Andy Ruina explains how bicycles balance themselves
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- Опубликовано: 30 сен 2024
- Most bicycles will stay upright as long as they're moving, even without a rider. Andy Ruina, Cornell professor of mechanics, describes recent research showing that the accepted wisdom about how bicycles balance themselves doesn't tell the whole story.
I was working and, I'm not sure why it popped into my head, but I realised I didn't know how a bicycle stayed upright. This video was actually a really good explainer. Also good to know that scientists aren't actually 100% certain on the effects that make it happen. What a universe!
Inertia, friction, self-steering due to leaning, are all at play here. From watching the bike I believe that the self-steering is the the largest contributor to keeping the bike upright. What the video does not show is the bike being pushed in reverse, the self steering effect does not work in that direction and the other factors aren't enough to keep it upright.
It doesn't self-steer in reverse because self-steering requires asymmetrical weight distribution of the steering wheel. Leaning the bike turns the wheel correctly when going forward because the weight is forward of the pivot point. This would be reversed when going backward.
I think this professor replaces explaining with giving the facts. What he's doing is giving us facts, rather than explaining why those facts occur.
After learning from other videos I think of bicycles as analogue computers.
I figured this out in dynamics class, it has to do with the "instantaneous centre of rotation ((IC))", the IC of a bicycle tire or any free rolling wheel is where the wheel is contacting the ground. I think about it in this way: The axle is constantly falling around the IC, the perimeter of the wheel is constantly catching itself and supporting the axle and the load attached to it. This explanation also explains how a unicycle stays standing.
I really want to make a video to help explain this.
sorta like walking.
This is very interesting; thank you for posting.
Angular momentum was deffinately the answer to the wrong question. Single track vehicles do not steer at the front. When a bicycle tips the front wheel complies with the new direction. A slip angle at the rear tire creates a turning moment about the verticle axis taking the center of mass over the wheels. Trail is what aligns a bicycle front wheel. Your scooter seems to have a mass forward of the front frame axis that also works but I wouldn't trust it at speed.
Lmfao notice the lack of cables , try doing with your bike and it will crash lol. Gravity "fooling people for 300 years" hey what is the formula for other Apples still on the tree lmfao.
Great Video.
Think the self correcting steering is the key. Wheel wanders , say left, increased friction at the contact point (side of tire forward) creates more drag on the wheel forcing the corrective steering and bike goes right-and-up.
In the automotive world when the steering axis hits in front of the vertical axis of the turning wheel (like on a typical bike) we call this “positive caster”. Positive caster causes self-alignment torque making your car steer straight ahead when you let go of the steering wheel while you’re turning - not recommended BTW. There are two main reasons caster causes self-alignment torque. When you turn car wheels the front axle/car actually lifts up very slightly. Then if you let go of the turned steering wheel the front wheels want to “fall back down” which is simply straight ahead. The second part of the self-alignment torque phenomenon and probably the greatest contributor is that a turned wheel on a bike or car is like a board with a front pivot being turned broadside into the wind. When a bike’s front wheel is turned it’s line of direction is no longer aligned with the rear wheel’s line of direction. This causes the outside edge of the turned wheel just behind it’s vertical axis to undergo a sideways force from the now unparalleled path direction of the rear wheel. Just like a wind vane always aligns with the wind’s direction a turned wheel on a bike wants to align with the direction of the rear wheel. Examine a new bike tire after undergoing some turns you’ll see cross wise scrubbing marks across its tread thus indicating the self-aligning torque phenomenon. Tires are meant to roll forward not sideways. If you truly want to see how a bike self-aligns place a bike on a tread mill with the wheel turned. Once you turn the treadmill on you’ll see the treadmill torque the front turned wheel back into alignment with rear wheel. As a BMX rider 40 plus years ago we knew if we turned our handle bars just past 90 degrees the self-aligning torque of the moving earth beneath our tires would push our handle bars to a complete reverse orientation.
Friction of the inner side of the tire seems like it would have a huge impact. If the bike leans right the caster effect would cause the wheel to fall faster causing more friction with more of the tire touching the ground causing the wheel to turn that direction.
7:21 Exactly my thoughts gravity is the input for stability
Awesome! Puts the theory that we don't understand why bicycles stay up to bed
I like this video because I have it figured out and he doesn't..
My guess is that has a lot to do with the inertia of a mass. If the bike steers, there's the inertia effect that will force the _upper_ mass of the bike to maintain its direction.
Since the inertia is correlated with the speed, it has to be a minimal speed where the inertia can defeat the force required to steer the front wheel. If the inertia is strong enough to steer the wheel, it will do so, making the bike to maintain its straight line so that the equilibrium is maintained.
In this case, it's the centrifugal force that acts as an inertia force and this is described by Newton's First Law: www.physicsclassroom.com/class/newtlaws/Lesson-1/Newton-s-First-Law
When a bike is in motion and leans, it will start steering. Immediately, the centrifugal force will push from the inner side. The bikes are constructed such that if you lean a bike, it automatically steers and if you keep it at perfect vertical position, it maintains a straight course.
Again, there has to be a minimal speed at which the centrifugal force it strong enough to defeat the component of the gravity that is decomposed on the perpendicular plane of the bike when the bike leans.
If you try the same experiment, but where the mass in concentrated at a lower point, under the steering point, let's say in the paddles, you will not get the same result.
Exactly! That is why there is almost no difference between a person riding a razor scooter or a bicycle to keep balance. It is surprising how little forward motion is needed to keep balanced on a razor scooter on such tiny wheels. Inertia is the biggest factor IMHO.
This makes me so sad to watch. I wish I had better inspiration in high school. Instead, the school was themed around sporting nonsense and didn't offer much in the science departments. Couple that with lazy parents who lived too far from the city to get me involved with extracurricular activities. Goddamnit this looks so fun to learn about. How does one restart life at 26?
Restart life at 26? You have just started your life. I would suggest reading as much as you can about the subjects you are interested in. Check out all of the amazing things people have self taught themselves and show others on the internet. Join technology clubs if this is your passion. Others would love to share their knowledge. And once you find what you want to do, get a formal education. Being self taught tends to leave gaps in what you know. A formal education is systematic and will take you on the full journey. Good luck, and never stop trying to learn more.
+Richard Potassium For one sir I would stop trying to compare yourself towards others gifts or talents, that for sure will make you miserable, and it is possible that you are not wired for one thing and good at something else, for example possibly bicycle physics is not your dharma, but don't let that keep you from enjoying other peoples knowledge and sharing in the diversity. We all have some special gift or talent that we can do, and we have a very special way of doing it, that is better than anyone that is alive, and everyone has that, because the universe is complete in it's totality, their are no spare parts. Also I would forget your age and chasing the clock, and follow what really makes you happy and know that nothing can ever be lost. "Good Luck On The Journey"
Van Gogh started painting at age of 27
FWIW, this is a college professor, not high school. However, I can relate to this comment SO much. I went to a very small school, with HORRIBLE science teachers.
YES! I learned new things today!
this is excellent
What about inertia, the mass going forward doesn't want to change direction?
Hmm, interesting idea. As I understand it, a bicycle steers to keep its balance so naturally it must constantly make slight changes in direction. Also, the bike with the fixed handlebars should have the same inertia as the un-tied version, but they do not behave the same way. Does that make sense?
yes exactly. the second I saw the blancing beam upright I knew this guy gets it its really not that difficult.
I appreciate the effort you put into this video. You deserve more views and likes than what you got.
Thanks for creating and uploading this video. Since we have E-bikes aren't self-stabilizing bikes the next step to minimize injuries from falling down. Or maybe people that are prone to falling down should be riding tricycles (back to their childhood!).
Totaly nonsens. The second wheel didnt neutralize the one gyro effect, it makes double. (!!) For shure. = If you turn two toy spin tops side by side in different directions, they NEVER fall down.
Its really very simple. As stated its not to do with the castor or gyroscope effects. The front wheel as a whole, is a mass forward of the rake angle. The bike leans left, the mass of the wheel also falls towards the left correcting for the lean. As a point of interest, if you push the bicycle fast enough, it falls over due to the gyroscopic effect of the wheel not allowing the wheel to fall into the lean. As an experiment, if you make a bicycle with a zero rake angle ( vertical ) it won't balance. However if you were to add a small mass forward of the vertical axis of the wheel it would restore the dynamics of a normal bicycle and steer itself. At least that's my theory 😉.
The rake of the fork has a lot to do with how stable it is, the rake on that fork is smooth and curving which gives a smoother ride, which means it is more stable, if that fork was completely straight it would be much twitchier and unstable. What this means is that the larger the rake the more stability it will have. think of it as a rutter in water, the longer it is (larger rake) the more speed it will have when adjusting to currents pushing sideways on said rutter, and vice versa with shorter rutters (lower rake). What this means is that without rake on a fork the bicycle would fall. Also, look at how trackstands work, this is when a rider is on the bike completely but is barely moving, he/she adjusts it by moving the bike back and forth while the front wheel is turned. Just a thought.
Actually, it's all linked to trail, and less rake (less curve to the fork) means more trail, which means more stability.
calfeedesign.com/tech-papers/geometry-of-bike-handling/