car's trajectory

Mark-T wrote:

>>
>> There you go. Of course that's not the optimal way for best handling, it
>> turns out that when you throw in vehicle dynamics, a little bit of slip
>> on the wheels sets the car up for cornering better than doing the
>> perfect low-speed minmal-slip geometry.
>
> Yes, but if you turn the steering wheel 30°
> left, where are you heading?
>
> Mark
>

What's the ratio of the steering gearbox? What's the length of the
Pitman arm? What's the length of the knuckle arms? What's the speed?
What's the road surface? What kind of tires? What are the alignment
specs? How is the car loaded? <insert about 100 other parameters here>

In case you haven't figured it out- you asked a question that doesn't
have an answer. Turning the steering wheel "30 degrees" doesn't mean
squat without all the rest of the vehicle dynamics.

On Jun 18, "Spaceman" > wrote:
> >>> If two points are moving in a circle around different points, is
> >>> there not a non-zero velocity between them? That tends to break
> >>> solid things containing those two points.
>
> >> The 2 points are not moving around 2 points,
> >> They are both moving around one point.
> >> One is moving faster WRT the other.
> >> 2 different size circles centered around the same point.
> >> that is all.
>
> > It's the same principle as the rear differential?
>
> hmm?
> It is the reason for a differential.

Why a differential in the rear axle, and
the Ackerman doohicky in the front?



Mark

Mark-T wrote:
> On Jun 18, "Spaceman" > wrote:
>>>>> If two points are moving in a circle around different points, is
>>>>> there not a non-zero velocity between them? That tends to break
>>>>> solid things containing those two points.
>>
>>>> The 2 points are not moving around 2 points,
>>>> They are both moving around one point.
>>>> One is moving faster WRT the other.
>>>> 2 different size circles centered around the same point.
>>>> that is all.
>>
>>> It's the same principle as the rear differential?
>>
>> hmm?
>> It is the reason for a differential.
>
> Why a differential in the rear axle, and
> the Ackerman doohicky in the front?

Real wheels don't make the angle wrt the cars straight line.
they are stuck always pointing forward.
but of course...
There are some vehicles that do let the rear wheels steer
also.
there is also trucks that have 2 steering axles in the front.
so if it is stuck wihtou being able to turn, you need differentials
or you need to be on dirt or not care about fast tire wear.

--
James M Driscoll Jr
Spaceman

On Jun 19, 3:12*pm, Mark-T > wrote:
> On Jun 18, "Spaceman" > wrote:
>
> > >>> If two points are moving in a circle around different points, is
> > >>> there not a non-zero velocity between them? That tends to break
> > >>> solid things containing those two points.
>
> > >> The 2 points are not moving around 2 points,
> > >> They are both moving around one point.
> > >> One is moving faster WRT the other.
> > >> 2 different size circles centered around the same point.
> > >> that is all.
>
> > > It's the same principle as the rear differential?
>
> > hmm?
> > It is the reason for a differential.
>
> Why a differential in the rear axle, and
> the Ackerman doohicky in the front?
>
> Mark

The rear axle needs a differential because the rear wheels are
rotating around a point that lies on the extended centerline of the
rear axle (as do the fronts) and therefore are describing circles of
differing radius. As a result the wheels are rotating at different
speeds, and you'd get significant tire scrub if they were locked
together (or you'd simply break stuff.)

nate

Mark-T wrote:

>>> It's the same principle as the rear differential?
>> hmm?
>> It is the reason for a differential.
>
> Why a differential in the rear axle, and
> the Ackerman doohicky in the front?

<blank stare>

You've GOT to be trolling.

</blank stare>

But in the event you aren't trolling: the answer is because the front
wheels aren't connected by a shaft (except in 4x4s and in that case
there IS a front differential), and the rear wheels don't steer.

In article <0ac98a89-81d4-4c25-bd61-
>,
says...
> On Jun 2, Steve > wrote:
> > >>>>>> If two points are moving in a circle around different points, is
> > >>>>>> there not a non-zero velocity between them? *That tends to break
> > >>>>>> solid things containing those two points.
> > >>>>> The 2 points are not moving around 2 points,
> > >>>>> They are both moving around one point.
> > >>>> Exactly the issue at hand. *JKK doesn't believe it.
> >
> > >>>>> One is moving faster WRT the other.
> > >>>> For some definitions of "faster". *;-)
> >
> > >>>>> 2 different size circles centered around the same point.
> > >>>>> that is all.
> > >>
> > >>> You missed my question and went off a tangent. *Take an object of
> > >>> dimensions of reasonable size moving circularly about a point.
> > >> You were arguing that a car didn't (move about a point), but thanks
> > >> for playing.
> >
> > > You had 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.
> >
> > http://lonestar.texas.net/~sglacker/...eometry101.jpg
> >
> > There you go. Of course that's not the optimal way for best handling, it
> > turns out that when you throw in vehicle dynamics, a little bit of slip
> > on the wheels sets the car up for cornering better than doing the
> > perfect low-speed minmal-slip geometry.
>
> Yes, but if you turn the steering wheel 30°
> left, where are you heading?

For the median.


--
Keith