Hello all,

How does a trailer follow the car/truck that is pulling it through bends, is
there some magic formula for it? All I can figure out is that the angle
between the two is related to the length of the trailer but beyond that I'm
a bit lost.

Is it clear what I'm asking?

TIA,

Thomas

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"Thomas" <tho### [at] gmxnet> wrote in message
news:web.3d6b57f7612a00a4bbe30ae0@news.povray.org...
> Hello all,
>
> How does a trailer follow the car/truck that is pulling it through bends,

    The trailer is physically attached to the car/truck.

> is there some magic formula for it?

    No. It's all down to the physical connection between the two, no 'magic'
is
required. In fact you do know magic doesn't actually exist don't you ?

;)

(sorry, couldn't resist...)
--
Pandora/Scott Hill/[::O:M:C::]Scorpion
Software Engineer.
http://www.pandora-software.com

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Pandora wrote:
>"Thomas" <tho### [at] gmxnet> wrote in message
>news:web.3d6b57f7612a00a4bbe30ae0[at]news.povray.org...
>> Hello all,
>>
>> How does a trailer follow the car/truck that is pulling it through bends,
>
>    The trailer is physically attached to the car/truck.

I know that ;)

What I meant is how does the angle between the two changes when the
combination goes through a corner, I would like to animate this. But at the
moment the trailer moves side ways, which doesn't look particular
realistic.


>    No. It's all down to the physical connection between the two, no 'magic'
>is
>required. In fact you do know magic doesn't actually exist don't you ?

Really???? ;)

Thomas

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Thomas wrote:
> 
> [...]
> 
> What I meant is how does the angle between the two changes when the
> combination goes through a corner, I would like to animate this. But at the
> moment the trailer moves side ways, which doesn't look particular
> realistic.

If you don't want to do an accurate physical simulation you can start with
some basic rules (for a 2 wheel trailer):

- the wheels of the trailer have a fixed distance to one another.
- the wheels of the trailer have a fixed distance to the link.
- the wheels can only move on the ground in their current direction.
- the wheels' directions are always orthogonal to the line between them.

So all you have to do is take care about these three rules being obeyed
while moving the whole system.  I suppose you have already modelled the
movement of the pulling vehicle so all you have to do is taking the
position of the car-trailer link and applying these rules in many small
steps along the movement path.  And if it doesn't look all right just use
smaller steps.  ;-)

Christoph

-- 
POV-Ray tutorials, IsoWood include,                 
TransSkin and more: http://www.tu-bs.de/~y0013390/  
Last updated 13 Aug. 2002 _____./\/^>_*_<^\/\.______

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"Thomas" <tho### [at] gmxnet> wrote in message
news:web.3d6b57f7612a00a4bbe30ae0@news.povray.org...
>
> How does a trailer follow the car/truck that is pulling it through bends,
is
> there some magic formula for it? All I can figure out is that the angle
> between the two is related to the length of the trailer but beyond that
I'm
> a bit lost.
>
> Is it clear what I'm asking?

Yes. I don't know the solution though.

The hitch point should shift based on the change of direction of the pulling
vehicle's front wheels while the rear wheel axle center acts as a pivot
point, maybe. I think you'd use the angle from along centerline of front to
rear wheels and match that for the trailer hitch to its wheels as though the
hitch were a front wheel.

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Christoph Hormann wrote:
>If you don't want to do an accurate physical simulation you can start with
>some basic rules (for a 2 wheel trailer):
>
>- the wheels of the trailer have a fixed distance to one another.
>- the wheels of the trailer have a fixed distance to the link.
>- the wheels can only move on the ground in their current direction.
>- the wheels' directions are always orthogonal to the line between them.


Hmmmm this might be usefull, but I was looking for something more physical
correct.

Just re-reading your four lines there seems to suggest that the trailer can
not make a curve at all since they only can move in there current
direction. Or is that just me mis reading it.

Thomas

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Thomas wrote:
> 
> >- the wheels of the trailer have a fixed distance to one another.
> >- the wheels of the trailer have a fixed distance to the link.
> >- the wheels can only move on the ground in their current direction.
> >- the wheels' directions are always orthogonal to the line between them.
> 
> Hmmmm this might be usefull, but I was looking for something more physical
> correct.

The limited physical correctness of this approach is just in terms of
dynamics.  Taking this into account would complicate the problem quite a
lot.

> Just re-reading your four lines there seems to suggest that the trailer can
> not make a curve at all since they only can move in there current
> direction. Or is that just me mis reading it.

The emphasis is on *current* direction.  You will probably have to weaken
this requirement a bit (i. e. not use it as a strict rule) to make sure
the distance between the wheels stays the same.

Christoph

-- 
POV-Ray tutorials, IsoWood include,                 
TransSkin and more: http://www.tu-bs.de/~y0013390/  
Last updated 13 Aug. 2002 _____./\/^>_*_<^\/\.______

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Christoph Hormann wrote:
> 
> [...]
> 
> > Just re-reading your four lines there seems to suggest that the trailer can
> > not make a curve at all since they only can move in there current
> > direction. Or is that just me mis reading it.
> 
> The emphasis is on *current* direction.  You will probably have to weaken
> this requirement a bit (i. e. not use it as a strict rule) to make sure
> the distance between the wheels stays the same.

BTW, you can also think of it a different way: The two wheels and their
axis always move on a circle with it's center somewhere on the axis.

Christoph

-- 
POV-Ray tutorials, IsoWood include,                 
TransSkin and more: http://www.tu-bs.de/~y0013390/  
Last updated 13 Aug. 2002 _____./\/^>_*_<^\/\.______

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Christoph Hormann wrote:

>BTW, you can also think of it a different way: The two wheels and their
>axis always move on a circle with it's center somewhere on the axis.


That's what someone here at work suggested as well, but the truck is moving
along a spline and I don't think that it is easy to determine the radius of
the spline at any given point.

Thomas

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Thomas wrote:
> 
> >BTW, you can also think of it a different way: The two wheels and their
> >axis always move on a circle with it's center somewhere on the axis.
> 
> That's what someone here at work suggested as well, but the truck is moving
> along a spline and I don't think that it is easy to determine the radius of
> the spline at any given point.

That's not the point, the trailer won't follow the same path as the truck
anyway, it was just meant to give an idea how things are supposed to work.

BTW, taking a piece of paper and drawing the trailer and it's movement
will be quite helpful for finding a good method calculating it's movement.

Christoph

-- 
POV-Ray tutorials, IsoWood include,                 
TransSkin and more: http://www.tu-bs.de/~y0013390/  
Last updated 13 Aug. 2002 _____./\/^>_*_<^\/\.______

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