316 10. SYSTEM LEVEL DESIGN
10.1 SUBMERSIBLE ROBOT
The area of submersible robots is fascinating and challenging. To design a robot is quite complex.
To add the additional requirement of waterprooﬁng, key components adds an additional level of
challenge. (Water and electricity do not mix!) In this section, we develop a control system for a
remotely operated vehicle, an ROV. By deﬁnition, an ROV is equipped with a tether umbilical
cable that provides power and control signals from a surface support platform. An Autonomous
Underwater Vehicle (AUV) carries its own power and control equipment and does not require surface
support. We limit our discussion to the development of an MSP430 based control system. Details
on the construction and waterprooﬁng of an ROV are provided in “Build Your Own Underwater
Robot and Other Wet Projects” by Harry Bohm and Vickie Jensen. We develop a control system
for the SeaPerch style of ROV as shown in Figure 10.1. There is a national competition for students
based on the SeaPerch ROV. The goal of the program is to stimulate interest in the next generation
of marine related engineering specialties [seaperch].
The requirements for this system include:
• Develop a control system to allow a three motor ROV to move forward, left (port) and right
• The ROV will be pushed down to a shallow depth via a vertical thruster and return to surface
based on its own, slightly positive buoyancy.
• ROV movement will be under joystick control.
• All power and control circuitry will be maintained in a surface support platform.
10.1.2 STRUCTURE CHART
The Sea Perch structure chart is provided in Figure 10.2. As can be seen in the ﬁgure, the SeaPerch
control system will accept input from the ﬁve position joystick (left, right, select, up and down) on
the MSP430F5438 experimenter board. The joystick has dedicated connections to the MSP430 as
shown in Figure 10.3.
In response to user joystick input, the SeaPerch control algorithm will issue a control command
indicating desired ROV direction. In response to this desired direction command, the motor control
algorithm will issue control signals to assert the appropriate motors and LEDs.
10.1.3 CIRCUIT DIAGRAM
The circuit diagram for the SeaPerch control system is provided in Figure 10.3.The joystick onboard
the MSP430F5438 experimenter board will be used to select desired ROV direction.There are three
LED interface circuits connected to pins 4.3, 4.5 and 4.6 of the experimenter board. The motors are