The Finished Unicycle

This unicycle really screams. I mean, it is REALLY FAST!! Trying to free mount it is somewhat of a challenge, it is so non-intuitive. But once on it's grit your teeth and go! I blistered the skin on my face my first outing.

The wheel was masterfully built by Val Kleitz at The Bikesmith in the Wallingford district of Seattle. The 6" aluminum cranks and 24" by 1.75" steel rim were donated by John Drummond at unicycle.com. It's built on a 24" replacement Torker frame. The pedals came off of my 20" Torker. The seat I'm presently using came off of my 24" Zephyr. The wheel has a 24" by 2.125" Kenda tire mounted on it in hopes that the ride would be a little squishier. The Kenda is a bit fat for the Torker frame so I will soon switch to a 24" by 1.75" tire.

I had estimated that the backlash measured at the pedal would be 0.020"-0.040" or 0.5mm-1.0mm. I measured it to be 0.055" or 1.4mm, slightly sloppier than I had hoped for but respectable considering the modification I had to make to the diameter of the planet shafts. They were reduced by 0.003" in diameter to compensate for the shift in shaft position caused by drilling the shaft holes into the planet cage rather than boring them. One can easily feel the backlash but it is nothing compared to the chain slack of a giraffe.

Tremendous technical advice was offered to me by the three instrument makers at the Nuclear Physics Lab, University of Washington. Hank Simons and Jim Elms from the Cyclotron Shop whose input is greatly appreciated, and David Hyde from the Nuclear Physics Lab student shop who also welded the sun gear assemblies for me.

The finished unicycle equipped as shown weighs in at 15 pounds 5 ounces or 7.0 kg. Now that I know it works, I may be replacing components with higher end stuff. After NAUCC and UNICON this year, I will probably break down the wheel and have a lightweight 27" or 28" wheel built around the hub to make a 42" wheel equivalent, lightweight cruiser.
 

Here is a view of the wheel built masterfully by Val Kleitz at The Bikesmith in the Wallingford district of Seattle.	This is another view of the wheel showing the hub from the righthand top side.
Completed unicycle, right side.	Completed unicycle, left side.
This is a view of the frame showing the hub from the lefthand side. The components are all el-cheapo. The frame is a 24" Torker frame. The cranks are modified 6" aluminum cranks donated by John Drummond at unicycle.com. He also donated the 24" steel rim. The pedals came off of my 20" Torker. The seat I'm using came off of my 24" Zephyr. The tire is a 24" by 2.125" Kenda. It's a bit fat for the frame so I'll probably switch to a 1.75" tire soon. Now that I know it works, I may start investing in some higher end components.	Proud, crazed owner and creator with his baby.

I was unhappy with the frame tab connection I started with. It was a wide sheet of 0.075" stainless steel sheet with a strap of 0.050" stainless steel sheet wrapped around the frame and attached with two 8-32 button head screws. That is shown in the photos above and it was kind of funky looking although I have no close ups. I briefly tried an arrangement with the tab cut down in width so it hides behind the frame. I attached this with a worm drive hose clamp and a small piece of rubber sheet. I was still unhappy with the lack of esthetic appeal. I settled on the attachment scheme shown in the close ups below. It is a shoulder bolt assembly of brass in which the back flange is 11/16" hex and the front flange is 5/8" round. The shoulder sections are 3/8" (10mm) and go through a hole in the frame. A small rubber sheet is placed between the frame and the frame tab. The assembly is compressed with a stainless steel 10-32 button head screw. I think it is much prettier and easier to disassemble for changing tires and such.

View of the new frame tab connection from the right side.	View of the new frame tab connection from the left side.
View of the new frame tab connection from the side.	View of the new frame tab connection from the top right.

Photos by Greg Harper and Karen Harper