I am considering a mechanical system that is able to retract and extend via servo control but with the drive mechanism being retractable itself. Doing so I will be able to have a multiplied retracting distance such that it can extend multiple times its fully "retracted" state (hope that makes sense). The problem with existing linear actuators is that they only extend 2x the length of the base cylinder. The best way I can think to solve this is via a "nested" cylinder arrangement which works on the principle that as it extends the diameter of the foremost cylinder will decrease so that they can be nested to be able to extend multiple times the length of the base cylinder. The issue is that I cannot drive the stacking cylinders with a ball bearing or ball screw since the screw is not retractable itself and the mechanism must also not achieve "retraction" simply by moving the screw linearly or past the servo. Are there existing mechanical mechanism that can accomplish this? Please ask away for clarification I tried my best to explain.

Sketch for reference

  • $\begingroup$ Yep, it exists. The type of extension-to-higher-multiples-of-collapsed length is often called telescoping. Thus, perhaps search for telescoping actuator $\endgroup$
    – Pete W
    Commented Jan 31, 2022 at 15:59
  • 2
    $\begingroup$ check out retractable automobile antennas $\endgroup$
    – jsotola
    Commented Jan 31, 2022 at 16:00
  • $\begingroup$ There are hydraulic cylinders that do this, sometimes seen on tipper trucks. $\endgroup$
    – Solar Mike
    Commented Jan 31, 2022 at 16:31


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