This video details the multi-year effort to build a new autonomous GPS-guided catamaran, designed to successfully complete a 56km waypoint mission around Bainbridge Island after a previous attempt failed due to mechanical issues. The project commences with the resourceful salvage of 18650 lithium-ion cells from a salt-water damaged power bank and an old robot battery. A central engineering challenge is the design of a waterproof "battery keel" hull, which the creator tackles by uniquely potting the entire battery cavity in silicone grease using a combination of vacuum and pressure, overcoming several technical hurdles. The video showcases the integration of 3D-printed hull sections, fiberglass reinforcement, a single Blue Robotics thruster, a Pixhawk autopilot, and custom navigation lights. Initial lake tests expose unexpected high buoyancy and a tendency to "submarine" at high speeds, leading to further design refinements like foam filling. Despite some remaining concerns regarding mission speed and steering precision, the boat demonstrates impressive resilience in wave conditions, preparing it for its redemptive autonomous voyage.
Building the Autonomous Catamaran: From Failed Missions to Greased Batteries
0:00 Previous Mission Failure & Initial Setbacks: The creator recounts a prior 56km autonomous boat mission that failed due to seaweed clogging propellers and corroded bilge pump sensors. A separate incident involved a salt-water submerged EcoFlow power bank.
0:54 Salvaging Batteries: The damaged EcoFlow power bank was disassembled, and many 18650 Li-ion cells were successfully salvaged despite being submerged in saltwater. Additional cells were recovered from an old solar-powered rover battery.
1:32 Cell Harvesting Process: The process of carefully cutting the spot-welded nickel sheets to extract individual cells was tedious and highlighted the inherent risks of short-circuiting the pack.
2:56 New Hull Design: A narrow, efficient hull was designed in On Shape, conceptualized as a "battery keel" to keep the center of gravity low by placing the batteries below the waterline.
3:41 Hybrid 3D Printing Construction: The boat's bow and several hull sections were SLA printed (FormLabs Form 4) for density, while 18650 cell holders were printed in PETG, with carbon rods used for alignment and structural reinforcement.
4:08 Battery Pack Assembly: The salvaged 18650 cells were spot-welded into a 3P (approx. 12V) configuration, and a 3S2P 2170 pack was added. A BMS was incorporated for battery balancing and charging.
7:08 Innovative Waterproofing (Grease Potting): The entire battery cavity was waterproofed by filling it with silicone grease using a grease gun, aiming to displace all water by filling every void and crevice.
10:52 Challenges with Grease Potting: The high pressure of the grease caused acrylic panels to bend and leak, necessitating the addition of more screws, clamps, and thinning the grease with dimethicone to improve flow.
11:09 Vacuum-Assisted Potting: A vacuum pump was used to aid the grease flow, pulling it through the battery cavities, though it also introduced some air bubbles that later needed to be purged.
16:01 Upper Hull Construction & Buoyancy Miscalculation: XPS insulation foam was used for the upper section of the hull to provide buoyancy, but the initial calculation was off, resulting in the boat riding much higher than intended ("narco sub" failure).
17:02 Design Adjustments: Due to the unexpected buoyancy, the foam was trimmed significantly, and the plan for a second counter-rotating motor was abandoned as it would not be submerged.
18:11 Fiberglass and Experimental Paint: The hull was reinforced with two layers of fiberglass. An attempt to paint with old gel coat failed, leading to an unconventional application of crayon wax for hydrophobicity, followed by orange spray paint for visibility.
20:03 Electronics Integration: A Pixhawk autopilot running ArduPilot Rover software, an RFD900X radio for control and telemetry, a waterproof Hitec steering servo, and a Blue Robotics ESC were installed in Tupperware enclosures for protection.
21:14 Custom Navigation Lights: Repurposed PCBs from a "color shadow lamp" project were adapted to serve as pulsed red, green, and blue navigation lights mounted on a folding mast.
22:06 Initial Lake Testing: The boat performed well in terms of speed and turning but produced a large bow wave, leaned due to single-motor torque, and "submarined" at full throttle, allowing water into the front of the hull.
24:04 Addressing Submarining: The bow and stern cavities were filled with two-part expanding polyurethane foam to prevent water ingress during high-speed operation.
24:17 Wave Torture Test: The boat successfully withstood simulated waves created by a chase boat, demonstrating its robustness and stability, despite constant rudder corrections and minor water entry in the electronics enclosures.
26:31 Final Assessment & Future Outlook: The boat is functional but operates at a relatively slow speed (1 m/s, estimating 15-16 hours for the mission) and exhibits overcorrection in steering, which will lead to servo wear. Despite its failure to be a "narco sub," it is ready for its new autonomous mission attempt.