Open Loop Diagram
The open loop block diagram uses the desired position and disturbance as inputs and the actual position on the Etch-a-Sketch as an output. The desired position vector is first converted to velocities using finite step size differentiation, then the velocity values are converted to PWM signals using the equations described in the previous section (Velocity Calculation). The disturbances are caused by slippage in the motor and in the gear train.
Closed Loop Diagram
The closed loop clock diagram uses feedback control to reject the disturbances due to noise and slipping in the motor and in the gear train. As shown below, the closed loop system includes 2 VEX 90-pulse quadrature encoders which provide feedback of the actual position. For this project, we have implemented proportional position control. After playing with the gains for a while, we found our ideal values to range between 10 and 15. Use of integral control is not necessary since our plant is rank zero and has no steady state error.
Transfer function (output = Y, input = D and R):
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