Twisted String Actuators: Surprisingly Simple, Cheap, and High Gear Ratio

Using "actuator" about software is uncommon of course, but considering other terms in use in Twisted ("deferred" as a noun, "errback", "reactor" pattern) it didn't surprise me.

  We spent a fair bit of time evaluating twisted string 
  actuators to build low-cost robots. Unfortunately, [...]
  their lifecycle is measured in the many thousands instead 
  of millions -- despite our best efforts at material 
  engineering.