Miniature, Lightweight, High-Force, Capstan Winch For Mobile Robots

Tech ID: 32814 / UC Case 2022-981-1


A capstan winch, which consists of a cable wrapped multiple times around a shaft in a single layer spiral, is the most efficient mechanism for pulling a load over a long distance. As the shaft rotates, the wraps of the cable slide along the shaft away from the motor before passing off it and through a tensioning device, which is responsible for maintaining holding tension in the free end of the cable. Because capstan friction increases exponentially with wrap angle, a low holding tension is capable of supporting a high load-side tension given a sufficient number of cable wraps. Commercial capstan winches tend to be bulky, as they are typically designed for marine or industrial use and employ steel cables or rope. A miniaturized capstan winch would be desirable for small, lightweight robotic applications, especially for space applications for which cargo weight significantly affects the cost of launching.


Researchers at the University of California, Santa Barbara have designed a miniature capstan winch for mobile robots that is compatible with low friction, ultra-high-molecular-weight-polyethylene (UHMWPE) braided cable. The lightweight, extremely strong UHMWPE cable allows the size of the device to be scaled down without drastically decreasing its load capacity. This miniature capstan winch replaces the self-tailing tensioning mechanism found in commercial capstan winches with a novel integrated self-tensioning mechanism that avoids the use of serrated teeth, which would damage the UHMWPE cable. Additionally, it avoids using a tapered shaft, which is commonplace in commercial capstan winches but can result in shaft weakness and failure at a smaller scale.


  • Compatible with ultra-high-molecular-weight-polyethylene (UHMWPE) cable, which is both much lighter and approximately 10 times stronger than steel cable
  • Scaled-down mass (~20 g) with relatively high load capacity (~5 kg)
  • More mass-efficient than other actuators at long stroke lengths
  • Suitable for use in small-scale mobile robots
  • Smaller size makes it cheaper to deploy


  • Space exploration, including in Lunar and Mars rovers
  • Small-scale robotics


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Other Information


Capstan Winch, Miniature, Load Pulling, Mobile Robots, Space Exploration, Rover, Mechanism, Polymer Cable, Lightweight

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