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There is a cheap brushed DC motor type that is often used in toys: enter image description here

Usually these are 3.3V with a no-load RPM over 10k. The advantage is that are very cheap. Under $1 at 1pcs. I am wondering if using any kind of "smart" control scheme it would be possible to control them so they'll spin at 10 RPM or less. Large torque not required.

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    \$\begingroup\$ This is done with a gearbox \$\endgroup\$
    – David777
    Feb 19, 2021 at 8:48
  • \$\begingroup\$ For a simple brushed DC motor, the speed is proportional to the voltage, except at the high and low ranges of the speed, where mechanical realities like friction dominate. I doubt you'll be able to spin it that slowly without some mechanical reduction (gearbox), only because at that low voltage there will just very little torque. \$\endgroup\$
    – spuck
    Feb 19, 2021 at 15:40

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It is really difficult to drive it electronically so slow without some kind of feedback (like an opto or phono wheel). It depends a lot on your torque profile, kind of load and required speed precision.

You can simply use the usual PWM, the motor winding does the current smoothing. Use a somewhat low frequency to have more resolution if needed. But given the high tolerances of these motor you'll probably need some speed feedback to make it work reliably.

David777 also recommended a gearbox. It's expensive but reliable and you get more torque. Some feedback or tuning will be required to keep the speed stable.

For really stable speed without any kind of control you may want a synch mains powered motor; they use them to run clocks since it works exactly with the mains frequency. it's more expensive, however.

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  • \$\begingroup\$ Getting a feedback signal is actually not difficult and will keep the price low compared to a gear box. Is there an IC of some sorts of a simple method to follow in order to enable good control or all the implementation of the control + correction based on feedback (PID?) is all custom and up to me? :) \$\endgroup\$
    – user733606
    Feb 19, 2021 at 10:17
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    \$\begingroup\$ The smart control system you are looking for to control this totally unsuitable motor for your application will end up costing you far more than the cheap stepper motor you should be considering. \$\endgroup\$
    – RoyC
    Feb 19, 2021 at 12:23
  • \$\begingroup\$ We don't know anything about your application but plastic gears and cogs are very cheap and easily got. Without a gearbox anyway, your motor will have next to no torque at that low an RPM (If you can even get it to rotate THAT slow smoothly. You select the motor for your application needs, not because they are cheap \$\endgroup\$
    – David777
    Feb 19, 2021 at 13:46
  • \$\begingroup\$ He didn't specify the torque requirements nor the effective speed tolerance it needs; it's difficult to choose between stepper and brushed without such data. He asked for a brushed and we suggested a brushed option. \$\endgroup\$ Feb 22, 2021 at 7:18
  • \$\begingroup\$ For control the old ICs did work in linear mode, not in PWM. At these speeds the lowest end MPU can do both PWM and speed measurements (assuming it has the timers); the control depends on the load you expect, a PI is a good start (add the D if you need it) \$\endgroup\$ Feb 22, 2021 at 7:21

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