Physics Asked by Sanjay Thakur on August 24, 2021
How to derive the relation between Euler angles and angular velocity and get this form:
$$
left.
begin{cases}{}
P
Q
R
end{cases}
right}=
left[
begin{array}{c}
1&0&-sinTheta
0&cosPhi&cosThetasinPhi
0&-sinPhi&cosThetacosPhi
end{array}
right]
left.
begin{cases}{}
dot{Phi}
dot{Theta}
dot{Psi}
end{cases}
right}
$$
$$
left.
begin{cases}{}
dot{Phi}
dot{Theta}
dot{Psi}
end{cases}
right}=
left[
begin{array}{c}
1&sinPhitanTheta&cosPhitanTheta
0&cosPhi&-sinPhi
0&sinPhisecTheta&cosPhisecTheta
end{array}
right]
left.
begin{cases}{}
P
Q
R
end{cases}
right}
$$
How to derive the relation between euler angles and angular velocity begin{align*} &text{The equations to calculate the angular velocity $vec{omega}$ for a given transformation matrix $S$ are: } \ &left[_B^Idot{S}right]=left[tilde{vec{omega}}_Iright]left[_B^I Sright],quad Rightarrow left[tilde{vec{omega}}_Iright]=left[_B^Idot{S}right]left[_I^B Sright] &text{or} &left[_B^Idot{S}right]=left[_B^I Sright]left[tilde{vec{omega}}_Bright],quad Rightarrow left[tilde{vec{omega}}_Bright]=left[_I^B Sright]left[_B^Idot{S}right] &text{with} &left[_B^I Sright],left[_I^B S right]= begin{bmatrix} 1 & 0 & 0 0 & 1 & 0 0 & 0 & 1 end{bmatrix}\ &text{$left[_B^I{S}right]$ Transformation matrix between B- System and I-System } &text{$left[vec{omega}right]_B$ Vector components B-System} &text{$left[vec{omega}right]_I$ Vector components I-System and} &tilde{vec{omega}}= begin{bmatrix} 0 & -omega_z &omega_y omega_z & 0 & -omega_x -omega_y & omega_x & 0 end{bmatrix}\ &textbf{Example: Transformation matrix Euler angle} &left[_B^I{S}right]=S_z(psi),S_y(vartheta),S_z(varphi) &S_z(psi)=left[ begin {array}{ccc} cos left( psi right) &-sin left( psi right) &0 sin left( psi right) &cos left( psi right) &0 0&0&1end {array} right] &S_y(vartheta)=left[ begin {array}{ccc} cos left( vartheta right) &0&sin left( vartheta right) 0&1&0 -sin left( vartheta right) &0&cos left( vartheta right) end {array} right] &S_z(varphi)=left[ begin {array}{ccc} cos left( varphi right) &-sin left( varphi right) &0 sin left( varphi right) &cos left( varphi right) &0 0&0&1end {array} right] &Rightarrow &vec{omega}_B= left[ begin {array}{ccc} 0&sin left( varphi right) &-cos left( varphi right) sin left( vartheta right) 0&cos left( varphi right) &sin left( varphi right) sin left( vartheta right) 1 &0&cos left( vartheta right) end {array} right] begin{bmatrix} dot{varphi} dot{vartheta} dot{psi} end{bmatrix} &begin{bmatrix} dot{varphi} dot{vartheta} dot{psi} end{bmatrix}= left[ begin {array}{ccc} {frac {cos left( varphi right) cos left( vartheta right) }{sin left( vartheta right) }}&-{ frac {sin left( varphi right) cos left( vartheta right) }{ sin left( vartheta right) }}&1 sin left( varphi right) &cos left( varphi right) &0 -{frac {cos left( varphi right) }{sin left( vartheta right) }}&{frac {sin left( varphi right) }{sin left( vartheta right) }}&0end {array} right] begin{bmatrix} omega_x omega_y omega_z end{bmatrix}_B &vec{omega}_I= left[ begin {array}{ccc} cos left( psi right) sin left( vartheta right) &-sin left( psi right) &0 sin left( psi right) sin left( vartheta right) &cos left( psi right) &0 cos left( vartheta right) &0& 1end {array} right] begin{bmatrix} dot{varphi} dot{vartheta} dot{psi} end{bmatrix} &begin{bmatrix} dot{varphi} dot{vartheta} dot{psi} end{bmatrix}= left[ begin {array}{ccc} {frac {cos left( psi right) }{sin left( vartheta right) }}&{frac {sin left( psi right) }{sin left( vartheta right) }}&0 -sin left( psi right) &cos left( psi right) &0 -{frac { cos left( vartheta right) cos left( psi right) }{sin left( vartheta right) }}&-{frac {cos left( vartheta right) sin left( psi right) }{sin left( vartheta right) }}&1end {array} right] begin{bmatrix} omega_x omega_y omega_z end{bmatrix}_I end{align*}
Answered by Eli on August 24, 2021
Here is how to evaluate the rotational kinematics of a rigid body from the Euler angles
$$boldsymbol{omega} = hat{imath} dot{Phi} + mathrm{R}_X ( hat{jmath} dot{Theta} + mathrm{R}_Y hat{k} dot{Psi}) tag{1} $$
Here is how to derive the above:
Consider the orientation to be defined as sequence of thre elementary rotations $$ mathrm{R} = mathrm{R}_X mathrm{R}_Y mathrm{R}_Z tag{2}$$
where $mathrm{R}_X = mathrm{rot}(hat{imath},,Phi)$, $mathrm{R}_Y = mathrm{rot}(hat{jmath},,Theta)$ and $mathrm{R}_Z = mathrm{rot}(hat{k},,Psi)$.
Now the derivative on a rotating frame dictates that $$ begin{aligned} dot{mathrm{R}}_X & = (hat{imath} dot{Phi}) times mathrm{R}_X dot{mathrm{R}}_Y & = (hat{jmath} dot{Theta}) times mathrm{R}_Y dot{mathrm{R}}_Z & = (hat{k} dot{Psi}) times mathrm{R}_Z end{aligned} $$
and
$$dot{mathrm{R}} = boldsymbol{omega} times mathrm{R} tag{3} $$ which is used to derive $boldsymbol{omega}$, the rotational velocity of the rigid body.
Starting from the product rule on the left-hand side of (3)
$$ dot{mathrm{R}} = dot{mathrm{R}}_Xmathrm{R}_Y mathrm{R}_Z + mathrm{R}_Xdot{mathrm{R}}_Y mathrm{R}_Z + mathrm{R}_X mathrm{R}_Ydot{mathrm{R}}_Z$$
and substitute the derivatives from rotating frames to equate to the right-hand side of (3)
$$ boldsymbol{omega} times mathrm{R} = left((hat{imath} dot{Phi}) times mathrm{R}_X right) (mathrm{R}_Y mathrm{R}_Z) + mathrm{R}_X left( (hat{jmath} dot{Theta}) times mathrm{R}_Y right) mathrm{R}_Z + (mathrm{R}_X mathrm{R}_Y) left( (hat{k} dot{Psi}) times mathrm{R}_Z right) $$
now start grouping and distribute the rotations. Note that $mathrm{R} (a times b) = (mathrm{R} a) times (mathrm{R} b)$ is used below.
$$begin{aligned} boldsymbol{omega} times mathrm{R} & = (hat{imath} dot{Phi}) times mathrm{R} + (mathrm{R}_X hat{jmath} dot{Theta}) times mathrm{R} + (mathrm{R}_X mathrm{R}_Y hat{k} dot{Psi}) times mathrm{R} & = left( hat{imath} dot{Phi}+mathrm{R}_X hat{jmath} dot{Theta}+mathrm{R}_X mathrm{R}_Y hat{k} dot{Psi} right) times mathrm{R} end{aligned} $$
or
$$ boxed{ boldsymbol{omega} = hat{imath} dot{Phi}+mathrm{R}_X hat{jmath} dot{Theta}+mathrm{R}_X mathrm{R}_Y hat{k} dot{Psi} } $$
Using linear algebra the above is
$$boldsymbol{omega} = pmatrix{1 0 0} dot{Phi}+pmatrix{0 cosPhi sinPhi } dot{Theta}+ pmatrix{ sinTheta -sinPhicosTheta cosPhi cosTheta } dot{Psi} $$
Answered by John Alexiou on August 24, 2021
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