Comment by mk_stjames | Hacker News Reader

Comment by mk_stjames | Hacker News Reader

It seems like it should say "It takes Two Neurons to Steer an already moving Bicycle".

The simulation is so simplified that I see no terms for the control of pedaling. Riding a real bicycle isn't just about steering and leaning a bit. You need to propel the bicycle a certain amount.

The paper buries this in the following:

  >Although the two-neuron network controller works well for a range of speeds, one thing the controller does not do is to try to dampen the instabilities that can arise when riding too slowly or in too sharp of a turn. (This would probably require a third neuron that isdedicated to this task.)

They say 'damping instabilities' but it is way more than that, because as anyone who has learned to ride a bike knows, the hard part is getting started at that zero point of forward velocity - how to apply torque to the crank at the same time as compensating with the steering to balance at such low momentum. It's not a trivial solution to 'damping instabilities' when getting going in the first place is the most difficult part (as any 5 year old child will demonstrate).

> Riding a real bicycle isn't just about steering and leaning a bit. You need to propel the bicycle a certain amount.

My impression from my vague recollection of learning to ride a bike (and the scattered times over the years I've seen others try) is that a pretty huge part of the battle is just learning to trust that going faster is literally how to avoid falling over, when the natural inclination of someone worried about that is to slow down.

>None of them made signiﬁcant use of the speed—they all managed to control the bicycleusing just the handlebars.

I think is where it refers to it.

Two to steer is still impressive. If we added in balance and pedaling/braking I wonder what the count would raise to then.

I'm don't think it's possible to start a bike by pedalling with zero forward momentum. You will fall over. You need to kick off - start pedalling with the bike already moving forward. So you're right, and a third neuron is certainly not sufficient. You need legs, too, and arms, and a torso, and motor neurons, and respiration/metabolism. Clearly, the paper has no practical application; if you need to ride a bike, it's far cheaper to hire a human to do it.

You absolutely can start a bike by pedaling with no forward momentum. You can see it when someone starts pedaling again after a track stand.

So now we need enough neurons to do a track stand too?? I don't have the neurons for that...

https://www.youtube.com/shorts/zwBW2Akw1P0

Possible, but more complex than most appreciate. Pushing a pedal down shifts the rider's center of gravity over that pedal, requiring the bike to lean in the opposite direction to maintain a straight line. This done by the rider counter-steering to command that angle. Watch in the video how the front wheel and lean angle alternates left-right in time with the pedal pushes. Once at speed, the gyroscopic forces of the front wheel mean the rider doesn't need as much lean angle, so the wobbles get less and less. Compare an accelerating motorcycle where the rider doesn't shift weight and therefore doesn't need to wobble the front tire.

If you orient the pedal so it's at about 9 o'clock, and hop on, the downforce will produce sufficient forward motion for steerage. Of course you can also push off with your other foot, but it's not essential. But that's another neuron. ;-)

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