Design Proposal

Problem Overview

The Sea Perch kit which the Navy provides for its Sea Perch competition makes use of very small, low powered, low cost motors to act as thrusters on an underwater submersible to be used in a pool.  These motors fall apart and break very easily.  The goal of this project is to modify the propulsion system and chassis of the Sea Perch kit so it can be used in rivers.

Design Constraints

Considering that we are designing this project ourselves, there are not many constraints in terms of what we can and cannot use.  The main constraint is we lack funding and therefore would like to keep this as low cost as possible so perhaps Sea Perch can implement it.

The other thing that has to be taken into account is there is a current in a river but not in a pool.  Therefore, the motors we ultimately use must provide more thrust than the Sea Perch motors.  Furthermore, we need to take the size of the motor into account when deciding on the shape and size of the chassis.

Pre-Existing Solutions

There are many pre-existing solutions to this type of problem.  However, we are trying to keep the solutions as cost-effective as possible in order that the Sea Perch kit might be redesigned within approximately the same current cost parameters, but instead implement the new changes which we propose.

One of the problems of the Sea Perch ROV is they are not hydrodynamic.  The typical ROV is in the shape of a square with three motors attached.  If the shape of the chassis of the submersible is changed to be flatter, the submersible may work better. There are many different shapes of submersibles which have been explored.  In general, the most hydrodynamic submersibles were the most effective.  These submersibles were typically flat or triangular in shape.  A team of Darmstadt researcher’s built a robotic fish that emulates the movement of a fish using waterproof actuators.  The shape of the fish is a very hydrodynamic shape.  While this approach is probably the best option for an efficient hydrodynamic submersible, it is not within our cost or time constraints.

Another problem with the Sea Perch submersibles is they do not use high quality motors.  Many different motors have been used on underwater submersibles to increase thrust.  However, in Sea Perch, no alternative is offered.  Furthermore, the propellers on the existing Sea Perch motors fall off.  Some submersibles use a special water resistant glue to hold the propellers on to the motor’s shaft.  Other submersibles actually have the propellers melted on to the motor’s shaft.

Going from a pool to a river is also a problem caused by current which many submersibles have already handled.  The ACE-ROV created by a team of students from Dalhousie University uses 1100 GPH bilge pump motors with custom built propellers.  They are placed in a way that allows for strafing from side to side and forward and backward, up and down.  Obviously, using higher-powered motors for thrust is one way of solving this problem.  Furthermore, changing motor placement can provide more thrust. 

Because there are so many ways of solving each of these problems and because there are multiple problems occurring at once, it is almost impossible to list all of the solutions.

Design Goal

Figure 1: 12V 350 GPH Liquid Pump

Figure 2: Schematic of Proposed Chassis
 and Motor Placement on submersible

            Ultimately, we are using a higher thrust yet still low cost motor to solve the problem of thrust.  We are using six 12 V 350 GPH Liquid Pumps (Figure 1) as the thrusters.  These motors are very sturdy and can be used with propellers, if modified.  Since we are trying to keep this project low cost, these motors are suitable because their cost is $14.95, each.  Not only are we just using different motors for thrust, we are also using motor configuration to our advantage.  By placing the motors in the configuration illustrated in Figure 2, our submersible will be able to turn faster because the two thrusters diagonal to each other will be used.  This will make it easier for the submersible to turn while current is also working against it.  When it needs to go straight, two adjacent motors will run, giving it more thrust than the one motor currently provided in the Sea Perch kit.

            We are using two of the motors for a buoyancy and ballast system that will raise and lower the submersible.

            We are also attaching a camera for purposes of orientation and ease of driving.  The camera we will attach is a low cost underwater camera which can be purchased at Cabela’s, a sporting goods store.

            We are making a tether for our robot as well.  We are also including a rope in that tether so that if something goes wrong, the submersible can easily be pulled out of the water without directly pulling on the wiring.

Project Deliverables and Schedule

Week	Item	Description
1	Blog and Brainstorm	-Set up the blog with the Home Page and Design Ideas Page. -Use the Design Ideas page to store and present brainstormed ideas.
2	Finalize Design	-Go through brainstormed ideas and decide which ideas are best. -Have a general idea of the placement of motors. -Have a general idea of the chassis shape and size. -Have a general idea of how the robot will be wired and programmed.
3	Decide what needs to be ordered and receive Sea Perch Kit.  Set up Home Depot/Lowes date.  Finish finalizing the design.	-Order Motors. -Receive Sea Perch Kit.  Decide what exactly will be used from kit. -Decide what else needs to be purchased and/or brought in from home. -Set up date to go to Home Depot or Lowes together. -Have a solid design.
4	Build Chassis and Thrust System	-Build chassis and install motors.
5	Build Buoyancy/Ballast System	-Build buoyancy/ballast system.
6	Wiring/Electrical	-Wire the submersible. -Install and test the camera.
7	Test Submersible in a Pool and Make Adjustments	-Test submersible in Drexel’s pool. -Make necessary adjustments after testing.
8	Test Submersible in the River and Make Adjustments	-Test submersible in the river. -Make necessary adjustments.
9	Final Adjustments and Final Paper and Presentation Preparation	-Make any minor final adjustments to the submersible. -Complete the final paper. -Complete the presentation. -Finish the Blog.
10	Final Presentation	-Give final presentation.

Cost Analysis

Quantity	Item	Cost Per Unit	Total Cost	Comments
6	Liquid Pump – 350 GPH(12V)	$14.95 + S&H	$89.70 + $13.18 (S&H) $102.88	http://www.sparkfun.com/products/10455
1	Sea Perch Kit	$0	$0	Donated by Navy
1	Cabela’s Underwater Camera	$99.99 + S&H	$99.99 + S&H	http://www.cabelas.com
Varies	PVC	Price Varies	$20-$30Cabel	The size of the PVC and cost of the PVC vary.  It depends upon what is included in the Sea Perch kit and how large the ballast tank will be.
Varies	Wire	Price Varies	$20-$30	The amount of wire and gauge of wire depends upon the controller and motors, both of which we have not received yet.  Also, depends upon the length of the tether.
1	Gorilla PVC Cement R04000 4oz Clear PVC Prima Glue	$5.00	$5.00	http://www.google.com/products/catalog?q=pvc+glue&hl=en&safe=off&client=firefox-a&hs=oFP&rls=org.mozilla%3Aen-US%3Aofficial&prmd=imvns&bav=on.2%2Cor.r_gc.r_pw.r_qf.%2Ccf.osb&um=1&ie=UTF-8&tbm=shop&cid=17554615529151053364&sa=X&ei=EMiQT-2XPKqX6QHZ8tiMBA&ved=0CJ4BEPICMAM