Suspension MUni



Another screenshots showing what it would look like in
compression.

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Rayden
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what orientation would the pedals be? If they were parallel
to the rigid shock then surely nothing would move in the way
it was meant to, and something would end up breaking?

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I shouldn't think it;d break if the pedals were parallel
to the not-really-a-shock. Looks like a pretty cool idea,
my only thoughts being if one set of telesocping metal
tubes will be strong enough to transmit all of the
rotational forces.

The other problem with all thse is that adding 3 shocks to a
wheel will be very expensive, and will weigh a lot.

Nice ideas though.

John

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This calls for a diagram...

Say you were hopping, if the cranks were parallel to the
shock, then the shock would be horizontal. All the wight
of the rider (the pretty green arrow) would be
transmitted along the shock, and the rim would all hinge
around the other end (the pretty red bit). Common sense
and physics tells us that, just for the purposes of
hopping, the whole thing would work better were it hinged
at the hub end. Unfortunately bitter experience tells us
that with the forces involved, the chances are that
something will bend or snap.

Most of us have had problems with cranks bending, there are
two of them to spread the load over, and they're only about
half the length that this shock would be, meaning there's
much less leverage involved. [image: http://www.unicyclist.-
com/forums/attachment.php?s=&postid=211032]

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Luke Duller ([email protected])
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The extra bit isn't a shock, the idea of that (I think,
apologies if wrong) is that because the hinge is at the rim
end the hub is no longer free to rotate within the wheel,
avoiding wind up. The 3 shocks will still take the majority
of the weight of the rider and the force from hopping. The
telescopic bit would transmit rotatioanl forces from
acceleration.

In the situation you describe, when you press down on the
pedals the telscopic not-a-shock would extend slightly and
tilt down at the rim end, so that the hub will move
downwards in a vertical line. It'd tilt backwards a bit as
well, but probably not by too much. The load would be taken
by the shock absorbers either extending or compressing.

John

P.S. this is a great distraction from revision. Pity the
exams in just over an hour. Ah well.

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Yes John, that is what I am saying. ALL your weight would
be on the three shocks. ALL the rotational force would be
on the telescoping pole (its not really a shock so I'm
going to stop calling it one). When you go off a jump the
telescoping pole would bend at the rim and extend, or
compress. There would be no pressure on it. ALTHOUGH if you
go off a jump and the tire wants to rotate, then you would
get pressure on it.

Other notes. There is no reason not to use more shocks
except expense. And the hinges might not like sideways
forces. Perhaps attach them the same way as spokes, at an
angle. This would require more shocks though. Or perhaps
extra geometry that does not support the suspension, but
prevents the rim from buckling sideways.

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Rayden
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The point I'm trying to make, although I'm not very
articulate in saying it, is that, because the telescopic
pole is fixed rigidly to the hub, and hinged at the rim, if
the pole were horizontal to the ground, then (hopefully) the
pole would not be able to bend upwards at the hub, and it
would not be able to extend or compress, because the force
would be on a different plane, and so the wheel would be
forced to hinge around the end of the pole.

If you're hopping with the pole horizontal, then your
weight, acting downwards on the hub, is effectively
rotational force on the pole, and we know from bitter
experience that the forces involved in trials, muni, and
hopping, are enough to bend and break even the best
equipment.

One of your screenshots seems to illustrate the situation
I'm trying to describe, In the pictue it shows the pole
bending downwards but it doesn't take into account the fact
that, when you're hopping, you're standing on the pedals,
and keeping them horizontal.

Basically, it's a very good idea, and I'm sure it could
work, but your drawings don't seem to take into account any
of the torque that would be transmitted through the metal
pole, and because in the drawings the hub can rotate freely,
the pole behaves as it would if it hinged at both ends.

Would it be possible in the software you're using to make it
so that the hub can't rotate?

How easy would it be to model the wheel actually in use? i.e
torque on the hub, weight visibly acting downwards, ground
visibly acting upwards.

It is of course perfectly possible that you've address all
these issues, and I just can't see it, in which case I
apologise for wasting your time.

personally I think you desgin a fully enclosed unicycle,
because I have to ride down to the supermarket now and its
just started pouring with rain.

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Luke Duller ([email protected])
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A problem I see with all of this that hasn't been addresed
is if you have ridden a suspension bike, when you get on
your weight compresses the suspension. And with the
suspension wheel the hub would be out of the center of the
wheel or the springs would have to be tuned exactly to your
weight to make the hub in the center of the wheel or I
think it would cause a lot of extra resistance. And I think
it would be great for drops, but unless the suspension was
springs only it would be awful for trying to hop, as bike
suspensions are dampend and it would absorb most of your
hopping energy. and if it wasn't dampend the suspension
wouldn't work very well on the trail. And another thing it
wouldn't work with rim brakes but I guess a disk brake
would work.

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That is an excellent point and not one I considered. If the
telescoping pole was a parallelogram then it could move up
and down but maintain its horizontal orientation. This would
make that part much more complex though. I'll see about
changing my model.

If you are asking about an animation, I can't do that
with this software. If you are asking about rigging it up
and then adding forces to see what happens, that I also
cannot do.

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Rayden
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Here is what i mean. It would work like an A-arm. The
parallelogram is hinged at all 4 corners. And would of
course still telescope, i just didn't model that.

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Rayden
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It keeps getting more interesting. Rayden's design is really
different, and it's hard for me to picture the forces
involved. I can see that each addition of more moveable
joints and other parts is going to up the weight, but let's
not worry about that and stick with the theory of making the
design work.

The main problem with Rayden's design, and I'm surprised
nobody has mentioned it, is the non-suspended spot in the
wheel. Each time you hit the non-suspended part (with the
rigid arm at the bottom), you won't have any suspension. If
your suspension is compressing from rider weight, you'll
have a big hop in the wheel as you go over this spot. I
guess there would be some amount of hop at the opposite side
from there as well. So it would be like riding on a non-
round wheel.

You could keep the suspension pretty stiff, like what I have
on my Wilder's seat post, but then you won't get as much
benefit from the suspension action. This is probably fine
for cruising on bumpy stuff.

Using shocks would be more for riding and dropping, and less
for hopping. For dropping, it's important that the rigid arm
not be perpindicular to the pedals!

Unfortunately I think the non-round issue would be the big
problem, before one would get too worried about the
strength of the rigid arm. That weakness could be covered
by building it to larger specs. For cranks and axles we've
been working with existing bike parts. For the wheel we can
start from scratch.

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John, the rigid piece telescopes. It can get longer and
shorter. It would do this any time the wheel is compressed,
whether this piece be vertical or horizontal.

As far as letting one of the 3 shocks act as the rigid
piece, I think it might affect the strength of the shocks
depending on orientation. Although I'm not certain of this
and it might work. But you would get the problem I think i
fixed with the parallelogram design. And adding a
parallelogram to a shock would be much more difficult.

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Aah. Much better!

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because they are easy, but because they are hard." -- John F. Kennedy,
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The key is the parallelogram. There is no need the rest has
to be shocks. They could be strong, stiff rubber bands done
like this.

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Rayden
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Close up of what I think the parallelogram would look like.
This one has a shock in the middle of it. Each vertical
cylinder is a hinge. I'm not so sure a shock in the middle
of the parallelogram would be good though. It would have to
be tuned differently due to its alternate length.

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Ok here is a question. Shock absorber versus spring. We have
all been assuming shocks would be better but why? There has
to be a reason. Of course we could build a protype of each
and see but I dont think that is going to happen.

I think there needs to be some sort of shock absorber or we
would be bouncing all the time. But what if we used a bunch
of springs (springs could be physical metal coils or rubber
bands. anything springy) but then add 3 small dampeners.
This might be lighter than 3 heavy duty shock absorbers.

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Rayden
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I've been assuming something like on bike rear suspension,
which is a spring (either air or coil) and a shock absorber
in one unit. It's possible that something could be designed
for a uni-specific shock/spring, but I don't know how it
would differ from a bike shock, or if the extra cost from
low production numbers could justify the improved
performance.

John

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