Why a glider?
underwater gliders travel very slowly through the water, they
disturb the surrounding water very little, allowing for
accurate and reliable data
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
ideal for long duration, environmental
monitoring missions; capable
of recording dissolved gas levels, pH, temperature, light levels and
optical sensing (for oceanic surveying and sealife recording),
depending upon the sensor array
this, there are few commercial solutions
available (and those that are available
are very expensive) and even fewer hobbyist
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 the roll of the mass. As the mass shall be bottom heavy, when it is rolled to the left, the centre of mass shall move left slightly, causing the glider to roll slightly left and curve while descending. Rolling the mass to the right causes the opposite effect. A planatary gearbox was chosen as it increases the torque and accuracy of the stepper motor, allowing for finer control of the glider's roll.
For the glider to move, the buoyancy engine takes in water and increases the density of the glider. When the density of the glider becomes greater than that of the surrounding water, the glider descends. The movable mass will move forward so that the centre of mass is towards the front and the glider will thus glide forwards. Finer control of the position of the masses will allow control over the angle of attack and therefore descent ratio. When at the bottom of the descent, the buoyancy engine will expel the contained water, making the glider lighter and more buoyant, causing it to ascend, moving forward again. An IMU would provide information concerning rotation to the microprocessor (likely an Atmel core)
Currently, the descent time will be dictated by a timer, however, a pressure sensor could allow finer control, as it would cause the glider to start ascending at a certain depth. An ultrasonic sensor could also be used so that the glider would descend until it is a set distance from the floor and then start ascending. However, both of these technologies would increase the complexity of the glider, as they would require access to the water and thus additional waterproofing, so will only be more seriously considered once a functioning glider has been produced (along with other more advanced sensors for environmental monitoring).
The following diagram shows how the glider will move through the water:
Below is a table of various specifications that the underwater glider must pass in order to fully function as intended. The specifications listed range from absolutely necessary for the glider to glide (watertight etc.) to requirements that allow it to function as an autonomous data-logging drone (way...Read more »