, I’ve been very unsuccessful at finding any so far.

I’ve attached a couple photos. The first is of the stepper… It appears to be a 200 step, 24vdc, and 0.24 A

It has 6 wires (black, white, wht/grn, wht/red, green, red).

I took some basic ohm readings across the leads and the second attachment is what I found.

If I can find a way to properly drive the existing steppers I think it would be best because they’re already designed and setup for the mechanical load.

[adafruit_support_bill]

OK. That is a NEMA23 frame motor with 6 wires. It can be run in either a unipolar or bipolar-series configuration.

For unipolar operation, you can use a simple driver such as a ULN2803: https://www.adafruit.com/product/970
In that configuration, you would use a 24v supply voltage. The black and white center-tap wires would be connected to the power supply and the Darlington drivers in the ULN2803 will be connected to the other wires. When a driver on the ULN2803 is turned on, it will pull its output to ground and the ~115Ω phase resistance would keep the winding current to a safe 0.2A. In this configuration only half of the windings are in use at any time.

For bipolar-series operation, you would need a dual H-bridge driver. The center-taps would be left unconnected, so you would be using both halves of each winding connected in series. Bipolar operation is more efficient since all the windings are being used. At 24v, you would get similar torque with half the current. Or you could use up to a 48v supply to get twice the torque while still keeping the current max within 0.2A.

The only dual H-bridge type stepper drivers we stock that will run at 24 or 48v are the synthetos boards: https://www.adafruit.com/?q=synthetos&p ... =BestMatch
Or you can roll-your own stepper driver with a pair of DRV8871 H-bridge breakouts: https://learn.adafruit.com/current-limi ... th-drv8871

Or check with http://www.pololu.com. They stock a wide range of stepper driver boards.
https://www.pololu.com/category/120/ste ... or-drivers

[BURevisfan]

Thanks for the information! It definitely helps... I have two more followups.

1) With the DRV8871 breakout board, can the AccelStepper library still be used with this? From what I read I think I should be able to but would like to confirm.

2) I read somewhere were increasing the voltage to the DC steppers increases it's potential speed. Is that true? Could I drive these 24V steppers with closer to 36V?

thanks,
Robert

[adafruit_support_bill]

1) Yes. AccelStepper supports a variety of stepper driver types. With the dual DRV8871 driver you would use the FULL4WIRE type: https://www.airspayce.com/mikem/arduino ... 764cabeea5

2) Yes - assuming that your driver and motor are compatible. That is explained in this guide: https://learn.adafruit.com/all-about-st ... he-stepper
The motors you are using have a fairly high phase resistance and inductance. That and the 6 wires which implies that they were designed for use in unipolar configuration with simple non-current limiting drivers.

The rated voltage is for use in a unipolar configuration where only half of the winding is used at any time. When powered with the rated voltage, the motor will follow Ohms law (I = V/R) and the winding resistance will keep the current to a safe level (24 V / 120 Ω = 0.2 A).

In a bipolar configuration you are using the whole winding, so the resistance is doubled. That means you can safely use use double the rated voltage without exceeding the current rating (48 V / 240 Ω = 0.2 A). This will give you significantly better performance than the unipolar configuration. The DRV8871 can handle up to 45 V.

In theory, it is possible to further increase speed and torque by increasing the supply voltage even more - provided that your driver has current limiting and can handle the voltage. But at that point you would be better off finding a more modern high-torque low-inductance stepper designed to deliver higher performance at more reasonable voltage levels.

[BURevisfan]

Sounds good! I ordered a pair of the DRV8871 boards this afternoon.

I can’t wait to get them so I keep testing.

Thanks again for the info.

[BURevisfan]

Good morning,

I'm still waiting on my DRV8871 board to arrive. They've shipped but USPS is ridiculously slow these days. But anyways...

I had a followup question on the DRV8871 boards. I understand from the tutorial that the Power+ & VM terminals and the Power- & GND terminals are tied together.

I have a couple assumptions I'd like to confirm and a question.

1) ASSUMPTION: Since I'm powering externally, I supply my external voltage to the Power + and - terminals.
2) ASSUMPTION: I do not (under any circumstances) connect VM to the Metro Mini that's controlling the board. Otherwise it would fry the output it's connected to.
3) QUESTION: Even though the Metro Mini and the DRV8871 are going to have different power supplies. Do I tie the DRV8871 GND to the Metro Mini GND? I would assume so since a reference is needed for the DRV8871 IN1/IN2 terminals.

[adafruit_support_bill]

1 & 2 - Correct. Power + and - will power the motor and the DRV8871 chip.
3 - Yes, you do need a ground connection from the processor to the DRV8871 to serve as a signal reference.