#dynasphere

The Dynasphere was a monowheel vehicle design which was patented in 1930 by Dr J. A. Purves. Purves' idea was inspired by a sketch made by Leonardo da Vinci. The vehicle had a top speed of 30 mph. – WTF Fun Facts

So this topic isn't particularly cohesive, mostly because it isn't a single device/invention, nor is it a particularly feasible idea! But it sure does make for good merchandisable toy designs. Or a good concept sketch by someone who's just trying to sell you something.

The monowheel! It's a giant wheel and you sit in the middle of it.

First off, I wasn't even aware these things worked from a physics perspective. Kind of seemed to me like you'd just fall over. They've even been around since the 1800s, originally powered by hand or pedals. The monowheel was even patented before the safety bicycle, which really shows that people will try something that looks cool before something that actually works.

It's noted that they're actually more stable than unicycles. When riding a unicycle, you risk falling off both sideways and forward/backward. At least a monowheel can only fall over sideways. They also are stable at a lower speed! Thanks, gyroscopic movement.

Well, that's basically all of the positives out of the way. When you take the rest into consideration, monowheels are a quite lousy novelty. It's hard to keep them upright when not maintaining forward momentum, and steering is equally tricky. How do you steer? I dunno, ask someone who knows how to ride a unicycle.

Nonetheless, there are many incidents of people trying seriously to make monowheels a thing. Spoiler: Nobody managed to make them a thing. This includes versions powered by gas engines, electric propulsion, and even a World War Two-era tank design that never got past being a model, the Kugelpanzer.

People have added propellers, rudders, fins, stabilizing wheels, gyroscopes, and many more additions trying to make the monowheel. They just look so cool on old Popular Mechanics magazine covers, so why not? Once you've added so many things trying to make it work, it feels like you may as well just add a second wheel and call it good.

Well, what you get with that second wheel, if you put them side-by-side and put the rider in between (instead of front and back like a bicycle), is a dicycle. The idea of a dicycle might sound as outlandish as the monowheel, but I'm sure you've actually seen them around. It's a Segway.

Wait, nope, still pretty ridiculous.

It sounds like the most commercially-successful of the monowheels was the Dynasphere, which still didn't really get past the prototype stage. A massive iron lattice with a driver in the center would be steered by leaning out of the side. Note that the thing weighed a thousand pounds, and steering was described as "almost impossible" along with braking.

Most concerningly, the Dynasphere had a reported tendency of "gerbiling". You know those videos of a hamster on a wheel where suddenly the hamster stops running and instead gets tossed around on the inside of the wheel? Yeah. Now picture that when you're doing the Dynasphere's 30 mile-per-hour top speed and attempting to brake.