Andy Ruina explains how bicycles balance themselves
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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.
Comments
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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.
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yes exactly. the second I saw the blancing beam upright I knew this guy gets it its really not that difficult.
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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.
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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.
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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?
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Awesome! Puts the theory that we don't understand why bicycles stay up to bed
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Great Video.
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What about inertia, the mass going forward doesn't want to change direction?
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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.
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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.
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this is excellent
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This is very interesting; thank you for posting.
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Does it still track straight without the handlebars?
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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.
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YES! I learned new things today!
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