The underwater glider is enclosed by a polycarbonate cylindrical body. The cylindrical body is used for its hydrodynamic efficiency and is typical of most underwater gliders. The glider is composed of four main subsystems: buoyancy, propulsion, external, and control, sensors and measurements. Each of the subsystems are also further de-constructed into smaller subsystems of mechanical and control. Throughtout the entire project, biomimicry was used for several different components to optimize the final design of the underwater glider.
Buoyancy Engine
The buoyancy of the glider is altered by four syringes that are actuated by a piston that moves on a rotating threaded rod that acts as a power screw. Hoses and hose clamps are attached to the ends of the syringes and are used to transport the intake and outake of water from the syringes through the four holes located on the front of the nose cone. Seperate components for the buoyancy engine are being held and supported by 2 sets of 4, 1/4 inch diameter, aluminum rods. The mechanical system for the buoyancy engine is controlled by a bipolar servo motor to allow actuation in both directions of the syringe [3], assuming linearity and decoupling of each subsystems, the output state of the system that is being controlled are the pitch angle, and rate, z and x axis velocity, and positions (labelled w, u, z, and x respectively) [4].
In the figures below you will see illustrations of the buoyancy engine in a collapsed view, along with an exploded view, and an exploded view drawing with part numbers that correspond to the part numbers on the bill of materials. All together the buoyancy engine consist of 18 different components and correspond to parts 1-18 in the bill of materials. .
Figure 2: Buoyancy Engine, Collapsed View
Propulsion Engine
The propulsion of the glider is controlled by a reciprocating mechanical system that converts rotational motion of a stepper motor into a linear back and forth motion. This motion is transferred to the soft tail of the AUV via wires, which results in the output of x-axis velocity(u), yaw angle and rate.
Figure 3: Throttle Engine Mechanism Concept.
Control, Sensors, and Measurements
The control, sensors, and measurements subsystem consists of an Arduino uno Microcontroller, a pressure sensor and the electrical circuit of the system. A pressure sensor was used to estimate the state of the robot. The main circuit is contained within a compact bracket in the middle section of the robot's cylindrical body.
External Subsystem
Just as important as the internal components of the glider, the external subsystem was designed to keep water from damaging the robot's inner components and electronics, while also stabilizing the roll angle of the robot to keep it upright. The external subsystem consists of a nose cone, wings, a keel, and clamps used to sucure the wings and the keel. The nose cone was designed to take form of a shape similar to the nose cone of a torpedo. This shape makes the front end of the glider more hydrodynamic and increases the maximum velocity of the glider. An extruded hole was added to the top of the nose cone and was used to mount the pressure sensor. Air foil shaped wings similar to that of a Boeing 747 aircraft were designed to control the roll angle and stability of the glider while it is underwater. Lastly, a keel was designed to also aid in the control of the roll angle and stability of the glider. The concept of the keel is similar to that of a keel from a boat but was designed specifficaly to balance the hydrodynamic forces acting on both sides of the keel in order to keep the glider in an upright position.
Figure 4: External Subsystem, Collapsed View