# double_rigid_pendulum.mbd

begin: data;
   problem: initial value;
end: data;

begin: initial value;
   initial time:   0.;
   final time:     5.;
   time step:      1.e-3;
   max iterations: 10;
   tolerance:      1.e-6;
end: initial value;

begin: control data;
   structural nodes: 2;
   rigid bodies:     2;
   joints:           2;
   gravity;
end: control data;

# Design Variables
set: real M = 1.; # Mass of Link1 and Link2
set: real L = 1.; # Length of Link1 and Link2

# Node Labels
set: integer Node_Link1 = 1;
set: integer Node_Link2 = 2;

# Body Labels
set: integer Body_Link1 = 1;
set: integer Body_Link2 = 2;

# Joint Labels
set: integer JoRevp_Link1       = 1;
set: integer JoRevh_Link1_Link2 = 2;

begin: nodes;
   structural: Node_Link1, dynamic,
      1./2.*L, 0., 0., # absolute position
      eye,             # absolute orientation
      null,            # absolute velocity
      null;            # absolute angular velocity
      
   structural: Node_Link2, dynamic,  
      L, 0., 1./2.*L,        # absolute position
      euler, 0., -pi/2., 0., # absolute orientation
      null,                  # absolute velocity
      null;                  # absolute angular velocity
      
end: nodes;

begin: elements;
   body: Body_Link1, Node_Link1,
      M,                                # mass
      null,                             # relative center of mass
      diag, 0., M*L^2./12., M*L^2./12.; # inertia matrix
      
   body: Body_Link2, Node_Link2, 
      M,                                # mass
      null,                             # relative center of mass
      diag, 0., M*L^2./12., M*L^2./12.; # inertia matrix
      
   joint: JoRevp_Link1, 
      revolute pin, 
         Node_Link1, 
            -1./2.*L, 0., 0.,                    # relative offset
            hinge, 1, 1., 0., 0., 3, 0., 1., 0., # relative axis orientation
            null,                                # absolute pin position
            hinge, 1, 1., 0., 0., 3, 0., 1., 0.; # absolute pin orientation
            
   joint: JoRevh_Link1_Link2, 
      revolute hinge, 
         Node_Link1,
            1./2.*L, 0., 0.,                     # relative offset
            hinge, 1, 1., 0., 0., 3, 0., 1., 0., # relative axis orientation
         Node_Link2,
            -1./2.*L, 0., 0.,                    # relative offset
            hinge, 1, 1., 0., 0., 3, 0., 1., 0.; # relative axis orientation
    
   gravity: 0., 0., -1., const, 9.81;
   
end: elements;