AnyForceConstraint

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1

Hi everybody!!!

I had trouble performing the demo on AnyForceConstraint from the reference manual. The aim is to apply constraints on forces, in particular reaction force.
When I ran the inversedynamics of the ArmModelStudy, I received an error message:
" ArmModelStudy2 : Model is kinematically indeterminate : Velocity and acceleration analysis failed : 17 independent constraints and 18 unknowns"

I couldn’t understand it, because the number of the rigid-body d.o.f and the number of the constraints are the same: 18

Arnaud

2

Hi Arnaud,

Even if the number of constraints would be same as the number of DOFs, the combinations of your constraints should be reasonable to be solved.

When I compared your model with our example, you changed the orientations of some reference nodes. Thus you also should check whether the MeasureOrganizer of your drivers are defined well or not.

Attached please find my modified version of your model.

I’ve changed the following things:

    AnyKinDriver BoxMotion = {
      
      AnyKinLinear Lin = {
        //Axis = z;
        Ref = 0;
        AnyRefFrame &WallRef = ..WallRef;
        AnyRefFrame &Box    = ..Box;
      };
      
      AnyKinRotational Rot = {
        Type = RotAxesAngles;
        AnyRefFrame &WallRef = ..WallRef;
        AnyRefFrame &Box    = ..Box;
      };
      
      DriverPos0 = {0,0,0,0,0,0};
      DriverVel0 = {0,-0.4, 0,0,0,0};
    };
    
    
    AnyKinLinear HandBoxMeasure = {
      //Axis = z;
      Ref = 0;
      AnyRefFrame &Box   = .Box;
      AnyRefFrame &Hand  = .Hand;
    };
    
    AnyKinEq HandMotion = {
      AnyKinMeasure &HandBoxMeasure = .HandBoxMeasure;
      MeasureOrganizer = {0,1};
      Reaction.Type = {Off,Off};     
    };

I could run the kinematic analysis of your model, but I could not run the inverse dynamics of your model. Maybe there are still some problems in the definitions of reaction forces.

I hope you can try to figure out whether there are some missing reactions or forces in your model.

Best regards,
Moonki

3