Double wheel giraffes

Unicycles and Equipment
1

Hello all,

I was thinking about the physics of unicycling yesterday and an intriguing point
hit me which I thought I would run past more experienced riders than me…

I have been a unicycler for about 4 weeks now, and I can ride forwards and
freemount reliably enough to use the unicycle as a means of transport. Fine
control on corners and hill-starts are still a bit wobbly. But, I was thinking
about how easy it is to ride forwards once you get the knack, and it struck me
that the important thing is that the unicycle wheel develops angular momentum
when rolling. My guess is that this angular momentum is effectively what makes
it easy to avoid sideways topples (like on a bike). Presumably this is why is is
harder to ride slowly.

Okay, nothing world-shattering here. But then I remembered seeing pictures of
giraffes with two wheels, where the pedals drive the top wheel which drives the
bottom wheel. I had assumed that the reversal of the pedal direction and the
sludginess of the drive would make these things hard to ride. But then it
occurred to me: on top of these problems, the wheels are rotating in opposite
directions so the total angular momentum is (close to) zero at all speeds! This
makes me think that such monsters would have little or no sideways stability of
their own.

Does anybody out there ride one of these cycles? Could you comment on my rather
vague analysis?

It also occurs to me that you could go one step further and make the bottom
wheel light and the top wheel heavy (so the total angular momentum was
opposite to what you expect). My gut feeling tells me that such a device would
be really weird to ride. I would even go as far as to suggest that you might
have to lean out around corners (!)

Maybe one of you two-wheelers out there could inflate the top tyre with
water (for weight) and give it a go. I’d love to hear about someone riding
like this. :slight_smile:

Cheers,

James Gifford <James.Gifford@anu.edu.au

2

RE: Double Wheel Giraffes

Isn’t Physics Fun!

I like it so much I’m finishing my PhD.

Anyway, a few thoughts on the angular momentum of unicycle wheels. Any effects
are likely to be small as the wheel is light (1 kg or so), of modest radius
(30cm), and is not spinning quickly (10km/hr). Gyroscopic effects are noticeable
on bicyles at speed, ie countersteering, but are not essential for bicycle
stability.

Somehow you’re saying that a unicycle tends to tight itself as you fall over .
(Typo -change tight to right) Do an experiment: Hold you unicyle beside you, run
as fast as you can, and then let go. Any gyroscopic righting effects should be
visible as your unicyle starts to fall and then miraculously rights itself. Let
me guess, it hit the floor fast and hard? Didn’t even wobble?

The gyroscopic forces on a falling wheel act to turn the wheel to the left or
right, depending on which wayit falls. So a normal wheel doesn’t just fall over,
but turns left or right, but remains basically upright. Try it and see with a
bicycle front wheel. By turning the center of mass remains above the tyre
contact area, and it stays balanced, but it doesn’t return to vertical.

On your unicycle, the center of mass is high, somewhere around your waist, so
you are much less stable than a simple wheel.

I’ll muck around with some figures this weekend and see what pops out, but I
think I’ve described the general behaviour correctly.

Mike Camilleri

3

Re: Double wheel giraffes

James.Gifford wrote:
|>
|> Okay, nothing world-shattering here. But then I remembered seeing pictures of
|> giraffes with two wheels, where the pedals drive the top
|>
|> Does anybody out there ride one of these cycles? Could you comment on my
|> rather vague analysis?

I see that the twowheeling fever is back. Please don’t call it a double- wheeled
giragge – it’s called a twowheeler or a two-wheeled unicycle. “Giraffe” is used
for chain-driven unicycles.

In November and December last year, we had plenty of discussions on this topic.
I am appending a few typical ones for your references. You can get everything
from the archives.

I can’t help but metnion that I as fas as I know I am the first to one to ever
build and ride such a machine. For unicycling history’s sake, please correct me
if I’m wrong. I got the idea from a drawing or picture in an old issue of the
USA bulletin, but I don’t if whoever sent that in ever actually built it or
rode it…

Regards, Jack Halpern

Kanji Dictionary Publishing Society 1-3-502 3-Chome Niiza, Niiza-shi, Saitama
352 JAPAN Voice: +81-048-481-3103 Fax: +81-048-479-1323

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>From bkonarsk@mcs.kent.edu Sat Nov 19 02:14:12 1994
From: pbennett@lssec.bt.co.uk To: unicycling@mcs.kent.edu Date: Fri, 18 Nov 94
15:49:21 GMT Subject: Looking for a new challenge

I’ve been thinking on and off about buying a two-wheeled uni. I think I was
first sparked off by a message Andy Cotter posted to this list which I saved way
back on 22 Jul 93 (my goodness, has this list really been going that long :wink:

> I have always wondered this question of ‘ruining’ my balance on one uni
> because I get used to another. When I started to learn a two- wheeler (wheel
> on top of a wheel so you pedal backwards to go forward), I thought that I
> would mess up my balance when I returned to a ‘normal’ unicycle.

Sounded like fun, but he went on to say

> Well I never mastered a two-wheeler

Now I don’t know cause I’ve never met the guy, but I get the feeling Andy’s not
such a bad unicyclist. So, just how easy are two-wheelers to learn? (Yes I’ve
almost made up my mind to get one, only I want to hear anyway.)

Another thought: would it be possible to build (or buy) and “extendible”
multi-wheeler, that starts of as a normal uni, but can be extended by bolting
extra wheels on underneath? That way if I never got the hang of the two-wheeler,
I could extend it to a three-wheeling mean giraffe. I guess the main problem
with this would be the make robust joints so that the extended frame was
nearly as strong as a solid pole.

So, who builds these things? DM? Siegmon? Sem? Where’s my best bet? Does anyone
have one? Has anyone ridden one? Does it really hot-up your backwards pedalling
as Andy suggested? Advice?

pab.

Paul Bennett pbennett@lssec.bt.co.uk Churchill Engineering Centre BT Software
and Systems Integration tel: (0171)728-7527 PP 6/7, 151 Gower Street, London.
WC1E 6BA fax: (0171)387-6743

From: jhalpern@cc.win.or.jp (Jack Halpern) To: unicycling@mcs.kent.edu ()
Cc: pbennett@lssec.bt.co.uk, unifoss@cerf.net (John Foss), kfuchs@winternet.com
(Ken Fuchs) Date: Sat Nov 19 9:04 JST Subject: Two-wheelers, multi-wheelers
Reply-to: jhalpern@cc.win.or.jp

To all unics out there, greetings!

(As former IUF president (ten-years), I must bury my head in shame and tell you
that “unic” is new to me. Will someone enlighten me?)

As far as I know, I am the first person to ever build and ride a two- wheel
unicycle. If I am wrong, please correct me. I got the idea from an old USA
newsletter. There was a diagram, but apparently no one had ever built one.

pbennett@lssec.bt.co.uk wrote:

|> > I thought that I would mess up my balance when I returned to a ‘normal’
|> > unicycle.

No, I don’t think so. It just feels a little strange when you switch, but
worry not.
|>
|> Now I don’t know cause I’ve never met the guy, but I get the feeling Andy’s
|> not such a bad unicyclist. So, just how easy are two-wheelers to learn? (Yes
|> I’ve almost made up my mind to get one, only I want to hear anyway.)

I learned in 1979/1980, I think it was was. It was very difficult, but in
those days in Japan riding one-foot was considered difficult and walking the
wheel an act of magic. I was accused by my friends that the reason I can do
these stunts was because I am “different” – that I know doubt “eat meteors for
breakfast” was the expressions they used (:->…

When you practice, you must concentrate on moving your upper body forward along
with the frame as you pedal backwards. It feels extremly weird at first, but
once you get the hang of it it will almost feel natural.

|>
|> Another thought: would it be possible to build (or buy) and “extendible”
|> multi-wheeler, that starts of as a normal uni, but can be extended by bolting
|> extra wheels on underneath? That way if I never got the hang of the
|> two-wheeler, I could extend it to a three-wheeling mean giraffe. I guess the
|> main problem with this would be the make robust joints so that the extended
|> frame was nearly as strong as a solid pole.

It is possible indeed. I have a two-wheeler that I can extend to a three wheeler
and to a four-wheeler. The frame is solid and heavy, but if you use good
materials it need not be. Anyway, its ridable. I rode the fourwheeler at the
opening ceremenies of a Japanese national meet. I normally use it as twowheeler
and it works just fine.

|> So, who builds these things? DM? Siegmon? Sem? Where’s my best bet? Does
|> anyone have one? Has anyone ridden one? Does it really hot-up your backwards
|> pedalling as Andy suggested? Advice?

These are of course all hand made. Try Tom Miller in the US and perhaps David
Mariner in the UK? In Japan its Tsukahara in Nagoya.

The best twowheel riders are probably in Japan, though Ken Fuchs is highly
skilled. Here are some skills that I can do or have seen done on two- wheelers.

1.  Riding forward 6. Free-mounting (two or three ways)
2.  Riding backwards 7. Switching from riding to idling
3.  Idling 8. Switching from idling to riding
4.  Idling one-foot 9. Hopping
5.  Spinning 10. One-foot forward

I’m sure there is much more not in the above list. BTW, probably the greatest
multiwheeler builder in the world is Tsukahara from Nagoya Japan. I have seen or
ridden his two-, three-, four-,five-, six-, seven- and eight-wheelers, and have
ridden Hayashi’s (also Nagoya) 13-wheeler. All but the last have the wheels in
vertical arrangment. The 13-wheeler is more or less pentagon shaped (I think
there is a picture of me riding in an old issue of OOW).

You may be interested to know that Tsukahara has also built me a one-and- a-half
wheeler that converts to a half-wheeler, both of which I demonstrated in UNICONs
and NUMs. He also built me a two-and-a-half wheeler, which after a couple of
hours practice we dismantled. It could be pretty dangerous because we used 20"
wheels and that made it pretty tall. When you practice on 1.5 and 2.5 wheelers
and lose your balance during the coasting part, you come down very fast and
very hard. Perhaps John should this to his list of what not to do on a uni…

BTW, I ended my adventures with multiwheelers by buiding and riding the silliest
uni ever invented – the zero-cycle. Yes, no wheel – just a hub, cranks and
pedals. The reason I no longer do it is because I can’t think of new ideas. That
is, I’m trying to figure out how to build a -1-wheeled (yes, minus one)
unicycle! The ultimate twowheeler I discussed in a previous posting is something
I should do one day, but it’s very difficult and expensive to build…

I know that Ken Fuchs once wanted to start a special-interest group on
two-wheelers. I’ll let him take over from here, if there are to be follow-up
discussions, as I am busy on my third dicitonary this year…

John Foss, if you’re reading this, you may want to use some of it as a basis of
an article on multiwheelers? I think the mailinglist has tons of stuff that can
be reedited into articles…

Stay on top,

Jack Halpern IUF Vice President

Kanji Dictionary Publishing Society 1-3-502 3-Chome Niiza Niiza-shi, Saitama 352
JAPAN Voice: +81-048-481-3103 Fax: +81-048-479-1323

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4

Re: Double wheel giraffes

At the recent British Unicycle convention Semcycle were demonstrating a range of
extension tubes which bolt on to the bearing housing of any XL trainer, allowing
you to create pick-and-mix multi-wheelers with any combination of wheel sizes.

This has to be a quick and convenient option for would-be multi-wheel
riders: the only disadvantages I can see are the strain on the bolts and the
fact that each wheel has an axle sticking out - not very good for the floor
if you drop it!

Peter

Peter Philip Workshop and Team Practice (all welcome) of the LUNIs 8-9.30pm
every school-term Wednesday London's Unicycle Hockey Team Acland Burghley School
Burghley Road peterp@foe.co.uk (opposite Tufnell Park tube) All views expressed
are my own London NW5 United Kingdom
5

Re: Double wheel giraffes

“James.Gifford” <James.Gifford@maths.anu.edu.au> (JG) writes:

JG> the unicycle wheel develops angular momentum when rolling.

JG> But then I remembered seeing pictures of giraffes with two wheels, where the
JG> pedals drive the top wheel which drives the bottom wheel. I had assumed that
JG> the reversal of the pedal direction and the sludginess of the drive would
JG> make these things hard to ride. But then it occurred to me: on top of these
JG> problems, the wheels are rotating in opposite directions so the total
JG> angular momentum is (close to) zero at all speeds! This makes me think that
JG> such monsters would have little or no sideways stability of their own.

I’ve never ridden one of these, so I can’t comment from experience, but as far
as the physics go, you are correct.

JG> It also occurs to me that you could go one step further and make the bottom
JG> wheel light and the top wheel heavy (so the total angular momentum was
JG> opposite to what you expect). My gut feeling tells me that such a device
JG> would be really weird to ride.

Well, no. It’s spinning in the opposite direction, but not all its properties
are reversed. What’s most significant is the plane of rotation, which hasn’t
changed. I don’t think it wouldn’t feel that different due to changes in angular
momentum. It might feel different for other reasons though.

JG> I would even go as far as to suggest that you might have to lean out
JG> around corners (!)

That sounds like fun, but without a counterweight that leans in, you’re going to
fly right off your uni. :slight_smile:

Seth Golub http://www.cs.wustl.edu/~seth/ sgolub@teknowledge.com
http://www.teknowledge.com/

6

Re: Double wheel giraffes

Peter Philip wrote:

>At the recent British Unicycle convention Semcycle were demonstrating a range
>of extension tubes which bolt on to the bearing housing of any XL trainer,
>allowing you to create pick-and-mix multi-wheelers with any combination of
>wheel sizes.
>
>This has to be a quick and convenient option for would-be multi-wheel
>riders: the only disadvantages I can see are the strain on the bolts and the
>fact that each wheel has an axle sticking out - not very good for the floor
>if you drop it!

This is a good option, for someone to just try riding a two wheeler. It should
hold together fine with normal forward, idling and backward riding, although I
have no experience using them. For more advanced skills or heavy use, you may
want to get another (non-bolted on frame) two wheeler for extra sturdiness.

Stay on Top,

Ken Fuchs <kfuchs@winternet.com