At least bicycles are stable. This onewheel thing cannot work without a computer balancing it (+ the rider). If it fails the rider falls on their face. It would be the equivalent of a bike fork breaking.
Bicycles are entirely stable without a rider as long as they’re moving. The human is only really necessary to provide motive power. There are a ton of videos showing this.
It is totally unlike the intentional instability of a modern jet fighter.
Bicycles fail safe unless a wheel falls off or both brakes fail simultaneously.
Balancing onewheelers - if the control or power system fails, you immediately go down, hard. And since the cruising position is weight shifted forwards, it's 100% nose dive.
The onewheel is an inherently bad, unsafe design. The long board that a rider stands on is ever liable to stick into the ground and throw a rider. Compared even to a monowheel (not the safest mode of transportation in itself), it is downright scary.
Generally, rider of a unicycle or similar self-balancing device puts his life and limb in the hands of an unknown microcontroller programmer. The software on those things should be regulated as strictly as the airplane autopilots.
It does seem utterly counterintuitive that a vehicle that cannot balance by itself would be able to balance with the addition of a heavy rider elevating its center of gravity. Usually making an object top-heavy renders it even more unstable, and bicycles are not stable to begin with.
And adding a rider on top of a bicycle does make it more unstable, but the amazing flexibility of the human brain allows us to transform that instability into stability, kind of like how modern fighter jets are intentionally unstable to make them more manoeuvrable.
Bicycles are a marvel of physics and biology working together.
Yeah. My point is that balance isn't an issue on a bike. The rider might not be able to hold on, but a bike is perfectly capable of keeping itself upright. Sometimes even to the detriment of the rider.
Low speed accidents where a rider drops a bike isn't enough of a concern to design something like this, so I'm ignoring those for the above statement.
I think the author should give more credence to it not being intuitive that people could easily learn to balance on a bicycle. The other examples he gave - horse, canoe - are stable without a rider. If you put a canoe in the water, it will stay upright. Horses, obviously, are stable without a rider. A bicycle without a rider will fall over.
I don't think it's obvious that putting a human on a long, two-wheeled vehicle will make it more stable than that vehicle is on its own. I think it's also not obvious that most humans can quite easily and quickly learn how to balance a bicycle.
I think it really comes down to the fact that these single wheelers don't support the operator without power. You can stand on skateboard, slow down, and come to a complete halt and it's still working as intended. On a bike you will eventually topple from one side or the other, but the way a bikes works means the rider is supported in a natural position for a long time.
When the one-wheeler loses power it just nosedives, the front hits the ground and they halt immediately.
I wonder if they could save some of the danger by placing small, unpowered wheels in the front and back so when they dip they can at least keep moving.
The balance idea is raised and rejected, but as I understand it it's a huge part. The issue isn't about humans balancing on the thing (as with the examples of canoes or horses that are already stable at rest), but rather that a bicycle _does not balance unless it is moving_, and moreover making it balance depends on the fact that it has steering – fix the front wheel in place and you can't ride it.
This is not intuitive, except with the benefit of hindsight.
That sounds like a unicycle, which is a hundred times harder to balance than a bicycle.
The physics of how a bicycle balances itself when you are moving is very different than that, complicated, and quite unintuitive. Basically when the bike starts to lean to one side, the rotation of the front wheel causes it to steer to move the bike underneath the direction you are leaning. This happens several times a second, and faster than a human can react.
> Some kinds of instability are slow enough that we can control them. For example bicycles are unstable, but many of us eventually learn to ride them.
Actually, bicycles are only unstable when they are moving slowly (or stopped), and most people never learn how to stabilize one in this unstable regime. It can be done, but it's very, very hard.
Yep. A bike is self stabilizing due to the design of the dropout on the fork. If you lean left it automatically turns left which will push you upright again.
It is hard to not stay balanced on a bike. Unless you are on uneven or slippery surface, or do other stunts, the only way you can really fall is if you are moving too slow or you are deliberately forcing your handlebars to turn very hard.
It's true that increasing trail and rake both increase stability. But curiously, a bicycle can be made stable with both negative rake and negative trail.
An interesting take on this, with both mathematical modeling and real prototypes, can be found at [1]. Note also that gyroscopic stabilization is not necessary: in the prototypes, a counter-rotating extra wheel cancels out the angular momentum of the front wheel.
According to the authors, it's not yet even proven that a stable bicycle must turn towards a fall. Almost the only sure thing, so far, is that "at least one factor coupling lean to steer must be present". We know a lot of sufficient conditions for stability, but not what is necessary.
The conclusion of the paper: "As a rule, we have found that almost any self-stable bicycle can be made unstable by misadjusting only the trail, or only the front wheel gyro, or only the front-assembly center-of-mass position. Conversely, many unstable bicycles can be made stable by appropriately adjusting any one of these three design variables, sometimes in an unusual way. These results hint that the evolutionary, and generally incremental, process that has led to common present bicycle designs might not yet have explored potentially useful regions in design space."
EDIT: here's a not-paywalled version of the paper linked in the submitted article.
reply