Joint reaction force vector orientation during flexion/extension motion

Main Forum
1

Hello. I need joint force direction vector angle (angle in degrees or radians) when {0, 30, 60) represents the elbow flexion angle in degrees. I attach my model. What should I do?

2

Hi,

Attached please find a modified version of your model which enables the visualization of the elbow joint reaction forces.

Here is the pieces of code which I’ve added to your original main file:

    HumanModel.Right.ShoulderArm.Seg.Humerus.fe = 
    {
      AnyRefNode ReferenceNode =
      {
        ARel = RotMat(-pi/2, y);
        
        AnyDrawRefFrame DrwFrame = 
        {
          RGB = {1, 0, 0};
          ScaleXYZ = 0.1*{1, 1, 1};
        };
      };
    };

    AnyForceMomentMeasure2 ReactionMeasure = 
    {
      AnyForceBase& reac = .HumanModel.Right.ShoulderArm.Jnt.FE.Constraints.Reaction;
      AnyRefFrame& ref = .HumanModel.Right.ShoulderArm.Seg.Humerus.fe.ReferenceNode;
      AnySeg& seg = .HumanModel.Right.ShoulderArm.Seg.Humerus;
      AnyVec3 Flocal = F * ref.Axes;
      AnyVec3 Mlocal = M * ref.Axes;
    };    
    
    AnyDrawVector DrawReaction = 
    {
      AnyRefFrame& ref = .HumanModel.Right.ShoulderArm.Seg.Humerus.fe.ReferenceNode ;
      Vec = .ReactionMeasure.Flocal *  Main.DrawSettings.DrawSettingsSupport.Lin.ScaleFactor;
      GlobalCoord = Off;
      
      PointAway = On;
      
      Line = 
      {
        RGB = {1, 1, 1};
        Thickness = 0.005;
        End.Style = Line3DCapStyleArrow ;
      };
    };

Flocal variable in the ‘ReactionMeasure’ object will display the local representation of the elbow joint reaction force.

So I think you can simply calculate the necessary angle by using some vector operations.

I hope this may help you.

Best regards,
Moonki Jung