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Velkine Engineering · September 15, 2026 · 6 min read
Sizing actuators for legged robots
A practical torque budget for hip and knee joints, and why continuous torque, not peak torque, decides the motor.
Start from the stance
Static knee torque is roughly the share of body weight on that leg times the horizontal distance from foot to joint.
Add the dynamics
Jumps and stairs can demand two to three times the static torque for short bursts. The motor thermal limit, not peak torque, usually sets the continuous rating.
Checklist
- Mass budget with margin
- Worst-case leg pose
- Gear ratio versus backdrivability
- Thermal model of the motor
Tell us what the system needs to do.
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