Contact force direction

Main Forum
1

Hi,

I have a question about the definition of the contact force direction. Attached is a part of the pipetting model. The model can run by loading “Main.any”. This is a small independent model. I run it on v3.1, it also works on v5.1.

The thumb is pressed on the pipette button. The contact force should be normal to the Center-of-Pressure of the button; however, it seems always in the direction the global system. I have tried to change “F” to “Flocal” in Force3D, but had no effects.

John

2

Hi,

I have a quick look on your code.

In ‘contact_force.any’ file in your model, I added a line like this:

AnyDrawVector DrawSupport1 = {
  AnyRefFrame &ref = .CenterOfPressure1;
  Vec = 0.002*.ForceOnPressureCenter.F;
  PointAway = On;
  DrawCoord = Off;
  Line.RGB = {0,0,1};
  Line.Thickness =0.001;
  Line.End.Thickness = 2*0.0075;
  Line.End.Length = 2*0.0075;
  [b]GlobalCoord = Off;[/b]
};

Then you can see the different result of force visualization.

Best regards,
Moonki

3

Moonki:

Thanks! The contact force is now shown in correct direction by adding “GlobalCoord = Off”.

I have here a further question for the same model. I have changed “F” to “Flocal” in AnyForce3D, but don’t see any difference. I don’t know if this has a physical effect on the model.

John

4

Hi John,

The number of active reaction and driver forces of your model is less than the number of degrees of freedom. So the inverse dynamics can’t do solve your model.

When I looked your model, you may have to modify ‘thumb_drivers.any’ file to increase the number of active reaction and driver forces.

This can be one solution:

AnyFolder Drivers = {    
  //---------------------------------
//  AnyKinEqSimpleDriver CMCMotion = {
    AnyKinEqInterPolDriver CMCMotion = {     
    AnySphericalJoint &Jnts = Main.ThumbModel.Jnts.CMC;
    
    AnyVar AD0 = (-10/180)*pi;
    AnyVar FE0 = (-20/180)*pi;
    AnyVar PS0 = (160/180)*pi;

    Data={PS0-Main.jnt_data_T.Data[2]*pi/180,AD0+Main.jnt_data_T.Data[0]*pi/180,FE0+Main.jnt_data_T.Data[1]*pi/180};
    T=Main.jnt_data_T.T;
    Type = Bspline;
    BsplineOrder = 4;

    //Reaction.Type = {Off,Off,Off};
    Reaction.Type = {On,On,On};
//    
    
  }; //CMC driver

Then you may be able to see the change according to your choice:

AnyForce3D ForceOnPressureCenter ={
  AnySeg &ref1=.CenterOfPressure1;
  AnyVar Friction = 0.0;
  AnyVector fn = -Main.force_data_T(t);
  AnyVector ft = fn*Friction;
  //F={ft[1], ft[1], fn[1]};
  Flocal = {ft[1], ft[1], fn[1]};
};

I hope this may helpful to you.

Best regards,
Moonki

5

Moonki:

Thanks a lot! Now, my model does what is supposed to do.

John