Opitical Mouse for tracking robotic movement

Hello all. I have been working on a robot project with a group of friends and we have encountered a slight problem in making the robot
move properly. We decided to use stepper motors as the drive train system. Using stepper motors we know the relative telemetry of the robot but we have no way of compensating for the stepper motor skipping a step or wheel slippage. While debating different solutions we came up with the idea of using two optical mice mounted under the robot facing the ground to track ground movement as a secondary telemetry for correction.
I would like to know if anyone in this group has done this set up before and can post suggestions.
Thanks
Andy
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snipped-for-privacy@gmail.com wrote:

Someone posted a URL with a picture of a bot they were helping high school kids build in the past few months. It used an optical mouse. But instead of using it to track ground movement, they used it to track the wheel movement as a cheap shaft encoder. The wheel was large enough that they simply placed a sheet of paper against the wheel and mounted the mouse against the wheel looking at the paper (if I am remembering correctly)). I don't remember the name to Google for. Maybe the guy that posted will read your post and answer or maybe someone else here will remember who it was?
I don't know how accurate the mice are however. They don't need to be accurate to work as a mouse since you have constant feedback with the user. They might have more error than your stepper and wheel slipping combined.
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snipped-for-privacy@kcwc.com (Curt Welch) wrote:

Ah, I was able to find it with a bit of google work.
Here's a video news report about the bot ...
http://video.google.com/videoplay?docid 65197422869440629
And here's an article about it:
http://www.linuxjournal.com/article/9103
Both talk about how they used the optical mouse.
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I would've thought that the scroll wheel encoder would be easier to use (that's what they're made for aren't they?)
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The above project used a standard PC board running Linux which means it already had support for a standard mouse. It was probably easier for them to use that than to interface some type of encoder.
But sure, in general, shaft encoders are easy and cheap to build and would probably be more accurate than the mouse.
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Agilent (HP) makes the sensors (i don't know of other vendors) and you can find data sheets here;
http://www.avagotech.com/products/document-results.jsp?catIdI39
one example is; http://www.avagotech.com/assets/downloadDocument.do?idA5
some points to note - maximum speeds top out at about 14 inches/sec, and if sensing ground, depth of focus is typ 0.5mm.

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