mjbots

mjbots is a small American company known for its moteus motor controllers and the open design of quasi-direct-drive actuators for quadruped robots. Its home page shows three controllers on offer: the moteus-c1 (10–51 V supply, 5 A continuous and 14 A peak phase current, priced at 69 USD), the moteus-r4 (8–44 V, 12 A continuous and 32 A peak, 94 USD) and the moteus-x1 (8–54 V, 25 A continuous and 62 A peak, 169 USD). Each has an integrated encoder and interfaces such as I2C and UART; CAN-FD adapters, Raspberry Pi expansion boards and power distribution boards complete the range. Prices come from the maker's site and may change.

What counts is that the controller is open: code and documentation are public, and torque control lets you build an actuator with the compliance of its gearing, the kind described in “Actuators in Humanoid Robots” under quasi-direct drive. A low gear ratio and a strong motor give a joint that "feels" contact with the ground, which matters for the gait of quadruped robots.

In which robots? Our materials contain no documented parameters of mjbots actuators themselves and no list of robots using them, so we will not point to a model from our catalogue. Only the general product line is known: controllers for quadruped robotics. Finished quadrupeds such as MAB Robotics Honey Badger 4.0 or Unitree Go2 (see “Unitree Go2 Review: Prices and the Air, Pro, X and EDU Versions”) are bought as a whole, without choosing a controller; our materials give no indication that they use mjbots. The segment is covered in “Quadruped robots”. mjbots is aimed at hobbyist builders, universities and small teams of the school and laboratories kind.

For a robot's cost, a controller costing from tens to a few hundred dollars per joint means that a self-built drive costs less than a ready actuator, but in return the designer takes on the choice of motor, gearbox and cooling. On a robot with twelve joints the difference becomes significant. Alternatives are ready actuators from MyActuator and CubeMars, controllers from ODrive Robotics and servos from ROBOTIS. A controller in the 24–48 V class suits frameless motors and large external motors, but not industrial cobots.

For Poland and Europe we found no named distributor; this looks like direct sales from the USA, so shipping costs and customs duty have to be added. For novice builders the road starts with “How to Start Learning Robotics in Poland” and simple projects, before anyone commits to building quadrupeds.