Design Flow Chart*
|
| Pre Design Phase |
Mission Statement:
Mission Objectives
Environmental factors
Time to accomplish mission
Altruistic values of the mission
|
Mission Requirements:
Environmental factors
Objective
Geographic location, weather and hydrographic factors
Time frame
Mission tasking
Vehicle performance requirements
Operational support
|
| Design Phase |
Conceptual Design:
Project teams' research into systems
Functional specifications
Sketches and conceptual systems requirements
Budget estimate
|
Detail Design:
Detail design based on the conceptual design
Improvements of selected systems
Ready for construction
Budget and Bill of Materials
|
| Post Design Phase |
Construction:
Procurement of material and components
Fabrication of systems components
Component testing
Assembly of vehicle
|
Testing, Field Trials And Demonstrations:
Shop testing of vehicle
Evaluation of systems
Improvements after testing
Vehicle user operation manual
|
Operations:
Plan search patterns
Plan recovery
Logistics and field tasks assigned to team members
Execute plan
Use vehicle to search and recover canisters
Record keeping and images
Vehicle data management
Evaluate as circumstances dictate
Demobilization
Debrief
|
Final Report:
Evaluation of design
Future improvements |
| |
Troubleshooting
Simple Circuits* Troubleshooting is a method of solving technical
problems. Most electrical systems experience problems at one time or
other. They occur during the wiring phase of the project, when an error
in connecting the leads may have occurred and was overlooked at the
time, or something happens during transport or while in use. You do
not need to be a knowledgeable electronics tech to troubleshoot electrical
circuits. But it is important to approach the problem in a methodical
way.
For this example, the UUV has been built. This is the first power up
of the thruster system. But nothing happens. You close all the switches
to turn on the thrusters but there is no reaction.
Check to make sure the power from the supply is connected to the control
box terminal inputs visually. Physically "wiggle" the wires with the
power on to see if there is a loose connection. 90% of the problems
can be solved with a visual and physical check of a circuit. Always
check the power source connections first.
Check the fuses. Not just on the UUV circuits but also the power supply
as well. Maybe the plug or extension cord is not energized. Sometimes
the GFI is tripped. Check this.
If this doesn't solve it then physically check the tether as it comes
out of the control box, and the wires to the UUV from the tether. Again
visually and physically wiggle the wires with the power on.
If that doesn't do it then open the control box, and physically and
visually check all the wires in it. Sometimes a bad solder joint will
cause a problem.
The problem is that no thruster operates. That can mean only one thing.
The main power source to the switches is problematic. Anything past
the switches is not a problem at this stage. So get your schematics
out and trace all the wires. Look for wiring mistakes before the switches.
Look for bad solder joints or short circuits in wires that are close
to each other.
Anyway this is the procedure. Notice you didn't even use the multimeter
or any Star Trek level 1 diagnostic testing.
If this still doesn't solve the problem dig out the multimeter and start
measuring voltages according to the schematics you have made. Perhaps
the problem is in the switches or a broken wire or frayed insulation
grounding to the control box, where you can't see it.
If you have power out to all the tethers conductors, then the problem
is in the UUV.
Open the UUV termination can and check the wires visually and physically.
Anyway if you haven't got a solution by now, the only other problem
is that all of the thrusters are physically damaged. Not very likely.
So start over and go through it again.
That's it! Simple eh?
|
Propeller Matching
on the Project ROV*
As we have seen the real task in propulsion is to increase power efficiency.
To do this a propeller has to be chosen that optimizes the both the
motor and hydrodynamic characteristics of the vehicle. There are many
ways you can optimize the propeller. This optimization is called propeller
matching. For your project it is a simple matter of finding a propeller
that has the right pitch and diameter that the bilge pump motor can
handle.
There are large number of variables and combinations that can be changed
to create a propeller design. Most manufacturers usually design a small
number of props to a standard configuration in order to avoid overwhelming
the production process by designing custom propellers for every single
engine and boat. You may have noticed that the hobby model boat manufacturers
only produce a limited number of types of propellers. They match the
props to their own boat products. If you are trying to match a prop
to the bilge pump motors you have to so by experiment. There are not
enough values given or measurable to use calculations. Simply put you
want to get the most thrust for the least amount of power
The following is a simple propeller matching experimental set up.
- The first thing you need to do is determine weather you need high
speed or slow speed with reserve power for pulling. The project
ROV will need low speed and lots of torque for towing and lifting
the object and moving that boxy shape through the water. You also
want to be able to stop and start without much glide or overshoot.
So high thrust at slow speed is required.
- So from what you know of propellers and the swing space you have
available start by selecting a range of propeller diameters. Let
us say from 1" to 3" to start.
- Next select props with a different number of blades. (2, 3 or
4 bladed propellers). Also determine if they should be right or
left hand.
- Next look at pitch. Remember high pitch gives good power but can
the motor turn it without bogging down? If you want good towing
power the general rule is more blade area increased diameter but
low pitch. Anyway just try a few high and low pitched props. You
may not have to many choices. It seems most hobby props are high
pitch. Alternatively you could try an airplane propeller. In many
cases the longer two blades are more efficient. If you find it too
long you can always cut it down.
- Are you using a nozzle? If so this constrains the diameter and
affects some of the thrust characteristics. Sometimes it increases
thrust without increasing the motor loading. Other situations it
may make things worse. Just try it out.
- Construct a thruster test jig. This consists of a spring scale,
a slider, a carriage that moves along the slider and a way to clamp
the motor to the carriage. Attach the spring scale to a post on
the end of the slider. The other end of the scale attach to the
carriage. Mount the thruster with propeller facing so the scale
is pulled when the thruster is activated. Try and keep the area
behind the prop as clear as possible to minimize turbulence. When
the thruster is turned the carriage will move and pull on the scale.
Read the force in grams or ounces from the scale. This is the thrust
of the propeller.
- Now mount a thruster and prop. Use only three speeds. Try and
use the same power source or motor controller. Often motor controllers
will only give 90% of the power that a direct hookup to the battery
will. So for the best accuracy use the power source you have specified
for the ROV. Hook up an ammeter in series to the motor. Now using
low speed switch on. Make a chart to record amps and thrust. Record
both amps and thrust for low speed. Next use mid-speed. Record amps
and thrust. Lastly use high speed and record amps and thrust. Make
sure you label the propeller you used and record it in your chart
as well.
- Continue this test in the forward direction for all the propellers
you have chosen. Use you chart to record the results.
- If you want you can also do the same test for reverse thrust for
the different props.
- Graph the results using amps on the Y-axis and thrust on the X-axis.
Ideally the graph should be a straight line at a nice 45-degree
angle, in theory. But this is never the case in reality.
- From the data on the graph it is easy to compare the propellers
with each other. What you are looking for is the best thrust for
the least number of amps. Then it is your choice to decide on the
prop to use.
- When doing these tests always be aware of the rpm. If the motor
slows excessively this will be seen as an increase in amperage.
This is not a good situation. Do not exceed the amp rating of the
controllers and motor by more than one amp.
*Taken from MATE's Introduction to Submersible Technology course curriculum
modules. Copyright MATE Center 2000. |
