Buying guides

Every quasi-direct-drive joint actuator we track, ranked by peak torque and torque per kilogram, with picks by robot size and what to look for when buying.

Dexterous robot hands compared by active DoF, weight, tactile sensing, interface and price, with picks and what to look for when buying.

Research humanoid and bipedal robots compared by height, weight, degrees of freedom, compute, SDK access and price, with picks and what to look for when buying.

Peak versus rated torque, gear ratio, backdrivability, bus voltage, communication and encoders: what matters when picking joints for a legged robot or arm.

Why legged robots use 6:1 to 10:1 joints and arms use 30:1 and up: backdrivability, reflected inertia, stiffness and holding torque explained.

How much bandwidth a robot needs, when one CAN bus is enough, and what to check in a joint’s protocol before you buy.

A worked example: estimate static knee torque from mass and leg geometry, add a dynamic margin, then pick peak and rated torque.

What a frameless motor includes, what you must add, inrunner versus outrunner, and how to read KV and torque figures.

How gear ratio, gearbox efficiency, friction and reflected inertia set backdrivability, and how to judge it from an actuator datasheet.

Size a joint motor for heat and voltage: RMS torque over a duty cycle, I²R losses, KV and back-EMF, and the gear ratio trade-off.

How harmonic, planetary and cycloidal reducers work, how they compare on backlash, stiffness, efficiency, shock and size, and which robot joints use each.

How to choose encoders for a robot joint: absolute or incremental, multi-turn, motor or output side, magnetic or optical, resolution through a gearbox, and interfaces.

How to size a micro linear servo for a robot finger or small mechanism: stroke, force, speed, layout, motor, sensing and interfaces, with a worked example.