[ODE] value passed to dAddTorque isn't actually torque?

[Russ Smith]

the problem is not in ODE (whew!) ... you're calculating the body mass
but you're not actually setting the mass property of the body. add the
line:

  dBodySetMass (box_body,&mass);

at the appropriate point, then everything should work as expected.

russ.


On Mon, 23 Jun 2003 12:41:54 -0400
"Martin C. Martin" <martin@metahuman.org> wrote:

> Hi,
> 
> The picture at:
> 
> http://www.ai.mit.edu/~mcm/BlockAndHinge.jpg
> 
> shows a block in mid air, free to fall except for a
> hinge on one end (the red line).  If you do the math, you can show
> that gravity produces a torque about the hinge's axis of:
> 
> g M l/2
> 
> where l is the length of the box.  Therefore, if I apply an equal
> torque in the opposite direction, it should perfectly balance and the
> thing shouldn't move.  However, that's not what happens.  Instead, to
> balance it, I need the following torque:
> 
> g 1/2
> 
> That is, same as you'd expect, but without the mass.  That formula
> works for changes in:
> 
> - acceleration from gravity
> - box density
> - box length
> - box width
> - box height
> 
> Is this a bug in ODE?  It says that the torque needed to support a rod
> at one end is the same whether its made from lead or Styrofoam.  That
> seems wrong.  The source I used is below.  What can be done to
> fix/work around this?
> 
> Thanks,
> Martin


-- 
Russell Smith
http://www.q12.org