Page 155 - The ROV Manual - A User Guide for Remotely Operated Vehicles 2nd edition

always get a “bigger generator” (due to mission creep)—which typically sets the design spiral spin- ning out of control. The general rule is to make all components big enough (but not bigger), to high enough specifications (but not higher) while using materials of the best quality (but not better). This optimizes weight, performance, and cost (but is not an easy task).
The supply side of the requirements budget is then generated with any conversion from the resi- dent input power (e.g., AC to DC, high-to-low/low-to-high voltage, electrical to mechanical) result- ing in a loss in efficiency, thus increasing the input power requirement. Each component (e.g., cameras, lights, thrusters) has an individual power requirement. Each conductor has a resistance, as does each connection in the circuit. Each energy conversion costs efficiency. The power budget must balance in order to achieve the required operation at the end effector or sensor (as this is the mission). Supply must be greater than or equal to the demand (Figure 7.2) in order for the system to function as designed.
The power requirements progression, from the smallest of vehicles to the largest, emulates a logarithmic curve (Figure 7.3); as components are added, the vehicle size increases (and the power requirements take off!). All vehicles from OCROV to WCROV require some common components,
e.g., Generator
Supply
e.g., Junction box on vehicle
Supply≥Demand
WCROV
e.g., Vehicle components
Demand
7.1 Electrical considerations 143
FIGURE 7.2
Cables and connectors
Whips and jumpers
Top-side power budget diagram.
OCROV
MSROV
Cameras, lights, vehicle sensors Light electric thrusters
Heavy electric thrusters
Light pump for manips and tools Heavy pump for manips and tools
FIGURE 7.3
Size class of vehicle
Power requirements (in kilowatts) by component class and vehicle category.
Requirement point
Power requirement (in kW)