Mechanical

The brunt of the mechanical design for this project is contained in the craft. The craft is designed around two pontoons, which are each made from two 2-Liter bottles. These provide ample buoyancy and their length and wide spacing provide a stable platform to work with. The structure of the craft is composed of laser-cut Masonite. We chose Masonite because it is light, strong, readily machined on the laser cutter, and in our tests it held up well to submersion in water.

The craft is powered by two Maxon A-Max 30 DC motors with no gear reduction. The motors are connected to the twin propellers with universal joints, allowing the motors to sit out of the water while the propellers are submerged in the water, and pointing along the axis of travel. The use of two propellers, both with full forward and reverse capabilities maximizes mobility, including the capability to turn turn in place, and run in full forward and reverse by varying the speed and direction of the propellers.

The craft shoots water from the front, using an 800 gal/hr bilge pump connected to a constricting nozzle. By operating the pump via PWM, the flow through the pump, and thus the range of the water cannon, can be controlled dynamically.

Finally, the most water sensitive components are housed within a tupperware container on board the craft. The fore-aft positioning of the electonics box is also being used to control the overall weight distribution of the craft and to level the craft in the water.

Isometric view of SolidWorks model of the craft

Half of the drivetrain

The craft in action

The remaining mechanical design resides in the helm which is used to control the craft. The theme of our helm was Top Gun, complete with flight suit, oxygen mask, and flight control stick, and 'parachute' sack housing the electronics.

Most of the controls and displays are mounted on the control stick. The control stick provides a nice flat mounting surface for the force-sensing resistor as well as mounting for the game LEDs and the pairing 7-segment display. It also provides the user with a familiar, physical, and intuitive way to control the steering of the boat. Sensing of the flight stick angle is accomplished using a two-axis accelerometer mounted to be sensitive to pitch and roll. The chief challenges of the flight stick were packaging and cabling. Space within the interface portion of the stick is cramped, and roughly two dozen wires run down the shaft of the flight stick and into the electronics bag.

The cables running from the control stick go into the E128, which is located in the green bag below, along with most of the signal processing and circuitry. The final component of the control interface is the microphone which is used to control the throttle of th ecraft. By mounting the microphone inside the face mask, good sound isolation and consistent signals can be obtained from the operator.

Because of the non-structural nature of most of the helm, foam core, cardboard, and other found materials were used in most of the construction.

Full helm in action

The 'Flight Stick' controller

 

Bill of Materials