# How to lower the RPM of a motor without using PWM or gears?

I need to lower the RPM of a simple DC motor to almost 20 - 30 RPM for some reasons. I cannot use PWM signals or gears to lower the RPM of the motor (I know how to use them but I want a simple solution.)

Is there any other way that I could slow down this motor? I tried to lower the voltage going to the motor using resistors but it didn't work (for me at least, I connected the resistor between the motor's one wire and the positive terminal of the battery supplying 3 volts. Let me know if I did something wrong.)

I don't care about torque that much so it's not a problem if I lose some torque in the process.

Hoping for a trick that could slow down this motor without using PWM or gears.

• A correctly sized resistor will indeed do it, albeit by wasting power. You can get an idea of how big a resistor you need by measuring the current the motor draws at 3V. If the resistor drops too much voltage the motor will be unable to start. Trying to get such a low RPM is unlikely without a specially designed motor. 20 RPM is very very slow for a small motor, so for most 3v motors, you will basically have no torque left at all at that speed. With a resistor you can probably get down to half the motor's rated speed, and with PWM maybe 10 or 20%.
– K H
Jan 22, 2021 at 7:58
• The gears and PWM are the cheapest simplest options unless you're willing to accept 50% speed as minimum RPM for your motor.
– K H
Jan 22, 2021 at 8:07
• A gearbox IS simple; it's a no-brainer. On the other hand, a control loop with speed feedback to avoid the problems of intermittent cogging torque at low speeds seems much more complex i.e. not simple. Jan 22, 2021 at 10:01
• timing belt, with reduction ... even easier than gears Jan 22, 2021 at 14:59
• @PeteW, what speed would a DC motor run at? OP didn't say. Even if it was only 1000 RPM that would be 50:1 reduction. Jan 22, 2021 at 17:23