I have an application that needs two motors rotating at the same speed in opposing directions, the speed needs to be low and the holding torque fairly high. The target speed would be in the 0-10RPM range, I don’t need microprocessor control, a simple control pot to provide a constant/adjustable speed will do. The motors would need to run continuously for about 8 hours daily.
I have some bipolar steppers and an A4988 Pololu on hand from a 3D Printer project that I thought I might use, two steppers wired in parallel with the windings reversed on one. I thought perhaps I could use a 555 timer circuit to control the speed.
The question is, am I barking up the right tree here? Can I expect to run a pair of NEMA17 steppers for 8hrs daily at such low speeds with an A4988? Is this low speed range even attainable? Is there an existing controller or a kit I can buy to get this done? If not, does anyone have a circuit they could suggest I use?..
We are not aware of a stepper motor controller or kit that would work like you described. It seems like a 555 timer should be able to supply the HIGH and LOW logic signals required to step the A4988 at a regular rate, however you should be sure that you are using a voltage that is within the range of the logic voltage of the A4988 (3.0 - 5.5V). Also, stepping speeds in a stepper motor can be arbitrarily low, but you should keep in mind that the movements will occur in discrete steps.
There are multiple ways to run a stepper driver from a single logic signal. What is the voltage and current rating of your stepper motors and what voltage supply are you using? Are you planning on microstepping? Depending on the voltages and current ratings you are working with, it might be better to connect coils from the two stepper motors in series (which doubles the voltage required) rather than in parallel (which doubles the current). There is a limit to the amount of current the A4988 driver can provide (about 1A), however most of the small stepper motors I have seen are well below the voltage limit of the driver and the A4988 will run cooler when driving lower currents. Also, microstepping generally relies on controlling the current through the coils precisely, which should work better if the coils are connected in series. Alternatively, it is generally possible to run multiple A4988 drivers from a single logic signal source like the 555 timer.
Thank you so much for taking the time to reply and give such good advice, I never thought of running in series but that does make sense. These are steppers say 11V on the side, specs say up to 36V and 1.4A. I have some 5A 12VDC supplies on hand but nothing in 24V, so 12V (parallel) is easier for me to rig up with what I have on hand.
I broke out the old breadboard and am trying to put together a 555 pulse circuit, looks like it would be most logical to try and run one A4988 for each stepper if I run them at 12V. As far as microstepping, I havn’t gotten that far yet, there is no requirement for the motors to run super smooth though, I think 1.8 degree jumps will be just fine as long as the motors are turning at the same speed. Slow and steady with good holding torque is all I need.
Thanks again for taking the time to help me.
PS If you know of a good pulse circuit (555 or other) that I could use that would be helpful, right now I am winging it…
