Subject:
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Re: 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 20:08:19 GMT
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Viewed:
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603 times
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In lugnet.build, Terry Keller writes:
> On Fri, 18 Jun 1999 18:12:17 GMT, "G. Benedikt Rochow"
> <rochogb@eng.auburn.removethis.edu> wrote:
>
> >
> > 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?
>
> 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 in the
> suspension?
> But what interfaces with the worm to turn it?
Another axle, that's the whole trick.
\\\\\\\\\\\\\\\\\\\
=====[variable gap]========
\\\\\\\\\\\\\\\\\\\
> Any clarification available?
View from above:
o
...........
-o----D------
U
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U
F
- and D are the rear axle incl. stiffening technic beams and the
differential and attching crwon gear, etc.
... is the Panhard rod, which pivots at 'o' around (in terms of
looking at an upright monitor right now) vertical axis, to allow
the axle to swing straight towards you and back in different amounts
for the left and right end, and makes it go side-to-side a little,
which is why we need 2 U-joints rather than 1 (which doesn't affect the
length problem, really).
U are the U-joints,
| is the swinging drive shaft,
and F is where the fixed driveshaft comes out of the vehicle's frame.
So, if we consider the axle coming out of F as non-shifting, the axle |
needs to change in length when the rear axle moves.
(Alternatively, use a single swinging driveshaft for |, and the
lower U-joint then shifts, which locates the worm gear inside the frame
- possibly a better idea.)
-gbr
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Message has 1 Reply:
 | | Re: new (to me) use for worms
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| (...) Despite the ascii graphic, I think I get the idea. :-) I will have play around with this IRL - maybe try a clarified picture in LDraw. -- Terry K -- (25 years ago, 19-Jun-99, to lugnet.build)
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Message is in Reply To:
| | 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)
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