For this project here http://letsmakerobots.com/node/22474, I am needing a simple sensor to indicate the number of revolutions a tsecond that an axle makes. However this will be in a dirty/oily place (under isde of carriage bogie) so I am wondering on the best method of sensor to use. I think I have narrowed it down to three possibilites -
1/ Optical slot interupter with seperate encoding wheel. Probably easiest option but how prone to dirt and mis reading. Could be hard to clean.