DIY Dyno Double-Checks DC Motor Descriptions
Bubs wanted to know if his DC motors actually meet the specified torque figures, so he built his own dynamometer to test them.
There are specs listed in product descriptions (if you’re lucky) and then there is reality. The gulf between the two is often vast, especially when shopping through online marketplaces with unscrupulous sellers. Bubs wanted to know if his DC motors actually meet the specified torque figures, so he built his own dynamometer for the job.
A dynamometer is an instrument that measure the torque of a turny thing. You’ll frequently hear car guys talk about using a “dyno” to find objective power figures for their engines, so they can impress friends at the drag strip. But those measurements are useful for all kinds of applications, including electric motors for robots and machines.
Bubs built an inertial mass dynamometer, which measures torque by looking at how quickly an electric motor can accelerate a rotating mass. That method is ideal for a DIY dyno, because it really only requires a rigid frame, a mass to spin, and some sensor to monitor rotational speed over time (and therefore acceleration).
The frame and almost everything else on this dyno were 3D-printed. An opto-interrupter detects teeth in a 3D-printed wheel to measure speed and acceleration, with a rotational resolution of two degrees. The spinning masses (they’re called “load plates,” apparently) are 3D-printed discs with embedded steel bearing balls. Bubs designed those to be stackable, so he can adjust the mass to suit the torque of the motor being tested.
All Bubs needs to check a motor is a power, a logic analyzer to monitor that opto-interrupter, and whatever control input the motor needs.
In theory, this should work great. But it immediately broke during testing. 3D-printed parts aren’t always strong enough for the job. However, because the idea is sound, Bubs can rebuild his dyno stronger than before and start testing motors.