[ODE] Odd Hinge-2 Behaviour?

[Tom Maciukenas]

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>So you are implying that if I drive a car off a ramp at a very high
>speed, then ram the handbrake on while still in the air, the front end of 
>my car will
>suddenly shoot upward? Or, alternatively that if I drive slowly off a cliff 
>and then
>accelerate very rapidly, the front end will dip? These are the sorts of 
>things that are happening
>in my simulation.

Those are the physically correct things to happen, but it seems
you're getting them in the wrong direction.  The brake should make
it dip, and the gas should make it rise.

How do your brake/gas work?  Do they modify the value of the ParamVel
setting on the Hinge2 joint?  That's the way the Buggy works, and it
should behave properly.  If you're using a different method, that could
explain it.

One thing I noticed, I can't remember the numbers from your original
mail but I remember thinking that your wheels were rather heavy for
the car.  A typical situation is a 2500lb car with ~40lb wheels.  That's
a ratio of 62:1.  Reducing the mass of your wheels would reduce the
effect, but still not solve the problem of it going in the wrong
direction.  Hmm... have you somehow created a *negative* mass?  or
a negative moment of inertia?

-Tom

P.S.

An interesting side note:  On a motorcycle, the ratio is much closer,
so that in the air you can affect the angle of the bike by hitting
the gas or brake.  Riders use this to align the bike with the landing
ramp on jumps.  There was a great old Mac shareware game called
Motocross (I think) where you had to use that effect.


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>> Similarly, I have discovered that if I allow my car to fall freely,<BR>><BR>>I.e. there's no gravity (or "equivalently" no floor), it's floating in space?<BR><BR>Well, in this case just if there is no floor that the car is in contact with, e.g. if it drives off <BR>the top of a building then it will be falling freely for a short period.<BR><BR>>> then whereas you'd expect acceleration to cause the wheels to spin<BR>>> but not really achieve anything, both the wheels and chassis spin.<BR>>><BR>><BR>>That's exactly what you'd expect: the wheels would spin one way and the body<BR>>would spin the other.  Or are you seeing them spin the same way?<BR><BR>So you are implying that if I drive a car off a ramp at a very high speed, then ram the <BR>handbrake on while still in the air, the front end of my car will suddenly shoot upward? <BR>Or, alternatively that if I drive slowly off a cliff and then accelerate very rapidly, the <BR>front end will dip? These are the sorts of things 
 that are happening in my simulation.<BR><BR>-Thomas<P>When words aren't enough - Vodafone live! A new world of colour, sounds, picture messages and information on your mobile. <a href="http://ad.doubleclick.net/clk;4909903;7724245;q?http://www.vodafone.co.uk/live">
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