evaluation

[Pano]

Bye to all,

I have the following mechanical system in which the 3 axes motor meet in one point (spherical pole)I have to evaluate the drive torque necessary to the first motor (the green one) to rotate the whole structure.
I positioned the center point of the axieme on the center of the reference system that I added to the motor and aligned the axes so that the blue axis (axis z) of the sdr of the concida motor with the axieme y axis y.

at this point, having done some research on the web and read pdf various, I have to use the second eq cardinal of the dynamic so that:

c[SUB]m[/SUB]-c[SUB]r[/SUB]=j*(dw/dt)

where[SUB]m[/SUB] is the couple motrice, c[SUB]r[/SUB] the strong couple and j the moment of inertia.

what is not very clear to me is what value of j shown in the physical props of the axieme I must use I have to use i2 (wikipedia should be[SUB]yy[/SUB] of the inertia tensor) in the main card? or any value in the global card?

Thank you.

 

[meccanicamg]

same problem with solidworks that you do not understand how devil aligns the axes.
If the central motor has to turn all the toy, you must use the moment of inertia compared to the central vertical axis, that is the blue one of the reference system.
If you want to know if it is right, create a cylinder where its moment of inertia is easy to calculate. positions in the axieme and rival the thing. so you know if it's right or not.
is the only system not to miss the reference system.

 

[Pano]

I know that I have to use the moment of inertia compared to the blue vertical axis, but I can't, because inventor does not allow to change the sdr with which to calculate the physical properties (instead I think that with solidworks you can).
the systems you see in the midst of the engines I added them in the part of the motor and then I aligned that of the axieme (which inventor uses to calculate everything) with that of the green motor so that the axis (z/blu) of the motor (which makes everything rotate) is aligned with that y/verde of the axieme sdr.

I tried with a 10mm steel radius cylinder and get:the moment of inertia compared to y is mr[SUP]2[/SUP]/2, or 0.018*10[SUP]2[/SUP]/2=0.9 kg*m[SUP]2[/SUP].
Where does that 0.231 come from? ?

 

[meccanicamg]

I hate when you don't have the right numbers. Isn't that you didn't draw it on the center of the three floors? There's something wrong and I don't think we can't make a simple calculation. . .
with global or central buttons find the right value?
And yet it should be a simple information to have, but all the time I lose some means because I do not find a logical rule.

 

[Pano]

I hate when you don't have the right numbers. Isn't that you didn't draw it on the center of the three floors?

the 3 yellow lines you see at the base of the cylinder are of the refractive system of the part

with global or central buttons find the right value?

I also tried with a ball with the sdr in the center of the samethe moment of inertia is 2*mr[SUP]2[/SUP]/5 = 2*0,004 kg * 10[SUP]2[/SUP] mm / 5 = 0,16 kg*mm[SUP]2[/SUP]where does the 0.041 come from? (global, baricentre, main are all numerically equal)

Now I try to ask about the fourm of autodesk directly, let's see what they say

 

[Pano]

solved, the problem was to confuse diameter/ray using the remote control; after this I can subterranean:

But I took a nap on inertia and I realized that:
the main card: calculates moments compared to a sdr with origin in the mass center and axes aligned to the main axes of inertia ( getting the main moment of inertia and the diagonal matrix)
the global card: calculates moments compared to the sdr of the part/axis
the baricentro card: calculates moments compared to a sdr with origin in the mass center and axes aligned to the sdr of the part/assieme

therefore, summing up, if they place the structure with the origin of the solid sdr to the green motor coincident with the origin of the sdr of the axieme and align the axis of rotation of the motor with the axis y of the sdr of the axieme I have to use the iyyy value that I see in the global card; should be correct