A legged robot is mostly joints: three per leg on a quadruped, five or six per leg on a biped. Here is what each one needs and where to find it.
Joints
- Hips and knees take the highest torque and need to be backdrivable for impacts and force control: quasi-direct-drive joints (12:1 or less).
- Ankles and slow, loaded joints can use high-ratio and cycloidal joints for more torque per kilogram.
- Custom joints built into the leg structure start from frameless torque motors.
- Small robots fit compact joints under 500 g; full-size robots often need 100 N·m or more at the knee.
Around the joints
- Motor drivers for bare motors, encoders for output position, and brakes to hold a pose with power off.
- Batteries, controllers, CAN adapters and cables.
- Complete research platforms: humanoid and legged robots. Financing is available: net terms or monthly payments.
Sizing
Start from the worst pose and body weight with the joint torque calculator, then read Sizing joint torque for a legged robot, QDD vs high-ratio joints and Backdrivability in robot joints.
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