Reaction forces in Global reference frame?

Archive AnyScript Yahoo archive
1

Hello

I have been using the Simple arm model generated in the tutorial
“Getting started with AnyScript”.

To get the reaction forces in f.x the elbow I have used in the AnyChart
Main.ArmStudy.Output.Model.Jnts.Elbow.Constraints.Reaction.Fout
As I understand this is the reaction forces in the joint in the
reference frame defined by the first node in the joint.

I would like to have the reaction forces in the GlobalRefFrame. Is
this possible and in that case how?

Best regards
Marie

2

Hi

Your understanding of the reaction forces is correct: the reaction
force is given in the coordinate system of the first reference frame
in the joint.
It is possible to display it in the global reference frame. For that
you have to make a scalar product of the joint constraints
reactions times the transposed orientation matrix of the local
frame, please see example below.

As the Fout output of the elbow joint is a 5 components vector (3
force reactions and 2 moments reaction) and the orientation matrix
is a 3x3, it’s not possible to make the scalar product directly. You
have to separate Fout vector in 2 three-component vectors (one for
the forces and one for the moments).

here are the lines you have to add in ArmStudy:

AnyOutputFun ElbowReacForce =
{
Val = {.Model.Jnts.Elbow.Constraints.Reaction.Fout
[0], .Model.Jnts.Elbow.Constraints.Reaction.Fout
[1], .Model.Jnts.Elbow.Constraints.Reaction.Fout[2]}
*…ArmModel.Segs.UpperArm.ElbowNode.Axes’;
};
AnyOutputFun ElbowReacMoment =
{
Val = {.Model.Jnts.Elbow.Constraints.Reaction.Fout
[3], .Model.Jnts.Elbow.Constraints.Reaction.Fout[4], 0}
*…ArmModel.Segs.UpperArm.ElbowNode.Axes’;
};

You will now have two new output functions giving you the reaction
forces and moments in the elbow joint in the global frame.

You can also have a look at this folder in the file section of the
group: SmallExamples. There is a file explaining how to make the
coordinate transformations, please see the
file “CoordinateTransformations.any”

Please ask again if you have further questions

Best regards
AnyBody Support, Sylvain

— In anyscript@yahoogroups.com, “lund.marie” <lund.marie@…>
wrote:
>
> Hello
>
> I have been using the Simple arm model generated in the tutorial
> “Getting started with AnyScript”.
>
> To get the reaction forces in f.x the elbow I have used in the
AnyChart
> Main.ArmStudy.Output.Model.Jnts.Elbow.Constraints.Reaction.Fout
> As I understand this is the reaction forces in the joint in the
> reference frame defined by the first node in the joint.
>
> I would like to have the reaction forces in the GlobalRefFrame. Is
> this possible and in that case how?
>
> Best regards
> Marie
>