[themagician]

It's possible that the board just fails for any number of reasons.

I had a Boosted Board fail on me once. No idea why. It just powered off randomly while I was riding. Wasn't going downhill, wasn't full battery, wasn't a depleted battery. It was a bit scary to suddenly feel the power go out, but I was able to safely come to a stop. I was probably going about 15 MPH. I never figured out what happened. It turned right back on. This was the first time the board gave me pause. I kept riding for a few months until I did actually get hurt—100% on my own stupidity. I tried to go over some train tracks while leaning too much on the front trucks and was going fast, but not quite fast enough to cruise over them, and the wheels properly got stuck in the tracks, so I got to experience the fun of flying. Fortunately I was not critical injured, just extreme bruising. Helmet 100% saved my life though.

This is the same kind of thing that can happen with a OneWheel—only no user error is needed for it to happen, merely a power failure. OneWheel either needs an integrated solution that allows you to roll out in the event of a power failure, or some kind of redundancy to ensure the probability of a power failure is effectively zero. Anything less leads to (preventable) death.

[rainsurf]

Sure, anything can fail.

For these kind of "catastrophic failures" I think the important thing is the probability of the event.

I am not aware of evidence showing a Onewheel can fail at an unacceptable rate.

[themagician]

The difference is that when most things fail (something that will happen), they do not result in instant deceleration. When your iPhone experiences a power failure it usually just doesn't turn back on. If a car experiences a power failure the brakes still work. Even if the brakes DO fail, you can still at least try to come to a safe stop—and it's possible you can.

When the power fails on a OneWheel there is almost no possibility of a safe stop. You are getting launched.

[rainsurf]

Yes, agree with you both - probability * severity. The severity is high (unless you know how to run off the board - that lowers the severity quite a bit). The probability is unfortunately unknown.

[chabons]

I think the severity of the event is also important. A Onewheel requires power for stability (it's an inverse pendulum), and as a result does not fail-safe. An occasional motor failure on an e-bike would be a non-event, as it fails to a safe state. An occasional brake failure would be significant.