Stepper Motor Control: Replicating Rotation at Point A at Point B

[pavadrin]

To the viewer of this post,

I wish to create a device which can replicate a rotation at point A at point B. What I was thinking was using a stepper motor to replicate the rotation at point B through the use of a controller and have some sort of mechanical-to-digital device which could incode the rotation at point A. I also need this system to be able to operate at different speeds, so that the rotation at point A is replicated at point B.

What would I need for the mechanical-to-digital encoder? Could I use another stepper motor?
What sort of controller would I need to use for the stepper motor to mimic the rotation at point A?

Many thanks for your advice and time,
pavadrin

 

[pavadrin]

PS: Not quite sure if it is the correct section of physics forums, if so sorry

 

[berkeman]

EE is a good place to ask this. You would use a quadrature shaft encoder to help you read the motion of the control knob (like the encoders used in computer mice to read rotation). The easiest way to take that as input, and drive a stepper motor as outputs, is to use a microcontroller (uC) evaluation board. You can look into the "Basic Stamp" series, and also the PIC series of uCs by Microchip.

 

[mgb_phys]

Another good place to start is http://www.arduino.cc/
It's cheaper and more capable than a stamp (there are also a lot of cheap clones)

The software is free and has a good community behind it, there are examples of stepper motor and PWM control

 

[dlgoff]

Maybe a different method would be to use a http://en.wikipedia.org/wiki/Servo" . Probably depends on what angles you need to duplicate.

 

[pavadrin]

Thanks for all the replies. Basically I need to replicate a rotation of >180 degrees, so maybe even a servo might work. How would I go about controlling a servo? The same way as a stepper motor?

Thanks,
pavadrin

 

[mgb_phys]

Normally a PWM, - easy to generate from most micros or you can build a little circuit with a 555 and a trigger

 

[EnergyChina]

There are several ways for this.

 

[dlgoff]

There are several ways for this.

Yes indeed and here is a site with lots of info.
http://www.educypedia.be/electronics/motorservo.htm"

Regards

 

[pavadrin]

thanks, wealth of knowledge from this place is amazing

 

[vk6kro]

There used to be devices called SELSYN motors which did exactly this.

You just rotate one of them and the other one, connected by wires, rotates to the same position. They need an AC power supply for excitation.

They were used so that you could sit at a transmitter and see which way your directional antenna was pointing.

They were used in WW2 to see which way a gun was pointing from inside a tank.
Apparently they are also used in the Panama Canal to tell if the gates are open or not.

No idea if you can still get them though. None on Ebay at present but a lot of hams would have them.

There is a good article in Wikipedia about them.