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Originally Posted by Alan Anderson
The "larger and smaller patches of carpet" will appear to be moving by "smaller and larger distances" as seen by the sensor. If you travel three feet, the mouse will record a certain number of counts. If you then raise the mouse and travel the same distance, the mouse will record fewer counts.
An optical mouse works by tracking offsets in the image at the sensor. The image at the sensor is a scaled representation of the carpet being viewed. The scale factor varies with distance from the carpet. If the distance is not kept perfectly consistent, the resulting measurements are likewise not consistent.
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Right, but I still think this will be more accurate than anything else out there. I think it's entirely possible to keep the mouse within a 8mm range. And how long is it really going to be out of whack? A few tenths of a second perhaps... So lets say it misses 300 counts. That's a few inches off, and even if this happens fairly regularly its still so much dramatically better than any other robot navigation solution. It's not going to be perfect, but it will be better than it needs to be.
I think the bigger issue will be different surfaces, which will have to be accounted for by using banner sensors to detect changes. This will be interesting.
At the very worst, infrared and ultrasonic sensors are precise enough that they could be mounted near the optical sensor and used to scale data live. I really don't think it will come to that though.