Hey, I am having difficulty with stepper motor noise again and investigating options for a high torque, low speed (150 rpm or so) motor solution. I’m revisiting my research with the gimbal motors and control boards.
As before, I have a problem not being able to find economical control boards, especially ones that give high torque at low speeds. The boards I can find basically reduce motor power to achieve lower speeds, and the motor achieves equilibrium with whatever power it is fed. That could work, but if the motor is loaded for any of a dozen different reasons, that would change RPM and the microcontroller woulndn’t know. I can implement some photointerrupter or something to monitor the motor and use a pid controller in the code to control the speed of the motor, but that all costs money, not just in parts but design and testing and assembly and…
Gotta try to keep it simple, a motor control board that would regulate rpm a little better would help.
This is for the OpenERV project, which BTW has come a long way, I invite anyone here to have a look at it and let me know what you think. The license isn’t perfect yet, but I hope to improve it, it’s just not done yet.
This is now for the purpose of driving the rotating thermal wheel, rather than pumping air, so the power requirements are much lower, however it shows that the importance of good quality motors is very high, I encountered the same problem, basically, twice, in a single project: need some quiet, inexpensive motor solution. Noise is pollution, there are lots of places you want to keep it down. I tried the TMC2209 stepper driver and it can do quiet drive at very low rpm like 10 rpm, but not above that. It doesn’t get enough torque to drive the thermal wheel from the center of the wheel, even a touch of grease causes too much drag and halts everything. It can’t be that touchy in the field. I have to use some kind of gearing or belt. If I do that, it’s hard to use a gearing ratio of less than about 8:1, which means the stepper has to go a lot faster.
I would like to keep things open source and using an open source ESC would be great.
Truth be told all I really need is the driver stage, with charge pump for the high side mosfets. I could probably get the pwm signals from the RPBI pico I’m using, I tested another rectangular wave control board and it’s quiet enough for my purposes, I don’t really need sine wave or FOC drive even.
It would be good to make available a good driver stage, the truth is I think that’s the major thing missing here, the L298n units are really not very good for the task and they are the only budget option. The low efficiency is a real issue.
I was not clear if it is important to have a stage during the operation of the half h-bridge where the output is high impedance, i.e. neither connected to ground or to positive, or if the L298, which cannot provide this, is practically usable despite the inability to do that. In any case my previous experiments with the L298, documented on the forum, indicated it wasn’t capable of quiet drive, even the retangular wave unit I have is better. It’s not clear to me why, if this is soluble with a different PWM waveform or not.