Existing Models
Biological Propulsion Mechanisms
Final Concept
Prototypes
Construction
References
Concepts
Initially in the project, concepts were created with the propulsion, buoyancy and overall shape of the system. As the project was furthered, it was more efficient to describe concepts for components of the system as most of the designs for buoyancy did not drastically impair or effect concepts for propulsions etc.
Propulsion Concepts
Concept 1
The first concept suggested is modelled on a fish and fins. The sinusoidal movement of the body of a fish and the flapping motion of the tail can be attributed as the main inspiration for this concept. The concept had problems where the reacting moment would cause instability in the body of the craft. Other problems included the difficulty in dividing the tail into sections to cause a sinusoidal movement.
Concept 2
The second concept was taken from the book “Optima for Animals” and “Animal Mechanics” by McNeil Alexander. It consists of a rotating disc with tails attached around the circumference. The danger of this concept was in the difficulty of mimicking natural materials and the control system in operating the flagellum effectively.
Concept 3
The third concept was to use the motion of a squid to inhale water and exhaust it in a jet. This was a concept that had problems with the mechanism of mechanically inhaling the water and exhausting it without having large systems of pipe work or causing a considerable drain on the driving system.
Concept 4
The fourth concept was to use paddles mounted on a rotating disc or a set of tracks to push the water back and so drag the ROV forward similar to a paddle steamer. The main problem with this concept occurred in the drag caused by the paddles or blades returning to the forward position negating the propulsion that they previous provided.
Buoyancy Concepts
Concept 1
The first concept for buoyancy was the implementation of a main air tank near the top of the craft. This tank was to have a hole in the bottom open to the water and allow the venting or injection of trapped air to increase or decrease the overall density of the tank and so change the upward force exerted on the craft.
The main test of the design was inflating and deflating the inner tube from a small bicycle tyre to see the effect it had on lifting and lowering a given weight. The test proved the design to be hard to control with the up thrust being too large or the complete opposite where the weight rapidly sank.
Concept 2
The next concept provided was to use a material similar to foam to coat the body of the ROV to bring it close to neutral buoyancy. A small air tank was then to be installed in the system that would obtain neutral buoyancy for the craft when half full. Filling or emptying of this small tank would permit control of the depth of the craft. Due to the small nature of the tank the acceleration provided would be significantly decreased and as such would allow greater control.
Difficulties arose in the expense of equipment to supply compressed air to the tank. Another risk in the concept was the difficulty in controlling the volume of air in the tank indeed the tiny volume changes required to obtain neutral buoyancy were deemed too difficult for the scope of this project.
Concept 3
The third concept took inspiration from the previous two however included the understanding that buoyancy, negative, neutral or positive does not alter as depth varies. This is due to the increase and decrease in pressure on the top and bottom of the craft being proportionate to each other.
The general principle is for the craft to be slightly positively buoyancy then using a pump displace water vertically thus forced the craft itself down. The added safety of this concept is that in result of a failure in the mechanism the positively buoyant craft should surface of its own accord. Buoyancy control may be obtained either through air tanks, foam or small attachable weights and the method of displacing water may be achieved by using electrical pumps designed to operate whilst submerged.