[ODE] Adjusting a body's mass

[Geoff Carlton]

In addition, the distribution of weight is determined by the dMass 
struct, since the geom shape has no affect on the actual physics beyond 
determining the contacts.  The dMass determines the inertia of the body, 
which can be a fairly subtle effect - it will change the way the body 
spins in the air, how it tumbles, etc.  So even if the centre of gravity 
doesn't change, dMass will be needed to get proper results - you could 
have all the weight in the middle, or if you have a massive pair of 
weights at the front and the back.

Geoff

Jon Watte wrote:

>Mass translation is ignored by the body, so you have to caculate what the 
>actual center of gravity is, and put the body there (typically by offsetting 
>any geoms and joint attachment points from the body).
>
>A second, inferior, solution is to add a number of bodies to the main body, 
>all attached with fixed joints. This will perform worse, and lead to less 
>stability in the simulation.
>
>Cheers,
>
>			/ h+
>
>  
>
>>In my particular case, I want to add and remove "weight" in certain places on my vehicle 
>>chassis such as a fuel tank, or a driver, or a rocket launcher.  My hope is that I can 
>>make the vehicle front or back "heavy" and it will affect the steering.
>>    
>>
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