[ODE] modified ODE tests

[Adam Rotaru]

    Hi, 

  I also made some modifed test_ examples, I post
them here if anybody would like to have a look.
I tried out chains -- blocks connected by
hinge joints.  I also tried a loop chain, which --
to my surprised -- worked!

http://www.geocities.com/adam_rotaru/tmp/ode/test_closedchain.cpp.txt
makes a closed 7-link chain.

http://www.geocities.com/adam_rotaru/tmp/ode/test_dropchain.cpp.txt
is similar to the boxstack, but you
can also drop 4-link chain pieces (press c).

Screenshots: 
http://www.geocities.com/adam_rotaru/tmp/ode/dropchain1.png
http://www.geocities.com/adam_rotaru/tmp/ode/dropchain2.png
http://www.geocities.com/adam_rotaru/tmp/ode/dropchain2t.png

Here are some further comments:
 
- test_dropchain occasionally causes the simulator
to enter an endless loop (apparently).
 
- my chains sometimes explode, but maybe less often
than the test_chain1 and test_chain2 examples.
 
- ariculated chains (only hinge joints) work quite
well.

- even closed chain works, and relatively well.

- in my chain I implemented collision between
connected
elements.  Without it the chains often
self-intersected, and
stayed that way.  Collision works in my case because
the
connected links are not touching normally, there is
some
spacing between them.  Their corners penetrate only
if the angle between them is less than 90 degrees.

- I could not use the library functions to multiply
a vector by a matrix.  So I included some utility
functions
for this, which is porbably a waste.  This is used
for
the initial positions of chains.
 
- I found that replacing the infinite mu in the
contact handling reduced the number of explosions.
 
 
cheers,
  Adam



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