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Rigid Bodies; Euler's Eq of Motion derivation 
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#1
Mar2408, 04:31 PM

P: 56

Problem
Derive Euler's equations of motion for a rigid body from the Lagrange formulation (for generalized coordinate [tex]\psi[/tex], the third Euler angle). Applicable Formulae Euler's equations of motion (what we are trying to derive) are: [tex]I_{1} \dot{\omega_{1}}  \omega_{2} \omega_{3} (I_{2}I_{3}) = N_{1}[/tex] [tex]I_{2} \dot{\omega_{2}}  \omega_{3} \omega_{1} (I_{3}I_{1}) = N_{2}[/tex] [tex]I_{3} \dot{\omega_{3}}  \omega_{1} \omega_{2} (I_{1}I_{2}) = N_{3}[/tex] Lagrange Formulation: [tex]\frac{d}{dt} \left( \frac{\partial T}{\partial \dot{q_{j}}} \right)  \frac{\partial T}{\partial q_{j}} = Q_{j} [/tex] Attempt at a solution It seems I need an expression for the kinetic energy T of the rigid body in terms of the Euler angles. I would then plug that into the Lagrange equation above for [tex]\psi[/tex], and reduce it to the desired form. The kinetic energy is given by: [tex]T = \frac{\vec{\omega}\cdot\bar{I}\cdot\vec{\omega}}{2}[/tex] and the angular velocity in terms of Euler angles is: [tex]\vec{\omega_{x,y,z}}=\left( \begin{array}{c} \dot{\phi} sin\theta sin\psi + \dot{\theta} cos\psi \\ \dot{\phi} sin\theta cos\psi  \dot{\theta} sins\psi \\ \dot{\phi}cos\theta + \dot{\psi} \end{array} \right) \cdot \left( \begin{array}{c} \hat{x} \\ \hat{y} \\ \hat{z} \end{array} \right)[/tex] I've already started working on it, but it seems like a lot of work. Am I on the right track, or is there something I'm missing here? 


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