Source-linked AI summary
CougarTail & CUB: A General-Purpose Mast and Central Utility Board for Cylindrical Underwater Enclosures
Ben Washburn, Clayton Smith, Eli Gaskin, Brighton Anderson, Braden Meyers, Brady Moon, Joshua Mangelson
TL;DR
Cylindrical underwater enclosures leave limited usable space when electronics use stacked rectangular PCBs, while integrating compute, power, sensors, and communications is difficult. The paper presents CUB, a circular CM5-and-STM32 board, and CougarTail, a companion GPS and dual-band antenna mast. On CougUV, CUB reduced the electronics allocation from 200 mm and 709 g to 25 mm and 156 g, while the components were bench tested and integrated with the platform.
Problem
Rectangular PCB stacks inefficiently occupy cylindrical underwater-enclosure volume, and underwater systems require difficult integration of compute, power management, sensors, and communications.
Method
The paper develops CUB, a circular 4-inch CM5-and-STM32 board with power and auxiliary connections, alongside CougarTail, an open-source GPS and dual-band antenna mast.
Results
CUB reduced CougUV electronics from 200 mm and 709 g to 25 mm and 156 g, while CougarTail retained above-water data rates after submersion and achieved 1.07 m mean horizontal GPS accuracy with 100% fix reliability.
Takeaways & Limitations
The co-designed board and mast provide a compact, versatile hardware foundation for underwater sensing, autonomy, power management, and surface communications.
Abstract
from arXiv · showhide
Cylindrical watertight enclosures are widely used across various underwater systems, from unmanned underwater vehicles (UUVs), to remotely operated vehicles (ROVs), to various sensor platforms. However, electronics are typically built on rectangular PCBs arranged in horizontal stacks, which inefficiently occupy the circular cross-section volume that is critical for both payload capacity and buoyancy management. This paper presents CUB (Central Utility Board) and CougarTail, a general-purpose system designed to address this gap. CUB is a circular PCB sized for 4-inch-diameter enclosures that consolidates a Raspberry Pi Compute Module 5 (CM5) and an STM32 microcontroller, while also providing power management features and auxiliary connections. Mounted coaxially, CUB reduces the electronics stack of our CougUV from 200 mm of tube length and 709 g to 25 mm and 156 g, returning that length and mass budget to payload and buoyancy trim. CougarTail is an open-source companion sensor mast that houses a GPS antenna and two dual-band (2.4 and 5 GHz) omnidirectional PCB antennas. Both components are validated through bench testing and integration on a CougUV platform, our small open-sourced torpedo UUVs.
I. INTRODUCTION
Underwater vehicles face tight enclosure-space, electronics-integration, and near-surface communication constraints. This paper introduces CUB and CougarTail as compact, general-purpose hardware intended to address those challenges.
- I. INTRODUCTION: The system targets limited underwater volume, costly custom enclosure work, and unreliable GPS and wireless connectivity near the surface.These constraints restrict payload capacity and often require vehicle-specific integration from scratch.
- I. INTRODUCTION: CUB is a circular CM5-and-STM32 board for 4-inch enclosures, while CougarTail is an open-source mast carrying GPS and dual-band antennas.The components also provide power management, auxiliary connections, and connectivity for underwater systems.
- I. INTRODUCTION: The paper contributes a compact modular CM5 compute and I/O board, a custom sensor mast for surface GPS and wireless communications, and validation on the CoUGARs platform.The stated contributions combine hardware design with platform-level testing.
II. RELATED WORK
Low-cost underwater vehicles need compact electronics for power, sensing, processing, buoyancy, and communications. Existing rectangular-board stacks waste cylindrical enclosure cross-sectional space, motivating a circular mainboard and an additional surface-communications mast.
- II. RELATED WORK: Rectangular COTS boards stacked along the tube axis inefficiently occupy cylindrical enclosure cross-sections and reduce available space for buoyancy adjustment.Connectors and supports further increase the displaced volume.
- II. RELATED WORK: Coaxial circular PCBs use enclosure space more efficiently but require custom designs matched to the enclosure diameter.CUB addresses this trade-off with a circular mainboard for a standard 4-inch enclosure.
- II. RELATED WORK: UUVs also need mast-mounted antennas for surface communications and GNSS, so the paper adds a mast to the CoUGARs system with emphasis on ease of assembly.The mast extends the related-work design space for low-cost UUVs and ROVs.
III. CUSTOM PCB DESIGN
CUB consolidates power and data systems onto a cut-circular board that fits coaxially inside commonly used 4-inch Blue Robotics acrylic tubes.
- III. CUSTOM PCB DESIGN: CUB uses cut-circular geometry to minimize footprint and pass-through inconvenience while maximizing board area inside 4-inch acrylic tubes.The design consolidates previously separate systems onto one board, reducing wiring complexity and increasing reliability.
A. Power Management
CUB provides protected battery input, monitored power distribution, external switching, servo power, and independent USB-C access for CM5 programming.
- A. Power Management: CUB accepts a 4S lithium-ion battery through an XT90 connection and adds a 50 amp fuse, current sensor, external power switch, and 7.5 V servo output up to 5 A.A USB-C connection can power and program the CM5 without powering the entire board.
B. Embedded Processing System
CUB combines Linux-capable CM5 processing with STM32 control and broad sensor, actuator, and communication connectivity.
- Embedded Processing System: CUB combines a Linux-capable CM5 with an STM32 microcontroller, using UART communication to pair high-level processing with lower-level task handling.The STM32 manages GPIO-based sensor communication and PWM servo control.
- Embedded Processing System: The board supports leak and water sensors, an external ESC, four fin-control servos, a status display, and Digi XBee radio communication.The CougarTail antennas connect to the CM5 and radio through UFL connections.
D. Development Support Features
CUB supports field development through integrated power, debugging, and expansion features, while CougarTail uses a compact sealed mast to support surfaced communications.
- Development Support Features: CUB provides controlled payload power, extensive processor and peripheral connections, and built-in diagnostic interfaces for prototyping and field troubleshooting.Its relay supports two 3 A payload sockets, while headers expose power, GPIO, I2C, SPI, UART, and CAN connections.
- Development Support Features: CougarTail places GPS, WiFi, and RF antennas in a compact mast that extends above the waterline when surfaced, addressing signal attenuation during shallow submersion.The mast uses a custom housing and insert, with cables routed through a polyurethane tube.
- Development Support Features: The mast assembly is epoxy-encapsulated and backfilled in a PETG shell, with the coating providing a theoretical depth rating above 100 meters.The GPS antenna is positioned at the top for an unobstructed sky view, while WiFi and RF antennas sit lower in the housing.
- Development Support Features: Surface operations use RF radio for mission parameters and startup signals, reserve WiFi for nearby SSH access, and rely on SeaTrac X150 USBL underwater.This division assigns different communication links to surfaced and submerged operation.
V. TESTING AND RESULTS
Testing covered the CougarTail performance summary and GNSS accuracy measurement, with the systems bench tested and deployment onto CougUV in progress.
- Testing and Results: Bench testing of CUB and CougarTail preceded deployment onto the CougUV platform, with results intended to characterize system performance and platform improvements.The supplied testing passages identify the evaluation as bench testing and describe deployment as in progress.
- Testing and Results: Table I is identified as the GNSS accuracy summary, but the supplied passages do not provide its numerical results.
- Testing and Results: Figure 4 summarizes continuous GNSS accuracy during a representative mission and WiFi and radio throughput measured at controlled distances from 5 m to 100 m.The figure covers both navigation accuracy and communication performance across standoff distances.
A. Space and Weight Improvements
CUB substantially reduces the CougUV electronics footprint and mass, returning enclosure resources to payloads, ballast, or buoyancy management.
- Space and Weight Improvements: 200 mm and 709 g become 25 mm and 156 g with CUB, reducing occupied length by 87.5% and mass by 78%.The recovered 175 mm can support sensor payloads, ballast, or buoyancy foam, while 553 g is removed from the trim budget.
B. Mast Data Rates and GPS Performance
CougarTail’s GPS antenna maintained reliable positioning, while the mast preserved above-water data rates after submersion. Cart-based testing also exercised the integrated sensing, control, and communication pipeline.
- Above-water data rates showed no degradation after submersion, supporting the effectiveness of the epoxy-and-shell seal against water ingress.The mast’s actual depth rating remains untested; greater-depth pressure testing is planned.
- Throughput testing evaluated WiFi and radio links at distances from 5 to 100 meters while CougarTail was mounted on a CougUV interfacing with CUB.The resulting throughput as a function of range is presented in Fig. 4.
- A cart-based waypoint-following test recorded positions while CUB processed live sensor input and actuator commands, exercising the end-to-end pipeline.
- 1.07 m mean horizontal accuracy and 100% fix reliability were recorded over a 232.6 s GPS trial, with no dropout gaps.
C. Mission Results
Cart-based waypoint missions validated CUB and CougarTail’s integrated sensing, waypoint-following, and vehicle-control functions under realistic timing. The system is designed as a compact, versatile electronics and communications solution for cylindrical underwater enclosures.
- Cart-based waypoint missions validated real-time sensor ingestion, waypoint-following logic, and corresponding vehicle-control commands.In-water waypoint missions remain planned future work for closed-loop validation.
- CUB and CougarTail combine a circular 4-inch-enclosure PCB with a co-designed mast providing GPS, radio, and WiFi for underwater platforms.CougarTail designs and assembly instructions are openly available, while CUB design access requires contacting the authors.