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Inverse Dynamics - 2 Rigid Bodies connected with hinge

  1. May 15, 2013 #1
    I am trying to simulate and animate inverse dynamics. So I need to calculate torques. I started out by just taking a rod which rotates about its COM, applied a torque and then just used [itex]\tau=I\alpha[/itex] to make sure I get back the same torque I applied. Next, I attached the rod to the ground with a hinge joint. This time to get the torque I used the parallel axis theorem to get [itex]\tau=(I_{COM}+Mh^2)\alpha[/itex]. So my next step is to attach a second rod to the end of the one attached to the ground. What I am stuck on now is I am not sure how the two rods interact.

    For example how do I calculate the torque on the rod connected to the ground? When it is just one rod I used the aforementioned [itex]\tau=(I_{COM}+Mh^2)\alpha[/itex], but now with the other rod attached to it, what else do I need to take into account? Is there a negative torque on the opposite side?

    Note: For now I have disabled gravity.

    I would appreciate any insight. Thanks
  2. jcsd
  3. May 15, 2013 #2


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    If you are not familiar with Lagrangian dynamics, this would be a good excuse to do so.
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