Re-design 8 ft Unicycle

Hi,

I am building my own 8 ft giraffe unicycle. I have designed one before and posted it on a previous forum and recived feedback for it, and from that feedback have changed a few things.

Here is the previous forum:

From my previous design, areas I have adapted are:
Add triangles for strength (previously square frame)
Remove some cross members (previously 5)
Think about forward/backward support
Work on strength of attachment from frame to bottom bracket

Could I please have some thoughts/comments of my re-design and some possible areas of improvement.

Thanks

Looks like an interesting project. How big of a wheel do you intend to use?

700c with a flip flop hub with a fixed hub on both sides so that it is dual chain driven. This will hopefully make it safer.

Pichler’s giraffes, which have been around for some time, use the same design; so I guess it should work.
Chain tensioning screws for the dropouts might be helpful to get the two chains evenly tensioned (but maybe it’s not an issue, I don’t know).

While you’re at it, you can also build a clone of the Kingcycle, a British recumbent classic (see attachment). The frame isn’t all that different :wink:

kingcycle.jpg

Missing from the design:

materials (cromoly? aluminum?)
dimensions (tube diameter / thickness)
attachments (welding? nut and bolt?)

This design might work with one type / size of material but not another.

I am using steel 1 inch tubing. I have calculated the bending moments and stress of the size i want to use and it is safe with a 15 stone weigth.

The thickness is 1 inch x 10 SWG mild steel, and i will have it powder coated.

I will weld the whole frame together as i feel this will be the safest option and will prevent small movements that could orrour when using nuts and bolts.

When you push sideways against a tube (such as your “bottom” bracket tube), you shouldn’t push against it radially with a thin tube. The load should be spread so that part of it is imposed in more tangentially.
I’d use oval or rectangular-section tubing for the fork legs. It should make it stiffer fore and aft too.

Wheel:
700c is kind of silly. If speed is what you want, you should be closer to the ground. :slight_smile: Since giraffes are more for show, 20" is the common size because it lets you fit more riding into a smaller space, makes it easier to idle, etc.

Drivetrain:
with 1" steel tubing, your giraffe will be pretty heavy. A dual chain setup looks cool, but is a bit of overkill unless you plan to perform on it (a lot). As an alternative, you could make your axle with a different size sprocket on each side, and effectively have two different “gears” by taking off the wheel and turning it around.

In 1933, Walter Nillson rode across the US on giraffe that was 8 or 9’ tall. It was to win a $10,000 prize from Ripleys Believe it or Not, which he did. That was a ridiculously huge amount of money during the Great Depression! He had a switchable wheel with two different sprockets.

Frame strength:
One way to maximize the strength of square tubing is to turn it 45 degrees. So it has corners in the front and back. A little more complicated on the welding, but definitely stiffer than doing it “square”. Tom Miller (The Unicycle Factory) used to build his tall giraffes that way. He used wider square tubing (2"?) for a main center beam, with a piece of 1" welded corner-to-corner to form each fork leg. This worked for giraffes of 8-12’ or so. They were heavy, but super-strong.

I think that 10g 1" tubing is too small and thick. You would gain more strength and save weight by going to bigger tubing and thinner wall. Your problem I think will be flexing, not stength. Also best to go to high grade tubing that has a tendency to be stiffer.

The other thing to consider is that a flip flop wheel is designed for load in a single direction, even with a lock ring. We stopped using these at unicycle.com about 10 years ago due to their inherent problems and developed the safety sprocket system. This uses a double disc brake hub with a plate sprockets.

Roger

Anyone thinking tall Oracle? :roll_eyes:

i was thinking 36in girrafe

You mean, like this?

It’s huge ! Is the tang on the leg down low, a step to help freemount ?

how fast is that!!

Not sure about that, but I would guess so.

It’s actually geared down to a 20" or 24" so it’s about the look not the speed.

I designed a 12 foot unicycle in my college engineering class awhile ago that works really well. I modeled it after Tom Millers square tube design. The best part is I made it so it broke down in 3 four foot sections so it could fit in my trunk. I also could leave the middle part out and it would then be an 8 footer. I can see of I still have the designs and send them your way if you want, just let me know. The only draw back was it is heavy but very strong and durable.

Jamey,

It would be cool to see your design if you can find it.

You should use one of those hubs. Also, as someone mentioned above, don’t leave out the chain tensioners, which are kind of essential for controlling your chain tension.

Notice that the big wheel doesn’t improve the giraffe-riding experience. Beau clearly isn’t enjoying riding it at all. :slight_smile:

That’s what it looks like. Stepping directly onto a 36" tire would be a bit much. That way, you could go from the step to the pedal.

Yes, a professional performer’s unicycle is kind of the opposite of a sport unicycle. The #1 requirement is that it doesn’t break. Making it modular also usually adds to the weight. Jamey, did you have a Tom Miller one before your custom one?

I went from a 6 foot Schwinn to a 10 foot hand made 10 foot Tom Miller look alike that I built in high school. But the 10 footer didn’t break down and was a pain to transport so then I built the 12 footer. Loved it and still have it and have never had any issues with it. But as soon as I started traveling in planes a lot with it I always had to use a bike box and eventually it got too expensive so I had Wyganowski from MN make me a new one that was half the weight and broke down to fit into a standard suitcase. He used oval tubing but do not remember the exact metal he used.

Wow, I just looked thru my old college paper regarding my 12 foot design. Very funny to read 10 years later. I uploaded to google docs for any of you to look at, as well as my power point presentation. Don’t make too much fun of me. :smiley:
Unfortunately I don’t have any of the drawings or appendixes. :frowning:
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