[TowerTalk] Regarding Worm Gear Drive Winches

Dan Zimmerman N3OX n3ox at n3ox.net
Mon Jul 20 12:27:26 PDT 2009

> Depends on the particular worm gears (more specifically, the pitch of
> the worm).  It's like whether you can backdrive a lead screw. Sometimes
> you can, sometimes you can't.  The finer the pitch (= higher numerical
> gear ratio) the more likely you can't backdrive.

You have to be a little careful too, even if it "appears" to be self

The mechanism that disallows back-driving is ultimately that the static
friction becomes stronger and stronger under load when you try to backdrive,
"locking" the thing in place.

But if you have some vibration and a moderate load, just like any other
frictional pinning, it might creep.

And if it gets going, then you aren't looking at a static friction situation
anymore, and it might not be *dynamically* self locking.

 And as N2JFS says, it might be easier to backdrive over time.

So I'd say don't rely on it.  And that's what worm gear drive manufacturers
would say: don't rely on a self locking worm drive in place of a proper
braking system in an application where it may be dangerous if it slips.


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