Page 169 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

FIGURE 7.15
Common joystick.
7.2.2 Motor control electronics
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7.2 Control systems 157
Since OCROV and MSROV systems use mainly electronic motors for thruster-based locomotion, a study of basic motor control is in order.
A basic control of direction and proportional scaling of electrical motors is necessary to finely control the motion of the submersible. If only “On” or “Off” were the choices of motor control via switches, the operator would quickly lose control of the vehicle due to the inability to make the fine corrections needed for accurate navigation. In the early days of ROVs, the simple analog rheo- stat was used for motor control. It was quite a difficult task to control a vehicle with the operation of three or four independent rheostat knobs while attempting to fly a straight line. Later came digi- tal control of electric motors and the finer science of robotics took a great leap forward.
The basic electronic circuit that made the control of electronic motors used in robotics and industrial components so incredibly useful is known as the “H-bridge.” An understanding of the H-bridge (discussed later in this section) and the digital control of that H-bridge will help significantly with the understanding of robotic locomotion.
Consider the analysis of a simple electric circuit (Figure 7.16). As discussed earlier in this chap- ter, Ohm’s law gives a relationship between voltage (V), current (I), and resistance (R) that is stated as V 5 IR. In Figure 7.16, the current and voltage are known, and thus the resistance can be calcu- lated to be 3.0 Ω.
7.2.2.1 Inductors
An inductor is an energy storage device that can be as simple as a single loop of wire or consist of many turns of wire wound around a core. Energy is stored in the form of a magnetic field in or around the inductor. Whenever current flows through a wire, it creates a magnetic field around the wire. By