Re: What is the simplest way to control a motor's speed

Hi Doug,

The reason that PC's or microcontrollers are so popular is the basic
properties of AC motors require manipulation of both the volts and
amps. the volts to hz ratio cannot be done with a simple
potentiometer.

then the DC motor speed controller is simple as direct DC voltage
controls motor speed.

The problem with either of these is that motors use a fan, usually
mounted on the shaft to keep themselves cool. slow speed=no cooling.

The stepper motors you probably have are small, many are probably
less than 2 inches square. Some may be a little less than 2.5 inches
square. these are simple stepper motors. They can run from near
zero speed to a pretty good speed, but lose power the faster they
turn.

You did not mention how fast you want to spin the motor or how much
work you plan on doing with it. if you need 20,000 RPM, then get a
cheap trim router from Harbor Freight and a router speed control.
the pair would cost less than $35.00 The $10.00 speed control is for
DC brushed motors only, so if you have a 110 VAC, DC brushed motor,
you only need the speed contorl.

if you want to drive a stepper, www.jameco.com offers simple low
powered stepper motor kits. most likely you have 6 wire motors.
These are uni-polar and are easy to find kits to run.

If you have 4 wire motors, (bi-polar) these are also simple to run.
but the method of driving them is different.

With a PC, you can connect 4 CMOS transistors and drive one stepper
directly.

Lastly, as you learn more about steppers, you will find that they
operate best at about 20 times the nameplate voltage. This means
each stepper has a sweet spot of power and speed. less voltage, less
speed, less power.

Another thing you will learn is that to achieve the sweet spot on
your steppers is pretty much the end of the calculation. first you
need to know what you want to drive, how much power you need... that
sort of stuff.

I am not sure if I answered your questions, but maybe I gave you a
starting point.

Dave

--- In CAD_CAM_EDM_DRO@y..., "wdnick" <wdnick@y...> wrote:
> I have a couple of boxes of stepper motors mostly salvaged from old
> printers and copiers. I also have a few small 5-24V DC motors
laying
> around. Eventually, I'm going to build myself a small CNC machine,
> but until I have time and resources my current project seems fairly
> simple. I need to control a motors speed over a range of 0 to near
> 100% with a potentiometer. I don't care anything about reversing
it,
> what it's position is, or if it is a stepper or dc or RC servo. I
> would prefer the cheapest and simplest way out. I have found tons
of
> stuff on the net, but everything seems to be oriented around a
> microcontroller or PC control and all I want is a simple speed
> control. Can someone give me a suggestion on where to look for a
> prebuilt solution or a decent kit?
>
> Thanks,
> Doug Nicholson