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[SOLVED] Analog position/speed control of a stepper motor

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cstoos

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I am designing (on paper only at the moment) a camera mounting system. If a use a dc stepper motor as the drive system, is there a way to create a feedback control setup that is purely analog or do I have to convert it to digital at some point?

For added clarity, the motor does NOT have a position sensor, so I will be using a mag pickup and running that through a frequency to voltage converter, which will essentially be my return signal.

Any information, specific or conceptual, would be helpful. Thanks.
 

By design, a stepper motor will operate at a wellknown speed (unless loosing steps), so you won't need a speed or incremental position sensor for it. A zero or index position sensor may be required to calibrate the drive position.
 
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    cstoos

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Initial position is not really the issue, I just need constant angular velocity out of it. The reason I was wanting to add a simple controller is because I assume (maybe wrongly) that as the battery life drains the speed will become less and less constant. For long term exposures (say, 4 hrs) the angular velocity must be constant.

I realize that a step motor isn't exactly constant in its rotation, but at steps of about 1.8 degrees or less it won't affect the accuracy since it will be geared at about 30:1.

If I am wrong than hopefully you just saved me some work.
 

Yes, you just need a timer (e.g. 555) and a counter/logic circuit, that generates the pulse sequence for the stepper.
 
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    cstoos

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Cstoos, I think you are confusing the effects of battery voltage. A stepper and sequencer will move the same distance at approximately the same step speed as long as there is sufficient power to turn the rotor. The speed is dependent on the control pulse rate, it is only the torque that drops as the power becomes limited. If you are gearing 30:1 and I guess moving a telescope, the amount of torque needed would be relatively small.

Brian.
 
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    cstoos

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Thanks for the help guys. Yeah, the camera mount is for astro-photography. I guess this is turning out to be more simple than I expected, and that is good. That is, as long as the stepper motor works the way I need it to. The mount is a bit heftier than most.

I am also looking at a plug in option when available, but that I am better with and can figure out. They really should teach us mechanical guys a bit more EE stuff.

Anyways, thanks for the info. Appreciate it.
 

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