Compact Capstan Drive for Robotics

A minimalist, silent, high-torque capstan drive optimized for lightweight robotic systems such as quadrupeds. Designed for ease of printing (no supports), ease of assembly, and precise motion using a simple string-wrap mechanism. Compatible with AS5600 encoders for closed-loop position control.

Tested with 220° of motion using 1.5mm 200 lb Dacron which is overkill, but I assume should be compatible with other thin high-strength cords, such a masonry twine.

Silent operation using a 3-wrap string spool
Why Capstan Drives Beat Gears
No gear noise – ultra-quiet operation ideal for stealthy or lifelike motion

No broken teeth – eliminates one of the most common failure modes in geartrains

No grinding – smooth, continuous motion with no mechanical clash

Minimal wear and tear – string and spool contact is gentle, even over extended use

Zero backlash – inherently compliant and tight with proper tensioning

High precision – ideal for closed-loop systems using encoders

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