My Lego model has a winch on the front. It's a simple spindle with a reel on it with a rubberised cog for winding at one end and two cogs at the other (as shown below).

Is there a technical name for the cog/gear on the blue spindle that stops the cog on the grey spindle spinning freely? Is this a common mechanism in real machinery?

Also, assuming this relies on friction and that the effectiveness will be reduced with wear and tear, how would that be mitigated in real equipment?

The gears/cogs in question


I would say that you have a ratchet. Ratchets do fail. The Brownian Ratchet is a simple thought experiment done by thermodynamic physicists that shows that ratchets need to fail - otherwise you could extract energy from absolutely nothing - a contradiction of the Laws of Thermodynamics.

Wear and tear on ratchets are mitigated via lubrication of parts of course, but bigger systems rely on things like governers for real mechanical control instead of a ratchet.

  • $\begingroup$ The image more closely resembles a brake than a ratchet. There's no pawl or mechanism for disengaging the gears to allow play in the winch. $\endgroup$
    – Air
    Jul 7 '15 at 17:15
  • $\begingroup$ I was torn on this as well - I called it a ratchet solely because of Wikipedia's description of a "low backlash" kind of ratchet, which uses a frictional "gear" with a pawl. The little blue gear functions as an effective pawl, slowing down with braking wear pad action on the grey gear. The play of the grey gear's teeth work as an gear. Unfortunately, it is a Lego model - a true ratchet or a true wear pad brake would be difficult to fabricate out of the plastic, so this is what you get instead. $\endgroup$
    – Mark
    Jul 7 '15 at 17:31
  • $\begingroup$ The "common mechanism in real machinery" might use either (or both) but I'd still call the one in the model a brake because it arrests rotation equally in both directions. Even the toothless type of ratchet described in the WP article has a preferred direction of rotation. $\endgroup$
    – Air
    Jul 7 '15 at 17:42
  • $\begingroup$ Kind of an academic distinction since, as you point out, a plastic Lego model bears little resemblance to real machinery from a technical standpoint. $\endgroup$
    – Air
    Jul 7 '15 at 17:45
  • 2
    $\begingroup$ This is much more similar to a parking gear than a ratchet. A ratchet allows movement in one direction only - this allows no movement $\endgroup$
    – Ethan48
    Jul 8 '15 at 13:51

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