Remote focus project

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bill123
Posts: 3
Joined: Thu Sep 30, 2010 9:28 am

Remote focus project

Postby bill123 » Thu Sep 30, 2010 12:48 pm

I am working on a project to remote a mechanical focus knob on a projector to a desk in the auditorium. I am looking at the CMK series stepper motor and controller to turn the focus shaft. The common motor type is 1.8 degree steps or 200 steps per revolution. The rotary pulse switch I found that gives pulses on one pin when rotated CW and the other pin when rotated CCW should work with the 2 pulse input mode of the controller. My problem is the switch has 20 pulses per revolution and the motor 200 steps so the focus will be 1/10 the movement of the knob. Using a smaller degree step, a gear head motor or step angle options all make it worse. I could possibly belt the motor to the focus shaft with a larger pulley on the motor but I was hoping to go direct.
Trying to stay economical is there a way to make the motor steps larger or do you know of smaller step rotary pulse switch. Can an encoder interface to the controller in 1 pulse mode with A phase to PLS and B phase to DIR or do I need an interface circuit. I know encoders can have very fine steps but are more expensive and all I need is a small knob on the desk.
We tried a slow motor with a forward reverse toggle switch but the motor either went to fast or coasted past the optimal focus point.
Please any suggestion to help me move forward on this project would be appreciated. Thanks.

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omsupport1
Posts: 99
Joined: Thu Nov 19, 2009 10:34 am

Re: Remote focus project

Postby omsupport1 » Thu Sep 30, 2010 1:22 pm

bill123,

You mentioned that you used a "slow motor" with a fwd/rev switch. Was the "slow motor" the same stepping motor?

Using a simple pulse generator with a fwd/rev switch is what I would recommend. Are you capable with building a simple electronic circuit? A simple 555 timer chip, a toggle switch and a potentiometer should be able to do what you want rather well, without the over run issue.

I have attached a circuit diagram of what I am refering to. You should be able to buy these parts from any Radio Shack type store for very little money.

In order to use an encoder, you would have to "block" whatever channel you don't want to use so as to not "confuse" the driver as to which direction it should be rotating.

Let me know if you have any other questions.
Attachments
Timer555.pdf
Pulse generator circuit
(16.23 KiB) Downloaded 554 times
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bill123
Posts: 3
Joined: Thu Sep 30, 2010 9:28 am

Re: Remote focus project

Postby bill123 » Thu Sep 30, 2010 4:04 pm

The motor in another room has a large gear reduction and coasts after power is removed so we are trying to find a better control circuit. We would also like the focus to follow the turning of a knob so with fast scene changes you can feel how much you moved the knob and go back.

bill123
Posts: 3
Joined: Thu Sep 30, 2010 9:28 am

Re: Remote focus project

Postby bill123 » Thu Sep 30, 2010 4:08 pm

You are suggesting a servo type control that might work but we would like control from the auditorium and the projection booth. I don't think you could have both work at the same time and if you switched between them the focus would jump to the position of the other potentiometer.

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omsupport1
Posts: 99
Joined: Thu Nov 19, 2009 10:34 am

Re: Remote focus project

Postby omsupport1 » Thu Oct 07, 2010 11:08 am

bill123,

It sounds like you may want to look at some type of joystick controller that can be actuated via a rotary motion via a knowb instead of the joystick. Unfortunately, I am not familiar with that type of product.

You might consider looking at a dc brush type motor with an anaog speed controller to do what you want to do.

Good luck!
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