Electronics experts: How to control a motor with a rheostat to adjust position?

[flot]

Here's a basic question for you guys who are into electronics -

I have a motor that I need to turn 180 degrees, to move a valve from open to closed and vice versa. However, I would also like to have *adjustment* capability, so that I could stop the valve at any point in between 0 and 180 degrees.

Ideally, I would have a simple dial type switch, so that as I turned the dial back and forth, the motor would emulate the switch position. Does that make sense? So every time I moved the dial, the valve would move in exactly the same way.

What I'm wondering is how involved something like that would be, and what exactly would be needed? Would I use a stepper motor and some custom controller, or ???

 

[Demon-Xanth]

I'd just use a stepper motor so you can move it to a position with a known digital sequence. And then you KNOW you're in that position. The only other way to be sure of where you're at would be position sensors (whether mechanical, optical, or otherwise)

 

[Mark R]

A servo motor will do what you want.

Essentially a sensor (like a rheostat) is attached to the motor shaft and produces a feedback signal. A control circuit compares an input signal and the feedback signal and commands the motor to move in the appropriate direction.

 

[flot]

Ah yes, I said stepper, but I think I really meant servo.. I did a bit of reading online and that does sound like close to what I want... but haven't had much luck locating suppliers and/or a cheap and easy control circuit... I've found some $$$$ stuff but it's all way more detailed than what I need...

 

[nebula]

Yep servo is better here. In theory, in could be done with a stepper but more complex. Check out Jameco they have some inexpensive stuff. I'm not sure how well there website works, may be more benificial to get a paper catalog. I sometimes order from them for work.