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Originally Posted by Alan Anderson
We used a test jig with adjustable height and a strip of carpet on a moving platform. During one trial, after I adjusted it for the best focus (as determined by the reported image quality from the sensor), the measured travel from one end of the platform's range to the other was on the order of 400 counts. As long as nothing disturbed the height of the mouse it was very repeatable, with the cumulative distance returning to zero over many cycles back and forth. However, raising the mouse by a couple of millimeters decreased the measurement to about 380 counts. Lowering it a similar amount increased it to about 440. That much variation is probably what you'd get just driving across a smooth carpet, and pretty much wipes out any chance of using the system to get an accurate reading of the robot's position on the field.
To improve things much, you'd have to employ three-dimensional imaging. I doubt there are any cheap devices available to do that.
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Could an ultrasonic or infrared range sensor be used to read height, and scale input values accoordingly?