I Built a Robot Dog Using... Rope?
Aaed Musa, an independent robotics builder, explains how he designed and tested Cara, a 31-pound robot dog whose joints use rope-driven capstan drives.
In this talk
- 0:01
Why use capstan drives
Musa says Cara is his fourth robot dog and uses tensioned Dyneema DM20 rope wrapped around drums to drive her joints. He describes the capstan drive as a precise, quiet, low-cost speed reducer with virtually no backlash. After correcting how he calculated drum diameters, he developed a capstan drive with an 8:1 ratio.
- 3:43
Building and programming a test leg
Musa chose a five-bar linkage and paired large brushless motors with low-ratio capstan drives for high torque and responsiveness. He tuned motor controllers, programmed homing and inverse kinematics, then tested foot movement and basic stepping. A third degree of freedom lets the leg step in different directions.
- 7:12
Designing the full robot
Cara uses a Teensy 4.1 microcontroller, an RC remote, and a 24-volt drill battery. Her modular design includes detachable legs, bracing plates, electronics housings, a handle, and flexible TPU feet. Musa uses carbon fiber tubes and high-strength printed materials for the frame and other parts.
- 12:32
Finding a smoother gait and fixing failures
Musa compares triangular, rectangular, and cycloidal step trajectories, choosing the cycloidal path for smoother lift-off and landing. During testing, a rear leg link snapped, prompting stronger part designs and shorter steps. He also used an IMU and new inverse kinematics equations so Cara could tilt her body to maintain balance.
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