Suspension MUni



Rayden wrote:
> *I still like my parallelogram design which would
> eliminate windup *

I don't think it would completely, there would be a
little bit of slack in either direction when you pressed
down on the pedals. They would wind up until they were
touching, at which point they would begin to transmit the
forces to the rim.

Whilst they were not touching, they would just act like two
shocks would, and wind up until they were touching.

Depending on how much play there was, this could actualy be
slightly harder to ride than a wheel where the shocks wind
up, because there would be no resistance to the rotation of
the pedals. If the parallelogram was dampened, then it might
be less noticable, or if the two sides were as close as
possible together, but that would mean it couldn't move very
far before we had the same problem as with the earlier
design with the telescopic pole.

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Rayden wrote:
> * ... I still like my parallelogram design which would
> eliminate windup... *

I'm a bit confused about how the Rayden's design works.

It looks like the corners of each parallelogram are hinged
to allow the mechanism to deform from strictly rectangular
to any parallelogram. If the rim side of the parallelogram
is the fixed reference point then the hub side can swing in
an arc but must stay parallel to the rim side. The idea is
that staying parallel is the same thing as preventing
windup. Have I got this part right?

If this is correct, then each parallelogram allows the hub
to move only in an arc centered on its rim side. Since there
are four mechanisms there are four arcs, and since each arc
swings on a different path there is only one place the hub
can be. Each mechanism would effectively be a stiff pair of
spokes and the hub would be locked into place as if it were
part of a conventional wheel. Rayden, clearly this isn't
what you have in mind.

You describe the spoke legs of the parallelograms as
telescopic, but if they telescope independently then there
is no reason why the hub and rim sides of the parallelogram
should stay parallel. What's missing is a method for keeping
the telescopic legs equal in length as the parallelogram
expands and contracts.

This won't be easy to do because the telescopic legs must
carry the pedaling forces. I've got to make another picture
of this so I'll continue in a following post.

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Diagram that goes with previous post:

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I see what you mean. I'm having a bit of trouble visualizing
how to prevent this. I drew this up and it might fix it,
might not. I will include another picture showing why it
would prevent the hub from spinning independantly.

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The first image is how it should rotate. The third is how it
would rotate without the extra piece. The 2nd is showing why
the piece prevents one side from rotating without the other.

And yes whoever asked about the parallelogram telescoping,
it does, i just didn't draw that up in my models. This model
of the parallelogram has it.

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I like a lot of these ideas, but I'm curious as to why we
want a suspension muni in the first place. A good muni right
now already costs at least $400, and a greazt one runs about
twice that. And none of these are suspended. Not to mention,
most of them weigh a hefty 15-17lbs. The added suspension
would add about 2 lbs at least, and at least another $200.
Have you ever been in a situation where the squish of the
tire was inadaquate? If you truly need suspension for your
riding, the solution is not to build a suspension muni, but
to lower your seat and practice. It's cheaper, easier, and
more effective than building a suspension muni.

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gerblefranklin wrote:
> *I like a lot of these ideas, but I'm curious as to why we
> want a suspension muni in the first place. A good muni
> right now already costs at least $400, and a greazt one
> runs about twice that. And none of these are suspended.
> Not to mention, most of them weigh a hefty 15-17lbs. The
> added suspension would add about 2 lbs at least, and at
> least another $200. Have you ever been in a situation
> where the squish of the tire was inadaquate? If you truly
> need suspension for your riding, the solution is not to
> build a suspension muni, but to lower your seat and
> practice. It's cheaper, easier, and more effective than
> building a suspension muni. *

And where is the fun in that? This has nothing to do with
practicality.
:)

And besides, how many of the greatest inventions were
practical before they were invented?

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Rayden wrote:
> * The 2nd is showing why the piece prevents one side from
> rotating without the other. *

It looks like the mechanism just jams, which isn't the
effect you need. Here are a few hints:

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gerblefranklin wrote:
> *I like a lot of these ideas, but I'm curious as to why we
> want a suspension muni in the first place. *

Gerblefranklin, you make a lot of good points. In
another couple of pages I'll elaborate on them. In
answer to your specific question, it isn't a matter of
need. It's the challenge. Mountaineers climb mountains
"because they are there;" engineers design things
"because they are not there."

Reminds me of this joke:

"There are three kinds of people in the world. Some
people see a crooked picture and ignore it. Others can't
stand imperfection and fuss with it until it hangs
straight. Engineers think, "this frame needs a solar-
powered device with sensors and actuators to straighten
it after it gets bumped."

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> Originally posted by gerblefranklin I like a lot of these
> ideas, but I'm curious as to why we want a suspension muni
> in the first place. A good muni right now already costs at
> least $400, and a greazt one runs about twice that. And
> none of these are suspended. Not to mention, most of them
> weigh a hefty 15-17lbs. The added suspension would add
> about 2 lbs at least, and at least another $200. Have you
> ever been in a situation where the squish of the tire was
> inadaquate? If you truly need suspension for your riding,
> the solution is not to build a suspension muni, but to
> lower your seat and practice. It's cheaper, easier, and
> more effective than building a suspension muni.

Think of the mtb evolution. First there were no-suspension
mountain bikes. Then came the front suspension, people
started to ride down hills, and later the double suspensions
appeared. Now biker do gap of 40 feet on their full 12'' of
travel machines. Muni is still young and in full evolution.
We are used to ride the ''hard-tail'' munis, but maybe fully
suspended unicycles would develop another type of riding
(more terrains rideable), or just make the super technical
trails more comfortable. As for the weight and cost of the
product, it doesn't matter to me: these will probably lower
since there will be more and more of suspended munis.
P.S.: And YES I've been in a situation where the ''squish''
of the tire was not enought.

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Rayden wrote:
> *cyberbellum, you said the parallelogram would jam, but I
> am assuming that it would be built well enough so that
> instead of jamming it would transmit the force. Seems like
> it would work to me... *

The middle diagram in your last sketch shows the upper
telescopic leg bent, with the interior part jammed in the
exterior part. Hence my assumption.

The middle diagram also shows the left end and the right end
out of parallel. Since this is the effect you are trying to
achieve it seems that the design isn't all that effective.

The short version is that, even though from a pure math
perspective it seems promising, from an engineering
perspective it would be impossible to make parts stiff
enough to do what you want. The problem is with the basic
geometry of the solution. Even a mechanism built like an
engine block would allow some angular play in the rim
element. I could go on and explain why, but that would
require a page or two of math and solid mechanics and I
don't have that kind of time or energy.

The midday heat is over here in DC so I'm about to follow
gerblefranklin's advice and go out for a ride. Yesterday I
went a couple of miles on my 29"er with only one UPD (if you
don't count the dozen or so UPDs just trying to get
started). Today I think I'll work on my freemount with the
20" unicycle. I still haven't managed better than a 10%
success rate. I know I can do it - the 20" is such a toy -
but I've got some sort of mental block going.

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"Rayden" <[email protected]> writes:

> 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 don't think dampers are a good idea. First, after
compression during a drop, dampers would tend to make the
wheel roll unevenly (eccentrically). Second, work dont on
the damper would be wasted energy.

Ken
 
"nickjb" <[email protected]> writes:

> Ken Cline wrote:
> > * ... Second, work dont on the damper would be wasted
> > energy.
>
> This arguement is used against using suspension in
> mountain biking but I know from my own experience and from
> the racing world that overall it saves energy.

I didn't make that argument about suspension bikes.

I think there is a critical difference in the case of the
suspension wheel. Here, the dampening would be placed inside
the wheel. Every revolution you pedal, you'd be fighting to
compress the dampeners that are engaged sequentially are the
wheel goes around. All of that energy is wasted. Remember,
the dampening action is against the rider's complete weight
plus dynamic pedalling force. On a bicycle, you're only
fighting the dynamic component of pedalling force.

Anyway, the fact that dampening will make the wheel tend to
ride eccentrically after a compression event is an even more
worrisome concern to me. Any Dampening must be light enough
to allow a significantly higher frequency than the maximum
pedalling cadence.

Ken
 
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