Hello
I am in the process of creating a new library and am stuck somewhere. I have created a library called FourBarLinkage for performing simple positional, velocity and acceleration analysis. While performing a simple positional analysis(with the 4 bar system being massless and at rest), I am facing a sight difficulty. I connect the components and simulate the model and it gives me the results. But the values of the angle it calculates seem random and are not within the standard values(0 to 2pi) . The values of the angles calculated vary from -100 rad to +200 rad. I am confused as to why this is happening and as a result I am not able to feed in and calculate the resultant angular velocities(as the angles calculated vary largely).

Please find the Library and the model code below.

Thanks
Pratyush

===================================================================================================================================
package FourBarLinkage
  import SI = Modelica.SIunits;
  package Connectors
    connector RevoluteA
      SI.Position Coordinate[2];
      flow SI.Force Reaction[2];
      annotation(Icon(graphics = {Ellipse(rotation = 0, lineColor = {0,0,255}, fillColor = {100,100,100}, pattern = LinePattern.Solid, fillPattern = FillPattern.Solid, lineThickness = 0.25, extent = {{-70,70},{70,-70}})}));
    end RevoluteA;
    connector RevoluteB
      SI.Position Coordinate[2];
      flow SI.Force Reaction[2];
      annotation(Icon(graphics = {Ellipse(rotation = 0, lineColor = {0,0,255}, fillColor = {200,200,200}, pattern = LinePattern.Solid, fillPattern = FillPattern.Solid, lineThickness = 0.25, extent = {{-70,70},{70,-70}})}));
    end RevoluteB;
    partial model BarEnds
      annotation(Diagram(), Icon());
      RevoluteB b annotation(Placement(visible = true, transformation(origin = {100,0}, extent = {{-12,-12},{12,12}}, rotation = 0), iconTransformation(origin = {100,0}, extent = {{-12,-12},{12,12}}, rotation = 0)));
      RevoluteA a annotation(Placement(visible = true, transformation(origin = {-100,0}, extent = {{-12,-12},{12,12}}, rotation = 0), iconTransformation(origin = {-100,0}, extent = {{-12,-12},{12,12}}, rotation = 0)));
    end BarEnds;
  end Connectors;
  package Components
    model Bar
      extends FourBarLinkage.Connectors.BarEnds;
      parameter SI.Length l(min = 0) "Length of the Bar";
      SI.Angle theta "Angle with the +ve X axis";
      annotation(Icon(graphics = {Rectangle(rotation = 0, lineColor = {0,0,255}, fillColor = {0,0,255}, pattern = LinePattern.Solid, fillPattern = FillPattern.None, lineThickness = 0.25, extent = {{-82.6185,17.1558},{83.5214,-18.5102}}),Text(rotation = 0, lineColor = {0,0,255}, fillColor = {0,0,255}, pattern = LinePattern.Solid, fillPattern = FillPattern.None, lineThickness = 0.25, extent = {{-77.6524,-29.7968},{75.8465,-55.079}}, textString = "l=%l"),Text(rotation = 0, lineColor = {0,0,255}, fillColor = {0,0,255}, pattern = LinePattern.Solid, fillPattern = FillPattern.None, lineThickness = 0.25, extent = {{-57.3363,61.851},{53.7246,17.6072}}, textString = "%name")}));
    equation
      b.Coordinate[1] = a.Coordinate[1] + l * cos(theta);
      b.Coordinate[2] = a.Coordinate[2] + l * sin(theta);
      b.Reaction[1] = 0;
      b.Reaction[2] = 0;
    end Bar;
    model Ground
      extends FourBarLinkage.Connectors.BarEnds;
      parameter SI.Length l(min = 0) "Length of the Ground";
      annotation(Icon(graphics = {Rectangle(rotation = 0, lineColor = {0,0,255}, fillColor = {0,0,255}, pattern = LinePattern.Solid, fillPattern = FillPattern.None, lineThickness = 0.25, extent = {{-86.2302,24.8307},{87.1332,-28.4424}}),Text(rotation = 0, lineColor = {0,0,255}, fillColor = {0,0,255}, pattern = LinePattern.Solid, fillPattern = FillPattern.None, lineThickness = 0.25, extent = {{-75.395,27.5395},{74.0406,-17.1558}}, textString = "Ground")}));
    equation
      a.Coordinate[1] = 0;
      a.Coordinate[2] = 0;
      b.Coordinate[1] = l;
      b.Coordinate[2] = 0;
      a.Reaction[1] = 0;
      a.Reaction[2] = 0;
    end Ground;
  end Components;
end FourBarLinkage;

====================================================================================================================================

model Test
  FourBarLinkage.Components.Ground ground1(l = 0.4) annotation(Placement(visible = true, transformation(origin = {-7.67494,-23.4763}, extent = {{-12,-12},{12,12}}, rotation = 0)));
  FourBarLinkage.Components.Bar bar1(l = 0.2) annotation(Placement(visible = true, transformation(origin = {-35.6659,20.7675}, extent = {{-12,-12},{12,12}}, rotation = 0)));
  FourBarLinkage.Components.Bar bar2(l = 0.4) annotation(Placement(visible = true, transformation(origin = {23.4763,48.307}, extent = {{-12,-12},{12,12}}, rotation = 0)));
  FourBarLinkage.Components.Bar bar3(l = 0.5) annotation(Placement(visible = true, transformation(origin = {47.8555,6.77201}, extent = {{-12,-12},{12,12}}, rotation = 0)));
equation
  connect(bar3.b,ground1.b) annotation(Line(points = {{59.8555,6.77201},{74.7938,6.77201},{74.7938,-23.1015},{4.32506,-23.1015},{4.32506,-23.4763}}));
  connect(bar2.b,bar3.a) annotation(Line(points = {{35.4763,48.307},{43.9157,48.307},{43.9157,19.2131},{26.9898,19.2131},{26.9898,7.09055},{35.8555,7.09055},{35.8555,6.77201}}));
  connect(bar1.b,bar2.a) annotation(Line(points = {{-23.6659,20.7675},{0,20.7675},{0,48.307},{11.4763,48.307},{11.4763,48.307}}));
  connect(ground1.a,bar1.a) annotation(Line(points = {{-19.6749,-23.4763},{-62.754,-23.4763},{-62.754,20.7675},{-47.6659,20.7675},{-47.6659,20.7675}}));
  bar1.theta = 1.00;
end Test;