How can control RPM of DC Motor

nuiseng191 · electronics forum beginner Joined: 10 Apr 2007 Posts: 5

It sounds like there are some real experts on this site.I was hoping someone could help me out. I have a 12v DC hobby motor with a 700mA supply. What I'm trying to achieve is 3 speeds.Low, med, and high with a 3 position switch. I've come to realize that on an AC motor this would be a piece of cake but not so much for a DC. Is a "pulse width modulator" the only way this could be done? I saw a few on Ebay for cheap but they do not ship to Canada. Does anybody have any useful suggestions or simple schematics they would not mind sharing? This is the only real hold up in my project. Thanks anyone and everyone

Electromotive Guru · electronics forum beginner Joined: 07 Jun 2006 Posts: 27

Speeds on a DC brushed motor are hard to control without a flywheel on the motor in the first place, and then that introduces a lag in response. Whether response is important or not, posting your expectations for the performance of this drive is necessary for any plausible design.

mrksem454 · electronics forum beginner Joined: 28 Apr 2010 Posts: 3

Well, Gearmotors are the usual answer, I assume that you want a constant angular velocity. That leaves out steppers and even brushless servomoters as at 1 rpm they would be pretty lumpy. A synchronous AC motor could do it, but most aren't designed for speeds that low. Some torque motors could do it, but 1 rpm direct is pretty slow.

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