Roboticist Josh Pieper has been developing his mjbots quad A0 quadruped robot for around a year now, and he recently uploaded some new updates on his progress over on his Hackaday page. The robot is similar to MIT’s Mini-Cheetah in design and dynamic movement capabilities, only it's low-cost, fully open source, and features a series of custom leg servos and controllers, all powered by a Raspberry Pi 3B+.
Pieper made the robot’s legs using a series of brushless Moteus M80 servo actuators and gearboxes, each outfitted with a Moteus controller he custom-designed around an STM32F446, which can power a motor with a peak power of over 400W. He essentially copied the Mini-Cheetah’s planetary gear set that drives the legs, which has 3D-printed appendages, an all-metal power train, a shoulder and upper leg rotation of 1800, and a lower leg rotation of 1600.
According to Pieper, he is on his fourth revision (R3.1) of the Moteus controller as well, which he outlines as having up to 24V of input, a 50A peak phase current, 400W of peak power, and has FOC control with an integrated AS5047 magnetic encoder. It also features a 3Mbit RS485 connection with two possible protocols — one that offers size efficiency for real-time control, and another providing introspecting nearly all internal state.
As mentioned earlier, Pieper has uploaded his progress report, along with a project log; however his website provides a detailed walkthrough of the mjbots quad A0 build. Complete with videos, schematics, files, and relevant links for those who would like to recreate the robot themselves.