internal spring in seatpost

Julian Orbach (julian@uq.oz.au) wrote:

>On a related tangent, I was riding the other day with the seat clamp too loose,
>and I found myself slowly sinking. I got to thinking, perhaps you could modify
>a unicycle so the seat shaft was attached to an internal spring; the seat
>bounces up and down (not left to right!) as you ride. I figured only
>unicyclists would be impressed though.

You might have something there–make a unicycle more like a pogo stick for
hopping. It seems to me you could get more height to your bounces this way.

Other considerations:

On the rebound, the seat post travel would have to be arrested abruptly by some
sort of mechanical stop so you could grab the seat and pull the uni up with you.

There would have to be some way to keep the seat post (and the seat) from
turning in relation to the wheel, like oleo struts on airplane landing gear.

Some sort of preload adjustment for the spring.

Dennis Kathrens

RE: internal spring in seatpost

I think this would look neat, but serve little purpose, except maybe
on distance rides. Since while hopping, you are supposed to be
slightly over the seat, and have most of your weight on the pedals,
“seat spring” would do little to help you hop higher. If one could
make an “off road” axle that had a spring loaded center, so that when
you jumped, the cranks and pedals would flex towards the bottom, and
then rebound, that might help you hop higher. This however would be
much harder to build. Got any ideas as to a semi-simple way to do
this? put on your thinking caps! Karl Frankowski (Madison, WI)

Re: internal spring in seatpost

I think that George Peck, the off road unicyclist from alaska had Tom
Miller build an air-oil dampened uni, and alas, after lots of $$$$$$$
the unicycle hurt George’s knees. Plus, since a shock is made to keep
the rider level, rather than bounce the rider, it wouldn’t be be good
for height. And, on a unicycle, since you don’t travel fast enough to
have to worry about bounces throwing you off, a shock seems kind of
pointless. Karl ( by now you know me )

Re: internal spring in seatpost

> And, on a unicycle, since you don’t travel fast enough to have to worry about
> bounces throwing you off, a shock seems kind of pointless.

I’d be willing to bet a reasonable sum that you don’t ride down flights of
stairs very often :slight_smile:

Terry “I’ve been bounced off my uni backwards forwards & sideways” Jones.

Re: internal spring in seatpost

>From: schecter@tfs.com (Mark Schecter)
>
>> then I remembered something else I thought of a long time ago… I
>> wonder if it would be possible to have a variable diameter wheel?
>>
>> ]ain
>
>If you mean variable diameter chainwheel, I recently saw a drawing in a book on
>the history of bicycles where gearing could be changed by such a device. But,
>if memory serves, chain slack was taken up by a tensioner. I don’t think a
>tensioner will work well, unless it can be fixed in position while riding.
>Here’s why:
>
[snip]
>
>BUT, every single time you transition from forward to backward thrust, you will
>first compress the tensioner spring, before having a direct connection from the
>pedals to the wheel, and every time you reduce thrust, the tensioner spring
>will decompress and take up slack until you add thrust and recompress it. In
>other words, you are interposing a spring between your output and the input
>to the (driven) wheel. It
[snip]

How about a ‘tensioner’ where the tension (how much the tensioner is pushed
against the chain) is determined by the distance between the pedals and the
wheel axle? Some sort of direct lever that pushes outward more when the distance
between the pedals and the wheels are less? Then the tensioner wouldn’t care
what the tension is on the chain, you’d just have to get the geometry right (I
can see a few trial chains snapping with this approach).

/

\ 0 | Bert Neff --|-- bneff@melpar.esys.com
| Leesburg, Virginia USA
/ \

Re: internal spring in seatpost

From: “Charles A. Clinton” <cac@teclogic.wa.com>
>I have seen clown bicycles with off center hubs; the hubs bob up and down as
>you ride. You could do the same on a unicycle, though I suspect it would be
>pretty tricky to ride… what am I saying … it was tricky to ride to begin
>with… go for it…

I’ve actually ridden one of these. The center was offset maybe 3-4 inches
(that’s 7-10cm for you metric peoples). It was weird but not really that
difficult (couldn’t be if I did it).

Jerry Carson jcarson@mcgh.org

Re: internal spring in seatpost

Julian Orbach (julian@cs.uq.oz.au> wrote:
>(Please, no arguments about whether unicyclists or jugglers are like clowns.
>There is enough of that in rec.juggling at the moment.)

We are as much like clowns as we want, or appear, to be. Since unicycles are
often associated with the circus, many people will not see anything other than
that. It’s up to us to change their perceptions.

How can a dummy like me hook up to rec.juggling? Somebody please lemme know.

Thanks, unics!

John Foss, President International Unicycling Federation unifoss@cerfnet.com

Re: internal spring in seatpost

> Julian Orbach (julian@uq.oz.au) wrote:
> >perhaps you could modify a unicycle so the seat shaft was attached to an
> >internal spring; the seat bounces up and down (not left to right!)
>
> On the rebound, the seat post travel would have to be arrested abruptly by
> some sort of mechanical stop so you could grab the seat and pull the uni up
> with you.
>
> There would have to be some way to keep the seat post (and the seat) from
> turning in relation to the wheel, like oleo struts on airplane landing gear.
>
> Some sort of preload adjustment for the spring.
>
> Dennis Kathrens

The elements of this have all been in production for a long time, and need only
be adapted (not necessarily easy, of course!). Some high-end mountain bike head
sets (front fork) include a spring and shock. I’ve seen motorcycle front forks
with pneumatic preloading. One could also preload with a ring at one end of the
support spring, with ramp stops, as is commonly done on the rear shock mounts of
motorcycles.

Hmm, I hear the gears of a group mind grinding into action …

>> Mark Schecter

Re: internal spring in seatpost

> I think that George Peck, the off road unicyclist from alaska had
> Tom Miller build an air-oil dampened uni, and alas, after lots of
> $$$$$$$ the unicycle hurt George’s knees. Plus, since a shock is
> made to keep the rider level, rather than bounce the rider, it
> wouldn’t be be good for height. And, on a unicycle, since you don’t
> travel fast enough to have to worry about bounces throwing you off,
> a shock seems kind of pointless. Karl ( by now you know me )

This points up some unclarity on the purpose of the gizmo we’re musing about
here. One purpose seems to be:

    Put a spring under the seat to promote pogo-sticking.

while the other seems to be:

    Put a spring/shock under the seat to smooth out the ride.

I think the difference is essentially whether or not you use a shock to damp
(stop) oscillations. Which one are we trying to achieve?

Two other thoughts:

          1 /Why/ did George's knees hurt?

    2 Any vertical movement of the seat changes the distance to the pedals.
    Would a moving seat compromise control? Or is it a question of degree,
    to be tuned through trial and error?

Re: internal spring in seatpost

Oops, I sent my last response before reading this!

> I think this would look neat, but serve little purpose, except maybe
> on distance rides. Since while hopping, you are supposed to be
> slightly over the seat, and have most of your weight on the pedals,
> “seat spring” would do little to help you hop higher. If one could
> make an “off road” axle that had a spring loaded center, so that
> when you jumped, the cranks and pedals would flex towards the
> bottom, and then rebound, that might help you hop higher. This
> however would be much harder to build. Got any ideas as to a
> semi-simple way to do this? put on your thinking caps! Karl
> Frankowski

I think the semi-simple gizmo you want here is called a “big tire”. <grin>

PS A removable shock for distance rides only might be just the ticket! OOO,
I know! It replaces part of the seat post, and can be locked or unlocked,
as needed!

Re: internal spring in seatpost

> >BUT, every single time you transition from forward to backward thrust, you
> >will first compress the tensioner spring, before having a direct connection
> >from the pedals to the wheel, and every time you reduce thrust, the tensioner
> >spring will decompress and take up slack until you add thrust and recompress
> >it. In other words, you are interposing a spring between your output and
> >the input to the (driven) wheel. It
> [snip]
>
> How about a ‘tensioner’ where the tension (how much the tensioner is pushed
> against the chain) is determined by the distance between the pedals and the
> wheel axle? Some sort of direct lever that pushes outward more when the
> distance between the pedals and the wheels are less? Then the tensioner
> wouldn’t care what the tension is on the chain, you’d just have to get the
> geometry right (I can see a few trial chains snapping with this approach).
>
> /
>
> \ 0 | Bert Neff --|-- bneff@melpar.esys.com
> | Leesburg, Virginia USA
[i]> / [/i]

Good idea! That goes into the hopper.

Re: internal spring in seatpost

On Nov 21, 10:45am, Mark Schecter wrote:
> Subject: Re: internal spring in seatpost
> > Julian Orbach (julian@uq.oz.au) wrote:
> > >perhaps you could modify a unicycle so the seat shaft was attached to an
> > >internal spring; the seat bounces up and down (not left to right!)
> >
> > On the rebound, the seat post travel would have to be arrested abruptly by
> > some sort of mechanical stop so you could grab the seat and pull the uni up
> > with you.
> >
> > There would have to be some way to keep the seat post (and the seat) from
> > turning in relation to the wheel, like oleo struts on airplane landing
gear.
> >
> > Some sort of preload adjustment for the spring.
> >
> > Dennis Kathrens
>
> The elements of this have all been in production for a long time, and need
> only be adapted (not necessarily easy, of course!). Some high-end mountain
> bike head sets (front fork) include a spring and shock. I’ve seen motorcycle
> front forks with pneumatic preloading. One could also preload with a ring at
> one end of the support spring, with ramp stops, as is commonly done on the
> rear shock mounts of motorcycles.
>
> Hmm, I hear the gears of a group mind grinding into action …
>
> >> Mark Schecter
>
>-- End of excerpt from Mark Schecter

There already exists shock absorbing seat posts for the bicycle industry; some
of these possibly have sufficent travel and adjustment ranges to acheive the
desired effect; If your unicycle uses one of the several bicycle standard seat
post sizes, and your seat uses the bicycle standard seat rail system, then one
of these puppies would fit right in. If anyone is interested, I could track down
some manufactuers and specs. – Charles

Re: internal spring in seatpost

–snip–
> > > >perhaps you could modify a unicycle so the seat shaft was attached to an
> > > >internal spring; the seat bounces up and down (not left to right!)
–snip–
> > The elements of this have all been in production for a long time, and need
> > only be adapted (not necessarily easy, of course!). Some
–snip–
> There already exists shock absorbing seat posts for the bicycle industry; some
> of these possibly have sufficent travel and adjustment ranges to acheive the
> desired effect; If your unicycle uses one of the several bicycle standard seat
> post sizes, and your seat uses the bicycle standard seat rail system, then one
> of these puppies would fit right in. If anyone is interested, I could track
> down some manufactuers and specs. – Charles

Yes! That would be great, and would speed the process of people acquiring and
testing possible solutions. Thanks, Charles.

>> Mark

Re: internal spring in seatpost

> I see what you mean about the tensioning though… how about if the spring
> was in fact a parallelogram device with the chain going around the outside?
> it would be supported then and a constant length…

Yes, this makes some sense. I’ll play with the concept for a while and see
what comes out. I immediately wonder whether the “corners” sticking out
wouldn’t be very vulnerable “in the unlikely event of an unplanned dismount”,
if ya know what I mean. But maybe that could be handled with size, position,
angles, and so on.

> or how about having a uni with a bend in the middle?
>
>
>
> _/ <- seat
> |
> |
> -o- <- pedals \ \ o <- swivel joint / / / / O <- wheel (bigger
> than this
>
>
> (hmm, ASCII drawings not my strong point :wink:
>
> the chain would be in two segments, the pedals would connect to a cog on the
> swivel joint, and there would be another chain going down to the wheel… the
> chain would thus be kept tensioned, and the seat could bounce up and down
> (spring loaded swivel joint…)
>
> I imagine riding forwards would be ok, but I’m not sure about the necessary
> geometry of the thing…
>
> ]ain

This looks like a lot of fun! I can see the rider from the side, rolling along a
path like a boat on ocean swells. I think the chain tension would, as you
describe, work out, although I think changes in thrust would tend to
compress/decompress the swivel joint spring. But, hey, that’s not a problem,
it’s a feature! I’ll give this one more thought, too.

BTW, sorry my response has been so slow - I’ve been workin’ a lot this week.
Talk to ya soon.

>> Mark

  • ------------------------ * ----------------------------------- *
    | Mark Schecter | “Please identify yourself.” |
    | schecter@tfs.com | (Self checks pocket mirror) |
    | | “Yes, that’s me.” |
  • ------------------------ * ----------------------------------- *

Re: internal spring in seatpost

> This points up some unclarity on the purpose of the gizmo we’re musing about
> here. One purpose seems to be:
>
> Put a spring under the seat to promote pogo-sticking.
>
> while the other seems to be:
>
> Put a spring/shock under the seat to smooth out the ride.
>
> I think the difference is essentially whether or not you use a shock to damp
> (stop) oscillations. Which one are we trying to achieve?

My original suggestion was for neither of these reasons. It was intended to be
just a silly stunt. Traditional-style clowns often have bicycles with the hub
off-centre, so as they pedal, the bicycle “bucks”. This was intended to have a
similar effect.

(Please, no arguments about whether unicyclists or jugglers are like clowns.
There is enough of that in rec.juggling at the moment.)

As I pointed out, though, this bouncing may not be noticed by
non-unicyclists (insert preferred word here); probably only unicyclists
would appreciate the stunt.

Which is not to say that the same idea couldn’t be used as a shocker, or as a
pogo stick.

Here is another variation. Work out some way of keeping the chain on, and then
do a similar spring mechanism between the pedals and the wheel. That way, the
distance between the seat and pedals is fixed - but will you lose control with
the chain loose when it is compressed?

Regards,

Julian

– Julian Orbach (julian@cs.uq.oz.au) – University of Queensland,
Brisbane, Australia

Re: internal spring in seatpost

> My original suggestion was for neither of these reasons. It was intended to be
> just a silly stunt. Traditional-style clowns often have bicycles with the hub
> off-centre, so as they pedal, the bicycle “bucks”. This was intended to have a
> similar effect.
–(snip)–
> Probably only unicyclists would appreciate the stunt.
–(snip)–
> … then do a similar spring mechanism between the pedals and the wheel.
–(snip)–
> – Julian Orbach (julian@cs.uq.oz.au) – University of Queensland, Brisbane,
> Australia

I guess we’ve gone off on somewhat of a tangent! But your idea about a spring
mechanism may have applications to the geared giraffe idea I’m working on, as
well. You’re a veritable fount of ideas, Julian!

< but will you lose control with the chain loose when it is compressed?

I do think that more that a tiny amount of slack in a chain is unworkable, if
only because the chain would tend to come off. I take it from Jack Halpern’s
recent writings that it’s possible to ride with 1.5 or 2.5 wheels, the odd half
being composed of “slack”, but that’s just beyond practicality for most of us
mortals, don’t you think?

Anyway, my head is buzzing with ideas, gotta go. Thanks!

>> Mark

Re: internal spring in seatpost

How about a giraffe with a collapsable drive shaft instead of a chain?

Dan

From: schecter@TFS.COM (Mark Schecter) Date: Tue, 22 Nov 1994 14:55:14
-0800 (PST)
Cc: unicycling@mcs.kent.edu X-Mailer: ELM [version 2.4 PL23] Content-Type:
text Content-Length: 1204

> My original suggestion was for neither of these reasons. It was intended to
> be just a silly stunt. Traditional-style clowns often have bicycles with
> the hub off-centre, so as they pedal, the bicycle “bucks”. This was
> intended to have a similar effect.
–(snip)–
> Probably only unicyclists would appreciate the stunt.
–(snip)–
> … then do a similar spring mechanism between the pedals and the wheel.
–(snip)–
> – Julian Orbach (julian@cs.uq.oz.au) – University of Queensland,
> Brisbane, Australia

I guess we’ve gone off on somewhat of a tangent! But your idea about a spring
mechanism may have applications to the geared giraffe idea I’m working on, as
well. You’re a veritable fount of ideas, Julian!

< but will you lose control with the chain loose when it is compressed?

I do think that more that a tiny amount of slack in a chain is unworkable, if
only because the chain would tend to come off. I take it from Jack Halpern’s
recent writings that it’s possible to ride with 1.5 or 2.5 wheels, the odd
half being composed of “slack”, but that’s just beyond practicality for most
of us mortals, don’t you think?

Anyway, my head is buzzing with ideas, gotta go. Thanks!

>> Mark

Re: internal spring in seatpost

>
> How about a giraffe with a collapsible drive shaft instead of a chain?
>
> Dan

Dan, you clever devil! That’s something to think about fer sure! A splined
shaft, just like a real machine! Hmm, whirr, whirr …

–(snip)–
> spring mechanism may have applications to the geared giraffe idea I’m
–(snip)–
> < but will you lose control with the chain loose when it is compressed?
–(snip)–
> I do think that more that a tiny amount of slack in a chain is unworkable,
> if only because the chain would tend to come off. I take
–(snip)–

Mark

P.S. Are you at Oracle in Redwood City?

Re: internal spring in seatpost

Mark Schecter <schecter@tfs.com> writes:
> I do think that more that a tiny amount of slack in a chain is unworkable, if
> only because the chain would tend to come off.

insert some sort of spring loaded device with cogs on the end between the
chains to keep it taut?

                    O O
                   | |                         / \
                   | |                         / \
                   | |                       o-----o
                   o-o \ /
                   | |                         \ /
                   | |                          O
                   | |
                    O

]ain

Re: internal spring in seatpost

I said earlier…

> insert some sort of spring loaded device with cogs on the end between the
> chains to keep it taut?

   then I remembered something else I thought of a long time ago.. I
   wonder if it would be possible to have a variable diameter wheel?

]ain