Required Hardware

Flight Controller Board →
Processes the pilot input and sensor data, and controls the lights and actuators on the vehicle.
Onboard (Companion) Computer →
Streams video and relays communications between the autopilot and control station. Enables custom device/sensor integrations
Control Station (Topside) Computer →
Sends operator input to the vehicle, and receives and displays information from the vehicle.
Joystick / Gamepad →
Allows the operator to directly control the vehicle, using stick movements and button presses.
Camera →
Allows the operator to see and record from the vehicle's point of view. If paired with a tilting mount or other gimbal it can be moved during operation.
Electronic Speed Controllers (ESCs) →
Used to control the speed/thrust of motors and thrusters.
Thrusters →
Used to maneuver a vehicle in marine environments. The number and orientation of thrusters on a vehicle determines the degrees of freedom (DoF) it may maneuver in.
Power Sensor / Battery Monitor →
Measures the voltage and current consumption to estimate power capacity and usage.
Power Supply / Battery →
Supplies and distributes power to all onboard electronics, including the high current draw of the thrusters. A regulator converts the main supplied power (from a battery or otherwise) into appropriate steady voltages for the more sensitive electronics.
Tether →
Provides low latency high-bandwidth communication between the onboard computer and the control station, which other technologies are poorly suited to.

Recommended Extra Hardware

Tether Interface →
Converts an ethernet connection to a signal type more suited to long distances and different tether types.
Pressure Sensor →
Allows estimating vehicle depth.
Camera Tilt Mount / Gimbal →
Used to move and/or stabilise the camera, for smoother video feeds and looking around without needing to rotate or move the whole vehicle.
Lights →
Used to improve camera visibility in low light conditions (e.g. at night, under cover, or deep under water). Important for visual inspections and navigation.

Additional Components and Peripheral Devices

Leak Sensors →
Detect and provide warning if a leak occurs, before it gets to and damages the electronics in an enclosure.
Sonars →
Allows measuring range to surfaces, or acoustically imaging targets. Can be helpful for navigation and terrain following, especially in structured environments without alternative positioning systems. Robust to poor lighting and water clarity.
Positioning Sensors (GPS / DVL) →
Allows waypoint and target-based navigation, position holding, and location-tagged data collection.
Other Sensors (Temperature, Salinity, Thickness, etc) →
Can be helpful for research, or estimating related phenomena (e.g. sound speed for sonar and acoustic positioning performance).
Servos →
Useful when a component needs to be actuated or rotated. They can be inside an enclosure to rotate cameras, or depth-rated and used outside of enclosures.
Ethernet (Network) Switch →
Provides ethernet-based expandability without loading the onboard computer, including simple interfacing with IP cameras and other sensors that have an ethernet interface.
Electrical Switch →
Allows turning a circuit on/off inside an enclosure without needing to open it. Can be used for arming safety, or for disconnecting power to the control electronics to reduce idle power usage.
Electronic Switches (Relays and MOSFETs) →
Enables the autopilot and/or onboard computer to control higher voltage (>5V DC) and high power circuits via software.
Grippers and Manipulators →
A gripper is a useful tool for picking up small objects, attaching recovery lines, or freeing a snagged tether. Other manipulators may be useful in cleaning, inspection, or repair tasks.
Indicator Lights →
Used to provide visual indications of electronics and/or software status and errors, especially with opaque enclosures.
Acoustic Modems →
Provides low bandwidth underwater remote communication. Can be used with autonomous vehicles or untethered devices/sensors, or as a short term emergency backup if the vehicle tether gets severed.