nishiki12

Hey y'all, so this summer I want to build a monowheel, alot like this one. It's gonna be pedal powered, and made from parts from Menards. My plan right now is to use 2 of these metal bars and bend them into a circle. After that, I'll use 1" vinyl tubing as a makeshift inner tube, and use a couple of old bike tires to form one big tire. My question right now is whether or not it would be easy to bend 2 6' lengths of steel into a close-to-perfect circle without any special tools, like a metal bender. I plan to do this to form the metal ring, with a sheet of plywood and some blocks. Do you guys think it'll work? If not, what are your suggestions to make a circle?

General Geoff

You'll want two parts of this wheel, the rim upon which the tire/inner tube are mounted, and a slightly smaller, much stronger circle to support it since you can't run traditional spokes to a center hub to keep the rim true.

You can source the rim, tube and tire from an "ordinary" or penny farthing bicycle.

nishiki12

@ General Geoff I thought of that, and my inside frame (the part I ride on) will be a square with castor wheels at each corner, along with washers to keep the parts from seperating.

UniChris

I strongly suspect you need a hoop rolling setup to do this right, ie, 3 metal rollers with the spacing of one of them adjustable.

That's not necessarily an absurdly expensive piece of gear these days; there are import variations of a lot of such machinery which you can probably clean up, or improvise one from scratch.

But it's likely a little beyond hardware store sourced fabrication - while perhaps not impossible without you'd find the project a lot easier with access to a basic lathe, milling machine, and welding gear.

I saw a gasoline powered monowheel at a unicycling event once. It was fun to watch, but I came away with the impression that it's wasn't as untempered fun to ride as it seems like it should be - there are a number of practical downsides though I don't recall their specifics.

Narrow solid-tire penny farthing type wheels have unique piroutteable handling qualities when used in a sit-on unicycle, and I'm not sure that's what you'd want for this versus a 2 to 3 inch diameter tube rolled into a wheel and given a rubber perimeter tire strip, even though also not pneumatic. It might be worth trying to contact Sem Abrahams at Semcycle as he's both sold unicycles with penny farthing type wheels, and owns and rides the McLean Wheel powered monowheel that I saw.

nishiki12

Can the Home Depot bend metal into a circle for me?
They cut some for me once.

UniChris

No. At most they'd have a conduit bender, this is quite different. There are videos on youtube of monowheels being made, and others of both conventional and penny farthing bike rims being rolled to diameter. Watching those will give an idea. I think the term is hoop rolling.

LanghamP

Unless you enjoy building these kinds of things, a more practical monowheel are the various ready-to-ride electric unicycles available over the internet for between $300 to $2000. I have several of these and they are both very fun and very practical, so much so that I had to be careful not to ride them everywhere; as door to door transport I found myself getting no exercise.

https://www.ewheels.com

veganbikes

They make these things called Unicycles, why build some odd project when you can get a cool unicycle!

rollagain

Nishiki, that steel you referenced is no good. It's low-carbon, meaning it's soft--you could easily bend those pieces with your bare hands. In practice that means it won't hold its shape when used in any load-bearing capacity. A common length of actual gas pipe would hold its shape a lot better, partly because of its cross-section.

Notice the construction of the Ben Wilson monowheel you referenced: he's used bicycle frame tubing, which is engineered to carry loads without deforming.

If you want to build this at the cheapest possible cost and without needing special metal-forming equipment, I'd suggest going with wood, probably a cabinet- or marine-grade plywood. That would get you the wheel and the inner frame, and you'd want to make those laminated in overlapping arcs with plenty of good glue. Of course, that involves some woodworking tools and lots of clamps. Making both pieces perfectly round and concentric will be a trick, too. Then you can add metal plates to support the drive, seat, handlebars, etc. You could maybe make the seat and handlebar of wood also and integrate them into the frame with some graceful curves.

Think about fiberglass, too; though I don't think it would be rigid enough for this all by itself.

Both the wheel rim and the inner frame need to be made of the same material, otherwise temperature changes could cause one or the other to shrink or expand and cause problems.

I hope I haven't discouraged you; this could be a really fun project.

Doug5150

If you live near a major lake or coastal area then a boat repair shop may be able to bend the tubing for you.
Boat shops that do repairs on BIG boats always have a tubing roller (the piece of equipment that you need here) because they must be able to make replacement boat railings.

Alternately--if you live in the USA, then Harbor Freight sells a tubing roller for $180. It probably isn't the greatest quality but it is probably the lowest price for something new and bicycle tubing is pretty thin.

UniChris

Been there, done that, hopefully getting up early tomorrow to do it some more...

Arguably a monowheel is to a sit-on unicycle what a recumbent is to a diamond-frame bike: different, novel, better in some ways, worse in others...

Apart from the sci-fi coolness factor and potential utility as camera platforms, rather boring. You don't want to go faster than you can run, so a powered scooter makes more sense for transport. Though having access to them for a while was what got me to get a pedal uni of my own and finish learning to ride it.

Teamprovicycle

you could get a penny they have a big wheel you just ride on top instead of inside lol

UniChris

Sure a penny is an enticing concept for efficiently rolling along, and I'd very much like to get one.

But think for a minute about what a brief stop involves on a penny. With a monowheel, you just put your feet down.

Also a monowheel can be, and essentially has to be geared if human cranked. A penny is huge in diameter because being direct drive the only gearing is the wheel radius divided by crank length. A monowheel is only big so that you can sit in it.

Though that need for multiplication gearing would complicate making a pedal-powered one. A gas engine matches quite nicely to a little roller, but to pedal power it, you need a gearing system which gets the tangential velocity of a little plastic drive roller up to whatever speed you are hoping to travel. The diameter of the monowheel itself has no role in the gearing, effectively you are riding around on the little drive roller at whatever speed your multiplied pedaling can turn that.

nishiki12

So I did the math, and if I took 2 bicycle wheels with diameter 2 ft each, I could cut them, bend them out, weld them together, and get a 4 ft diameter hoop, right? (That was a hell of a run-on) Wouldn't this be like what rollagain mentioned?

Also, if I used an inner frame in the shape of a square like , wouldn't it handle all the stress b/c of you know, physics? I plan to build the inner frame out of steel square bars, which I'm pretty sure are very strong.

If none of these work, how thicc do you think the outside rim would have to be, if I made it out of the same metal as before? I have a friend that's a blacksmith, and he can help me out, so no problem with bending, welding, etc.

Yes I'm going through with this.

Kontact 

A square with rollers in the four corners isn't going to support the rim - it will just buckle on the bottom between the roller corners.

If you want to make something like this out of cheap stuff, use laminated wood. It will be much stronger and lighter than any metal you can bend to shape. People still make and use wood rims.


And regular inner tubes would be much easier to vulcanize together to make an uber-tube than trying to put a valve in some other kind of tubing.

nishiki12

What if I used a diamond shape, with a castor wheel at the very point of tangency to the ground? Or just put like 5 wheels at the bottom, like road wheels on a tank?

Also, I'm using the vinyl tubing as an airless tire, since its walls are so thick.

Kontact 

Whatever shape you use, the wheels need to be arranged something like they are here:

rollagain

If you wanted to make two bike rims into one big one, you'd have to find steel rims because aluminum ones would be destroyed bending them that much. Then you'd still have an unsupported rim (as in, no spokes, no hub), so you'd need to add another circle inside of it like those third-worlders did (honestly, welding in sandals and without any eye protection--yikes). You're making a circular girder.

And that 'same metal as before' still won't be any good because it's still soft steel and it still has no cross-sectional stiffness. Please don't buy any of that, at any thickness.

I see someone else here has echoed my suggestion of plywood. Now I'm going to also suggest that you start with a scale model, maybe one-quarter scale. That will teach you a whole lot about your design before you commit to the full-scale version. I've modeled things before and made surprising discoveries as well as confirming calculations.

Describe your idea to your blacksmith friend and see what he says; they do know about steel.

nishiki12

Thank y'all .

I've made a scale model out of Legos when I was 12, so I know what design to follow, and I will follow up and my smith what he thinks I should do. Thanks for all the help so far!

UniChris

Honestly, I think you'd do best to start by contacting people who made or have them, and asking what size and type of tubing the rim is hoop rolled from.

Then see if you can rig up the rollers to do that. I don't think you'll be able to do it suitably by any lesser means, like bending around wooden forms, etc.

Only worry about the rest of the project once you have a very round rim.

UniChris

Fallacy alert: all steels have pretty much the same stiffness, over a small range of variation. Thickness and geometry, not exotic alloys, are how you make a steel item stiffer.

What meaningfully varies is the yield strength - the point at which they don't spring back after you remove the applied force.

rollagain

Believe what you want to, but if there weren't significant differences in the way alloys and carbon content affect characteristics, nobody would bother. Now, why don't you go make a bicycle frame out of the cheapest low-carbon steel you can buy and tell us how well that bike performs?

smarkinson

Roll a 2 inch tube into a circle (or get an engineering firm to do it for you). Cut up some tyres and glue them to the outside for grip (that's what it looks like in the OPs original pic). Build the rest of the machine.

redmax monowheel

LanghamP

You've never ridden an electric unicycle? They are amazingly useful as last mile transport, and are demonstrably faster than any other vehicle in an urban environment when you include parking a car or locking a bicycle. I average between 15 mph to 26 mph, depending on stop lights, to the 4.5 miles to work and back whereas on my bicycle I'm lucky to reach 13 mph average.

The latest generation all seem to have a top speed of 30-35 mph and have a safe range of about 30-40 miles. Throw one in the back of your car and never worry about parking again.

If you find electric unicycles boring, then just go faster. They are exceptionally dangerous, not like hit a car and die, but more like hit a tiny walnut on the ground step off/tumble.

Going back to the original topic, I think there is great value in attempting to do something like this. Everytime I've built something I've always learned a great deal; the physical manifestation of your idea is both challenging and rewarding. It makes you a better person regardless of the subject.

UniChris

Because stiffness, the subject of your erroneous claim to which I responded, is not the same thing as strength.

In this case however, it's likely that low carbon steel probably would work for many parts of the project.