I'm wondering if anyone has any experience or thoughts on a roller chain based optical interrupt encoder. Imagine a motor that drives a wheel using standard roller chain, e.g. #25, 1/4 pitch. The open space in the links of the chain transmit the light and the pins in the chain block it resulting in a pulsed encoder signal.
I can imagine a problem related to chain tension that might result in the chain contacting the transmitter or the receiver, but that should be surmountable by placement and design.