Optical sensor for use with retroflective tape

[dellagd]

Originally Posted by Tom Line

I know many teams used retroreflective tape and an optical sensor to measure wheel rpm last year. I'm curious if the ones who did found a good low-cost sensor. We're in a space crunch (as I suspect everyone is!) and don't have any way to attach encoders to the drive shaft.

I've found a few optical sensors that are retroreflective. Some are either ridiculous-expensive. For instance, $100 for a banner sensor. Others are nice and cheap in the $12 range, but don't list a maximum switching frequency! We're looking at rpm's that may range up to 10,000.

Here's what we (And I believe 341) did to track their shooter RPM.

Get out one of those photoswitch sensors (Unfortunately they're out of FIRST Choice) and attach it about a centimeter away from your rotating object.

Attach a piece of retroreflective tape to the rotating object and adjust the photoswitch so that it only triggers when the wheel passes.

After this its just programming. I believe we used the hardware counters (I cant remember exactly what its called) available on the CRIO to count the super fast pulses the sensor gives at those speeds. Our readings were just as accurate as any of those handheld tachometers you can buy.