===== Ball and Beam NXC Code =====

Use the additional library (dist-nx) to get the Infra Red sensor data. ( save it on the same folder of your NXC Code and include it using #include).


{{::dist-nx-lib.rar|}}
{{::nxc_codes.rar|}}

** NXT CODE **

 {{:code1.jpg?direct|}}
 {{::code2.jpg?direct|}}
 {{::code_3.jpg?direct|}}
 {{::code5.jpg?direct|}}
 {{::code_6.jpg?direct|}}

** TUNING THE CODE **

 After introducing the file saving function and the necessary commands to get the data , the system response was slowed down. ( oscillating more than before ). So i made some tuning: 
  * KP=1 and KD=0.60
  * No waiting time inside the if statements
  * 50ms waiting before starting the control loop again.

 The new result is:

 {{::the_last_response.jpg?direct|}}

 {{youtube>Jp9xxLjVyi0?medium}}

** Modifying the Code **

 One way to make the motor movement smoother is to change the rotation commands "PosRegAddAngle" for power commands  "OnFwd" and use the power input as the PID equation ( Power=KP*(delta distance) + KD*(ball velocity). ). 


Insted of using :
<Code>

if (position >21)
{
PosRegAddAngle(OUT_A,-position);
Wait(18);
time=time+40;
}

// Ball is close to set point


if (position<21 & position >0)
{
PosRegAddAngle(OUT_A,0);
time=time+60;

}

if (position <0 & position>-21)
{
PosRegAddAngle(OUT_A,0);
time=time+60;
}


// Ball is far from the set point (negative side)
//Rotating positive angles make the beam go down
if (position < -21)
{
PosRegAddAngle(OUT_A,-position);
Wait(18);
time=time+40;
}


Wait(40);


// After rotating an angle , goes back to 0 degree ( equilibrium position ).
PosRegSetAngle(OUT_A,0);
</Code>

You can just use:

<Code>

power = KP*(dist-d_setpoint) + KD*(velocity);
OnFwd(OUT_A,power)

</Code>

Depending on the direction of the ball , the power variable can change from positive to negative. And the "OnFwd" command with negative power argument runs exactly like the "OnRev".
 You will have to change the gains a little bit (from using rotation commands to power commands ) , but it will make the platform to move smoother