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robert2222

servo control

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Hi I have have just joined and wondered if anybody could help me out I want to construct a way of controlling a servo for a remote follow focus for a video camera.

please see the video below:

http://www.youtube.com/watch?v=HpQWm759NW8

I have some expereince with servos etc, but wondered how I would control the servo using the same method, both back and forth preferably with up to one revolution in either direction to cover all the focus range? Also which type of servo would work the best?

anybody got any ideas or pointers in right direction.

Thanks

robert.

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The mechanics of what you want is on the video you linked to. For the electronics you need to produce a 1ms to 2ms pulse every 20ms. The easy way is to find a servo tester or someone that can program a PIC chip to do the job, failing that it can be done with NE555 timer chips. Try a search.

Terry

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Along with building the servo signal generator, just about any commercially made "servo tester" would work too. They tend to cost under $25, are very compact, and will have a knob to turn. For the servo, the Hyperion Atlas digital servos are extremely programmable and would allow you to precisely set the servo speed and travel endpoints. Otherwise, just about any quality mini or standard servo should work. All this stuff should be available from a well stocked local hobby store.

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OK many thanks for the input, you seem to be telling me that I should get a servo tester for the control, and the servo you suggest is the Atlas, but I see this will only travel 180 degrees I will need one that goes futher than that at least 180 to 270 degrees of travel (from zero to infinity focusing).

How would I get this, sorry to be so thick when you start talking about NE555 chips and 1ms to 20ms pulses I get very confused.

I also want to be able to control the servo with a thumb dial mounted to bars that support my camera see here:

http://www.redrockmicro.com/microShoulderMount/index.html

I wonder if there would be someone out there who would be willing to make me this set up and I will pay them for time and materials.

robert.

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... you seem to be telling me that I should get a servo tester for the control,

I avoid telling anyone what to get -- I'm merely mentioning that the hobby shop may already have what you need. Frankly, it's just one of many options. Keep in mind that this forum is mostly DiY'ers, so that is the direction most of us go. If it was my project, I'd design something rather than buy it ready made (because that is what I enjoy doing). :) If you want to do that then the net is full of servo control projects (the R/C PPM signal is well documented too). Google would yield an endless amount of stuff for you to leverage off of.

I will need one that goes further than that at least 180 to 270 degrees of travel (from zero to infinity focusing).

Some servos can be hacked for 270 degree movement. But, a reliable way that uses unhacked servos is done just like you see in the video you posted. As shown, the rotation is mechanically "amplified."

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