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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Sat, 19 Jun 1999 00:50:40 GMT
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Viewed:
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613 times
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On Fri, 18 Jun 1999 20:08:19 GMT, "G. Benedikt Rochow"
<rochogb@eng.auburn.removethis.edu> wrote:
> 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
> |
> |
> 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
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 --
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Message is in Reply To:
 | | Re: new (to me) use for worms
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| (...) Another axle, that's the whole trick. \\\...\\\ =====[variable gap]======== \\\...\\\ (...) View from above: o ......... -o----D------ U | | U F - and D are the rear axle incl. stiffening technic beams and the differential and attching crwon (...) (25 years ago, 18-Jun-99, to lugnet.build)
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