Problem Overview
The problem addressed with the Seaperch project is that water quality testing is difficult and expensive in water where active currents are present. The project is to create a small submersible that is stable and maneuverable in water with currents. There have been many technological advances in underwater propulsion and navigation in recent years, but they have been mostly limited to large scale submarines. This project will implement propulsion techniques to optimize the small-scale submarine.
Design Goal
One
goal of the Seaperch project is to modify the submersible to increase stability
and maneuverability in a current. This will be achieved by redesigning the
propellers, changing the motor orientation, and modifying the chassis. At least
two propellers will be designed using ProEngineer computer software and created
by Drexel’s rapid prototyping machine. The motors will be moved and tested at
several different positions and orientations on the chassis. Substantial
testing will be done to determine the most efficient propeller design and motor
orientation.
The
second goal of the project is to test water quality. This will be done using
sensors mounted to the submarine. A depth gauge will be used to accurately
determine the submarine’s position. Sensors that will test the water will be a
temperature sensor and a pH sensor.
The
design will be unique because the final design will be determined by the
results of independent testing. The propeller prototypes will be based on
designs found through research, but the most effective one will be found
through testing.
Design Constraints
The original design
is directly based off of a kit with an instruction manual. The original
submarine parts were limited the materials included in the kit, and it was
constructed according to the instructions laid out in the manual.
New propellers will be constructed
using Drexel’s rapid prototyping machine. The machine makes parts out of
plastic, so the propellers will have to be plastic. The propellers will be much
smaller than the size limitations of the machine. The size of the propeller
will be limited by the motors in the Seaperch kit. The motors have limited
strength, so the propellers must be small enough for the motors spin them
sufficiently. The new propellers must also be mountable to the motor shafts.
There is a propeller mounting device included in the Seaperch kit, so the new
propellers will be designed to be compatible with the device.
The three motors are originally
mounted to the PVC chassis of the submersible in the positions and orientations
described in the instructions. They can be moved to any part of the chassis
that is large enough to hold the motor mounts. Since the motors are mounted to
PVC pipes, the pipes can be twisted to change the directions the motors face.
The chassis is constructed out of ½”
PVC. Any modifications will be made using the same material. The kit only has
about 6 inches of excess pipe and no left over PVC joint pieces. Modifications
requiring more than the supplied amount of PVC would be limited by the budget
because more material would need to be purchased.
Existing Work
The idea for a propeller comes from back in the third
century BC from Archimedes, who found that spiral screws could be set inside a
cylinder to life water. It was not until
1796 that the first basic propeller for a steamboat was built by John Fitch,
and it was still shaped like a screw. Propellers
act according to Newton’s third law of motion and can be used in water and to
move across the air because as they spin, they push air or water molecules
behind them, causing the craft to move forward.
The propellers are usually made of two, three, or four blades that stick
out of a central hub at certain angles. The
hub is attached to a motor that makes the propeller spin around. The first existing submarine was built for
the Union Navy in 1861 by the French inventor Brutus De Villeroi, which used an
oar-propulsion system. This was
exchanged for a screw propeller in 1863, however the Alligator had to be cut loose because of a storm and is currently
lost. Since then, propellers have been
modified and improved so they can be used in all submarines.
There is a difference in materials for propellers as well as speed depending on which kind of craft is going to be made. For an aircraft, propellers are usually made of hollow steel, lightweight aluminum, or magnesium allows. They spin quickly because air is very thin, so in order to push a lot of air, there needs to be a high rotation rate. For a ship or a submersible, the propellers used are made of copper alloys such as brass, shown in figure 1, so that the blades do not corrode in salt water. These spin at slower rates because water is denser than air, so the blades do not need to spin as fast as those in an aircraft. The blades are angled to determine how quickly it moves when it turns. This angle is called a pitch. Not only are they angled, the blades are twisted as well so that as it spins, the pitch of each blade changes as you go along the length of the blade. This angle is what allows the propellers to push air and water backward, allowing the ship to move forward.
Figure 1: Submarine Propeller
There is a difference in materials for propellers as well as speed depending on which kind of craft is going to be made. For an aircraft, propellers are usually made of hollow steel, lightweight aluminum, or magnesium allows. They spin quickly because air is very thin, so in order to push a lot of air, there needs to be a high rotation rate. For a ship or a submersible, the propellers used are made of copper alloys such as brass, shown in figure 1, so that the blades do not corrode in salt water. These spin at slower rates because water is denser than air, so the blades do not need to spin as fast as those in an aircraft. The blades are angled to determine how quickly it moves when it turns. This angle is called a pitch. Not only are they angled, the blades are twisted as well so that as it spins, the pitch of each blade changes as you go along the length of the blade. This angle is what allows the propellers to push air and water backward, allowing the ship to move forward.
Project Deliverables
- Constructed SeaPerch with attached motors
- Documented process of optimizing propulsion
- Pro Engineer files of redesigned propellers
Project Schedule
WEEK 1: Determine design constraints and goals once kit
has been received.
WEEK 2: Start and finish construction on the chassis,
control panels, and motors and mount motors on the chassis.
WEEK 3: Test and become acquainted with SeaPerch and fix
ballast issues, if any.
WEEK 4: Begin extensive research into motor and
submersible propulsion.
WEEK 5: Finish motor designs and submit parts to
rapid-prototyping machine.
WEEK 6: Acquire sensors for the SeaPerch and determine
where and how they will be used.
WEEK 7: Test redesigned motors and depending on results
determine if new designs need to be made.
WEEK 8: Attach sensors and test functionality
WEEK 9: Final tests and changes
WEEK 10: Presentation
Budget
http://www.seaperch.org/order_kit
Amazing Goop Marine Adhesive - $4.67
References
C. Woodford. (2011,
July 25). Propellers [Online].
Available: http://www.explainthatstuff.com/how-propellers-work.html
Submarines: History –
The U.S. Navy’s First Submarines [Online]. Available: http://www.onr.navy.mil/focus/blowballast/sub/history4.htm
References
C. Woodford. (2011,
July 25). Propellers [Online].
Available: http://www.explainthatstuff.com/how-propellers-work.html
G.
Pytel. (2011, April 15)Submarine’s
propellers and CAD/CAM in military shipbuilding [Online]. Available: http://cadcammodelling.wordpress.com/2011/04/15/submarines-propellers-and-cadcam-in-military-shipbuilding/
Submarines: History –
The U.S. Navy’s First Submarines [Online]. Available: http://www.onr.navy.mil/focus/blowballast/sub/history4.htm
