Re: GearBox LockBack design

Hi Don & Brian,

>Don:
>It's not quite as simple as that. If the only criterion for an irreversible
>mechanism was that it increased motion/rotation, the overdrive gear in your
>car would bring it to a screeching halt.

John2005:
Generally, the output member *decreases* motion, i.e., in the case of a
worm gear, the input member (worm) may make several revolutions
compared to the output member (pinion gear) which may only make 1
revolution per 10, 20, 40, etc. worm revolutions, depending on the
drive ratio.

I did not mean to imply that this was always the case or a requirement,
but that this is *generally* the case with a non-backdriving mechanism.
You usually have this type of trade-off.

The analogy you and Brian used with a ramp, is a good way to describe
it.

In the case of a cam, if the ramp has *any* incline, a roller follower
will always backdrive the cam. At the cam dwell, there is zero incline,
and the follower cannot backdrive the cam at the dwell position.
However, the trade-off is that at the dwell, rotating the cam, does not
move the follower for whatever duration the dwell lasts, but it will be
non-backdriving for the duration of the dwell.

I was just saying that *in general* and depending on the mechanism, you
have some type of trade-off with a non-backdriving device, where the
input member usually moves for a greater distance or angular
displacement, than the output member (at least for the non-backdriving
portion of the gearing or device).

John

.

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