Countersteering Confession

[thealmightytaco]

to test this theory, ride your bike on a straight (closed) road at say, 80k. pull on the right handlebar, or push on the left one (invokes the same effect to the front wheel). do NOTHING else. do not shift any weight at all.

report back what happens to the bike.

The wheels move out from under the bike to the side while the centre of gravity of the bike stays put, hence the bike topples and I turn. I tested that out last year when I first joined this site. But I'll report on the bmx wheel test tomorrow...

[Skyryder]

Countersteering isn't only due to gyroscopic effect. Compare a bike to balancing a pole on your hand (eg a baseball bat or a broom). If you want to move the pole to the left, you have to move your hand quickly to the right to get it to lean to the left, then you move your hand to the left to move the pole. To prevent it from falling over, you have to move your hand quicker than the pole, so that it goes back to a bit past vertical (leaning right slightly), and you can then slow it down and balance it at vertical again.

Same sort of thing with a bike, except that it's the front wheel's contact patch that moves from side to side (the rear wheel follows) and the bike leans.



Have you ever tried turning with your hands off the bars? The steering geometry on most (all?) bikes is set up so that if you shift your weight, the bike will turn. I remember someone posting here about someone on a scooter riding it down a hill (with them as pillion) without hands, just shifting their weight.
On my bike I occasionally mess around seeing how I can corner with my hands off the bars (only just off, ready to grab them...). Have to do it going downhill though because otherwise the bike slows down too much.

The balancing pole thing is a pretty good way of describing the principle of counter steering. The difference being the verticle (pole) and horozontal (bike) Yes you can change direction just by shifting weight, but this is not counter steering. The change in direction is caused by off centering weight from axis and the gyoscopic force is regaining equilibreum. If the weight is off set continously from the axis there will be a continouse turn and the bike will not run in a straight line until the weight is centered inline with the bikes axis.

Someone mentioned that counter steering can be directly controlled (my words). Who ever this was I stand corrected from my earlier position that countersteering is an automatic response in cornering. This comes down to a learned cornering technique in which weight shifting and agressive steering comes into play.

I just look at where I'm going and god willing that's where I go. That's my technical advice on counter steering.

Skyryder

[terbang]

I don't think so. AFAIK the swashplate adjusts the angle of attack of the blades in alignment with the helicopter, not 90° before.

Umm wrong there mate it does. Fixed wing are not the only things I can fly. It does it 90deg before the desired reaction

[marty]

The wheels move out from under the bike to the side while the centre of gravity of the bike stays put, hence the bike topples and I turn. I tested that out last year when I first joined this site. But I'll report on the bmx wheel test tomorrow...

when the bike leans, in the absence of any other inputs (eg hands off the bars), the front wheel turns initially due to the rake of the headset, and the movement of the centre of gravity off the centreline - the c of g is acting (straight down) to one side, and the mass will want to turn towards it. as the wheel turns, it is having an input to it via the forks and subsequently the axle, and precession will begin to take place. the greater the rake, the greater the rate of turn. (with extreme rake the rake input will be much stronger than presession input) if you continue to input the lean without touching the bars, the turn radius will become tighter and tighter. if you halt the lean (you will have to actually lean back to overcome/equal precession, the turn rate will stabilise.

[terbang]

Tomorrow I'm going to pull a wheel off the bmx and see what happens. The wheel needs to roll over sideways when you pull one end of the axle back toward yourself for gyroscopic effect to aid in turning the bike...

Didn't you do that one in your physics lessons at school. Believe me it will behave 90 deg to what you think it will.
I'm with Marty on this one. It is only Gyroscopic precession that rolls or leans the bike when countersteering.

[terbang]

Ok if the bike had flat profile wheels or rollers like a road roller (or a cage for that matter) rather than profiled motorcycle tyres then how would it turn..?

[marty]

The wheel is never fixed, and as you pull on the right the wheel steers out to the right, while the bikes COG stays put, so the bike falls over. I'm still with erik.

Tomorrow I'm going to pull a wheel off the bmx and see what happens. The wheel needs to roll over sideways when you pull one end of the axle back toward yourself for gyroscopic effect to aid in turning the bike...

the bottom of the wheel is essentially running in a fixed plane on the road - it doesn't slide sideways (unless you're in the shit).

hold the bmx wheel in 2 hands vertically (although a vertical gyroscope has the axis in the vertical, and actually spins in the horizontal plane) in front of you, and i guarantee the top of the wheel will move to the left, when you pull the axle rearwards, which is the same as inputting to the wheel (the rotating mass) with a push from the right (by your chest)

[M1CRO:Me]

They don't.. Helicopters are simply a machine thats trying to crash, and its only the faith of the pilot that keeps them in the air.

sounds like an advocate for quantum mechanics

[M1CRO:Me]

the bottom of the wheel is essentially running in a fixed plane on the road - it doesn't slide sideways (unless you're in the shit).

hold the bmx wheel in 2 hands vertically (although a vertical gyroscope has the axis in the vertical, and actually spins in the horizontal plane) in front of you, and i guarantee the top of the wheel will move to the left, when you pull the axle rearwards, which is the same as inputting to the wheel (the rotating mass) with a push from the right (by your chest)

When you try this, consider this concept
By the wheel turning, your changing the circumference of the turning front wheel. Grab a paper cup (one where the base has a different diameter than the end you drink from), and try rolling it on the ground.. Ask the question, why it doesnt go in a straight line? and you will start to get some better insight into it... Otherwise, come to the RRRS course!!

[laRIKin]

Counter steering does not so much turns the bike around the corner.
It makes the bike lean over in to the corner so you can go around it.
It is used more to start the turn and finish a turn.
You only use it to change the (lean) angle of the bike.

I think that you use the gyroscopic effect of the front wheel to push against (a bit like a wall or a lever) to push the bike down in to a corner or to get the bike back up to vertical.

Other wise when you have your knee down, it would be impossible to counterbalance the bike up right again as you are way passed the point of balance.
That is unless you can lean your body passed the vertical point to get the bike to stand up again. (I would like to see that)

When you just lean a bike in to a corner (with out hands off the bars) the wheel turns the the way you want to go, but you will not be leaning the bike over as much, but will still go around the corner, but not as fast.
Because if you go passed the point of no return you will not be-able to straighten up the bike again.

[Jantar]

When you try this, consider this concept
By the wheel turning, your changing the circumference of the turning front wheel. Grab a paper cup (one where the base has a different diameter than the end you drink from), and try rolling it on the ground.. Ask the question, why it doesnt go in a straight line? and you will start to get some better insight into it... Otherwise, come to the RRRS course!!

In order for the cup (or any decreasing radius surface) to remain in contact with the floor, there must be sufficient force to keep the surface in contact with the ground (ie to overcome the gyroscopic effect.)

Watch what happens at that strange sport called bowls. The bowler can get the bowl to turn in without counter sterring because of two seperate effects. First there is a weight bias which causes the bowl to want to lean in the direction of the turn, (like leaning a bike) then there is the shape of the bowl which causes the surface to have a different profile as it leans more (like your paper cup). Counter steering helps with the weight transfer, and tyre geometry helps with the right profile.

[laRIKin]

This is the short version.

http://www.vf750fd.com/blurbs/counter.html

Countersteering works by moving the wheels out from under the bike.

Try this experiment: Balance a broom upside down on your finger. With a few minutes' practice you can keep it upright pretty effectively. Once it's reasonably stable, try moving it to the left. You'll quickly find that for the broom to move to the left, it must be leaning to the left. You do this by moving your finger to the *right*, which moves the end of the broom handle out from under the center of mass of the broom. This is exactly the same mechanism as countersteering. Your bike has some inherent stability when it's moving, which will tend to keep it upright. When you want to turn, you must lean the bike.

Countersteering moves the wheels out from under the center of mass of the bike, causing it to lean in the opposite direction. Gyroscopic precession has little bearing on countersteering. It does have a significant effect on the feel of the bike, since it tends to keep the front wheel from being turned. However, consider this: If gyroscopic precession were the primary driving force in leaning the bike, one would expect that bikes with large front wheels would turn in very quickly. As it turns out, though, this is not the case, and in fact is just the opposite of what is seen in actual practice.

Once the bike is leaned over, the trail of the front end causes the front wheel to turn into the curve, and the round profile of the tires causes the bike to experience camber thrust steering (similar to rolling a cone, which travels in a curved path), which cause the bike to go around the curve. When it's time to straighten out, countersteering is again used, this time to move the wheels back underneath the center of mass of the bike and cause it to stand up.

[erik]

...and yes, the input to a swashplate on a helicopter rotor is 90deg to the desired action....

Umm wrong there mate it does. Fixed wing are not the only things I can fly. It does it 90deg before the desired reaction

Damn, you're right about the swashplate.
http://science.howstuffworks.com/helicopter6.htm
http://en.wikipedia.org/wiki/Precession

It'd be nice to be right for a change, but I'd rather learn where I'm wrong than continue to be wrong, so cheers.


I still think I'm right about countersteering though...

The balancing pole thing is a pretty good way of describing the principle of counter steering. The difference being the verticle (pole) and horozontal (bike)

The bike isn't horizontal, it's like a vertical pole except because it's got two wheels, it can only fall over sideways, not forwards and backwards as well (like a pole would).

the bottom of the wheel is essentially running in a fixed plane on the road - it doesn't slide sideways (unless you're in the shit).

It doesn't have to slide sideways, it tracks sideways when you turn the bars due to forward motion of the bike. The same way that a car's front wheels track right when they turn right.

I found this article:
http://en.wikipedia.org/wiki/Bicycle...cycle_dynamics

which I haven't seen before and haven't fully read now, I'm a bit tired and feel like I've been staring at the screen too much. But it seems to support the idea that motorcycle (and bicycle) steering isn't exclusively due to gyroscopic precession.
Here's one quote from the article:
"If the steering of a bike is locked, it becomes virtually impossible to ride, but if the gyroscopic effect of rotating bike wheels is cancelled by adding counter-rotating wheels, it can still be easily ridden."


Cheers for the above post, lemans, that explains it clearly

[marty]

how does rotating a wheel change its circumference? the only thing that changes is its static mass becomes dynamic. it is that dynamic rotating mass that involes the gyroscopic precession. GP does not apply to a wheel at rest.

the paper cup turns because it has circles of different diameter, and it will always turn towards the smaller diameter. it has nothing to do with gyroscopic precession.

what's an rsss course?

here's a question for you. get a roll of 2" masking tape. roll it quite quickly on a smooth concrete floor. 1 - it won't roll in a straight line for long. 2 - when it starts to turn, it rolls on the OUTSIDE edge - for instance, if it's turning left, it will be rolling on the right edge. why is that?

[M1CRO:Me]

...what's an rsss course?...

Read about it here...