Mechanical Design
The following segments describe the mechanical design of the boat, and thus show our design process and justify our final design.
General Boat Design
After many hours of deliberation and iteration, our team decided to jump for the catamaran design. We chose this because it provides:
(1) Wide base, which allows a large flat plane on which to build
(2) Stability, which is ensured by the wide base and low center of gravity
(3) Open center, which allows us to funnel crab pots beneath our boat, ensuring a clean scan of the RFID
(4) Coolness, catamarans are cool
After settling on the catamaran, we also opted for a tank drive. This means that we had a motor attached beneath each hull. With this type of setup, we had two significant advantages. The first major advantage is maneuverability. With dual motors, we can turn in place, which is a significant advantage considering the size of Terman Pond. If we designed around a single motor, we would need to drive forward or in reverse in order to turn. Using two motors prevents this problem entirely. The second major advantage to using dual motors is being able to place them away from the center-line of the boat, and beneath the hulls, where they are protected from crab pots, other boats, and all other dangers.
(1) Wide base, which allows a large flat plane on which to build
(2) Stability, which is ensured by the wide base and low center of gravity
(3) Open center, which allows us to funnel crab pots beneath our boat, ensuring a clean scan of the RFID
(4) Coolness, catamarans are cool
After settling on the catamaran, we also opted for a tank drive. This means that we had a motor attached beneath each hull. With this type of setup, we had two significant advantages. The first major advantage is maneuverability. With dual motors, we can turn in place, which is a significant advantage considering the size of Terman Pond. If we designed around a single motor, we would need to drive forward or in reverse in order to turn. Using two motors prevents this problem entirely. The second major advantage to using dual motors is being able to place them away from the center-line of the boat, and beneath the hulls, where they are protected from crab pots, other boats, and all other dangers.
Hulls
As mentioned above, the hulls allowed for a wide base, provided stability, and protected the motors. Our hulls were constructed from pink construction foam, also known as extruded polystyrene foam. The front of the hulls, as can be seen in the picture to the right, were rounded in order to funnel the water around the hulls in an efficient manner. Towards the front of the hulls, the motors were recessed into the foam. The output shaft of the motor travels through the foam, which is sealed at both ends to ensure water-tightness.
Drive Train
The drive train is comprised of two motors, sunk into the pink foam. This allowed for more construction room, better water protection, and a lower center of gravity. The motors are rigidly attached to the pink foam using a standard face mount. The output of the motor shaft was connected to an output axle through a universal joint, which allows for the angle difference between shafts. The watertight output axle transversed from the motor bay to beneath the hulls, where a propeller was rigidly attached to the shaft. The propeller is comprised of two blades with a total span of 50mm and a strong forward pitch. According to the hobby shop, these propellers were designed for high torque, low speed motors, which is exactly our strategy, considering our motors.
The motors run at approximately 5000 rpm no load at 12V. Because only one battery was used, the motors were run at an average of 7V, which means a slightly lower rpm. Using a single battery was necessary in order to allow space for the rest of the circuitry and because 14V would have yielded too much current draw for our motor drivers to handle.
The motors run at approximately 5000 rpm no load at 12V. Because only one battery was used, the motors were run at an average of 7V, which means a slightly lower rpm. Using a single battery was necessary in order to allow space for the rest of the circuitry and because 14V would have yielded too much current draw for our motor drivers to handle.
Crab Amount Indication
In order to communicate the crab on the boat to the operator, we selected a simple servo with a fluorescent flag. This technique was very effective, in that it was quickly designed, built, and implemented. After completing all the functionality for its designed purpose of indicating crab numbers, the servo, because of its simplicity, was also used in the debugging and team assignment process. It was a great tool for visually indicating changes occurring within the bits of the PICs, which are slightly difficult to see with the naked eye, even when squinting.
Defensive Driving
One of the core designs of our boat was our desire to avoid building any devices for attacking other boats. Instead, our hope for winning was to rely on our maneuverability, speed, and defense strategies. To further protect ourselves, and to make the operator look silly, we chose to mount the funnel and the accompanying waterlogged sensor on a stepper motor. As an operator is driving the boat, they can rotate their hips, which when sensed by the controller, will be transferred to the rotation and translation of the waterlogged sensor. If it's not already hard enough to shoot a moving target from another moving target, adding an additional element of rotation compounds and already difficult task of waterlogging another boat.
Waterproofing
Unfortunately, circuits aren't fans of swimming, so it was a high concern to ensure the waterproofing of all circuits and motors. All circuitry was contained within a single rigid plastic box in the middle of the boat. Using a single large box was useful, because it reduced the amount of wires having to leave the box. Any wire leaving the box was sent through the side of the box, and the hole was reinforced with waterproof caulk.
The motors propelling the boat forward were sealed in the hulls of the boat, beneath a watertight roof of acrylic, designed with a lip. This lip would require the water to move vertically upwards before it could enter the motor compartment. As mentioned earlier, the motor compartment was sealed with caulk on the interior and lower sections of the hull. This level of redundancy makes engineers feel better.
The stepper motor is safely sealed by creating an umbrella by using the lower quarter section of a 2-liter pop bottle (yes, I said pop and not soda). As shown to the left, the stepper motor sits on a high pedestal, with an large plastic umbrella extending beneath the motor's lowest point. Water can reach the motor, but it must splash awkwardly upwards, which is expected to be a rare occurrence.
Each of these techniques was incrementally tested, in order to ensure correct functionality. Once this was ensured, the ensure system was assembled and again tested to ensure everything was water tight. No problems were every experienced due to unexpected leaks.
The motors propelling the boat forward were sealed in the hulls of the boat, beneath a watertight roof of acrylic, designed with a lip. This lip would require the water to move vertically upwards before it could enter the motor compartment. As mentioned earlier, the motor compartment was sealed with caulk on the interior and lower sections of the hull. This level of redundancy makes engineers feel better.
The stepper motor is safely sealed by creating an umbrella by using the lower quarter section of a 2-liter pop bottle (yes, I said pop and not soda). As shown to the left, the stepper motor sits on a high pedestal, with an large plastic umbrella extending beneath the motor's lowest point. Water can reach the motor, but it must splash awkwardly upwards, which is expected to be a rare occurrence.
Each of these techniques was incrementally tested, in order to ensure correct functionality. Once this was ensured, the ensure system was assembled and again tested to ensure everything was water tight. No problems were every experienced due to unexpected leaks.
Hand Controller
Step 1) Get a box (Radio Shack project boxes work well)
Step 2) Cut a hole in the box.
Step 3) Put your junk in the box.
Step 4) Don't open the box. In fact, it's better if you screw it closed.
We really didn't focus on how the HC would look so much as we how it would work. We needed an appropriate way to detect the orientation of the user's hips. A box with a compass in it rigidly attached to a belt was a reliable way to do just that. Similarly, we had to house accelerometers, LED displays and a button in something the use could easily grip. A long simple box seemed like an easy way to go. While we're at it, let's just put everything else into one bigger box. No space for batteries? Stick those on the side with velcro.
Having sealed boxes ended up looking pretty cool. To keep with the professional looking theme, we also used standard size/shape cable jacks (ethernet and phone) to ensure the correct polarity when connected and present an interface the user would be familiar with. As a last minute addition, there's a little hole in the big box (bottom left corner, just above the belt in the below image) through which the low battery indicator would shine (if necessary).
Rather than decorate our boxes, we developed our theme by using a fishing vest and safari hat to accompany our little black project boxes. See the user photographs in the multimedia page for the teaching staff and plenty of others wearing our HC.
Step 2) Cut a hole in the box.
Step 3) Put your junk in the box.
Step 4) Don't open the box. In fact, it's better if you screw it closed.
We really didn't focus on how the HC would look so much as we how it would work. We needed an appropriate way to detect the orientation of the user's hips. A box with a compass in it rigidly attached to a belt was a reliable way to do just that. Similarly, we had to house accelerometers, LED displays and a button in something the use could easily grip. A long simple box seemed like an easy way to go. While we're at it, let's just put everything else into one bigger box. No space for batteries? Stick those on the side with velcro.
Having sealed boxes ended up looking pretty cool. To keep with the professional looking theme, we also used standard size/shape cable jacks (ethernet and phone) to ensure the correct polarity when connected and present an interface the user would be familiar with. As a last minute addition, there's a little hole in the big box (bottom left corner, just above the belt in the below image) through which the low battery indicator would shine (if necessary).
Rather than decorate our boxes, we developed our theme by using a fishing vest and safari hat to accompany our little black project boxes. See the user photographs in the multimedia page for the teaching staff and plenty of others wearing our HC.
