Using Mini Cheetah-Style Brushless DC Motors for CNC Applications

Robots like the Mini Cheetah developed by MIT and the Boston Dynamics Spot have gained a lot of attention, and now we’re starting to see some of their high-end hardware trickle down to the hobbyist market. In particular, the motors used in robots like those are now available at a relatively affordable price. They’re large brushless DC motors that pack a lot of power, and have many features built-in that make them very convenient to use. You can use them to construct your own robot, but Bart Dring is experimenting with how to use them for CNC applications.

The specific motor that Dring is testing is the GIM8008 made by Skyline Innovations. It can be purchased from China via Ali Express for $359. That’s a hefty price tag for a motor, but you are getting a lot for your money. The motor is capable of handling a whopping 40 amps, though Dring is only using 10 amps for the time being. Most importantly, it has a built-in driver and encoder that make it possible to use it in applications that are normally reserved for stepper motors. That hardware lets you set the exact position of the motor, which is absolutely indispensable when you need precision control.

These motors are open source and the firmware is available, which Dring is taking advantage of to learn how to control them. They have a built-in STM32F446 microcontroller, which can be accessed and reprogrammed as needed. The motors can be controlled via UART (Universal Asynchronous Receiver/Transmitter) or CAN (Common-Area Network). They can be reprogrammed with an inexpensive ST-Link V2. So far, Dring has figured out how to control the motors as intended, and has created some new firmware. He plans to do some further testing on the motor’s accuracy, and then will build some sort of machine utilizing the motors — possibly a SCARA robot. If you’re interested in these motors, be sure to look over Dring's documentation and follow along with his progress.