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Unread 29-02-2004, 23:18
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Re: Optical Sensors Used as Encoders?

Quote:
Originally Posted by uvabrad825
I'm sure on past robots teams have tried to use their optical sensors as an encoder by placing bits of reflective tape on a wheel/sprocket and counting the number of times a sensor mounted to read the pieces of tape was 'activated' (I'm not a programmer so I don't exactly know the correct terms).

Our team is considering pursuing this idea once we uncrate our robot at regionals, having the programs pre-written. We are planning on putting 8 evenly spaced pieces of reflective tape on the rims of our back wheels, and mounting two optical sensors to appropriately interact with the pieces.

I was wondering if any teams in the past have had success (or lack of) with this procedure, and if so, what the optimal setup(s) are (tape spacing, distance from sensor to wheel, etc..). Our programmers are very good at what they do, so I don't think that will be a problem. Any advice would be greatly appreciated!

We did this exact thing last year and ot worked out pretty well. We split the coupling on our motor with tape. (half tape) and then made a quadrature encoder by using two optical Banners at 90 degrees from each other. THis way we knew of the wheel was spinning forward or reverse.

This worked out well, and given the ratio of this motor coupling to the output wheels, we had about a 3" resolution on out drive position.

It all worked out pretty well, but the thing that killed us was momentum when we stopped driving the motor. We had much overshoot at first, and much oscillation when we tried to impliment feedback.

Good luck,
-Quentin
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