Sanity Check Your Engines With This Dynamometer

As you get ready to pop the hood of your RC car to drop in a motor upgrade, have you ever wondered how much torque you’re getting from these small devices? Sure, we might just look up the motor specs, but why trust the manufacturer with such matters that you could otherwise measure yourself? [JohnnyQ90] did just that, putting together an at home-rig built almost from a stockpile of off-the-shelf parts.

To dig into the details, [JohnnyQ90] has built himself a Prony Brake Dynamometer. These devices are setup with the motor shaft loosely attached to a lever arm that can push down on a force-measuring device like a scale. With our lever attached, we then power up our motor. By gradually increasing the “snugness” of the motor shaft, we introduce sliding friction that “fights” the motor, and the result is that, at equilibrium, the measured torque is the maximum amount possible for the given speed. Keep turning up that friction and we can stall the motor completely, giving us a measurement of our motor’s stall torque.

Arming yourself with a build like this one can give us a way to check the manufacturer’s ratings against our own, or even get ratings for those “mystery motors” that we pulled out the dumpster. And [JohnnyQ90’s] build is a great reminder on how we can leverage a bit of physics and and a handful of home goods to get some meaningful data.

But it turns out that Prony Brake Dynamometers aren’t the only way of measuring motor torque. For a disc-brake inspired, have a look at this final project. And if you’re looking to go bigger, put two motors head-to-head to with [Jeremy Felding’s] larger scale build.

 

2 thoughts on “Sanity Check Your Engines With This Dynamometer

  1. It’s a cool build, and I’m glad he gets some recognition – I’ve been following him for quite a while, and there is a lot of interesting content.
    That being said, I think the article would be more interesting if it also took into account some of the feedback given in the comments section on the video. Several very valid points were given about obvious uncertainties in the measurement.

    1. Yes, probably someone already mentions it in the coments, but for measuring the torque you could measure the reaction force on the engine block instead of the shaft. But you need a load on the shaft.
      That’s why dynos use large cilinders of a known mass and diameter.

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