This project took up most of my brain for quite some time. Luckily for me Alan Tepper (PPUT) has a lot of spare parts from which new unis can be pieced together. The photos attached show a 4-stack I built using five 24" forks, four 24" wheelsets, a 4-way galvanized pipe junction and a lot of sawing and drilling. It stands about two meters tall and feels like you are driving a tank. Sorry the pictures are blurry, I only had my phone with me. BTW: no welding involved!
In a typical even-numbered stack you have to pedal backward to go forward but, since the two middle wheels go the same direction, they act like a single wheel in terms of rotation (like a 3-stack). The center 4-way junction has short 1/2" pipes screwed into all four “inlets” onto which the frames slide and are secured by heavy duty seat post clamps. You can see the junction labeled “F R” so I could remember which is front and rear ;). Each of the pipes has a self-tapping screw inserted through the junction keeping it from coming unscrewed (thanks Tim for the suggestion).
I added support struts in a square pattern from frame to frame attached by the screws inherent to lollipop style bearing holders. Turns out to be a good use of old lollipops! The struts have a turnbuckle on one end which allows adjusting the tension and some degree of fine tuning how the wheels fit together. This seems to be the hardest part to get correct and stable. Since the top two frames (one is upside down) holding the wheelset including the pedals isn’t a lollipop style I drilled holes and used self-tapping screws to attach the struts to the top frame.
I wanted to use 20" wheels but couldn’t get them to touch so opted for 24". As it was I had to cut down the frames to get the tires as close to each other as possible. The bugger is rather bottom heavy so requires effort to get the wheels rolling, which increases the chance of slippage between wheels. I could only ride it a couple of meters but one of my teammates (Sarah Shilot) rode it across the gym the long way so I know it’s possible. I’d love to be able to include it in our cadre of 3 and 5 stacks in performances but only time will tell how practicle it turns out to be.
A fascinating bit of structural engineering using some bits from the hardware store and old unicycle parts. Great way to breathe some life back into some old lolipop unicycles! And all those turnbuckles mean you should be able to make frequent and easy adjustments (like in mid-parade) for alignment and tire pressure.
It should ride, as you said, like a tank with sluggish performance. Turning will take some effort due to the mass being out the front and rear, but nothing a decent rider can’t get used to.
I think walking the wheel on it would be a great challenge for a more advanced rider due to all that steering mass!
One suggestion was to add nother small wheel contacting the large rear wheel, then you could lean back and ride it recumbant. I think you would be spending most of your time holdng on for dear life pedaling backward!
It really wasn’t that difficult once most of the design was figured out. I started by thinking I could build a 4-way “seat post” to fit in the middle and allow anyone with enough extra parts to build the uni from there. Found out it’s harder to get the wheels to touch than originally planned, nothing stock does the trick so ya gotta do some cutting. I’m ADHD so once I get a thought in my head it’s hard to let go of it! Fortunately, not many thoughts pass through my head.
Haha join the club! My guess is there are lots of other ADHDers on these forums! And a common misconception is that we cannot focus on anything very long; well, in a lot of situations that’s true, unless the person with ADHD likes what they’re doing, and in most cases as well as my own, I HYPERFOCUS and tend to really excel at the stuff I like. Really cool design btw!