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So, for a small home-made engineering project I have cannibalized a 14.4 V DC 20 A motor from a Bosch battery powered screwdriver/powerdrill to spin a flywheel. I'm still using the trigger (drillswitch) from the powerdrill to control the speed of the motor but I want to switch this control for a variable resistor w/ potentiometer for preciser control. In other words, I am trying to make a speed control. How do I do this? What do I need? I will still be using the 15 V 1.5 Ah battery.

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  • \$\begingroup\$ You can find PWM motor controllers on ebay and aliexpress, or any shop that does RC (radio control) toys like cars etc. \$\endgroup\$
    – bobflux
    Apr 5, 2018 at 11:32

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If it is truly a DC motor you simply apply power to and it runs, then you can PWM the DC. I'd use a suitable N channel MOSFET as a low side switch controlled by whatever generates the PWM. Put a Schottky diode in reverse across the motor to give the inductive kickback current a safe place to go. Start with a PWM frequency in the 24-30 kHz range.

If it's a brushless DC motor, then you need something more complicated because the circuit has to do the commutation too.

The drill already has a suitable motor controller in it. The first approach might be to see what the trigger control does and either actuate it directly or mimic its effect.

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