[Math] the angular velocity in an inertial frame given the angular velocity in a body fixed frame

physicsrotations

At a given time t, the rotation matrix R has the value:

$$R=
\begin{pmatrix}
0.675 & −0.1724 &0.7174\\0.2474 & 0.9689& 0 &\\−0.6951& 0.1775&0.6967.
\end{pmatrix}$$

The angular velocity in a body fixed frame $\hat ω^b$ at that same time t is:

$$\hat ω^b=\begin{pmatrix}0& −1 &0.9689&\\1 & 0 &−0.2474\\−0.9689&0.2474&0.
\end{pmatrix}$$
What is $\hatω^s$, the angular velocity in an inertial frame?

I know that
\begin{align*}\omega^s:\dot q &= \dot RR^Tq\\&=R\hat\omega^b\end{align*}

Therfore I did on Matlab:

>> R = [0.675 -0.1724 0.7174; 0.2474 0.9689 0; -0.6951 0.1775 0.6967];
>> wb= [0 -1 0.9689; 1 0 -0.2474; -0.9689 0.2747 0];
>> R*wb

ans =

   -0.8675   -0.4779    0.6967
    0.9689   -0.2474         0
   -0.4975    0.8865   -0.7174

Which is none of the provided answer:

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Best Answer

This is down to the relationship between the angular velocity in the fixed body frame ($w^b$) of a rigid body and in the inertial frame ($w^s$) given a rotation matrix.

You have the wrong equations above for $w^s$ and $w^b$ The points don't come into it.

It should be as below: ($R^T$ is the transpose, $\dot R$ differentiated against time ($t$))

$$ωs=R\dot R^T$$ $$wb=R^T \dot R$$

The missing piece needed to calculate $w^s$ is $\dot R$.

Take the $w^b$ equation and pre-multiply each side of the equation by $inv(RT)$

$$inv(R^T)R^T\dot R= inv(R^T)wb$$

$$\dot R=inv(RT)wb$$

Now you know $R$ and $\dot R$ So you can calculate $ws=\dot RR^T$

You can confirm this by seeing that the answer is one of the 4 options above.