- Designing the underwater glider
- Printing and assembly
- Testing movement assemblies
- Component selection
- Schematic creation
- Testing specifications
- PCB Design
- PCBs and soldering
- Waterproofing problems
The CAD model
The model is viewable on the Onshape online platform here (requires webGL)
Movement test video
Why a glider?
Traditional unmanned underwater vehicles depend upon active propulsion, limiting their range and runtime, making them unsuitable for long duration monitoring missions. Underwater gliders use a buoyancy engine to change the mass of the glider, allowing them to ascend and descend through the water. With power only being used to power the engine intermittently, gliders can typically run for weeks or months without recharge, making them ideal for environmental monitoring. Yet there are few commercial solutions available (and those that are available are very expensive) and even fewer hobbyist projects exist.
As underwater gliders travel slowly through the water, they disturb the surrounding water very little, allowing for accurate and reliable data recording. Underwater gliders are normally AUVs (Autonomous Underwater Vehicles) and can run a pre-determined route without requiring human interaction. Their low speeds and autonomy, combined with long battery life, make underwater gliders ideal for long duration, environmental monitoring missions, capable of recording dissolved gas levels, pH, temperature and optical sensing (for oceanic surveying and sealife recording).
The glider is open-source, with 3D printed components combined with readily available hardware, allowing it to be assembled for a low cost. Given the openness of the project, the project could be forked to produce alternative designs suited to particular scenarios. For instance; changing the tubing to aluminium to become a deep sea glider; using a unique sensor array for specialised applications; changing the buoyancy engine size to increase speed.
I am looking to use the open-source ArduSub (based upon the popular ArduPilot) autopilot platform, allowing the glider to be controlled using a standardised interface.With this technology available, there would be a wide variety of uses. For instance, with increasing interest in product transparency and traceability, environmental monitoring is becoming increasingly important; a kelp farmer could use the glider to monitor water conditions (temperature/pH/nutrition levels/pollution) during a season of growth and push the measurements to a blockchain. The kelp/seafood could be packaged with a QR code, which would direct you to a web frontend, presenting the conditions during the season of growth. The use of the blockchain for measurement storage would remove the chance of measurement tampering, so the consumer would know both the conditions that their food grew in and what they’re eating.
Above: A block diagram outlining the how the glider could be used for product traceability
The buoyancy engine that I have designed uses a threaded rod to move the ends of the syringes when rotated by a stepper motor, causing the plungers to take in water. When water is taken in, the volume of the glider remains constant, but the overall mass increases, therefore the overall density of the glider increases and the glider becomes less buoyant.
At the centre of the glider will be a mass that controls pitch and roll. The mass shall be composed of Lithium ion batteries and a pewter casting, to form a substantial mass, so that it has sufficient control over the glider. The pewter mass shall be formed by pouring molten pewter into a printed PLA negative mould, inspired by a hackaday article. The mass shall control the pitch and roll of the glider. The pitch will be dictated by a stepper motor connected by a threaded rod to move the centre of mass forwards and backwards, thus moving the centre of gravity forwards and backwards, affecting pitch. A secondary stepper motor shall drive a planatary gearbox to control...Read more »