5.1 Modeling Using MPLAB® Mindi™

The classical way of modeling a DC motor is as two differential equations, one for the mechanical and one for the electrical dynamics as shown in below:

$J\ddot{\theta }+b\dot{\theta }=Ki$

$L\dot{i}+Ri=V-K\dot{\theta }$

MPLAB Mindi is only capable of simulating circuit elements, therefore the mechanical equation is transformed into an equivalent circuit representation. This is achieved by saying that $R_{los}=b/K^2$, $L_I=J/K^2$ and $i_{emf}=\dot{\theta }K$. This gives the differential equation:

$L_I\dot{i_{emf}}+R_{los}{i}_{emf}=i$

$L\dot{i}+Ri=V-i_{emf}$

The model of the DC motor consists of three parts; Motor_Electrical, Motor_Mechanical and Motor_Load.