How many samples per revolution are you picking up?
Currently 4. I have experimented with 1, 2 and 4 pickups. The main problem with my pickup is that PLA doesn't block IR light so I have to cover the disk with electrical tape. I then cut out the holes in the disk with an X-acto knife and the edges aren't as clean as the 3d printed part.
Your angular velocity will be the same no matter where you are on the disc. Linear velocity will change, but that will not matter.
Do you have any gear reduction at all in the setup? 15ms is about 4000 RPM without any gear reduction, so not very good. I thought you were saving all the data to an array then do a serial dump after the run.
Yes, sorry. Wrong velocity. The big wheel didn't really work any better anyway. No gear reduction but the data points are timed revolutions not a polling. Every 15msec, it records the next 1/4 revolution time and equates that to RPM. I have been playing around with 2 different ideas. The first being the improvement of the Simple Dyno sketch. The second is dumping the whole run to an array using the Minima (doesn't work with SD yet or my Win7 shop computer. Had to bring a Win10 computer down to the shop).