Two-wheeler details wanted...please

As I’ve mentioned before, I’m going to build a two wheeler with two 12" wheels. I’ve decided if it’s at all possible I want it completed before UniNats so I can show it off and let people have a ride of it. That means I really need to get to work and come up with a design for it.

I’ve never seen a detailed photos of a two wheeler so I’m still not completely sure how they work. Here are my main questions:

  • How many parts do two wheeler frames consist of?
  • What happens around the axle of the top wheel?
  • Is it worth making a frame that will allow a variety of wheel sizes?

For that last question, I thought it would be fun to have one with a biggish wheel on top and a tiny wheel on the bottom.

I think I’ll be able to design it in a couple of days and then have a chat to Ian (my frame builder) and hopefully get it done and painted just before UniNats. Hopefully.

Thanks everyone,
Andrew

Tony, Ken, Sofa, Max, John (Foss), Dustin, Gilby…you all know the answer. Sorry to be so annoying but I need to start building! :slight_smile:

Here’s a pic of Steve Pavarno on his two-wheeler. It was built so that that it can be taken apart and used as a normal unicycle.
I think the main thing is to make sure that the tyres have good contact so they don’t slip.

uni_twoclose.jpg

Another pic

uni_twowheel.jpg

Thanks Tony. So is the connection just a normal main cap bearing style one where the bottom caps are welded to the lower fork legs? I have trouble accepting that that would be stable enough.

Andrew

No, on Steve’s unicycle has a wide steel plate with the bearings set in it which mates with another plate on the fork extensions. Clear as mud?

Re: Two-wheeler details wanted…please

You have the standard unicycle frame, then and bearing holders and then two blades to extend down to the bottom wheel.

On the custom one I had built, it was pretty much like a miyata bearing holder, but had another connecting piece on the bottom, which connected to the blades.

Probably not, but, it depends on how you want to use it. 12" wheels are pretty small and so are 16" wheels. Thought 16" are fine for learning, 20" provide the best for normal use.

Here’s a semcycle set up…

Top Connection

Bottom Connection

Okay, I think I get it. Is it something like in this diagram (see attachment)?

Dustin,
I don’t know whether or not it’s my computer but I can’t see the photos. Could you please try attaching them again?

Thanks,
Andrew

Sorry…I guess it would help if I actually attached the diagram.

I just had a look on unicycle.com and found that all the Semcycle ones have the normal main cap bearing holders above and below the top axle. I’m sure this is probably illustrated in Dustin’s photos.

So can I assume that just using normal main cap bearing hoders is acceptable? Has anyone had problems with forward and backward play in their Semcycle 2 or 3 wheelers? I guess it would be less of an issue with 12" wheels.

Gilby,
Although the two 12" wheels may be harder to ride, I still want to use them because it’ll be more of a novelty that way and I think I’d enjoy it more.

Thanks,
Andrew

This is really quite embarrassing…third time lucky!

untitled.bmp (569 KB)

does this work?

dblwhl top connection.jpg

I’d recommend not going with that design. The semcycle 2-wheelers I’ve ridden had two problems. Once was that the wheels were not close enough and therefore caused a lot of slipping between the wheels. You can somewhat solve that by using fatter tires. The other problem is that the wheels are sometimes crooked with each other.

You’re better off doing something that will hold the bottom blades firmly in place to the frame.

The Semcycle that I use has the opposite problem: The whls are too close so I end up running low tire pressure. I run 30psi in the bottom tire and 20psi in the top, any more and it gets really difficult to pedal.

Side question: Are others getting the pictures in my first post or is it just something with Andrew’s computer? If you aren’t getting the pics, how do I post more than one pic without using attachments? PM me or let me know here: uni at dustinkelm dot com thanks…

The pics you posted are on your computer and are not accessable on the 'net. You need to upload them to a web page to put them inline in a post, or you can attach one at a time in a post.

Re: Two-wheeler details wanted…please

“andrew_carter” <andrew_carter.u3j3l@timelimit.unicyclist.com> wrote in
message news:andrew_carter.u3j3l@timelimit.unicyclist.com
> - How many parts do two wheeler frames consist of?
I don’t think there is a strict rule on this, depends on your design.

> - What happens around the axle of the top wheel?

I think the top wheel axle is just bog standard unicycle Now the diag
you drew on the 22nd , showing the extensions, and Dustins pic sums up those
examples of the extensions that I have seen. I would think though, that for
heavy duty use, some additional, more substantial bracing might be worth
thinking about. My understanding of those bearing holders is that they
should not be tightened up too much, not really the same situation at the
joints around the top axle, as it is on a normal uni. I don’t think some
extra strength here would go amiss.

> - Is it worth making a frame that will allow a variety of wheel sizes?

Yes, because, by changing the TOP wheel diameter you effectively gear up(
or down) the speed of the beast, given a set rpm of the feet. And of
course it widens the challenge of riding the damn thing. Smaller wheels
would probably “mesh” rather better, less twisting side to side.

> For that last question, I thought it would be fun to have one with a
> biggish wheel on top and a tiny wheel on the bottom.

Nice concept, and it will have no effect on your speed. It may indeed feel
very little different when ridden, despite changing through a range of
different lower wheel sizes. (some degree of speculation here 'cos if
you think I am getting up on one of those…no way)

Naomi

Re: Two-wheeler details wanted…please

I guess you know it goes in the opposite direction that you pedal :slight_smile:
To go the same direction as you pedal, you need odd wheels, 1, 3, 5, 7 etc
:wink:

“andrew_carter” <andrew_carter.u4ujx@timelimit.unicyclist.com> wrote in
message news:andrew_carter.u4ujx@timelimit.unicyclist.com
>
> Thanks Tony. So is the connection just a normal main cap bearing style
> one where the bottom caps are welded to the lower fork legs? I have
> trouble accepting that that would be stable enough.
>
> Andrew
>
>
> –
> andrew_carter - www.unicycles.com.au!
>
> HTTP://WWW.UNICYCLIST.COM/GALLERY/ANDREW
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>

does this work?

  • Yes, thanks a lot. That’s exactly what I was looking for. Apart from the wheels being too close to each other, have you had any other problems (eg. wheels being crooked)? Are you satisfied with the strength of the connection in your picture? Do you think this connection would be strong enough with two 12" wheels? I also got your email and replied to it.

One was that the wheels were not close enough and therefore caused a lot of slipping between the wheels.

  • Isn’t this due to an incorrect length of the fork legs and not the bearing holders?

The other problem is that the wheels are sometimes crooked with each other.

  • Do you think this would be an issue with the smaller 12" wheels?

Nice concept, and it will have no effect on your speed. It may indeed feel very little different when ridden, despite changing through a range of different lower wheel sizes.

  • I’ve decided to leave this for a later project…but I will do it eventually (along with the seated hand-driven uni, suspension recumbent, and many more :)).

I guess you know it goes in the opposite direction that you pedal

  • I should hope so. :slight_smile:

I think unless somebody can convince me otherwise, I’ll go for the standard bearing holders and just two 12" wheels. I’m in a bit of a rush to get it completed and to be able to ride it before UniNats and I can’t help thinking that there will be less stress on the holders with such small wheels and short fork legs. As I said, I will some day make another with a big wheel on top and a tiny wheel on the bottom.

Thanks a lot for all your help everyone.
Andrew

Re: Two-wheeler details wanted…please

andrew_carter <andrew_carter.u4rjj@timelimit.unicyclist.com>

>Tony, Ken, Sofa, Max, John (Foss), Dustin, Gilby…you all know the
>answer. Sorry to be so annoying but I need to start building! :slight_smile:

A simple and very good two frame design is that used by Tom Miller of
The Unicycle Factory, especially for 16" and smaller wheels. It is
basically just a Schwinn frame extended below to hold the second wheel.
It is a simple adaptation of my original design where my 3/16" x 3"
diameter washer which holds the standard Schwinn unicycle bearing with
snap rings is replaced by about a 2 1/2" square rather than round
washer. These washers are of course welded to the upper and lower frame
sections which are simply 3/16" x 1 1/2" flat steel stock. A bolt holds
the two frame halves and seat post together. Holes for the lower wheel
are drilled so when the tires are pumped up they are mutually compressed
by about 1/2".

There are previous posts to rec.sport.unicycling which provide further
details.

Sincerely,

Ken Fuchs <kfuchs@winternet.com>

Wheel positioning…

Okay, I’ve ordered myself two 12" wheels and a hub and crank set. I’ve also had a brief chat to the frame builder so everything seems just about ready to go.

How close together should the wheels be? I’ll be using the type of tyre that you see on cheap kids bikes so they’re pretty chunky which I gather is a good thing for two wheelers. How much should they be compressed when in position?

Thanks,
Andrew