You've had some good suggestions by other posters. A stepper motor with
drive is available from All Electronics for $25. It's a kit, but I've
built other stepper driver kits (not this one) and they're [retty simple.
If you need *exact* speed control, you're going to need some sort of
controller that has a feedback mechanism - a tachometer or encoder attached
to the motor shaft. If "close" is good enough, if it doesn't matted if the
motor slows slightly under load, then a simple controller would work. How
do you determine speed? The old-fashioned way was a stroboscope. There
are also non-contact optical tachometers. If you want cheap-and-dirty
(hey! a CHAD tach!), you could print out either a wheel or a strip with
properly spaced lines. Under a fluorescent light (or neon bulb), with the
right dimensions, the lines will appear to stand still.
how about this one or similar:
Two-finger trigger and lock-on switch
does that mean I can rev it up to a certain rpm and click a swicth to keep
it at that rpm?
Ok here is a couple of eBay hits.
This will be a good control ~ http://tinyurl.com/98gt4
This should do the trick for the motor ~ http://tinyurl.com/9s3qw
From this point you need a 24v supply, and an enclosure to mount the drive.
Then power the thing up, Pick a point on the potentiometer, measure the RPM
and mark the setting.
Hope this helps
Ok, that one is wide open.
How much torque do you need?
How repeatable/accurate do you need to be on the speed?
Do you need constant torque across the speed range?
Do you have a weight limit?
And most importantly, how much do you want to pay?
Here is a couple of ideas
Search eBay under the string "servo motor" I just did and there are several
motors and amplifiers available.
I also checked McMaster and there are several motor and controller
combinations you can assemble. Although I was not able to get any workable
combination for under $300.
Or you can buy a electric RC drive motor and a variable speed drive and
then hack a circuit to replace the receiver.
Along the same lines as the RC solution, I understand some model train
enthusiasts use PWM (pulse width modulated) speed controls you can control a
tiny DC motor with.
I found this page about little LEGO motors and they seem to have the rpm
range that I am looking for...
Can I assume that by altering the voltage I can control the rpm? Or is that
what a motor controller does?
In some cases altering the voltage changes the speed. I won't go into the
theory, but if all you do is simply reduce the voltage you will reduce the
torque the motor can deliver. at some point the torque available will drop
below what is required to turn the unloaded rotor.
The controller uses full voltage all the time and, keeping it simple,
switches on and off real fast, thus lowering the voltage the motor
"perceives". This is called PWM or pulse width modulation.
The rapid on/off cycling can often be perceived as a whistling sound.
Hope this helps.
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