Solution 1.4.4 DC Motor Power Amplifier E a θ Heliopot V θ Σ V r + Figure 1: Block diagram of motor with feedback The block diagram is shown in Figure 1. This is the archtypical control problem. The motor's shaft position  is sensed by the heliopot as a voltage. The desired shaft postion is input as a voltage, V r , and substracted from V  . The di erence E = V r ;V  is fed forward through a power ampli er which supplies an electrical signal of sucientpower to the armature windings of motor. In the gure E a represents the voltage that appears across the armature windings. 1