(API) Robot API - get bar forces at user local axis - calcgamma question

[Anonymous]

Hello,

I have a free-form roof steel grid where I want to calculate the in-plane and out-of-plane bending moment of my bars at each connection.

I have read all the posts about how to set the gamma angle in my bars, but when I do it, I don't get the right orientation:

I take two bars at the connection I want to analyze.

I create two vectors, from the connecting node to the end nodes of the bars.

I calculate the cross product of the two vectors, that gives me the normal vector of the plane between the two bars = mynormal

I calculate the gamma angle that my bar should have to be orientated in the direction of the plane I want (mynormal in global coordinates) :

foundgamma = myRobotBar.CalcGamma( mynormal(0), mynormal(1), mynormal(2))

myRobotBar.gamma = foundgamma

I dont' get the right angle. By doing it aproximately with the Robot GUI, I get a gamma angle of -37 degrees, with my script 1.38 .

I have check every step and it is right, the only thing I cannot check is the function CalcGamma, because I don't know the z local axis vector

Does the function CalcGamma returns the angle in radians or degrees?

Alternatively I would like to get the local z vector of my bar in global coordinate, so I can calculate the angle myself and transform the moments to the axis I want.

How can I do this?

I have been working on this for days, any help is greatly appreciated.

Cheers,

V.

[Rafal.Gaweda]

Alternatively I would like to get the local z vector of my bar in global coordinate, so I can calculate the angle myself and transform the moments to the axis I want.

Bar.GetLocalMtx    to get transformation matrix

Example :

http://forums.autodesk.com/t5/robot-structural-analysis/api-macro-for-nodal-displacements-in-local-c...

[Anonymous]

Thanks Rafal for the quick reply.

I have several questions about the GetLocalMtx:
Description
Function returns transformation matrix for the bar local system.

What does that means?
If I multiply LocaMtx by (0,0,1), do I get the Z local axis in global coordinates?

Is LocalMtx the transformation matrix that transform a vector given in local coordinates to a vector in global coordinates?

Also, do you know if in Robot 2014 Calcgamma retuns the angle in degrees?

Many thanks,

V.

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[Rafal.Gaweda]

Is LocalMtx the transformation matrix that transform a vector given in local coordinates to a vector in global coordinates?

Local to global : vector x transposed mtx

Global to local : vector x mtx

Also, do you know if in Robot 2014 Calcgamma retuns the angle in degrees?

Degrees, I guess