- #1

Tymofei

- 8

- 2

- Homework Statement
- Dynamics

- Relevant Equations
- General moment eq

**Summary::**Just a simple 3d rigid dynamics question which I am trying to solve by placing coordinat system differently from original solution.Everything looks ok but results are different.

**Mod note: Post moved from technical section.**

Thats my question.As you see coordinate system was located at center of mass.I just shifted it to point A and recalculated values.

Everything was same except Inertia about z and y-axis which was multiplied by 4.But at the same time moment effect coming from gravitational force was included to calculations so i thought they will cancel each other.But results was different than was mentioned on the original solution.

I know it looks nonsense trying to figure it when i already have solution but I am kind of obsessed .

By the way my values were:

My values for coordinate system placed at point 'A':

w_z = 6 rad/s

w_x = 2sin(theta) rad/s

w_y = 2cos(theta) rad/s

w_x/dt = 12cos(theta) rad/s^2

w_y/dt = -12sin(theta) rad/s^2

I_z = I_y = 6*10^-3 , I_x = I_xy = I_xz = I_yz = 0

Sum M_x = 0 = M_A_x

Sum M_y = 6*10^-3 * -12sin(theta)* -6*10^-3 * 12sin(theta) = -144* sin(theta)*10^-3 = M_A_y

Sum M_z = 6 * 10^-3 * 2 sin(2theta) = M_A_z - 0.8*9.81*0.075*sin(theta) ==> M_A_z = 6 * 10^-3 * 2 sin(2theta) + 0.8*9.81*0.075*sin(theta)

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