HobbyKing Cheetah: How Cheap Drone Motors Could Power Running Robots
Motor Characterization for Small Running Robots (2016)
I characterize six cheap brushless motors from HobbyKing to see if they can work as actuators for small running robots. Each motor gets a teardown and measurements of torque constant, resistance, and motor constant. The Turnigy Multistar Elite 5010 stands out with the best motor constant, while the Flycat i-Rotor 5010 disappoints. The goal is to build a 2-DOF leg prototype using these hobby motors.
The hobby remote-control-things market has produced an abundance of cheap, light, super powerful motors. This type of motor has showed up in my fleet of small electric vehicles, and many other people's vehicles, multi-copters, airplanes, etc. long before me. But not in robots as precision or fast, torque controlled actuators.
- num42
[1] The author of the posted article, Ben Katz, designed the MIT Mini Cheetah during his master’s program. His thesis has become very popular in the robotics community as a reference for actuator design, and it is freely available online.
Thesis: A low cost modular actuator for dynamic robots
https://dspace.mit.edu/entities/publication/b85069e2-f1cd-47...
https://www.youtube.com/watch?v=nmViQ1T03Rk
[2] Unitree, LIMX Dynamics, and other Chinese robotics companies may also have referenced or been influenced by his actuator design in the evolution of their own actuators.
https://www.militarytimes.com/industry/techwatch/2026/08/18/...
[3] Ben, tear down a Chinese version of the Mini Cheetah.
https://robot-daycare.com/posts/2022-11-02-mini-cheetah-clon...
https://www.youtube.com/watch?v=t5SHUWb6kH4&list=PL8H6WijZPO...
- sashank_1509
This was a monumental change to the field, basically all the humanoids you see now started with this. To someone outside the field:
1. Boston dynamics pioneered hydraulic actuators (for their humanoid Atlas) and some really complex motors for their quadrupeds (I don’t think they ever explained their design)
2. There was a whole research line on Series Elastic Actuators that was pursued in the quadrupeds from Europe, famously Anymal from ETH Zurich.
The main problem they were trying to solve was high torque density with back drivability. If you wanted large torque, you could use a high gear ratio but then you lose back drivability and the walking becomes really stiff. MIT Cheetah basically custom built a motor with a really large radius that just output a really large torque. So to summarize, we had hydraulics, a really complex motors + spring mechanism, a really complex large motor to solve this problem and they all required huge amounts of money and complexity ( arguably MIT cheetah was simple but I heard thermal management was a big headache, and the entire robot cost millions)
Ben Katz, then at MIT, showed that you could use regular BLDC Motors, heavily used in drones with a small gear ratio, like say 1:10 or 1:20 and get a really good torque density, backdrivability tradeoff. It started around the above blogpost, in the coming year as a part of his masters thesis, he build the MIT Mini Cheetah, that was also the first quadruped I saw that performed a backflip, (maybe Bost […]
- hingler36
Ben's writeup of the mini-cheetah actuator remains one of the best resources to learn about robot actuator design and control