Testing motor performance... how do you do it?

Hello, VEX forum.

Before building the actual robot, me and my partner have been thinking about testing out our motors and choose the best ones to use, as we have like 40 393 motors. But we are wondering how to efficiently do it.

We thought of testing motor by their free speed. We assume that motors with higher free speed will perform better. Therefore, we wrote a simple code in easy c. The tested motor is attached to an encoder. The motor spins for 15 seconds and the encoder get the value and zeroes itself every half of a second. In the end the cortex outputs the highest and lowest recorded value. We tested a few motors out to see their speed and consistency.

However, the battery voltage drops, therefore we cannot guarantee the accuracy of the test. We are also trying to find a way to test PTCs to find the longest lasting ones.

Excellent teams who are trying to find this advantage, how do you do it?

Thanks very much!:smiley:

Free spinning is not a good test, as you are testing the motor speed, but not it’s actual power. They should be tested under a load so they are straining a bit, like lifting something heavy with a winch and timing it.

Test each motor multiple times, but not right after each other. Using a bench power supply solves the problem with batteries.

For stalling, you could hold the motor and time how long it takes to stall. Not sure you accurate that would be, though.

Another thing you should also do is visually inspect the internal gears for any signs of damage. If you know, it is good to classify how badly motors have been beat up where ever they were installed. For example, an intake probably has less wear than a direct drive with a trigger happy driver.

It’s probably been discussed somewhere, but does anyone know how to decode to serial numbers to get the date out of them so you can get a general idea of how old they are?

Thanks Kevin.

The winch idea sounds good. I’ll try to figure out a mechanism that can do that. I have a whole summer to do that.

I have seen the PTC experiment performed by jpearman. According to his experiment, the performance variation can be big. He did his experiment by assigning motors a constant current. Not sure if the software I have can do that…

Recently I built a motor test bed from VEX material plus two light extension springs. The motor drives a sprocket and chain to stretch the springs. The motor runs until it stalls and the spring stretch distance indicates stall torque. Release the motor power as soon as stall is achieved!

Thank you so much. This is such an amazing idea! Except constantly replacing motor is a little bit of trouble. But yes, amazing idea and definitely will CAD one this summer. Maybe the black elastic tubing is better… right?

The downside to elastic tubing is it is harder to measure torque as elastics don’t follow hooke’s law. With a spring, if you know the spring constant (or calibrate with a weight) the force can be found by multiplying displacement by the spring constant. To get torque, multiply that by the radius of the sprocket or pulley you are using.