Re: [tuxracer-devel] Keyboard

[Jasmin P. <jf...@mu...>]

On Sun, May 28, 2000 at 04:25:13PM +0100, Peter Allen wrote:
> I am not sure on the physics yet (I've only done first year 'A' level
> physics so far...) (Please comment and say thats not going to work etc)
> 1. Tux could stick a leg  hard into the snow, and use it a as a pivot.
> For practical reasons I think the pivot would need to be a lot further
> out that tux's leg, so this wouldn't look 100% realistic.  The physics
> of this are fine, but I was planning on making it so the pivot could
> only take a certain force, so if tux was going faster than that
> the pivot would slip, and tux would lose velocity (due to friction).
> I can't quite work out the physics of this, despite my best efforts
> with the ascii art.

It's not easy to do this "correctly" because of the model that's being
used.  For physics purposes, Tux is modelled as a single particle.  This
means that torsion on Tux can't be modelled, since the particle is
infinitesimally small.  A better model would take into account the fact
that when Tux's left arm (or foot) is sticking into the ground, the drag
on his left side is greater than on his right side; as a result he would
turn in that direction.

As I see it, there are a couple of options.  You could just copy and
modify the current turning code so that the magnitude of the frictional
force was increased when doing a sharp turn; this probably won't do
exactly what you want, but with sufficient tweaking it might come close.
The other would be to forgot about implementing this with forces and
manually manipulate Tux's velocity and/or position (instead of having it
automatically updated by the ODE solver).  There might be some gotchas
there, though -- I haven't looked at that code in a while so I'm not
sure what problems might crop up.

(There is also a third option -- implement a better physical model that
takes into account angular momentum, etc. -- but that's probably more
work than you had in mind. :)

Hope this helps,
Jasmin

-- 
Jasmin Patry               Master's Student, Dept. of Computer Science
jf...@cg...         http://www.cgl.uwaterloo.ca/~jfpatry/