Poor Man’s Dyno or Motor Checker

February 23, 2009 · Posted in How To, Maintenance, Videos · by simon

I wanted to compare some motors, and wanted a simple way of reading RPM. So I needed an RPM counter of some sort. I thought about making one, but I quickly came across some on ebay.

I ordered one up, and it’s quite a bit bigger than I expected it to be, but that’s not a big deal.

It works very simply, you stick some reflective tape to whatever is rotating, and shine the laser on it. The reflective part needs to be less area than the non-reflective part. It then just counts the reflections and displays the RPM.

Brilliantly simple. Sure, it doesn’t check anything else, no torque measurements, or current measurements etc, but for a quick and dirty comparison it’s great.

It is of course important when checking motors to ensure that the voltage is similar on all of them. So use a fully charged race pack, and test them all at the same time, one after another.

I could even go so far as to test them under load, such as fitting them into a car and using the drivetrain as a load, as long as it’s the same conditions for each motor then it should be consistent and useful.

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