[ODE] Odd Hinge-2 Behaviour?

[adam.moravanszky@novodex.com]

>>
I don't see why this is so, since it is not the wheels that suddenly begin
turning faster of their own free will, it is some small part of the chassis
(a cog or a flywheel or whateve r) that begins rotating faster. Therefore,
could it not be that the wheels are spinning in the opposite direction in
the sense that you mean?
Again, I wish to emphasise that I will be happy to accept that I am wrong
(i.e. that my simulation is already correct, rather than requiring more
work), but would really like someone to make that desperately clear if it
is so.
<<


It is so.  First, when using ODE, you are not modeling cogs, you are attaching
two rigid bodies with a joint, and then requiring a relative angular velocity
at the joint.  The fact that this setup happens to model a real car quite
well is something you will have to accept, though I believe someone has
already pointed out real life uses for the effect you are seeing.  This
effect also for example necessitates the tail rotor on a helicopter. The
reason why both of the attached bodies will have to start rotating is quite
self evident: physics is symmetric, and there is no preferred body.  The
difference in inertia (mass) of the two bodies makes one effectively easier
to rotate, so it will accelerate faster.   However, the case you seem to
desire, that only one start to rotate compared to the world reference frame,
will only happen if you fix that body (give it infinite mass) in the world.

>>
> With all due respect, Newtonian physics '101' (American for introductory?)
will simply tell me that every force has an equal and opposite reaction.
Therefore, I see no reason why the chemicals being burnt inside my engine
may not be turning some sort of cog attached to the wheels, causing the
rotation of the wheels to be the reaction to that particular action, and
yielding acceleration with no rotation effect on the chassis whatsoever.
<<

Conservation of energy may become a bit involved in this case, but don't
forget about conservation of (angular) momentum, which is the key here.
 

When words aren't enough - Vodafone live! A new world of colour, sounds,


I hope they are enough in this case..  :-)

--Adam