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Midterm

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									Human Powered Submarine
     Controls Systems




      Team 2007-2008

         Jeff Poirier
         Corie Drake
        Matt Ledoux
         Amy Wing
        Dan Getchell
       Chris Briggeman
Human Powered Submarine: Control Systems




    Introduction ................................................................................................................. 3
    Tow Cap ...................................................................................................................... 3
    Replacing “Stuff Box” ................................................................................................ 3
    Fly By Wire................................................................................................................. 3
    Tow Tank .................................................................................................................... 6
    Bow Planes.................................................................................................................. 6
    Manual Controls.......................................................................................................... 6
    Window Replacement ................................................................................................. 7
    Conclusion .................................................................................................................. 7




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Human Powered Submarine: Control Systems


Introduction

This is a brief summary of the progress made by the Human Powered Submarine: Control
Systems group during the Fall 2007 semester. It will cover all of the accomplishments
made thus far in the design process. Also mentioned will be goals for the following
semester.


Tow Cap

The tow cap was designed for towing the submarine
through the water without causing damage to the nose of
the sub. The first step in this process was to figure out a
way to get the measurements of the inside of the nose of
the submarine. The solution was to line the inside of the
nose with plastic and fill it with Great Stuff expanding
insulation foam. This created a template from which the
final tow cap was cast. A rubber mould was created
which was then used to form the final cap which was
made of plastic. The cap was then sanded and Bondo
was applied to smooth out the caps surface. A large
Eye-Bolt was used as the tow point. The force in the
bolt is distributed to the cone by an aluminum plate
beneath a layer of Bondo.

For stress/strain analysis see Appendix A & Appendix B
(sidebar)                                                     Figure 1 Finished Tow Cap


Replacing “Stuff Box”

One of the first problems addressed was the use of the so called “Stuff Box”. This box
initially contained all four actuators as well as the entire control circuitry and battery. It
was determined early on that the giant block of aluminum housed in the tail of the sub
was excessive. It was decided that the box would be removed. The linear actuator group
then took over the bulk of this design problem by making individual boxes for each
actuator. In the final design of the sub, there will also be a small box of either Plexiglas
or plastic located in the tail to house the electrical components. This will be completed
early next semester.


Fly By Wire

One of the biggest problems facing the design team this semester was the Fly-by-Wire
control system. This is intended to be the primary mechanism for steering the sub, so it is
critical that it works correctly. Thus far, progress has been slower than expected in


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Human Powered Submarine: Control Systems


programming and integrating with the submarine, though it appears that things are
beginning to go more quickly.

One of the most important advancements in this section of the design process is the
implementation of a joystick. The joystick will be the simple mechanism used to steer
the sub. The joystick itself was salvaged from an old PlayStation 2 controller and
appears to fit design specifications perfectly. The main requirement of the joystick was
that it be analog. Since an analog joystick is essentially two potentiometers mounted
perpendicular to one another, it will allow the pilot of the submarine to make turns of
varying degrees. That is, the amount of turn of the rudder or elevator is directly related to
the amount of movement of the joystick, as opposed to simply have a stick that sends
left/right up/down commands that do not vary in magnitude.

Below is a schematic showing how the joystick is wired on the PlayStation controller.




                                                                 Mounting Posts


                                                                 y-axis

                                                                 Optional
                                                                 Push-Button
                              x-axis

                              To Ground                      Button


                      Figure 2 Joystick as wired on PlayStation 2 Controller

Once the joystick was disconnected from the PlayStation controller it was prepared to be
hard wired to the control circuitry.

A problem that comes up with the controls of the submarine being analog is that the
program Basic Stamp will not be able to read it. It can only take inputs of a certain
degree and not varying. To bypass this problem we adapted a capacitor to fill with
electrons and discharge through a resistor network that consisted of the joystick and
another additional resistor. Since varying the angle on the joystick varies the resistance
of the circuit, at different angles of the joystick, the circuit has a different resistance. To
measure the difference in resistance (or joystick angle) the program measures the amount
of time it takes the capacitor to discharge all it’s built up electricity.




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Human Powered Submarine: Control Systems



The amount of time it takes for the capacitor to discharge is equal to the total resistance
of the circuit times the size of the capacitor.

                                             T  RC

Where
        T= time
        R= resistance
        C= capacitance

Since any given angle of the joystick gives a certain circuit resistance, the angle of the
joystick is now a function of the time it takes the capacitor to discharge. This can then be
scaled to the needed output of the servos for any given joystick movement. Below is the
schematic of the capacitor resistance circuit of which joystick angle is the only variable.



                     I/O Pin


                                 220 Ω                   10 kΩ
                                      .1 μ




                                    Figure 3 Joystick circuitry

The figure below shows a basic wiring setup of the fly by wire control chip.




                            Figure 4 Diagram for basic circuit board layout
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Human Powered Submarine: Control Systems


Tow Tank

In order to gain an understanding of how the sub will react in operation, it will need to be
tested in the tow tank. To gain access to the tank, confined space entry training as well as
lock out/tag out training must be obtained.


Bow Planes

Bow planes are used to help stabilize the trim of the submarine. This is done by forcing
the nose down, countering the buoyant force which was a large problem in previous
years. The bow planes also remove some of the burden on the rear control surfaces
regarding trim, freeing the control planes to focus on maneuvers. The design of the bow
planes is such that they are fixed, yet they are allowed to move slightly to adjust for
variations in speed. Though they are not adjustable on the fly, they are easily adjusted
between runs.




                  Figure 5 Bow Plane (left) and Bow Plane Attached to Sub (right)


Manual Controls

The manual control system was also a large problem for the design team. The original
controls were thrown together when the electronic controls failed in a previous
competition. This system needed to be of the same caliber as the electronic control
system so in the event of an electronic failure, the pilot could rely on the manual controls
to perform with the same level of certainty.

The manual controls consist of throttle cables which will be controlled by twisting a
handle which in turn twists the control surface. Some key modifications made this
semester are the moving of the control handles more toward the front of the sub as well
as manufacturing new handles which will not get caught on the pilot’s gloves.




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Human Powered Submarine: Control Systems


To move the handles forward, the mounting brackets were taken off and reattached
further toward the front of the sub. This allowed for more room for the driver to control
the submarine with more access and maneuverability.

The new attachments for the manual steering controls were made to be much thicker so
that the screw attached to throttle cables could be countersunk. Countersinking the
screws allows for smooth operation of the handles, without interference with the driver’s
hands. The new attachments also were designed with more precision as the old ones were
not up to the standards required.




   Figure 6 Newly mounted control                            Figure 7 Image of control handle
            mounting brackets                                         with throttle cable plate

The last step in finishing the manual controls is to attach them to the control surfaces.
This is where there is some overlap between the control group and the linear actuator
group. Because of this, a joint effort is being made in determining the best way to
combine each groups components. It has been decided that the manual controls will not
be able to be engaged “on the fly” but instead will need to be engaged in the event of an
electronic system failure by manually connecting the controls to the control planes.
Further development of this will continue next semester.


Window Replacement

Upon inspection of the submarine at the beginning of the semester it was noted that the
lower window was cracked and needed replacement. The cracks and non-unification of
the window could result in more drag when propelling through the water which would
ultimately slow down our top speed. This window was replaced with plexi-glass and
sealed on the inside and out using clear caulking.


Conclusion

There has been a substantial amount of work completed on this project this semester.
Although things were slow at the beginning they have picked up as the semester begins to


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Human Powered Submarine: Control Systems


come to a close. There were many bumps in the road as there was already substantial
work done on the sub at the start. Repairs and modifications took up a large amount of
time as did the planning and group training activities that were required. The design team
is now in full swing and it seems the bumps are all out of the road. Next semester the
team will be ready to work at a steady pace and begin completing milestones
immediately.




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