Sometimes I hate the algorithm and sometimes it shows me cool new robotics / mechanics / gadgets and makers. Aaed Musa has been working on something called a “Capstan Drive” which is a rope driven alternative to gears. By removing gears and teeth and replacing them with rope you cut down on noise, eliminate backlash, high torque, low inertia, and low cost – with the major costs being low range of movement and a vertical path for the rope to travel over. Aaed’s video is well worth a watch and blog well worth reading. But… if you want to get a sense of how the Capstan drive works…
The benefit of a planetary gear is that it’s a very vertically compact method for increasing rotational speed at the cost of complexity. With a Capstan Drive (I don’t know if this is supposed to be capitalized) the rope needs to be wrapped around the thinner shaft several times to prevent slippage. As Aaed notes:
One question that I had when first exploring this reducer was “why doesn’t the rope slip if it’s just wrapped around the smaller drum?”. The answer to that question lies in the capstan equation. With each turn of rope on a drum, the amount of friction increases exponentially. With 3-5 turns of rope, there is enough friction for slipping to not be an issue.
Aaed indicated he was using Dyneema DM20 cord as it has almost no stretch to it. I wonder if something like fishing line would work?
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