设定非线性系统Simulink框图，并观察在单位阶跃信号的输入下的输出曲线和误差信号。-Set the Simulink block diagram of the nonlinear system and observe the output curve and the error signal at the input of the unit step signal.

已知直流电动机拖动仿真框图，并利用Simulink提取该系统的总模型，并绘制系统阶跃响应和其曲线。-Known DC motor drag simulation diagram, and use Simulink to extract the total model of the system, and draw the system step response and its curve.