How to rotate a ring

I need to rotate a piece of optics that is about one inch diameter by one inch long over a 90 degree range. Either continuous controllable
angle or just 0 and 90 degree positions. Looking for ideas for either method. Is there a ready to go gear arrangement or servo that can accomodate this ? A servo could be linked (by gear, pulley, foam wheel, etc ) to a ring gear bearing holding the object, but I'm trying to come as close as possible to a ready to go solution.
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To what precision do you need to rotate the piece?

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Mielles Griot, Oriel, and Newmark Systems all sell systems for doing this with very high precision. Not cheap.
                John Nagle                 Team Overbot
Blueeyedpop wrote:

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You might look into the mechanisms used to rotate the antenna in a satellite dish low noise amplifier/block converter. They use a servo connected to a mechaism that rotates the receiving element 90 degrees back and forth.
It all depends on the size of the optics, which you didn't mention in your message.
If you're at all handy with tools you could build something. Use a largish gear and mount the optics inside it (drilling out the center as needed). Get three smaller gears and mount them at 12, 3, and 6 o'clock. Accuracy will be critical here. Mount a final last gear, connected to a servo, at 9 o'clock. This one rotates the center gear; the other three gears merely serve as pinions. You can get mating gears of different diameters from Servocity.com. They sell some that are made to attach directly to servos.
Finally check out Kelvin.com and look at their gear sets. They sell one or two that come with brackets for making various types of gear systems. They're pretty cheap...under $10 or so.
-- Gordon Author: Constructing Robot Bases, Robot Builder's Sourcebook, Robot Builder's Bonanza
Steve Parus wrote:

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Steve Parus wrote:

As others have suggested, you haven't provided enough information.
If all you need is rotation between 0 and 90, you could make two stops accurately and use a clutch type arrangement (e.g., motor driving a pulley via a loose belt). You could use magnets to insure good contact with the stops after the motor turns off. Maybe this isn't any more off-the-shelf than what you are already considering though.
Mitch Berkson
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there might be a "geneva mechanism" that you can purchase to fit your needs. Do a websearch and see. Constant or on/off motor input provides incremental rotary output, typically in 90 degree increments.
(Gawd, can you tell how old I am from that statement?)

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