This project was the final project for the class. We worked together once again in a team of 5. It was a great opportunity to get closer to the teammates from the previous project and work alongside them again.
In this project, we were assigned to design and manufacture an "acoustic sensor platform" with a handheld controller used to control the platform. The sensor platform would be used to detect drug trafficking underwater from the surface.
This is essentially a remote controlled boat. The functions of the platform are to be able to be controlled to move in all directions on a horizontal plane on the water surface with a constant and smooth speed. The constraints of this project resides in the material given to make the platform. The materials given to us were 2" thick Owens corning foamular, a 1100 GPH bilge pump, a standard servomotor, and other electronics used to relay signal to the platform for the controllers (Arduino UNO and xBee radio communication modules).
The boat would have to carry an extra 2lbs of dead weight to account for the weight of the acoustic sensor. This is not including the electronics to make the boat function. The boat was to be functional for up to 200ft distance away from the controller, and the electronic components had to be in a waterproof container on the boat.
The final test of this boat was a race on the Charles River, competing against the other teams and their designs, to see who's sensor platform performs the best and is fastest.
In this project, we were assigned to design and manufacture an "acoustic sensor platform" with a handheld controller used to control the platform. The sensor platform would be used to detect drug trafficking underwater from the surface.
This is essentially a remote controlled boat. The functions of the platform are to be able to be controlled to move in all directions on a horizontal plane on the water surface with a constant and smooth speed. The constraints of this project resides in the material given to make the platform. The materials given to us were 2" thick Owens corning foamular, a 1100 GPH bilge pump, a standard servomotor, and other electronics used to relay signal to the platform for the controllers (Arduino UNO and xBee radio communication modules).
The boat would have to carry an extra 2lbs of dead weight to account for the weight of the acoustic sensor. This is not including the electronics to make the boat function. The boat was to be functional for up to 200ft distance away from the controller, and the electronic components had to be in a waterproof container on the boat.
The final test of this boat was a race on the Charles River, competing against the other teams and their designs, to see who's sensor platform performs the best and is fastest.
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As always we had to begin with some sketchings. It was clear that this would be the most challenging project of all from the initial sketches as shown. There was a lot of back and forth and differing of opinions on how to make this boat perfect.
Together, after a lot of time planning to getting everyone on the same page of how the boat would come out, everyone came up with their own ideas of the design and gave each other feedback on the design of the hull of the boat. The main portion of the design would come down to the shape of the hull of the boat, how the boat would change direction, and the placement of the components. We decided that the shape, size, and dimension of the boat is the most important design of the project as it is the core integrity of the boat and it affects all the functionalities of the boat itself. For this project, we decided to work together on each design and components, contrary to the previous project where we worked independently on assigned parts. We believed that this method is more beneficial and more efficient as feedbacks can be given at all times and there are not as many independent parts in this project, however, the work can be delayed if members are not present to make big decisions. The team started out by researching boat hulls and shape to gather information on which shape is the most efficient in moving through the water surface. As well as, conducting several experiments on the components such as the pump, and foam pieces to check their integrity. A miniature size boat hull that we CADed also was printed just to see the shape and scale of what we had to work with. |
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Calculations were first made to be able to find the dimensions of the foam volume needed, which then moved onto designing the shape of the boat. Initially there were a few designs of the shape of the boat itself. The first design consist of having 2 hulls in parallel to create maximum stability however, the placement of the pump needed to be centered. With this design it was not possible without the pump hanging in the middle so the idea was abandoned.
The second design consisted of having 3 different hulls, 2 on the side and one in the middle to house the components and pump. This idea seemed good at the time, however, from our calculation and research, the team found out that we needed to minimize the front area of the boat to reduce drag forces, and therefore the idea shifted into the final design.
The final design of the shape of the boat consist of having only a single hull to minimize the drag forces. We still took ideas from the second design to have two minor 'hulls' on the two side of the boat to act as stabilizers although these supports would not be submerged at all times but would hover just above the surface.
The front shape of the boat was designed to be as sharp as possible to cut through the water and reduce drag while gradually increasing in size to the middle of the hull, to smoothly let the incoming water move along the sides of the boat. The shape of the entire boat is symmetrical as it is needed for the back of the boat to be curved as well as to reduce any turbulences that might affect the speed of the boat. Trying to design the boat symmetrically was challenging, since the foam needed to be carved by hand or by wire cutter which is also operated by hand. There was no machining done to create the boat shape, and that was difficult.
All the foam pieces were wire cut, glued together using waterproof adhesives, and shaped using belt sanders and different grit hand sand papers.
The second design consisted of having 3 different hulls, 2 on the side and one in the middle to house the components and pump. This idea seemed good at the time, however, from our calculation and research, the team found out that we needed to minimize the front area of the boat to reduce drag forces, and therefore the idea shifted into the final design.
The final design of the shape of the boat consist of having only a single hull to minimize the drag forces. We still took ideas from the second design to have two minor 'hulls' on the two side of the boat to act as stabilizers although these supports would not be submerged at all times but would hover just above the surface.
The front shape of the boat was designed to be as sharp as possible to cut through the water and reduce drag while gradually increasing in size to the middle of the hull, to smoothly let the incoming water move along the sides of the boat. The shape of the entire boat is symmetrical as it is needed for the back of the boat to be curved as well as to reduce any turbulences that might affect the speed of the boat. Trying to design the boat symmetrically was challenging, since the foam needed to be carved by hand or by wire cutter which is also operated by hand. There was no machining done to create the boat shape, and that was difficult.
All the foam pieces were wire cut, glued together using waterproof adhesives, and shaped using belt sanders and different grit hand sand papers.
Another significant part of the project was the pump and the steering design. There were two main ways to steer the boat: one was to use a simple, ordinary rudder, and the other was turning the entirety of the pump in the designated direction without a rudder. There was a lot of arguing within the team between these two design ideas. The advantages of the rudder design is the simplicity and foolproof method of it, while the disadvantage is that it creates an immense drag force on the underside of the boat, ultimately slowing it down. The turning pump design removes this drag force, however, significantly increasing the complexity of the design. The simpler option usually is always the better idea, but in the end we decided to abandon the regular rudder idea and create a system in which the pump could rotate itself. All rotations would be powered by using the servo motor.
The complexity of the moving pump design was in making the pump stable while it was spewing out water and turning at the same time. Since the pump cannot be secured in place, we had to design ways to secure the pump to one degree of freedom, turning on the z-axis only. The first design was to house the pump in a 3D printed cage, and rotate it within that case. This was impossible to do based on the placement of the pump. The bottom of the pump had to be below the surface of the water to suck in water, and the nozzle had to be above the surface of the water to shoot out and thrust the boat forward. With this large case design and whatever rolling and rotating mechanism that it worked with, there was no way to fit the whole assembly into the boat without is destroying the entire shape of the bottom of the hull.
The improved design was to just directly attach the pump to the servo using a part that held the pump in place, which also screwed into the servo. The pump was secured into this piece and tightened in place with a metal strap. By doing this, our team sacrificed some stability and security, since the entire weight of the pump was now held up by the servo. This connection between the pump top housing and the servomotor was the only thing securing the pump to the boat, and was done using metal screws into the servomotor itself. Initially there were doubts about the servomotor not able to handle the force and stress associated with the pump operating, but after some experiments the design worked.
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Once the mechanical components were in place the only thing left was the electronic components which would be housed in a waterproof plastic container in the middle of the boat to balance the weight of the pump and servo motor. Calculations were done using the masses of the electronics and the center of mass of the boat to ensure that it would be stable. The electronic components used were two Arduino UNO units and two xBee radio communication units, and several battery units to power the system. A set of these components are on board to the boat to power and activate the boat's pump and servomotor while the other set is on the controller. The controller and the boat connects via radio communication of the xBee which is connected to the Arduino programmed to give signals to the pump/servomotor depending on our controls. The xBees had to be programmed on the computer using XCTU software so that they knew how to communicate with each other and transmit signals. One was programmed as the transmitter and one as the receiver. The controller consisted of a switch to power the pump on/off instead of a button so the user do not have to hold the button down in order to power the pump for a prolonged period of time. I also designed and 3D printed a knob to be attached to the potentiometer so that we could control the direction of the boat through turning the knob, which turns the potentiometer, which sends a signal to the servo to rotate. The knob was designed so that it would feel very comfortable in hand, and so that minor adjustments on the potentiometer became larger turns on the knob. This made things more accurate. I designed the knob so that it would fit onto the turning portion of the potentiometer, and then a plate with grooves for it to twist on. The knob and plate secured to each other with a tight fit, but because of the design of the circular track, it was still able to rotate with ease. The housing of the radio controller was manufactured from .25" acrylic, which was laser cut for precision. The controller is transparent which makes it it easy to know whether the controller is on/off from the lights on the Arduino. The bright orange color helps easily identify the controller and was aesthetically pleasing. The top of the controller box was secured with a 3D printed hinge for ease of opening to check the components on the inside. |
The initial test of the boat on the Charles River, the boat works well with the pump and steering working as intended. There is a slight delay hard coded in the Arduino between the controller and the receiver on the boat created some issues with controlling but there were no ways of removing this, otherwise the controls work magnificently. In the final competition we believed that out of the 5 teams, our boat was competitively the top 2 fastest boat. From observations I think the larger boats were surprisingly faster than the smaller hull boat designs, this may be because the water tested on was not stable and stabilized boats were performing better. As well as the weight distribution on larger boats were more effective. During the actual race, our boat started off well, however, it became stuck with another team's boat and together rammed into a parked actually human sized boat which perhaps knocked out parts of the electronic components inside of our boat. The boat continued on for about 3 minutes until connection between the controller and the boat's receiver was cut and we lost control of the boat in the middle of the river a few hundred feet away from the shore where we are controlling. Several of the other team's boats also lost connection while en route. At the end we never did reach the finish line while only 2 out of 5 teams did.
From the competition, I believe that the main flaws of the boat was not in the mechanical design but the quality of the electronic components used. The xBee receiver had some problems during some experiments and tests as well which we could never figure out the problem. It is arguable that the lost connection was inevitable due to the components that we used.