OT How does a bicycle turn right when leaned right?

[John Doe]

Have you seen Razor's new Ripstik? The front end is the opposite of a
bicycle front end. The caster is leaned backwards. Search Youtube for
Ripstik demonstrations.

I understand that if you lean a caster forwards or backwards, the
wheel will try to keep itself pointed straight ahead. But I don't
understand what happens when you lean to the right (or left). I've
read that the reason a bicycle wheel turns to the right (when leaned
right) is to help put the bicycle back in its lowest position.

But, getting to the point... When I put a rear caster on a Ripstik
that is leaning forwards like a bicycle caster does, when the Ripstik
is leaned to the right, that back wheel is going to turn to the left.
Anybody disagree?

Thanks.

 

[Martin Riddle]

Have you seen Razor's new Ripstik? The front end is the opposite of a
bicycle front end. The caster is leaned backwards. Search Youtube for
Ripstik demonstrations.

I understand that if you lean a caster forwards or backwards, the
wheel will try to keep itself pointed straight ahead. But I don't
understand what happens when you lean to the right (or left). I've
read that the reason a bicycle wheel turns to the right (when leaned
right) is to help put the bicycle back in its lowest position.

But, getting to the point... When I put a rear caster on a Ripstik
that is leaning forwards like a bicycle caster does, when the Ripstik
is leaned to the right, that back wheel is going to turn to the left.
Anybody disagree?

Thanks.

Post this question in rec.bicycles.tech.
Theres a few guys over there that will understand the mechanics of
this.

Cheers

 

[Syd Rumpo]

On 18/08/2013 02:38, John Doe wrote:

,snipped>

I've
read that the reason a bicycle wheel turns to the right (when leaned
right) is to help put the bicycle back in its lowest position.

When a bicycle wheel is upright, the important part, the contact patch,
forms a rolling cylinder. When the wheel is leant to the right, this
becomes a slice of a cone and so rolls in a circle.

IOW, when leant to the right, the circumference of the left hand side of
the tyre rubber on the contact patch is greater than the right hand side.

This is particularly obvious on motorcycle tyres, which have a more or
less circular cross section.

Cheers

 

[DecadentLinuxUserNumeroUno]

On 18/08/2013 02:38, John Doe wrote:

,snipped>



When a bicycle wheel is upright, the important part, the contact patch,
forms a rolling cylinder. When the wheel is leant to the right, this
becomes a slice of a cone and so rolls in a circle.

IOW, when leant to the right, the circumference of the left hand side of
the tyre rubber on the contact patch is greater than the right hand side.

This is particularly obvious on motorcycle tyres, which have a more or
less circular cross section.

Cheers

It happens because of the rake angle of the front forks.

 

[Phil Hobbs]

It happens because of the rake angle of the front forks.

There was a Scientific American article--I think it was a guest Amateur
Scientist--about trying to make an unrideable bicycle. Reversing the
caster on the front forks did it.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510 USA
+1 845 480 2058

hobbs at electrooptical dot net
http://electrooptical.net

 

[Harry Dellamano]

I am surprised that no one has mentioned that the plant (bike) has a
"zero" in it's right half plane control loop.
Robots riding bikes may prove difficult.

Cheers, Harry

 

[John Doe]

Maybe referring to "The stability of the bicycle" April 1970 by David
Jones.

I agree with that stuff. It's not some cone shape, but it's also not
just the caster angle. If you roll a hula hoop, it will turn in the
direction that it leans, just like a bicycle front wheel. And the
faster you go, the more stable it is.

There are at least two forces at work, the caster angle and
gyroscopics. If you lean the caster to the front or to the back, the
wheel will tend to stay straight. But when you lean, the caster
effect, because of gravity, would turn the wheel in the opposite
direction. There just isn't a whole lot of castor effect on a bicycle
front wheel. However, there is lots of castor effect and little
gyroscopic effect on a Razor Ripstik.

Standing still, if you lean a bicycle to the right, the front wheel
will turn to the left.

 

[Syd Rumpo]

Maybe referring to "The stability of the bicycle" April 1970 by David
Jones.

I agree with that stuff. It's not some cone shape, but it's also not
just the caster angle. If you roll a hula hoop, it will turn in the
direction that it leans, just like a bicycle front wheel. And the
faster you go, the more stable it is.

<snip>

If you roll a hula hoop or a bicycle wheel slowly enough, any gyroscopic
effect becomes insignificant. It will turn right if it's leaning right
because of the conical rotating contact patch.

You can do this by holding a bicycle wheel at an angle to the vertical
while pushing it forward as slowly as you wish. The rolling cone thus
formed will naturally describe an arc. Try it.

Basic things first, then gyroscopes, rake and trail.

Cheers

 

[John Doe]

John Doe wrote:

<snip>

If you roll a hula hoop or a bicycle wheel slowly enough, any
gyroscopic effect becomes insignificant. It will turn right if
it's leaning right

In my experience it just falls over.

because of the conical rotating contact patch.

How does a hard plastic hula hoop deform into a conical shape?

You can do this by holding a bicycle wheel at an angle to the
vertical while pushing it forward as slowly as you wish. The
rolling cone thus formed will naturally describe an arc. Try
it.

The conical deformation is a theory in inline skating, too.

I have tried it, in fact. I'm dying to make an inline skateboard.
Many months ago, I tested the conical theory. I put five wheels
inline under a board. Even using easily deformed inline skate
wheels, the thing simply did not turn by leaning. Even when leaning
and at the same time putting my weight to the back like we do when
skating.

The likely real method that an inline skate turns is because the
skater generates rotating force. Leaning back puts the pressure on
fewer wheels, making the rotating axis shorter. Also, since the
wheels are pliable, the turning force applied causes the skate to
turn as the wheels grip and regrip the pavement while moving. That
and some sliding.

 

[josephkk]

I am surprised that no one has mentioned that the plant (bike) has a
"zero" in it's right half plane control loop.
Robots riding bikes may prove difficult.

Cheers, Harry

I do not believe that such a pole exists, The bicycle riding robots
already exist. Just youtube for it.

?-)

 

[Syd Rumpo]

In my experience it just falls over.

No, I mean you are wheeling it slowly, holding its axle at an angle from
the horizontal while you push it forwards. It will describe an arc
unless you force it not to, in which case the rubber will have to slip.

How does a hard plastic hula hoop deform into a conical shape?

The contact patch must have a non-zero size. If it's leaning, one side
will have a greater diameter than the other.

Think of a ball on an axle. If the axle is held at other than
horizontal, as you push the ball forwards it will turn left or right if
not physically constrained. There was in fact a wheelbarrow based on
this (the 'Ballbarrow', I think, invented by Dyson). It doesn't matter
how little downward force (weight) you apply, the geometry will make it
turn.

The conical deformation is a theory in inline skating, too.

It's more than a theory. The diameter of a bicycle tyre is greatest
around its centre line, the diameter decreases as you move away from the
centre line. If the wheel is not vertical then its contact patch is
essentially conical.

I have tried it, in fact. I'm dying to make an inline skateboard.
Many months ago, I tested the conical theory. I put five wheels
inline under a board. Even using easily deformed inline skate
wheels, the thing simply did not turn by leaning. Even when leaning
and at the same time putting my weight to the back like we do when
skating.

I don't know much about skateboards, but if the wheels were fixed in a
line, say like a bike with the steering welded straight, then canting
them over would have the effect of losing grip and skidding to some
extent. The wheels would want to describe an arc, but would be
physically constrained from so doing.

The likely real method that an inline skate turns is because the
skater generates rotating force. Leaning back puts the pressure on
fewer wheels, making the rotating axis shorter. Also, since the
wheels are pliable, the turning force applied causes the skate to
turn as the wheels grip and regrip the pavement while moving. That
and some sliding.

Dunno, but as I said, simple things first. Set a bike wheel rolling
along on its own and it will turn one way or t'other depending on which
way it starts leaning, and not because of rake, trail or gyroscopes, but
because of geometry. As it slows down and leans more, so the radius of
the arc it's following decreases until grip is lost.

Cars screech as they corner because their essentially cylindrical tyres
are being forced around an arc and grip can't be maintained, even at low
speeds. Bikes lean into corners and don't normally screech because
their circular cross-section tyres form conical contact patches
appropriate to the radius of the turn.

Cheers

 

[Harry Dellamano]

I do not believe that such a pole exists, The bicycle riding robots
already exist. Just youtube for it.

?-)

A RHP Zero does not prove insurmountable, just some heads up and maybe
lower loop bandwidth.
A little Goggling yielded this;
http://control.lth.se/media/Staff/KarlJohanAstrom/Lectures/BikeTalkKTH2006.pdf I also have a garage door with a RHPZ in its control loop, it must bepulled first before pushed open. That non intuitive $hit is all over the place. Cheers, Harry

 

[John Doe]

I don't know of any studies that prove the conical theory. And as
I said, my own experiment proved it wrong. And there's no way
you're going to get a conical contact surface out of a rolling
hard plastic hula hoop that turns in the direction it is leaning.
And, again, the faster a cycle travels, the more stable it is.
That's obviously due to gyroscopics. And anybody who has tried to
lean a gyroscop should notice that it turns.

Good luck with your theory, here on Earth.

--

 

[Syd Rumpo]

I don't know of any studies that prove the conical theory. And as
I said, my own experiment proved it wrong. And there's no way
you're going to get a conical contact surface out of a rolling
hard plastic hula hoop that turns in the direction it is leaning.
And, again, the faster a cycle travels, the more stable it is.
That's obviously due to gyroscopics. And anybody who has tried to
lean a gyroscop should notice that it turns.

Good luck with your theory, here on Earth.

Just geometry and observable reality. A hard plastic hula hoop on a
hard floor starts to turn but very quickly loses grip as the sideways
force overcomes friction and slips on to its side. A soft, more easily
deformed rubber tyre does much better and rolls around in ever
decreasing circles till it loses grip.

Experiments with counter-rotating wheels on bicycles have demonstrated
that the gyroscopic effect is small. You could look that up. The
Ballbarrow example proves steering by deformation of the wheel (ball)
into a cone. You could look that up too.

It's not magic. A flat surface - the contact patch - describing an arc
must have a conical shape unless it is being forced to slip.

Cheers

 

[DecadentLinuxUserNumeroUno]

Just geometry and observable reality. A hard plastic hula hoop on a
hard floor starts to turn but very quickly loses grip as the sideways
force overcomes friction and slips on to its side. A soft, more easily
deformed rubber tyre does much better and rolls around in ever
decreasing circles till it loses grip.

Experiments with counter-rotating wheels on bicycles have demonstrated
that the gyroscopic effect is small. You could look that up. The
Ballbarrow example proves steering by deformation of the wheel (ball)
into a cone. You could look that up too.

It's not magic. A flat surface - the contact patch - describing an arc
must have a conical shape unless it is being forced to slip.

Cheers

As a "wheel" of any kind begins to "lean over" at an angle other than
perpendicular to the surface it is on, the front edge of that "wheel"
begins to "step" out a turn that is described at other than the angle the
perpendicular rolling wheel describes.

When said wheel is on a perpendicular fork the arc described is small.
If the fork is angled forward, a "caster angle" and a "camber angel" is
introduced into the geometry and the arc is described with a greater
voracity.

what this says is that the angled fork capitalizes on the arc a tilted
wheel gets imparted upon it.

For a regular street tire, the contact patch is usually a nice ellipse.
during a turn... a 'leaning' turn, (which they all are)it rolls a bit
over toward the side of the tire tread and the contact patch actually
enlarges from the centrifugal pressure. I do not know what the shape
becomes. The conical reference sounds to me like a car tire with a wide
contact patch, which would turn a bit conical as the turn takes place.

Were one to turn such a wheel without any caster or camber
(perpendicular), a turn takes place due to the edge of the wheel
contacting the ground first pushing the whole assembly in that direction.

WITH caster and camber said wheel will cut away at a more aggressive
angle, and the way it contacts the ground is the reason.

On a bike, once the lean starts the aggressive angle change, a
centrifugal force even gets imparted and the bike will follow that track
all by itself, even setting the steering angle to its optimal position.

The fork rake angle, and the offset the front axle has with reference
to the axis the fork "steers" in are what set up the aggressiveness of
steering 'push' which gets imparted when the bike is leaned to one side.

This is why some bikes are easier to ride hands free than others. The
rate of change is too fast on some and the corrections come too slow.

 

[Phil Hobbs]

What a load of bollocks! Anyway, what are you doing here, Nymbecile?
Can't you find some bogs to clean? Be a good girl and run along now.

Cut the guy some slack. He's cleaned up his act amazingly--may we all
follow that example!

Cheers

Phil HObbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[Fred Abse]

camber angel

AKA pavement princess?

Only found in red light districts;-)

 

[josephkk]

A RHP Zero does not prove insurmountable, just some heads up and maybe
lower loop bandwidth.
A little Goggling yielded this;
http://control.lth.se/media/Staff/KarlJohanAstrom/Lectures/ BikeTalkKTH2006.pdf
I also have a garage door with a RHPZ in its control loop, it must
bepulled first before pushed open. That non intuitive $hit is all over
the place. Cheers, Harry

I missed that you are talking about a Zero rather than a Pole. Big
difference.

?-)