Differential steering challenge problem

I posed a challenge problem in today's guest lecture in the Embedded Systems Programming course.  The challenge is to efficiently control a simple differential steering robot.  The Acumen code below presents both the model of the robot (dsbot), a target object, and a very simple controller.  How well the controller performs is measured in the Main object by the total energy (e) at the end of the simulation.  My score was 161.3.  You are welcome to submit to me the code of an controller that performs better.


The only rule is that you can only send me the code for the controller.  In other words, the code for the robot, target, and the main program has to remain the same.


class dsbot () // Differential steering robot
  private x=0; x'=0; y=0; y'=0;
          a=0; a'=0 ; v=0
  end
  x' [=] v * cos(a);
  y' [=] v * sin(a);
end


class target () // A simple target moving in a circle
  private t=0; t'=0; x=0; y=0 end
  t' [=] 1;
  x = 2*sin(t/1.5);
  y = 2*cos(t/1.5);
end


class controller () // A simple controller
  private t =0; t'=0; // local time
  ex = 0; ey = 0; // Error in x and y
  ia = 0; // Input angle
  ov = 0; oap = 0; // Ouput v and a'
  end
  t' [=] 1;
  if t>0.1
  t = 0;
  // Control code goes here
  if (ex*ex + ey*ey) < 1 // Robot is close enough. Slow down 
    ov = 1   
  else
    ov = 4; 
    if   (   (ex>0 && cos(ia)<0) 
          || (ey>0 && sin(ia)<0)) 
       || (  (ex<0 && cos(ia)>0) 
           ||(ey<0 && sin(ia)>0))
      oap = -10
    else
      oap = 0
    end
  end
 else
 end
end


class Main(simulator)
  private r = create dsbot ();
          t = create target ();
          c = create controller ();
          d = 0; e = 0; e'= 0; // Measures of success
  end
  // Controller see robot
    c.ex [=] t.x - r.x;
    c.ey [=] t.y - r.y;
    c.ia [=] r.a;
  // Robot listens to controller
    r.a' [=] c.oap;
    r.v [=] c.ov;
  // Error over time
    d [=] sqrt(c.ex*c.ex+c.ey*c.ey);
    e' [=] r.v*r.v + 2*d*d
end