Linear Actuator Problem and DRV8835

Hello,

I am running a project using a Raspberry Pi and a DRV8835 motor controller board. I am also using the 5V power adapter so the DRV8835 supplies power to the Pi as well. I was using a 6" Concentric Linear Actuator (LA) with my project and had no issues. I just bought a Concentric 4" throw LA, and when I connected it the motor doesn’t move with commands from the 8835. I am running a 12V 10A power adapter for the project. Here’s the scenarios and results I tested:

1.) Replaced Raspberry Pi with the same model, no change in results.
2.) Swapped out the DRV8835 with a spare, no change in results.
3.) Measured voltage on Motor1 with no motor attached- I read voltage ramping up to 12V as expected.
4.) Measured voltage on Motor1 with the 4" LA attached, very small voltage (I assume this is because the motor is using it)
5.) Attached the 6" LA and ran the same tests, worked normally.
6.) Ran the example.py code with 6" LA on motor1 and brushed DC motor on motor2: normal results
7.) Ran the example.py code with the 4" LA on motor1 and brushed DC motor on motor2: 4" does not move, motor2 moves normal.
8.) Connected the 4" LA directly to a 12V source and it moves fine in both directions.

Any ideas here? In order to connect the LA to the DRV8835 I had to clip the molex connector off, so I am a bit worried that if this is a warranty issue I may be stuck.

Thanks,
Jay

The stall current of the linear actuator is about 10 amperes and it will draw that momentarily, every time it starts moving. The DRV8835 is totally unsuitable for driving it.

I use the VNH5019 motor driver pololu.com/product/1451 for similar linear actuators, and am very happy with their performance.

[quote=“Jim Remington”]The stall current of the linear actuator is about 10 amperes and it will draw that momentarily, every time it starts moving. The DRV8835 is totally unsuitable for driving it.

I use the VNH5019 motor driver pololu.com/product/1451 for similar linear actuators, and am very happy with their performance.[/quote]

Thanks for the reply. That’s a shame that the DRV8835 will work with the 10" linear actuator, but not the 4". I have been using it to carry loads of 40 lbs with no issues on the 10". The DRV8835 is very attractive because it has the Python library for support, and handles the 5V conversion for the Raspberry Pi as well. Looking at the VNG5019 series, it looks like there’s a dual controller for Arduino, but no other Pololu board seems to have any Raspberry Pi direct pin mappings. Looks like I have some work to do.

Pololu folks, are there any plans for a high current Raspberry Pi board in the works?

Thanks,
Jay

Hi, Jay,

As Jim pointed out, the DRV8835 is not at all appropriate for the linear actuators. That you have a 6" or 10" actuator working at all is likely because of unit-to-unit variations in the actuators and driver chips, and not proof that the system should work.

By the way, we do not have any general warranty, so no need to worry about clipping the connector changing anything on that front. We’ll still try to help you out, but if you kill a tiny driver by putting a big motor on it, the detail of what you did the wiring or connector is not really relevant.

We should have a higher-power motor driver board for the Raspberry Pi this summer.

- Jan

Hello.

This is a slightly late update, but we have released the dual MC33926 motor driver add-on board for the Raspberry Pi! It can deliver a continuous 3 A (5 A peak) per motor and comes as a kit or fully assembled.

- Jeremy

[quote=“JeremyT”]Hello.

This is a slightly late update, but we have released the dual MC33926 motor driver add-on board for the Raspberry Pi! It can deliver a continuous 3 A (5 A peak) per motor and comes as a kit or fully assembled.

  • Jeremy[/quote]

Thanks! I just ordered one and will give it a try. I also noticed in further work that my code wasn’t ramping up the motor speed, it was going straight to my max speed- which is why it was giving me an issue as well. This board is a good deal for what it does- there are very few high amp controllers for the Pi out there.