Well! If you insist on
running over helmets and sundry other road hazards, nothing will protect you.
A student at MIT has created a nearly self-balancing electric unicycle, imitating the kind of stability control seen in the Segway. Demonstrated in a YouTube video, the “Bullet” unicycle, created by MIT student Stephan Boyer, can’t manage to be self-balancing sideways, but does protect the rider from falling over in the …
I really like riding tip 5;
"When you first press the safety switch, Bullet will assume an upright position as fast as it can, even if you are in the way. So don't be in the way (it can run into your ankles or run over your foot)!"
I'm assuming, considering the seat height, standing to the side and not square on while powering in on is a given.
One of the cricket commentators (Ian Healy) decided to have a go on the Segway around the pitch the following day (while the cameraman was being interviewed about his crash), and ... well you can guess what happened next...
The way a uni balances sideways is via torso twist, which changes wheel rolling direction, allowing the contact patch to be translated side to side (while the wheel is turning, anyway). Actual turning is difficult because total angular momentum must be added in one direction and then removed, using only a tiny friction patch in contact with the ground. The turn is achieved via a combination of friction and "carving." It's a bit hard to describe, but the rubber tread must do some scraping during each turn, which is actually audible if you listen closely.
A ball-wheel that can be driven in any direction is great, the payolad can stay balanced, but true turning becomes nearly impossibe due to the large friction patch preventing any actual angular change. Making the ball low-friction doesn't help because the turn-carving action depends on the wheel's shape to work, which won't be present on a radially symetric ball.
The result is that you can easily go any direction, but you can only face one way. Hmmm, sounds kinda cool, actually...
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