>I'm trying to build an underwater tachometer for an AUV (autonomous
>underwater vehicle) being built at the University of Victoria by a group
>of engineering students.  What we hope to do is the standard shaft
>encoder scheme where one determines speed by counter the number of strips
>that pass by a photoreflector for a given time period.  As such, we are
>looking for an IR photoreflector that is contained in a waterproof casing
>(maximum depth we will be going is 30 feet).  Can anyone recommend such a
>photoreflector or an alternative way to match the speed of two motors?

Try a Hall effect sensor, with a magnet on the other side of the gap, like
OHB900 from OPTEK (www.optekinc.com) and glue it.
In france, Farnell sold it (www.farnell.com)

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