Flywheel RPM Measurement?

I was wondering what teams were using to measure rpm on their flywheels. I thought of a couple possibilities, but as far as I know, integrated encoder modules attached to the motor would not provide a very exact measurement, quad encoders would break if attached to a flywheel axle spinning very fast, and and the white paper with black line on it that jpearman used on his TBH algorithm test are, I believe, illegal in competition due to rule <R7>, which states that “Teams may add non-functional decorations provided that these do not affect the robot performance in any significant way or affect the outcome of the match.” The last one, however, I am not positive about, so please correct me if I am wrong.

We use the quad encoders, we broke a bunch of them early on, because they were on the same axle as the flywheel, then we moved them up the gear chain, so that the encoders spin 1/3 the speed of the wheels and haven’t had any problems

I am using a Quad encoder to control My robots PID control. It is directly driven by the motors, and takes accurate measurements of the flywheel speed. I haven’t had any problems with inaccurate measurements since I have been using it.

I believe that jpearman’s method of gauging RPM is competition legal per <R7> a.

<R7> Robots are allowed the following additional “non-VEX” components:
a. Any material strictly used as a color filter or a color marker for a VEX Light Sensor.