How to mitigate cogging when driving BLDC motors

When we decided on which motors we were to use for the platform, the main consideration was that they had to provide continous and smooth motion. Smooth motion is a requirement if the rig is to be used for recording video, and it might also be less scary for nearby wildlife.

BLDC motors were chosen, as they seemed to be the best option for smooth motion. However when we started writing our own code for the motorcontroller, we ran into some problems with a previously unknown fenomena, known as cogging.

Cogging is the uneven turning-resistance in electromotors due to different factors, one of which is the magnets passing over the stators, causing periodic peaks in turning resistance.

When running BLDC motors at low RPM's these effects become very pronounced. And the whole rig was continously shivering from torque ripple when turning.

The solution to this problem was implementing a gyroscope and a PID controller. The PID controller compensates for the motors uneven torque response, and the result is smooth rotation.

The first video is the platform without any compensation for cogging:


And this second video is after gyro and PID was introduced:


There are still some fine tuning left to do with the PID parameters.

The next version of the AimBot?

The project is coming to an end, and the last couple of weeks have been spent writing a report on the work we have done. We have also been doing a round of testing, and will be publishing a video on that matter sometime soon.

In the meantime you can check out this rendering of the AimBot with 3 axis: