I am a rookie to all this, but am working on a project to make an automated dog door as my dog has a habit of needing to go out in the middle of the night.
I have a raspberry pi and this stepper: ROB-09238 (12v, 0.33A) and am using the TB6600 stepper motor driver. I have it all working well, but not sure about my power supply as the motor gets extremely hot and I mean hot enough to fry an egg on it. The power supply is an old 12v 2.5A charger supply I had lying around.
Forgive me if I am wrong, but I always thought power supply amps only mattered if you try to draw more than the power supply has got. Requiring less amps was moot as devices only use what they use. Is the fact that the power supply is 2.5A the possible reason my motor is getting hot. It is so hot you can’t touch it, even when it is doing nothing.
FYI: if you think the raspberry pi is overkill to run a stepper, its not. This is one part of the project. It will also use bluetooth and i beacons to control the door access and also include a camera and locking mechanism which I am still working on.
Appreciate any feedback on the extremely hot stepper motor.
Sounds like a great project underway. What current setting have you got for the TB6600 (there are 8 options)?
Here’s the User Guide. Current settings are about midway through. I’m not familiar with that board; perhaps the current settings are just safety limits given you can’t define precise values. Some advanced stepper drivers will over-drive voltage to ensure max-torque is available at all times.
It’s worth mentioning that Stepper Motors do get hot, in general. The ROB-09238 has 32.6 ohm resistance for each coil. With 12V across the coil, that’s 0.368 Amps, which would be 12x0.368=4.41 Watts of energy per energized coil. If you are half stepping, then two coils are on during rotation (8.82 Watts).
That’s going to get warm and then notably hot soon after as the majority of that energy is dissipated as heat.
Hi Graham,
Thanks for the replies. Helped me heaps, the control settings is what I had wrong, I dropped the amps back started off as low as possible then slowly increased until I found its happy place. I noticed that when the amps were low the stepper made a high pitched squealing noise. But anything about 1.0 seemed to be ok. I am also doing steps at 1600 and am not sure if this is a microstep or not. I cannot work out what the normal 360 degree step value is for that motor.
Other than that, my project is coming along, slowly and I now think that the motor I have is not strong enough, I think I need more holding torque for when the door is closed to stop it moving. IE: a strong wind could move it. The current holding torque sounds good at 2.3kg but the design of the door has an arm of 244mm and force x lever arm distance reduces the effectiveness of the steppers holding torque. Can you recommend another motor of similar physical size but stronger holding torque?
You are using a pretty good servo controller, so you have lots of options. Holding torque is pretty close to the amount of power a stepper uses. If you multiply Voltage x Current of your stepper then you know how much energy it has to work with. Find a stepper that uses more power and you can home-in on some options
Side note, how about a servo motor to hold the door closed if not in use? Like a latch - design the latch in such a way that when it closes it can’t stall/bind against a solid edge.
Thanks heaps!
After my last reply to you it actually got me thinking and I have thought about using a push/pull solenoid.
Door closed the solenoid is in its off state with the pole extended (into a hole or bracket on the door. When opening, the solenoid will first retract before the stepper turns on. So use the solenoid kind of like a bolt latch.
