Subject:
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new (to me) use for worms
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Newsgroups:
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lugnet.build
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Date:
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Fri, 18 Jun 1999 18:12:17 GMT
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Viewed:
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556 times
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I recently noticed that the fact that worm gears slide
freely on an axle, which I've just regarded as slightly odd,
can actually be of some use; to my knowledge, it's the only
part that does so while being rotationally locked to the
axle.
What I hadn't realized in 13 years of owning several
of these (I don't remember what set they first appeared in, but
I immediately got several from a big toy store that (then) took sets
apart for spares) is that, within (very tight) limits, it makes
it possible to connect to axles that need to shift along the
rotation axis a bit. While it's not pratical for use in a
sequential transmission and similar far-shift applications,
it is useful for places where an axle swings from a U-joint
at one end, while the other is attached to something that
moves linearly rather than in an arc. An example
would be a vehicle's rear axle that is suspended with a Panhard
rod, i.e. moves up and down vertically, and a little bit
side to side, but does not move along the driveshaft axis.
The driveshaft, using two U-joints to accommodate the
left/right shift, will move away from the axle when going
above or below the horizontal position, but with a worm gear,
they van be connected.
This is actually the only way to make a suspended drive axle
where the wheels do not push in/out or change camber when
the height changes - not counting the 8428 setup where the
whole axle swings on 1 large swingarm (which is pointless),
and also not counting separate swingarms with geartrains
going up the arms (which is realistic for an off-road car, I
guess - though you don't often see Steyr-Puch Haflingers on the
road).
And considering the fact that vehicle size and thus width is
usually limited (most Lego tires just aren't 8880 size),
it is really the only 'nice' (camber-change-free) way to make
a compact suspended rear drive axle - narrow alternatives
being 8860-style single U-joints for each wheel, which is
16-wide not counting wheels (12 w/o a differential), or, for
reduced camber change, a single central U-joint, with the
differential on one swingarm, and a gear train up to the central
pivot axis (16-wide with diff; w/o diff, as wide as needed to
get tolerable camber change).
In other words, I've liked the Panhard rod setup ever since
seeing it described on this car:
http://www.math.uio.no/~fredrigl/technic/classical-racer/
and have now finally found a way to do a drive axle with
it. The worm gear can only handle a shift of just less
than 1 brickwidth (about 1.5 with substantial additional
hardware), but that's enough for this particular application
when choosing an appropriately long swinging driveshaft.
I haven't built this yet, but I didn't want to wait
*that* long.
Any other application ideas, thoughts?
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Message has 3 Replies:
 | | Re: new (to me) use for worms
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| (...) Interesting idea. But in thinking about it (without actually prototyping), I have a problem. You propose to use the worm on the drive axle, right? And the idea is that the worm can slide a little bit to and fro to adjust for the axles movement (...) (25 years ago, 18-Jun-99, to lugnet.build)
| | | Re: new (to me) use for worms
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| G. Benedikt Rochow wrote in message ... (...) I had never noticed this either, until I saw a web site by Michael Powell, who shows how to use the direction of rotation of a single motor to select between driving two different axels: (URL) I have (...) (25 years ago, 21-Jun-99, to lugnet.build)
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