Uncontrollability of a bricycle (2014) [video]

https://m.youtube.com/watch?v=rNQdSfgJDNM

by gballan • 8 years ago

539 227 8 years ago

m.youtube.com

gballan• 8 years ago

Paper is here: http://ruina.tam.cornell.edu/research/topics/bicycle_mechani...

maaaats4• 8 years ago

What you unconsciously do when turning, is to quickly turn it a bit in the other direction first in order to get the bicycle more to the other side of you, so you have a better balance point for the big turn. Not perfectly explained, sorry.

But try this: Try following a straight marker on the road on your bike. It's very hard. When you start going too much to the right, you will find it impossible to actually nudge the bike back to the left, unless you accept that you have to go further to the right first.

This also happens when driving close to a curb. It feels like it's sucking you in.

Adirael• 8 years ago

That's countersteering [1]. I find it very hard to explain but it's something that most people on a bicycle (at speed) or a motorcycle (again, at speed) do naturally.

[1] https://en.wikipedia.org/wiki/Countersteering

NLips3• 8 years ago

I'd like to especially highlight your 'at speed' point here. It's often claimed that _all_ steering on a bike requires countersteering, but that is false. Countersteering allows rapid change of direction, but if you're going in a straight line, then lean left and gently steer left (or just lean left and allowing the front wheel to steer itself), you _will_ go left, no countersteering required.

baud14725817• 8 years ago

On a bike, even at speed you can initiate a turn by simply leaning on the side.

rplnt3• 8 years ago

It's very easy to try. Go up to speed (20 km/h or so) and press on a handlebar, away from you. You will "turn" to that side even though the handlebars are moving in the opposite direction.

Moodles3• 8 years ago

I'm no physicist, but it seems the intuitive reason countersteering works is because when you turn, e.g. left, your center of mass also moves left because you need to lean left in order to turn. So if you turn left on your own this will move your center of mass left. And if you turn too sharply left your center of mass will be so far out that you will fall over. So turning right very quickly before turning left means that your center of mass suddenly shifts massively right, and therefore you get some extra time turning left while your center of mass is still busy shifting from right to left?

dahart8• 8 years ago

Counter steer happens at all speeds at all times on a two-wheel vehicle, it's just hard to notice at slow speeds, and confusing because you do steer right during the stable lean angle portion of a right turn, as depicted in the first image in that Wikipedia article.

I think counter-steering is misunderstood since people assume it means that if you're turning right then your steering has to be left of center. But counter-steering is referring to the direction of change, the steering delta, not the absolute steering angle. You always steer in the opposite relative direction from what you'd do in a car. This is still true on a bicycle at 1mph.

arnarbi• 8 years ago

Here's how I explained countersteering to myself: To turn left, I need to lean left. The easiest way to lean left is to pull the bottom of the bike, where the wheels touch the ground, to the right.

upofadown3• 8 years ago

Not fan of the term "countersteering". If you changed the mechanical direction that the handlebars rotated the front wheel I doubt anyone would bother to call it "prosteering".

A better way to think about this is that bikes turn by banking. The method of controlling the angle of bank does not map in a simple way to the direction of turn.

skookumchuck4• 8 years ago

I used to ride a bike with no hands. I was still able to countersteer! If I leaned to the left, the bike would lean to the right, the steering wheel would go right, then I could lean to the right into the turn.

lisper• 8 years ago

The best way I've found to experience this is to first learn to ride with no hands. This works best at speed. You actually steer by shifting your weight, but the easiest way to learn is is to grip the seat with your thighs and think about turning the bike by trying to turn the seat.

Once you can stabilize a no-hands ride, try pushing on the handlebar with one finger. You will find the the bike turns in the opposite direction of what you would naively expect. The harder you push, the tighter the turn will be in the "wrong" direction.

lmm5• 8 years ago

Try following a straight marker on the road on your bike. It's very hard. When you start going too much to the right, you will find it impossible to actually nudge the bike back to the left, unless you accept that you have to go further to the right first.

Not true - you just have to shift your weight to the left.

fwdpropaganda4• 8 years ago

Not true - you just have to shift your weight to the left.

Not true - because of conservation of momentum (in the perpendicular direction) if you shift you weight to the left the bicycle will lean to the right and the center of mass will remain unchanged.

It's called countersteering, look it up.

gerbilly2• 8 years ago

I ride bike trials and have gotten good at keeping a straight line.

On a good day I can ride along the top of a handrail.

To keep a bike going straight at low speeds, you shift your weight, and by that I mean you swing your elbows or you knees, not your whole body.

You also can vary the sensitivity of the steering input by controlling how much of your weight is over the front wheel.

You can also use the front brake if you are deviating from your line. It allows you to push against the resistance generated to realign your center of mass.

trzmiel4• 8 years ago

The explanation is that you need to balance out centrifugal force F=mv^2/r.

"Sharp turn" has smaller radius, therefore much larger the force. By turning in the opposite direction first, you're making the turn much less sharp, increasing the radius and thus reducing the force.

eezurr• 8 years ago

I've wondered if following a painted line on a road with your bike is an example of Zen. The more I try to follow the line, the harder it is to stay on it. But when I stop trying/thinking about it, I have no problem staying on that line.

komali27• 8 years ago

And if you don't take a moment to occasionally look up from the line to consider your surroundings, you might crash into an Uber.

tzs• 8 years ago

But try this: Try following a straight marker on the road on your bike. It's very hard. When you start going too much to the right, you will find it impossible to actually nudge the bike back to the left, unless you accept that you have to go further to the right first.

This holds in general for any motion where velocity is a continuous function of time, doesn't it?

Let f(t) be your deviation at time t perpendicular to the desired straight path, with positive to the right and negative to the left.

If you are "going too much to the right" at time t, e.g., f'(t) > 0, then because f' is continuous there must be some interval around t such that f' > 0 at all points in the interval. That means that f is strictly increasing throughout that interval, e.g., "you have to go further to the right first".

russdill• 8 years ago

I've always thought of it like a plane, with the terms adverse yaw and adverse roll applying. The main difference is if your turn is uncoordinated, you fall over. Yaw is controlled via the handlebars. Roll is controlled via balance.

Just turning the handlebars causes adverse roll in the other direction. If you are falling to the left, turning the wheel to the right causes an opposite roll and restores balance.

Turning the handlebars the opposite way momentarily is a great way to start a turn because of the adverse roll that it causes.

kikoreis• 8 years ago

I don't watch Youtube, so it's hard to assess the point being made, but zero gravity implies no normal force and therefore friction. Bicycles need friction for both drive and steering, as I and many others have painfully experienced!

aidos• 8 years ago

Which is why you'll miss the point that "the bicycle is, for balance purposes, effectively in zero gravity".

It's actually a really fascinating clip — though I suspect you're not going to watch it. For anyone else, you can start here to see it in action.

https://youtu.be/rNQdSfgJDNM?t=1m

The original video is only 3 minutes long.

roryhughes• 8 years ago

https://hooktube.com/watch?v=rNQdSfgJDNM (youtube mirror site)

IshKebab3• 8 years ago

Maybe skip commenting on YouTube videos that you refuse to watch? I'm sure there must be a rule here about commenting without rtfa?

Jaruzel• 8 years ago

Actually the rule (guideline) is the inverse:

"Please don't insinuate that someone hasn't read an article. "Did you even read the article? It mentions that" can be shortened to "The article mentions that." "

It's fine to comment without reading/viewing the submission, and I'm sure many of us do :)

Although, I am curious as to why kikoreis doesn't use YouTube?

ageofwant• 8 years ago

Title is misleading.

A 'bricycle' in zero gravity is unsteerable

nicky02• 8 years ago

Surely is shows that a bricycle in earth gravity is unsteerable.

donkeyd• 8 years ago

Actually, I'm pretty sure it'll be unridable too. But you're right, the video isn't about that.

IshKebab3• 8 years ago

A bricycle is a bicycle in zero gravity.

Should be "a bicycle in zero gravity is unsteerable".

sohkamyung• 8 years ago

That clip (and the research paper) is from 2014. Should a year tag be added to the headline?

rurban2• 8 years ago

Well, it IS perfectly ridable, but unsteerable. You need a straight road. Bicycles in space are still usable, as long as you just go ahead, e.g. as the jogger in Kubrick's 2001.

jowsie• 8 years ago

I feel like learning to steer it would be just as possible as learning to ride a bike you steer and pedal in reverse. You just need to get past your muscle memory.

pwinnski• 8 years ago

It doesn't seem like you watched the whole video, where they explain the "why."

larkeith6• 8 years ago

Unless I'm misunderstanding the physics, it would be quite literally impossible, not a matter of learning - any attemp to steer results in the angle of the bike moving in the opposite direction an amount directly proportional to the change in direction, and with gravity being cancelled out by the spring (or in 0G), there is no way to rectify the tilt except by steering back to the original course.

Technically, you can steer temporarily - if steering right by 20° tilts you to 45°, you can ride at 45° (actually, it's possible that a 45° turn would always relate to a 45° tilt - I'd need to think on it), however your allowed directions are determined entirely by your starting direction; if you started pointing South, there would be no possible way to move North, and would likely only be able to operate the bike in the 160° - 200° range, looking at the video.

tantalor• 8 years ago

You need a straight road

You should be able to turn if the road were curved, e.g., a velodrome (https://imgur.com/gallery/YqbXa)

rurban2• 8 years ago

I would still love to try that out by myself. I have the theory that by going extremely slowly you could successfully steer a bit. The problem is only the centrifugal force.

ajuc• 8 years ago

First of all without gravity and weight wheels won't get grip on the road, so no matter if it's a bicycle, tricycle, or a regular car - you can't drive it in 0 gravity, it will just jump away from the road.

IshKebab3• 8 years ago

Yes but ignoring that, or using magnetic wheels, you still can't steer it.

contravariant• 8 years ago

If you have a force pushing it onto the road wouldn't that suffice to make it steerable?

sliken• 8 years ago

Cars emit exhaust, that thrust however small could be used to move the car around. Granted not quickly.

cx_in_the_chat• 8 years ago

Cars require oxygen to operate, there's no oxygen in space.

dcow• 8 years ago

This is not what they mean by zero gravity in the video.

dreen• 8 years ago

A bicycle on the moon on the other hand... now that would be fun

larkeith6• 8 years ago

Or even better, an aerocycle - human-powered flight is almost impossible on Earth, but in 1/6 g you could do some very fun stuff.

IIRC, Arthur C Clarke mentioned races of that sort of vehicle in one of his works, so credit to him.

djsumdog• 8 years ago

In Kim Stanley Robinson Mars trilogy, one of the characters talks about being on one of Mars's moons, and how they had to be careful because a good running start could get you to escape velocity.

bagacrap• 8 years ago

Wouldn't that require a thicker atmosphere?

torrance• 8 years ago

This reminds me of the backwards brain bicycle a bit [1]. I get that the argument they’re making here is one of physics - but failing to ride a counterintuitive bike isn’t something that can just be ‘done’ without a lot of practice!

[1] https://youtu.be/MFzDaBzBlL0

maaaats4• 8 years ago

I have been trying to ride the other way on my fixie[0] lately. I think this is kinda the same. I know what I have to do, but instinctively it all gets wrong. I can kinda override it, but then my reactions are way too delayed. So here's hoping for it will click some day..

[0]: A fixie is a bike with no freewheel. So the pedals follow the back wheel, and the other way. So if I pedal backwards, the bike goes the other way.

kaybe2• 8 years ago

The sport trick cycling has this in a lot of tricks. You might find some advice there if you want.

stevehawk• 8 years ago

huh.. I grew up on a fixie.. I wonder if 20 years later I would just pick it up again.. or 30 years later..

note to self knock up wife.. get child fixie bike.. take bike for self when kid is at school xD I'm sure the experiment will be worth the college debt.

rhinoceraptor• 8 years ago

I can't ride straight backwards, but I can ride backwards in a circle from a trackstand fairly easily.

dancek• 8 years ago

Driving backwards is much more difficult than driving forward because the bike doesn't self correct that way and the steering is quite unstable.

I tried to learn riding backwards last summer, too. Eventually I stopped because I needed the bike for actual riding and my knees preferred having a freewheel. A ridiculously low gear seemed to help, I tried 40x20 (on a 622 with 165mm cranks) for a while.

sumedh• 8 years ago

Back in the day I could easily ride a bicycle without using my hands from the start with just one or two pedal stroke. I believe riding a backwards bicycle would have been easier if you dont use your hands.

skookumchuck4• 8 years ago

That's how to win his $200 prize!

tcfunk• 8 years ago

Reminds me of the time I learned Dvorak.

justadudeama2• 8 years ago

I was going to say the same thing. And when I wen't back to QWERTY, it eventually switched and I could type fast.

samstave2• 8 years ago

Random anecdote/fact; an ex GF in HS was Dvorak's niece... she didn't have very nice things to say about him, just said he was super full of himself. I was really interested in meeting him, but after all the things she had to say about him, I lost interest, and stopped thinking I would be "cool" to switch to dvorak.

skookumchuck4• 8 years ago

The thing is, I don't actually know what the editing commands are on my editor. My fingers know them, though. Sometimes I watch my fingers to see what the command is.

laythea• 8 years ago

Awesome link. Thank you.

rkuykendall-com• 8 years ago

His videos are amazing. I recommend Prince Rupert's Drop among many many others.

https://www.youtube.com/watch?v=xe-f4gokRBs

skookumchuck4• 8 years ago

A long time ago I saw a documentary where a guy wore special glasses that turned everything upside down. He wore them all day except when sleeping, and masked his eyes when sleeping. After a couple weeks, suddenly the world was right side up again.

But taking the headset off, now everything was upside down.

B1FF_PSUVM• 8 years ago

https://en.wikipedia.org/wiki/George_M._Stratton

Interesting dude. Experiments seem to have been about a century ago.

(I thought I'd read that this had been done earlier, but Stratton comes up when looking for "glasses that turned everything upside down" as mentioned)

trumped• 8 years ago

I suspect that this one is more like if you were stuck in space with no propulsion and nothing to throw... so you can't move.

RunningRabbit• 8 years ago

Discovery Channels Mythbusters tested if one could cycle underwater, which failed too.

amelius• 8 years ago

Reminded me of this great Smarter Every Day video:

https://www.youtube.com/watch?v=MFzDaBzBlL0

(both interesting and funny)

rootlocus• 8 years ago

This sounds very similar to the spinning dancer illusion [1] where your brain locks into a configuration where it can see it rotate in one way or the other, but you can't control when or which.

[1] https://en.wikipedia.org/wiki/Spinning_Dancer

loco5niner2• 8 years ago

I can control the direction. It kind of feels similar to 3D stereograms where the image just kind of 'snaps' into place, but in this case, she starts spinning the other direction. Kind of fun and quirky, and you really have to do it on purpose.

michaelmcdonald• 8 years ago

Why is she not wearing any type of safety gear / a helmet?!

jrootabega2• 8 years ago

Yep, your head will crack open from a four foot drop at any speed. And how about a helmet where the strap is actually clipped and tightened?

corobo• 8 years ago

Hope they don't play any kind of sports in that sports room they're testing in then!

recursive2• 8 years ago

Yep, your head will crack open from a four foot drop at any speed.

I highly doubt this. The amount of force required to crack a human head open seems to be much more than what you can generate in 4 feet of free-fall.

stefan_• 8 years ago

Do you wear a helmet to work? Much more dangerous environment as the statistics show.

larkeith6• 8 years ago

More dangerous than riding a bike? I exceedingly doubt that, could you link those statistics?

upofadown3• 8 years ago

Dunno, people probably do actual gymnastics in that gym with no safety equipment at all.

I suspect that there is some sort of cultural thing here where it feels more dangerous because someone is touching a bicycle. In particular it is probably some sort of car culture thing. In such a culture there is a tendency to aggressively ignore the danger of cars. That seems to cause a tendency to overestimate the danger of other transportation modes.

userbinator• 8 years ago

She's in a large room with no other traffic, and not going fast at all. The risk of anything is extremely low.

lifeformed• 8 years ago

My coworkers dad died from falling off a bike in his driveway at zero speed. He had no helmet and hit his head on the pavement and instantly died.

nightcracker• 8 years ago

Fascinating. This is the content I enjoy seeing most.

stinos• 8 years ago

Interesting read as wel, link in first answer etc: basically, the exact physics between why cycling even works, seem yet to be a bit unclear: https://bicycles.stackexchange.com/questions/4656/what-makes...

glaberficken• 8 years ago

This is a very interesting video that debunks some common theories of how the bicycle balancing works, and also proposes some extra insights (although no definitive theory yet)

https://m.youtube.com/watch?v=NcZCzr9ExKk

Also see this one for extra footage of the Gyroless, "trail-less" TMS bicycle that still manages to balance itslef

https://m.youtube.com/watch?v=LbeENKn5kZU

gmueckl• 8 years ago

Can someone explain to me why the authors neglect to mention nutation and precession on a vehicle that consists of non-negligible spinning masses? I don't get it.

Moodles3• 8 years ago

I suspect running will similarly be difficult in a low gravity environment: proper technique in running is basically falling forward and your legs moving to continually prevent it. Without gravity to fall forward, it's probably very hard to move efficiently.

mabbo2• 8 years ago

A few scifi authors have talked about this idea. I forget which book/author[0], but one of remember suggested that children born on the moon had naturally developed what was called a "kangaroo run" that let them move quickly, that immigrants from Earth couldn't copy well at all.

[0] One of you is about to tell me exactly the name and author now, aren't you?

Moodles3• 8 years ago

"kangaroo run" certainly seems like a good description of the running technique the Apollo astronauts used to move around.

cecilpl2• 8 years ago

You are thinking of the Red/Green/Blue Mars series by Kim Stanley Robinson.

THE_PUN_STOPS• 8 years ago

It’s not zero gravity but I recommend this video from an Apollo mission:

https://m.youtube.com/watch?v=HKdwcLytloU

monkeynotes• 8 years ago

Really highlights how you have to throw a bike slightly into the opposite direction[0] to a turn in order to get it to turn. When she tries to do this in the zero-gravity mode the bike just rolls over in the opposite direction without being able to kick the front wheel into the turn.

[0] https://www.youtube.com/watch?v=llRkf1fnNDM

tlb• 8 years ago

I suspect you can ride it with a hack: either raise your center of gravity (to get into bike mode) or lower it (to get into trike mode).

Retric2• 8 years ago

Or simply turn at lower speeds/make less sharp turns as they still had some control. It would simply have made a less interesting video.

Similarly with the zero gee pendulum keep going far enough and the end would move to the left as it's only so long. Then reverse the process to move the pendulum to an arbitrary position. Alternatively, use vastly slower motions and the friction with the arm will counteract tiny momentum changes.

grayhatter• 8 years ago

Am I the only one who thought throughout; "I could turn that thing, just drag your foot across the outer most wheel in the direction you want to turn." Let the friction, and unequal spinning speeds to the work.

(The wheels can't be locked to each other, otherwise that would also cause the bricycle to be unable to turn, thus invalidating the whole experiment.)

PeterisP• 8 years ago

The wheels certainly can be locked to each other, that's how standard kid tricycles work - all it means that in turns some slipping/friction is inevitable.

Uncontrollability of a bricycle (2014) [video]

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