Project background, a cart autonomously travels along rail tracks. It stops at regular intervals, turns some lights on and takes a photo. It then turns the light off and the cart moves along for another distance interval. The cart can also be controlled in manual mode with a PS4 bluetooth controller.
I have everything working reasonably well. My only issue is that it's a bit slow (approximately 0.8km/hr).
I have two 26Ncm stepper motors driving the system at the moment driven by two pololu a4988 drivers 26Ncm stepper
I tried to increase the speed by 50% by increasing the wheel size, however there isn't enough torque in the motor to get it unstuck if it runs into trouble, i.e. there's just enough torque to keep it going and if it starts rubbing the flanges on the rail tracks it sometimes misses some steps. With the smaller wheels this didn't happen.
Anyway, so I bought some bigger stepper motors, these ones:45Ncm stepper
So I did a simple test to make sure the steppers work, I've connected the arduino to the a4988 driver and then to the stepper and ran some simple code, the exact same code as I used for the 26Ncm motors, I'm 100% sure the code is fine.
The stepper spins just as expected however it's super easy to stop from rotating with a little finger pressure. I put a wheel on the motor and it spins but if I do as much as breathe on it, it starts skipping steps i.e. it has just enough torque to spin the wheel.
I've tried slowing it down but I didnt get much improvement. The smaller 26Ncm steppers work much better, at least from my experience.
So Ive done a couple of things to try and solve it but no luck:
i. I checked with a multimeter and the current sits between 50ma and 100ma, I've tried changing the voltage from 10v to 36v, I didnt get any significant difference in the torque (it remains barely being able to keep just the wheel spinning with no load on it).
ii. Tried to slow/step it more slowly
iii. I adjusted the current limiter on the A4988 all the way up to 2A, but the motor still only draws 50ma to 100ma.
iv. If I just get the coils to hold and nothing spinning, again they take such little current.
v. Out of frustration I've tried ever combination of cable configuration just to be 100% sure that there wasn't an error in the datasheet.
I don't know what else to try, has anyone seen this sort of behaviour from a stepper motor before?
To be clear, I bought two of these things and they both have the same behaviour