Speed regulating an electric motor

[trains are bad]

I want a small DC motor that turns at a couple hundred RPM, constantly, at almost no load. Its actual speed isn't that important, because I can design around it, but it should be adjustable for trim. I'm building a belt drive record player.

I'm trying to think of something that I can rip a motor off of, but I can't think of anything. I have thought of using any DC motor, like say a warp feed motor, and using a pot to adjust it, but it's likely that friction, temperature, ect would cause the speed to creep or not be the same every time I started it up. It's probably possible to build a speed regulating circuit, but I have no idea how one would go about doing that.

[CaliMagFan]

arent most record players belt driven?... if not, then the one that i have in shambles is... it has a motor and it must have the regulating circut... i'm sure i can take that stuff out, cause i'm not going to use the player... lemme know if you want it... but then again, i'd think its not DC... cause it has a 110v ac plug.

lemme know.
-kr

[Big'n slo]

Jump on ebay and search for "DC motor speed control"
Plenty of cheap kits

[trains are bad]

Some are belt driven, some aren't. If you really don't want the motor, then I'd be glad to give you a few bucks for the guts. Or in the case that it's something worth messing with, the whole table. That it's 120v isn't a problem, I was just planning on using DC myself.

[ojhspyro89]

You could allways get a stepper motor say out of a printer or something. That way you can regulate the speed and you can also make it do scratching or whatever with the right computer program. Youd of course need a computer to run your record player...but itd be worth it.

[trains are bad]

I just threw away an inkjet printer, too. Just another justification for the expansion and continuation of my 'never throw anything away' philosophy.

[Tunaman]

sewing machine motor w/adjustable speed control...a dime a dozen anywhere

[Jaan]

I've used a "pulse width modulator" circuit with great success before. It's basically like turning a switch on and off constantly. It's good for motors that need full voltage to turn, like computer fans. A cheap kit is less that $5 from All Electronics (google that). All Electronics is also good for lots of other things too. Look around their site you might find exactly what you need.

[trains are bad]

But is PWM really 'speed regulated' in that regardless of load (within a certain range) the speed will be the same?

It almost seems like you would need a PWM, + some kind of servo circuitry to monitor motor speed and adjust the PWM to maintain it. Like RC airplanes nowadays have brushless motors and a speed controller that monitors motor speed through back EMF from unactivated coils. It seems to me that PWM would basically accomplish the same thing as a pot, albeit more efficiently, which may or may not work.

I thought of sewing machine motors too, but I have the same concerns. It seems to me that there is a difference between a 'speed controller' and a 'speed throttler (simple PWM, pot)'.

[ojhspyro89]

If you need a small stepper motor, ive got one in my basement on a printer. And when my motors come in, they are 116 oz-in gaurentee theyll spin that thing, I could sell you one of those for like 10 bucks or something if you need one. The one on the printer, you pay shipping and ill send you the whole printer...which is missing peices but works... i think.

[Jaan]

Jut out of curiosity, why are you building a record player? You can still buy them new.

There are many different designs for a pulse width modulator, some of course, more complicated than others. I don't know them all off the top of my head, but it seems that you could build into the circuit a feedback system that can self regulate the speed or the record.

[trains are bad]

Quite simply, to play records. I'm starting to back away from the idea now and consider just waiting to pick one up at garage sale or thrift store for cheap. It's probably more practical, and I have even less time than money nowadays.

[Jaan]

I have an older version of this turntable and it's excellent ...

Turntable

You can thank the rappers and DJ's for turntables still being made and sold these days. Just goes to show there's something good about everything.

Around Christmas time Guitar Center, Musicians Friend etc., always have turntable relatively cheap for all the budding 15 year old gangsta's in the suburbs and in PB Nation, if you want one new.

For the record (no pun intended) I got my turntable at a yard sale with a nice old Kenwood amp for $10 all together. There's plenty of them out there. I actually have 2 cheaper all in one units that are just sitting around if anyone wanted to carry them away.

[athomas]

If you are concerned about speed regulation of a DC PWM motor control, use an over rated motor. That way, a bit of change in the load won't affect the rpm, especially if it is gear reduced.

Gear reduced steppers would provide very precise control. No need for a feedback. If you are losing steps on a stepper motor, then your load is too high anyway.