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PostPosted: Sun Nov 05, 2017 8:10 pm 
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Joined: Sun Nov 05, 2017 7:02 pm
Posts: 1
Hi,

i'm trying to implement Featherstone's ABA so i decided to read Bullet implementation and came across this expression
Code:
   //...
   //zeroAccSpatFrc[i+1].setVector(-(rot_from_world[i+1] * linkAppliedTorque), -(rot_from_world[i+1] * linkAppliedForce ))
   //...


   zeroAccSpatFrc[i+1].addVector(
      angDampMult * m_links[i].m_inertiaLocal * spatVel[i+1].getAngular() * (DAMPING_K1_ANGULAR + DAMPING_K2_ANGULAR * spatVel[i+1].getAngular().safeNorm()),
      linDampMult * m_links[i].m_mass * spatVel[i+1].getLinear() * (DAMPING_K1_LINEAR + DAMPING_K2_LINEAR * spatVel[i+1].getLinear().safeNorm())
               );


   //...
   //zeroAccSpatFrc[i+1].addAngular(spatVel[i+1].getAngular().cross(m_links[i].m_inertiaLocal * spatVel[i+1].getAngular()));            
   //zeroAccSpatFrc[i+1].addLinear(m_links[i].m_mass * spatVel[i+1].getAngular().cross(spatVel[i+1].getLinear()));
   //...


which doesn't appear in featherstone's book

i understood this is sort of damping from constant names but where does this come from?


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PostPosted: Mon Nov 06, 2017 5:12 pm 
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Joined: Sun Jul 03, 2005 4:06 pm
Posts: 873
Location: Kirkland, WA
IIRC the squared omega (angular velocity) terms lead to simulation instabilities in practice. So Bullet added damping to improve stability.


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