Di-wheel bike that actually works | Hacker News Reader

Di-wheel bike that actually works

wired.com

50 pointspghimire21 comments

This thing cannot brake effectively in an emergency, which severely limits its real-world usefulness - it will just roll. The only route out of that, that I can see, is counter-rotating something with a large moment of inertia. If that something is the passenger, it will be extremely uncomfortable; if the mass is e.g. a flywheel, it'll add significantly to overall mass, reduce efficiencies, and add to overall forward momentum.

A long downhill stretch will also completely beat it (if it wants to maintain a constant speed downhill). Any flywheel or other counter-rotation system will have to keep accelerating for as long as the hill continues, or else it will tumble.

A small 3rd wheel for emergency braking would work (it could even be automatically lowered when the chassis has rotated over a certain amount), or you could just drive only at slow speeds. The Segway is a diwheel as well, and people don't worry about that.

The Segway has a relatively large moment of inertia to act as counter-torque when braking - the big human body sticking out the top of it - along with gravity, where the centre of gravity of the inertial mass is well away from the axis of rotation. It also travels slowly (I think the Segway is a more viable product at the speeds it travels at than the device in this article, which IMO really needs to go faster to justify being strapped in etc.).

You can prevent it from rolling by just sticking something out of the cylinder.

So what happens if you are riding at a good speed, and you hit a pothole or other obstacle that bends a wheel? That could make it so the carriage cannot rotate freely inside the wheel, leading to rapid rotation of the passenger. I would not expect a good outcome after that.

I think that is likely the downfall of this kind of vehicle. Yes, with slosh control you can make it work well in normal circumstances, comparable to other vehicles. The failure modes, though, lead to worse accidents than other vehicles, and I don't see any advantages of it in normal circumstances to counter that.

What happens to you on a bicycle when you hit something that bends your wheel? The outcome isn't great then, either.

Exactly. Spinning around a bit sounds a hell of a lot more safe than a face full of asphalt.

Well compared with a motorcycle or motor scooter, it seems like the rider could have a much better protective cage.

Beautiful if impractical. It could easily move as fluidly as a Segway with a bit of computer control and a few sensors.

That looks more like a portable circus ride. That rocking back and forth would get old really quickly.

Haha, I was thinking the same thing...they should put that on the midway! For some reason I also thought of the infamous South Park bike--the one with the interesting seat as a cool looking but maybe just a bit impractical powered 2 wheel transportation device.

So, is this actually a useful vehicle? Or is it just for circus stunts? The trouble with letting young bloods demo a new bike is, they don't ever use it normally.

For instance, can it accelerate without gerbiling?

Yup, with "slosh control" that they built into it.

If you watch the whole video, the answer is: Yes.

I read "slosh control" as avoidance of oscillations from the initial impetus of acceleration (i.e. jerk, the first derivative of acceleration and second derivative of velocity). Acceleration will effectively need to be limited to such a rate where the off-centre weight of the passenger + seat acts as counter-torque. Applying any more torque would cause gerbilling.

That's partially true, but before the 'slosh control' the rider was thrown 90 degrees at start and stop. Afterwards, it was only maybe 30 at most.

Since even a car has some of this effect, I think his 'slosh control' is working pretty well for a prototype.

I'm sure there are ways to take it further, though.

I think it's just being more progressive about the application of acceleration. From a motorbike analogy, it's just being extremely smooth about engaging the clutch while bringing up the revs. If you pop the clutch with high revs on a bike, it too will "gerbil" - i.e. wheelie, or even loop.

The world would be a better place if we all had these.

expect the rate of hitting pedestrians, other vehicles, and animals is really going to go through the roof due to inability to break effectively.

I'm pretty sure I saw one of those on an episode of South Park. It doesn't end well.

one wheels bad, two wheels good?

Reply on news.ycombinator.com