car's trajectory

[Nate Nagel]

| Androcles wrote:
| >
| >
| >>
| >>"JosephKK" wrote:
| >>
| >>|
| >>| You claimed that the tracks of the tires all pointed
| >>| to a single point. Put up the math (including the
| >>| geometry), 'cause i do not think it can be done.
| >>| __________________________________________
| >>|
| >>| It's not TRACKS. It's AXLE centerlines that all meet at a single
point.
| >>
| >>Nonsense. When the car is travelling straight the axle centerlines
| >>are parallel and therefore do not meet (by definition of parallel).
| >
| >
| > to elaborate, the centerline of the rear axle and the centerlines of
| > each front spindle all meet at a common point. As the vehicle travels
| > a path closer to straight ahead, that point becomes increasingly
| > distant from the vehicle itself, and when the vehicle is in actuality
| > traveling perfectly straight ahead, that point is infinitely far away.
| >
| > nate
| >
| > ===============================================
| > The centerlines of each front spindle do NOT meet at a common point
| > shared by the rear axle except for one identifiable and particular
turning
| > radius, as shown here:
| > http://www.androcles01.pwp.blueyonder.co.uk/Steering.gif
| >
|
| In a 100% Ackermann geometry system, they do - at ALL turning radii.

When the car is travelling straight the axle centerlines are parallel and
therefore do NOT meet (by DEFINITION of parallel).

Your argument fails because infinity is not defined, try dividing by
zero on any calculator.

I'm merely repeating the *definition* of Ackermann geometry. The fact
that you can't handle a piddly little infinity is of little concern to
me. Since "going straight" can easily be reworded as "an infinitely
large turning radius" I don't see any kind of issue with allowing the
distance from the vehicle of the intersections of all the turning radii
to go to infinity as well. As soon as you deviate, even slightly, from
straight ahead, you can find the intersection point clearly defined -
even if it is miles away (this is assuming, of course, an idealized
vehicle with no slop anywhere in the steering linkage.)

If you think about it, the Ackermann principle is very simple...
assuming zero slip angles at all tires (which is the assumption that the
whole principle is based on, and also why in some applications engineers
choose to ignore or modify it) BY DEFINITION the centerlines of the
spindles/axles have to meet at a common point for any non-zero turning
radius, as the vehicle is a single mass and therefore when turning has
to describe an arc with a single center. The zero slip angle assumption
defines the direction of travel of each wheel as being at an angle of 90
degrees from a line drawn from the center of that arc. Therefore indeed
lines drawn perpendicular to the direction of travel of each wheel, or
in other words, the centerlines of the spindles or axles, MUST meet at a
common point.

| I'm not sure what the heck your diagram is supposed to show,

Ok, so you are just another unintelligent argumentative fuckhead
I should not waste my time on.
*plonk*

yeah, I guess all those years messing with cars and taking engineering
classes makes me supremely unqualified to talk about something as basic
as Ackermann steering.

Why don't you DAGS for the definition of Ackermann steering and then
come back and apologize for your rudeness?

nate

 

[JosephKK]

Actually, I did. And unlike you, I understood it.

You couldn't have, otherwise you would have known not only it there no
math there, but that the value of Ackerman steering itself is debated.

There is no math (including

Which you previously hadn't a clue about, more likely.

I was aware of toe-in/toe-out since i was a teen a few decades ago. It
is a major reason why perfect 100 % Ackerman looks impossible, which
was part of the reason i keep saying bring the math. Spend some time
considering large turning radii with significant toe-in/toe-out.

How about you bring the understanding. Or at least try to phrase a
coherent question. What "math" can you not comprehend from the simple
diagrams that have been posted?

I can and will as soon as someone brings the math. If you want to
debate in presumptions and a very few over-simplified diagrams, have
fun. But you will win zero respect from me.

You once said "I don't believe it does" in reference to the fact that
the steering mechanism is capable of pointing the axes of all wheels on
the vehicle to a common point at the center of the turn. THAT fact has
been proven. The fact that different vehicles perform better under
weight-transfer with somewhat non-idealized angles so that some tires
are deliberately scrubbing is irrelevant to the closest thing to a
coherent question that you've posted so far.

But at what turning radii if any. Show all work, including dimensions
and trigonometric functions. Include kingpin slant in both
dimensions. Show the difference function from ideal to real versus
steering angle. Bring the _math_.

 

[JosephKK]

Please set up cases of about 100 % Ackerman, about 50% Ackerman,
and about 25 % anti-Ackerman. Cross this with 5 various steering
angles, various tire slips, and show/compute the position from above
of all arms and the position of the steering wheel. Show how percent
Ackerman and toe-in/toe-out varies with the various steering angles,
etc.,. You may include side loading effects. Show all dimensions and
state tire properties. Please give a link because that much binary is
unlikely to be allowed on many of these text-only groups.
_________________________________________________________

I think I see what you are getting at. I'll start with some links first:

http://www.auto-ware.com/setup/ack_rac.htm

Already found.

http://www.rctek.com/handling/ackerman_steering_principle.html

Better explanation than most.

These links show you the same simple explanation posted in this newsgroup,
plus the same simple diagram of the geometry, showing the reason for having
a common center of rotation for all vehicle axles. It is simple geometry,
commonly known as the Ackerman Concept. No math is involved.

Until you try to implement it. Of course you could just hack and
guess, but a little up front math will greatly reduce the number of
tries necessary. Adding feedback in the form of testing will reducing
it even more.

The articles also discuss racing cars, where tire distortion and slippage during
high-G turns cause a car's turning radius center to shift from its normal position.
Race car builders modify the geometry to compensate for the drift by varying
the angle (Ackerman angle) between the non-parallel bars of the 4-bar steering
linkage. The car is test-raced with a series of candidate angles until the best
turning control is obtained. Modifications must be done empirically based on
the dynamics of the race car and the track. No math is involved.

How can you imagine that essentially all modern consumer/delivery
vehicles do not have at least some approximation of Ackerman steering?
It is clearly not limited to the race track. Not even high armature
racing teams undertake the modification of steering/suspension
geometry without using serious simulation software to help them make
informed decisions about the value of race to race changes. If the
car and the pit crew are good enough and the design supports it you
can make in race changes.

Now I understand the confusion. When the newsgroup discussed the simple
common center of rotation principle, you wanted to display your knowledge of
exceptions under racing environments.

No, i wanted to challenge the ass-umption that perfect Ackerman was
achievable, and i still challenge that. The demonstration that it is
clearly not holy in racing circles was made clear by another's links.

Some posters mistakenly thought you
were arguing against the Ackerman concept, but you were actually expanding
on it in all seriousness, and not trying to be a trolling pedantic nit.

I actually want enough knowledge to consider writing some simulation
software. Thus, bring the math. There are dozens of example
steering/suspension geometries out there. I am just not quite
interested enough to take expensive SAE courses for barely a hobby.

 

[N8N]

I actually want enough knowledge to consider writing some simulation
software.  Thus, bring the math.  There are dozens of example
steering/suspension geometries out there.  I am just not quite
interested enough to take expensive SAE courses for barely a hobby.

Then I guess you're not interested enough to get an answer. You're
going to have to do research to get the answers you week, and possibly
spend some time as a chassis designer for a race team if you want to
explore non-100% Ackermann steering setups, proper applications of
same, and behavior of same.

For modeling of low-slip-angle street car behavior, pure Ackermann is
fine.

nate

 

[Androcles]

| Androcles wrote:
|
| > | >>
| > | >>Nonsense. When the car is travelling straight the axle centerlines
| > | >>are parallel and therefore do not meet (by definition of parallel).
| > | >
| > | >
| > | > to elaborate, the centerline of the rear axle and the centerlines of
| > | > each front spindle all meet at a common point. As the vehicle
travels
| > | > a path closer to straight ahead, that point becomes increasingly
| > | > distant from the vehicle itself, and when the vehicle is in
actuality
| > | > traveling perfectly straight ahead, that point is infinitely far
away.
| > | >
| > | > nate
| > | >
| > | > ===============================================
| > | > The centerlines of each front spindle do NOT meet at a common point
| > | > shared by the rear axle except for one identifiable and particular
| > turning
| > | > radius, as shown here:
| > | > http://www.androcles01.pwp.blueyonder.co.uk/Steering.gif
| > | >
| > |
| > | In a 100% Ackermann geometry system, they do - at ALL turning radii.
| >
| > When the car is travelling straight the axle centerlines are parallel
and
| > therefore do NOT meet (by DEFINITION of parallel).
|
| And also the limiting case

There is no fucking limit at which parallel lines meet, shithead, as anyone
with
half a brain would tell you.

*plonk*

--
Why did Einstein say
the speed of light from A to B is c-v,
the speed of light from B to A is c+v,
the "time" each way is the same?

1/2[tau(A)+tau(A')]= tau(B)
where
A = (0,0,0,t)
A' =(0,0,0,t+x'/(c-v) +x'/(c+v))
B = (x',0,0,t+x'/(c-v))
x' = x-vt

Ref: http://www.fourmilab.ch/etexts/einstein/specrel/www/figures/img22.gif

"Easy: he did NOT say that." - cretin [email protected]
According to moron van lintel, Einstein did not write the equation he wrote.
Androcles

 

[Rich Webb]

Nate Nagel wrote...

| I'm not sure what the heck your diagram is supposed to show,

Ok, so you are just another unintelligent argumentative fuckhead
I should not waste my time on.

You swine. You vulgar little maggot. You worthless bag of filth. As we
say in Texas, you couldn't pour water out of a boot with instructions
printed on the heel. You are a canker, an open wound. I would rather
kiss a lawyer than be seen with you. You took your last vacation in
the Islets of Langerhans. [snip...snip...]
I hope this helps...

I'm torn on whether this would sound better as done by Rowan Atkinson
in his best Blackadder voice (the world-weary series 4, perhaps) or by
the late Graham Chapman as, say, Yellowbeard.

 

[Rich Grise]

It's an interesting question. Why would someone who is in an online
conversation decide to start flaming? It's easy to understand flaming
back after someone else starts it, but why start the fight? And why is it
so often associated with the flamer just having been proven wrong about
something?

There is a psychology book that sheds some light on the root of such
behavior:


"The most hostile group was the one with high but unstable self esteem.
These people think well of themselves in general, but their self-esteem
fluctuates. They are especially prone to react defensively to ego
threats, and they are also more prone to hostility, anger and aggression
than other people.

"These findings shed considerable light on the psychology of the bully.
Hostile people do not have low self esteem; on the contrary, they think
highly of themselves, But their favorable view of themselves is not held
with total conviction, and it goes up and down in response to daily
events. The bully has a chip on his shoulder because he thinks you might
want to deflate his favorable self image."
-Roy F. Baumeister, _Evil: Inside
Human Violence and Cruelty_ p 149

This is in sharp contrast to the attitude that many people who work in
engineering have, which is to welcome being shown to be wrong. To them
(and I am one of them), the usefulness of having your mental model made
closer to physical reality outweighs any slight emotional embarrassment
from being shown to be wrong about something. This is in turn firmly based
on a lifetime of working with hardware and software that follows the rules
of physics, math, and information theory without caring how you feel about
it.

Yeah - being shown to be "wrong" is sort of a double-whammy - you're not
only wrong, which is devastating enough, but you've been a fool for
insisting that you're right. ;-)

Cheers!
Rich

 

[Rich Grise]

But at what turning radii if any. Show all work, including dimensions and
trigonometric functions. Include kingpin slant in both dimensions. Show
the difference function from ideal to real versus steering angle. Bring
the _math_.

And don't forget that ever-popular team, Caster & Camber. ;-)

Cheers!
Rich

 

[krw]

Geometry is part of math as trigonometry. Or did they forget to tell
you that? Like i said, put it up or shut up, whichever name you call
it by.

I have no need to do either. The geometry is obvious to anyone with
half an engineering brain. ...as are your lies and misdirection.

 

[krw]

From where do you get the compulsion to cast personal insults?

When I'd had enough of your loonacy.

 

[JosephKK]

Then I guess you're not interested enough to get an answer. You're
going to have to do research to get the answers you week, and possibly
spend some time as a chassis designer for a race team if you want to
explore non-100% Ackermann steering setups, proper applications of
same, and behavior of same.

For modeling of low-slip-angle street car behavior, pure Ackermann is
fine.

nate

Well shit then. I guess i will measure out my own car and set up the
sim. Bye, your lazy claiming arrogance.

 

[Rich Grise]

...
BTW, what app are you usintg to g=create the .gif files? I really like the
look.

I've used this in the past, back when it was just shareware:
http://www.tucows.com/preview/194830

I don't know if they still have a "free" version.

Cheers!
Rich

 

[Rich Grise]

When I'd had enough of your loonacy.

That's just an excuse - it doesn't say anything about the root cause of
your compulsion to be offensive.

In fact, most people I know except for the really brain-locked actually
rather enjoy my "loonacy".

After all, I grew up in Minnesota, and the loon is their state bird.
http://www.50states.com/bird/loon.htm ;-D

Cheers!
Rich

 

[N8N]

Well shit then.  I guess i will measure out my own car and set up the
sim.  Bye, your lazy claiming arrogance.

I'm not being arrogant. you just don't get it - people have defined
Ackermann geometry six ways to Sunday already in this thread. there's
been more than enough info. presented that you ought to be able to
model that fairly easily.

If you want to go deeper than that, there is no shortcut to mastery of
the subject.

nate

 

[Rich Grise]

I'm not being arrogant. you just don't get it - people have defined
Ackermann geometry six ways to Sunday already in this thread. there's
been more than enough info. presented that you ought to be able to model
that fairly easily.

If you want to go deeper than that, there is no shortcut to mastery of the
subject.

I was kind of surprised when I looked up "Ackerman Steering":
http://www.auto-ware.com/setup/ack_rac.htm

They don't actually turn the front wheels at different angles (which I
thought they did with the drag link/tie rod/steering knuckle geometry),
but they depend on the tires to have "slip", which isn't actually
scuffing, but a measure of how much the rubber can distort without
losing traction, which this guy spells "loosing".

Thanks!
Rich

 

[JosephKK]

I'm not being arrogant. you just don't get it - people have defined
Ackermann geometry six ways to Sunday already in this thread. there's
been more than enough info. presented that you ought to be able to
model that fairly easily.

If you want to go deeper than that, there is no shortcut to mastery of
the subject.

nate

Hell, how about a reference to a decent text? A few mediocre to
crappy websites to help a miniscule amount while claiming superior
understanding simply wastes all of our time. If you have real
understanding, present it. If you do not, don't waste my time.

 

[Rodan]

I was surprised when I looked up "Ackerman Steering":

http://www.auto-ware.com/setup/ack_rac.htm

They don't actually turn the front wheels at different angles
with the drag link/tie rod/steering knuckle geometry.
They depend on the tires to have "slip", a measure of how
much the rubber can distort without losing traction.
_________________________________________________

The article cited does not say that. It says:

"The Conventional Ackerman Steering concept is
to have all four wheels rolling around a common
point during a turn. The inside front tire must
be turned a larger number of degrees than the
outside front tire for this principle to work."

The article goes on to say:

"However, at RACING SPEEDS, tires develop slip angle
due to flex in the tires, so when tuning a RACE CAR,
take conventional Ackerman off the list of concerns."

Even under racing conditions the turned wheels may still
be at different angles from each other, but not the
conventional Ackerman angles. The modified angles are
determined empirically; by trial and error for the specific
race car and track in question.

Rodan.

 

[Nate Nagel]

Hell, how about a reference to a decent text?

I'd recommend checking out a college bookstore, at a school with a solid
engineering program.

A few mediocre to
crappy websites to help a miniscule amount while claiming superior
understanding simply wastes all of our time. If you have real
understanding, present it. If you do not, don't waste my time.

There's a reason college courses cost more than web access. I'm sorry
you feel that your inability to find everything you want for free to be
a "waste of time" but you're just going to have to suck it up and deal.


nate

 

[JosephKK]

I'd recommend checking out a college bookstore, at a school with a solid
engineering program.


There's a reason college courses cost more than web access. I'm sorry
you feel that your inability to find everything you want for free to be
a "waste of time" but you're just going to have to suck it up and deal.


nate

I took enough college courses in engineering to graduate. I paid the
nominal citizen subsidized rate for the tuition and bought and kept
all my books. I buy texts quite readily. To make the point, do you
have anything to recommend, or not?

 

[krw]

A person with half a brain DID just tell me that. However a person with
a WHOLE brain and a high-school education knows differently.

Come on. What do you want from Dimbulb? Halfa brain? Sorry, not
even two neurons to keep each other company. Only one, and it died
of loneliness.