Corbin Dunn
Redwood Monkey

Building a Tandem Unicycle

Machining, Unicycling

My last post introducing my Tandem Unicycle originally started out with a step-by-step process of how I built it, but for some reason I lost the post. Here is how I made my tandem uni:

IMG_6434.jpg

This idea is not my original idea. A few years ago at a “California Mountain Unicycle Weekend” a guy named LobbyBobster on the unicycle forums brought one and I gave it a try with Beau Hoover. Here’s a picture of the creator and their tandem, which looks much nicer than mine!

tandem unicycle P4060001.jpg

So, from seeing this uni two years ago and based loosely on this picture I set about making my own for no cost. I already had two old bikes that I got for free, so I was set to begin.

Materials:
* 2 Huffy Mountain Bikes

* 2 Unicycle Seats

Tools Used:
* Sawzall (with a bimetal blade)

* 4.5” angle grinder

* MIG welder

* Half round file

I took the wheels off of the old Huffy mountain bikes. One of the two rear wheels was going to become the main unicycle wheel, so I removed the rear cassette and saved the sprockets:

IMG_6365.jpg

The intent was to weld the two rear halves of the bikes together, utilizing the rear triangle that already exists. I used the sawzall to cut the front half of the bike off:

(NOTE: in this picture I already had removed the seat post clamp for another project — you should leave it on if you are making your own tandem).
IMG_6367.jpg

The rear triangle after I cut it free. Notice that the seat post tube is at an angle — I later cut it off and re-welded it vertical so it would be more “unicycle like”:

IMG_6369.jpg

And the rear triangle of the other huffy after I cut it free:

IMG_6370.jpg

I removed the main drive hub — one of the two has to be switched to the opposite side, and it worked well to remove both and re-grease everything after I welded it back together. Removing the hub was easy, even though I didn’t have the proper tool. I used a screw driver to get the reverse-threaded hub “bolt” out:

IMG_6372.jpg

IMG_6376.jpg

The next thing done was to cut off the vertical tube and cleanup the two holes left in the hub housing:

IMG_6381.jpg

I then needed to weld the seat post tube vertical. I used a half-round file to cut a slight fish mouth out of the tube so it would fit nicely over the rounded hub housing. I then created a hokey setup to hold it vertical, testing the straightness with a square:

IMG_6382.jpg

I tacked it, and welded it on. Note that the big holes are left:

IMG_6385.jpg

I cut a piece out of one of the horizontal seat post tubes to use as a patch:

IMG_6386.jpg

I tacked it on:

IMG_6393.jpg

and then completed the weld. There is a patch on each side to cover up both holes. I then repeated the process for the other bike half. At this point I attached the two halves to the wheel to get a feel for it, and cut a top tube to size after making sure the bottom pieces were inline with each other:

IMG_6395.jpg

The next thing I needed to do was to weld the two halves together. I prepped the steel and cut off the angled slot on one side:

IMG_6401.jpg

I clamped them together, making sure the bottom pieces were in the same line with each other — that way, each seat post tube is parallel with the other.

IMG_6407.jpg

After they were MIG welded together:

IMG_6416.jpg

At this point I decided to weld the freewheel on the rear hub’s cassette so it wouldn’t freewheel. Note that the hub spindle still turns free.

IMG_6420.jpg

The next part was to tack weld in the top tube in place, and cut some side tubes to fill in the frame:

IMG_6423.jpg

For the other side doesn’t look as good. It turns out the two bikes were different frame sizes, and I wanted the top tube to be horizontal, so I had to do some funkiness to get it that way:

IMG_6425.jpg

At this point I put the sprocket and hubs back together and stuck some unicycle seats in:

IMG_6426.jpg

The only thing left was to weld on two sprockets in the wheel’s hub. I took two sprockets of the same size (one from each cassette), with about the same number of teeth as the smaller hub sprocket (in order to get a 1-1 gear ratio). I made a spacer by grinding off some of the teeth on one of the sprockets and used some of the plastic spacers that were left.

IMG_6428.jpg

I then welded this to the hub (sorry, no picture).

At this point, the whole thing was put together with two chains, and I temporarily used a large sprocket in between two of the chains to keep the chain a little tighter:

IMG_6441.jpg

Left todo is to create a chain tensioner, and to paint the thing.

corbin

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WrestlermanA Unicycle Built for Two » Bike RumorFred BlasdelMonocycle vs tandem | Bebert and CoiRaff » Blog Archive » Suchst du noch ein Weihnachtsgeschenk? Recent comment authors
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[…] Building a Tandem Unicycle […]

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[…] Update: Full instructions, if you’ve got sufficient wild abandon, can be found here. […]

Buzz News
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Buzz News

Hi,

We write stories for the UK newspapers.

We would love to run a story about you.

Please could you email us so we can contact you for more information.

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nate
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Sweet dude! Cool to see the writeup on gizmodo!

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[…] any case, do take a look at Mr. Dunn’s tandem unicycle in detail or witness the dueling dangers in action via this motion picture […]

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[…] » corbinstreehouse.com […]

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[…] créé par Corbin Dunn : un monocycle en tandem.Et pour les bricoleurs, vous pouvez faire un tour ici où tout est […]

Fred Blasdel
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Fred Blasdel

What you refer to as the “main drive hub” is actually a “bottom bracket”, it took me a bit to figure out what you were talking about.

For one-piece-cranks like that, a big flat-headed screwdrivis is the proper tool, along with a hammer and maybe a pair of vise grips. They are crude, cheap, and meant to be easily serviced by 7-year-olds. As a bonus for your purposes, they can be run backwards with no problems, as the cups thread to the spindle and not to the frame.

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[…] Corbin’s Treehouse comes his frankenstein’s monster of a two-person unicycle.  How do you create such an […]

Wrestlerman
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Wrestlerman

This is so sweet!!

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