The Basics of Physical Computing with Electric Motors In the first several pages of this chapter, the concept of controlling a DC motor with a transducer (or sensor), microcontroller, and transistor relay driver was illustrated with simulated circuits and a physical control project. Using an electromechanical relay is a traditional approach to driving electric motors because they relay’s switching contacts are capable of handling several amperes of current. Electric motors are really electromechanical devices because they take an electrical signal (voltage and/or current) and convert it to mechanical motion. To overcome the mechanics of rotation, a high inrush current is required from the power supply driving the electromechanical part.
      In the example of the simple physical-computing DC motor control project discussed, the electromechanical relay had the burden of providing the power supply current using a pair of high-ampacity- rated contacts. But there is another alternative for controlling an electric motor: using a power transistor instead of an electromechanical relay. Torque and speed are two important parameters associated with electric motors, and the device that drives them must be capable of controlling these elements efficiently. A microcontroller, along with a power transistor, provides an efficient and clean approach to maintaining constant torque and speed control for electric motors.33098
      The embedded software inside the Arduino has a specialized computing/mathematical approach, using a tested procedure (algorithm) for maintaining torque and speed control for electric motors. An algorithm is simply a step-by-step procedure for calculations The output of the electric motor is constantly monitored by the microcontroller using a feedback transducer/sensor, which provides voltage or current signal data as it relates to the electromechanical device’s torque and/or speed. The embedded software of the microcontroller constantly checks to see if the signal data has deviated, and if so, makes adjustments to the output signal that’s controlling the circuit driving it. So, to some extent, the transducer or sensor that’s monitoring the output parameters of the motor is providing indirect physical-computing activity to the electric motor. Figure 4-15 shows a typical system block diagram for a physical computing–based DC motor controller.论文网
 
Figure 4-15. System block diagram for the DC motor control
Achieving Motor Speed Control with Physical Computing
The discussions in this chapter have been on simple control of DC motors—basically turning them on and off. The remainder of this chapter will explore controlling the speed of the motor using physical-computing techniques. You will be using potentiometer and photocell as input sensor circuits for interacting with the DC motor.
Potentiometer Input Control
       The first technique requires using a potentiometer (discussed in  Chapter 3) to provide an input signal that directs the microcontroller to adjust its output control signal to bias the transistor through modulation. The modulation is accomplished by changing the pulse width of the output control signal generated by the Arduino’s ATmega328 microcontroller. The technique of pulse width modulation (PWM; discussed in Chapter 1) allows for controlling the speed of a DC motor through a transistor. Switching the base at a predetermined frequency allows for the transistor to provide an average sourcing current to the DC motor’s stator for efficient speed control of the electromechanical component. Figure 4-16 shows a typical DC motor speed control technique using the Arduino as the PWM signal generator.
Figure 4-16. Circuit schematic diagram for a physical-computing DC motor speed controller
The construction of the circuit on the solderless breadboard has minimum component and wiring content. Also, there are only two jumper wires from the potentiometer and the base of the 2N2222 to the Arduino single inline header connectors. Figure 4-17 shows the final motor speed controller prototype. 电机物理计算英文文献和中文翻译:http://www.751com.cn/fanyi/lunwen_29982.html