Motor Characterization for Small Running Robots (2016)
Ben Katz characterizes six cheap hobby brushless motors to evaluate their performance and torque density for small dynamic running robots.
read it Provides a rare, hands-on mechanical and electrical breakdown of hobby brushless motors for low-cost robotic actuators.
summary
Ben Katz evaluates six affordable hobby brushless motors to determine their suitability as actuators for small running robots. By measuring line-to-line resistance and back-EMF using a drill and oscilloscope, he calculates key metrics like torque constants and motor constants. The teardowns reveal differences in winding quality, lamination thickness, and magnet fill across brands. These findings helped lay the groundwork for low-cost quasi-direct drive actuators used in modern quadruped robots.
key points
- Pancake-shaped motors with large diameters and small depths offer superior torque-to-mass ratios for dynamic running robots.
- Characterization metrics like the motor constant and torque constant help compare electromagnetic performance independently of winding patterns.
- The Turnigy Multistar Elite 5010 emerged as the top overall choice due to its superior winding quality, curved N45SH magnets, and thin laminations.
who should read it
Roboticists, hardware engineers, and builders interested in low-cost actuator design and brushless motor physics.
discussion warm
consensus
This foundational work directly enabled the MIT Mini Cheetah actuator design, shifting the robotics field away from expensive custom motors and hydraulics toward cheap off-the-shelf brushless motors.
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 …
Provides historical context on how this approach revolutionized quadruped robotics.
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