ROV uses

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Retrieving the toxic barrel
ROV and robotic arm construction
Author
Gary Scott
NSESs addressed
Abilities of Technological Design
1. Propose Designs And Choose Between Alternative Solutions
Students should demonstrate thoughtful planning for a piece of technology or technique.
2. Implement A Proposed Solution
A variety of skills can be needed in proposing a solution depending on the type of
technology that is involved. The construction of artifacts can require the skills of cutting,
shaping, treating, and joining common materials-such as wood, metal, plastics, and
textiles. Solutions can also be implemented using computer software.
1. Communicate The Problem, Process, and Solution.
Students should present their results to students, teachers, and others in a variety of
ways, such as orally, in writing, and in other forms-including models, diagrams, and
demonstrations. NSES p. 192
Motions and Forces
Whenever one object exerts force on another, a force equal in magnitude and opposite in
direction is exerted on the first object (principle behind thrusters and propellers). NSES
p. 180.
Electricity and magnetism are two aspects of a single electromagnetic force. Moving
electric charges produce magnetic forces, and moving magnets produce electric forces.
These effects help students to understand electric motors and generators. NSES p. 180.
Objectives
1. Students will investigate the design and operation of double pole double throw center
off switches.
2. Students will investigate the design and principles underlying the operation of
propellers (Newton’s Third Law).
3. Students will investigate electromagnetic phenomena and apply knowledge of
electromagnetism to construct a model of an electric motor as well as explain how it
operates.
Exploration
Now that the cargo box along with several barrels of toxic chemicals has been located a
remotely operated underwater vehicle must be built to retrieve the material.
Part 1 – Electricity, magnetism, and motors
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Compass construction
What is a compass and how does it work? In this activity you will build a compass and
save it for the next section when you construct a motor.
Materials
3 magnets with holes in the center
1 straw
2 pieces of #22 wire, 20 cm long
1 plastic cup
1 compass
Procedure
1. Bend the two #22 wires in half around your index finger.
2. Arrange the two magnets so that they stick together side by side, as shown. Push the
open ends of one wire one third of the way through the hole in the center of one of the
magnets. Now do the same to the other magnet with the other wire.
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3. Without removing the wire, separate the two magnets. Pull apart the open ends of the
wire and wrap each end aroun the long sides of the magnet. Bend the looped end up
over the top and let it project forward. Now do the same to the other magnet.
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4. Check to see if the sides of the magnets away from theloop will attrat each other. If
they repel, go back to Step 2, remove the wire from one of the magnets, turn it over,
and rewire it. The magnets should stick together, with the looped ends pointing in
opposite directions.
5. Insert the looped ends into the ends of the straw.
6. Balance the straw on your finger and push the pin down through the straw at the place
where it balances. The tip of the pin should project about 5mm below the bottom of
the straw. Do not make more than one or two holes in the straw of the pin will slip.
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7. Balance the straw across the top of the inverted plastic cup. Do not push the pin into
the plastic up. Adjust the balance of the straw compass by pulling out or pushing in
the magnets at the ends of the straw a little bit, as needed.
After you have balanced your compass, test to see if it points in only one direction when
you release it from different positions. Get a small compass from your teacher and
compare the direction it points to the direction that yours points. Does your compass have
a north and south pole? If so, place a small dot on the straw to show its north pole. Bring
the small compass close to your compass’ north pole. Which end of the small compass
(the north seeking or south seeking) is attracted to your compass’ north seeking end?
Using your extra magnet find a way to make your straw compass rotate. How can you
speed up or slow down the compass’ rate of rotation. Explain how you accomplished a
change in rotation speed.
Predict the effect decreasing the length of the straw on the rotation rate. Predict the effect
of using two or more magnets to effect the rate of rotation.
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Building a motor
Do you know what makes an electric motor work? In this activity you will build a simple
electric motor.
Materials
Straw compass built in last activity
1 coil of #21 coated hook-up wire, 1.5 m long
1 plastic cup
1 piece of #22 coated hook-up wire, 20 cm long
1 battery and battery holder
1 switch
2 # 16 rubber bands
Procedure
1. Using the piece of wire that is 1.5 m long, coil it around three of your fingers. Attach
the coils to the side of the inverted plastic cup with the two rubber bands. Connect the
coil to the battery and the switch. With the 20 cm long wire connect the switch and
the battery. Position the coil two finger widths away from the north pole of the straw
compass.
2. What effect does the coil have on the magnet when the switch is off?
3. Turn the switch on so that electricity will run through the coil. Is the north magnet
attracted or repelled by the coil?
4. Now, position the south pole magnet next to the coil. Predict what will happen when
you turn the switch on.
5. Make the straw compass a motor by causing it to spin continuusly in one direction by
just turning the switch on or off at the right time. Remember which end is being
attracted to the coil and which end is being repelled.
Building a spinning coil motor
Materials
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2 pieces of #20 bare copper wire, each 20 cm long
2 #16 rubber bands
1 plastic cup
3 #22 wires with alligator clips on each end
1 battery and battery holder
1 switch
1 piece of #28 enameled copper wire, 65 cm long
1 piece of sandpaper, 5 cm square
1 flexible magnet with hole in the center
Procedure
1. Start by making a loop in the middle of each of the two bare copper wires. Wrap them
around a pencil then slide the loop off the pencil.
2. Use the two rubber bands to attach the bare copper wire to the plastic cup.
3. Clamp an alligator clip to one end of each of the bare copper wires.
4. Hook up the rest of the circuit by connecting the battery and the switch to the alligator
clips.
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5. Next, begin to make the moving coil from the #28 wire. The wire has a thin coating
of insulation on it called enamel, so you will need to sand off the insulation at the
ends. This is so the electricity can flow from the bare copper wire through the thin
wire to the other bare copper wire. Sand about one finger-length of insulation gently
off each end of the wire. You can do this by folding the sandpaper in half and pulling
the ends of the wire carefully between the two sides of the sandpaper.
6. Wrap the wire around the battery several times. Leave the bare ends sticking out of
the coil. Slip the coiled wire off the battery. Wrap the bare ends three or four times
around the coil to hold it in a circular shape. Then bend the ends of the wire so that
they stick straight out on opposite sides of the coil.
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7. Place the ends of the coil through the loops in the bare wire on each side of the cup. If
necessary, bend the coil and adjust the loops so that the coil can spin freely, without
hitting anything.
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8. Place a magnet on the top of the inverted cup, underneath the coil. Turn the switch on
and blow gently on the coil to help it get started. If the coil will not spin continuously,
try adjusting the position of the magnet, the distance of the coil to the magnet, or
bending the wires.
Now that you have found out how to make the motor work answer the questions below.
i. Where do you think the electricity flows in this circuit? Draw a picture to help you
explain
ii. Do you think the coil is magnetized? Describe the evidence for your answer. Make a
drawing of your coil showing where the north and south are located.
iii. How can you make the coil spin faster or change direction. Explain how you
accomplished these two tasks.
iv. How does this motor compare to the spinning compass motor? How are they alike?
How are they different?
Commercially made electric motors
Electric motors are found in many everyday devices such as refrigerators, VCRs, and
many toys. In this activity you will disassemble a commercially made motor and explain
how it operates based on the simple models you have previously constructed.
Materials
Electric motor from last activity
Commercial electric motor
Steel nail
2 magnets
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2 strands of #20 hook-up wire, 30 cm long each
Procedure
Based on the electric motor you created, predict what kinds of parts you should find
inside of the commercially made electric motor.
1. To take the motor apart begin by using a nail to slowly bend the metal tabs away from
the plastic end of the motor as shown below.
2. Hold the motor case with one hand and push carefully on the motor shaft with one
finger.
3. The plastic cap will come off and you will be able to take the motor shaft out of the
case.
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4. Separate the motor into three pieces as shown below.
5. Look closely at each of the three parts. Think about how they were connected when
the motor was assembled. Explain how the parts are similar to the part of the motor
you made.
6. All the parts of the motor help in some way to make the motor run. Look at your
motor and figures above. Explain what you think the different parts of the motor do.
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How does a motor work?
Get your materials from the section on building a motor.
1. Take one of the bare copper wires off of the plastic cup. Slide the ends of the
remaining bare copper wire so that the loop is directly above the center of the cup.
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2. Slide the two pieces of hook-up wire under the rubber bands and bend apart the bare
ends that are protruding beyond the tape so that they make a "V”.
3. Connect to the battery holder and switch the ends of the hook-up wire that are no
taped together. Bend the wires so that the cup will not tip over when you let it sit
without hold it. This will be your test stand.
4. Place the armature of the motor you took apart on the test stand. Bend the wires so
that the armature fits and will not fall off. Can you figure out which end of the
armature needs to rest in the “V”? Screw the switch down so that electricity will flow
throught the circuit. Hold a magnet near the armature. Can you make armature spin?
5. Experiment with the two magnets to find the location that makes the motor spin the
fastest. Does it matter how close the magnets are to the armature? Does it matter
which pole of the magnet faces the armature?
6. Experiment to find as many ways as possible to make themotor turn slowly. What are
the different things you can do to make the motor slow down?
7. Experiment to find ways to make the motor change direction. How many ways can
you find?
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8. Think about how the parts of the motor fit together. Look at the diagrams and try to
put your motor back together carefully. The numbers indicate the sequence in which
the parts are to be assembled.
Part 2 – double pole double throw switch design
How do switches work? Your task is figure out how a double pole double throw switch
works and make a diagram of the internal design.
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Materials
9. 12 volt lantern battery
10. One double pole double throw (DPDT) center off switch rated at 3 amps.
11. One electric motor
12. 18 or 22 gauge hookup wire
13. One propeller
Procedure
7. Connect the battery to the middle terminals of the DPDT switch.
8. Connect the wires from the motor’s terminals to one end of the DPDT switch. Put a
propeller on the long shaft of the motor.
9. Trace the pathway of the connections from the positive terminal of the battery to the
motor.
10. Trace the pathway of the connections from the negative terminal of the battery to the
motor.
Which way should you push the lever on the switch to turn the motor on? Push the
switch’s lever to turn the motor on. Which way did the propeller turn?
How do you think the inside of the switch is designed so that current is transferred from
the middle terminals of the switch to the end terminals of the switch? Draw a diagram
that shows what the internal wiring of the switch looks like and show it to your instructor.
Using two pieces of wire how could modify your design so that flippin the switch’s lever
in the opposite direction would send current to the motor and cause the propeller to turn
in the opposite direction? After you solve this problem, draw another diagram that shows
what the internal wiring of the switch looks like and show it to your instructor.
Drew – I need a graphic showing the inside of the switch from the top and side.
Part 3 – propeller driven vehicle design
Your first task is to figure out how a propeller moves a vehicle. To do this you will need
a propeller, electric motor, wire, and the 6 volt lantern battery. After you connect these
components place the propeller and motor so the propeller is closest to you. Now,
connect the motor wires to the battery and notice which way the propeller turns. If the
propeller turns clockwise reverse the way the wires are connected to the battery.
Example, if the black wire is connected to the negative terminal, connect it to the positive
terminal. Disconnect one of the wires, set the propeller and motor down, and get your
paper and pencil so you can answer the following questions.
Predictions
Write down your predictions in complete sentences to the following questions.
i. If the propeller rotates counterclockwise which way will the right blade push the
air?
ii. If the propeller rotates counterclockwise, which way will the left blade push the air?
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Testing your predictions
Now connect the wires to the battery so the propeller rotates counterclockwise. Hold a
piece of paper about 6 inches from the backside of the propeller and notice which way the
paper moves.
iii. Why is the paper moving? Answer this question using the following words:
propeller, pushes, air, paper.
Your answer to question three needs some more thought. The propeller is pushing the air
backwards (towards the motor). If the propeller and motor were mounted on a boat or
airplane, which way would the boat or plane move?
Reverse the way the wires are connected to the battery. The propeller should be turning
clockwise.
Predictions
Write down your predictions in complete sentences to the following questions.
iv. If the propeller rotates clockwise which way will the right blade push the air?
v. If the propeller rotates clockwise, which way will the left blade push the air?
Testing your predictions
Now connect the wires to the battery so the propeller rotates counterclockwise. Hold a
piece of paper about 6 inches from the backside of the propeller and notice which way the
paper moves.
vi. Why is the paper moving? Answer this question using the following words:
propeller, pushes, air, paper.
Your answer to question three needs some more thought. The propeller is pushing the air
backwards (towards the motor). If the propeller and motor were mounted on a boat or
airplane, which way would the boat or plane move?
Concept formation
4. Make a diagram to illustrate how a propeller moves a vehicle forwards and
backwards. Use arrows to show the direction the propeller forces air to move and in
turn the direction the air molecules push on the propeller.
5. Using your diagram, write out an explaination of how a propeller moves a vehicle
forwards and backwards.
6. Now think about jet airplanes, rocketships, and squid. All three move by jet
propulsion, that is, in all three cases the propulsion system forces molecules to move
in one direction and the object then moves in the opposite direction. This phenomena
was described by Sir Isaac Newton and is often referred to as Newton’s Third Law of
Motion. In Newton’s own words, to every action there is always opposed an equal
reaction. The following sentence refers to Newton’s Third Law but has blanks for you
to fill in to make it complete.
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Two objects interact such that for every force exerted on one, there is an _____
and _____ directed force exerted on the other.
Concept application
Using your knowledge of motor operated vehicles (such as boats and planes)
imagination, and the materials supplied in your kit, design a remotely operated vehicle
(ROV) that can move forward, backward, right, left, up and down in the testing tank. You
should make a careful drawing for your design and include the position of the motors
with propellers and the body of the ROV. Indicate in your drawing which direction the
ROV will go when the propellers are turning clockwise and counterclockwise.
ROV Construction
Objectives
1. Students will construct a remotely operated vehicle that can pick up a ‘barrel of toxic
material’ in a tank of water five feet deep.
2. Density – air weight, water weight
3. Displacement, Archimedes principle
4. Pressure
5. Fluid dynamics
Exploration
Part 1 - Constructing the frame
Use your drawing from the concept application problem and PVC parts to construct an
ROV frame.
Where will you mount your motors so the ROV can go left, right, up and down?
Part 2 - Wiring the switches in the control box
1. Drill holes in your control box far enough apart so the switches won’t interfere with
one another. Determine which holes you will use for the left, right, and up/down
thruster wires. The holes should be just large enough for the switch shaft to fit
through.
2. Solder the switches as shown in the diagram before you mount them to the control
box. After soldering a switch put labels on the wires (e.g. left, right, up/down) so that
you know which wires to connect to the tether coming from the thrusters.
3. Secure the switches to the control box.
4. Connect the wires from the switches to the tether from the thrusters.
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Part 3 – Waterproofing the thrusters
Heat up toilet seat wax before you start this procedure. The wax should be just hot
enough to pour easily. You will use it step 7.
1. Drill a hole in the top of the film canister so you can thread the end of the 20’ wire
through the hole.
2. Tie a knot in the wire leaving just enough wire so you can solder the ends to the
motor.
3. Solder the ends of the motor’s terminals to the 20’ tether carrying power to the motor.
Make sure the knot can fit inside the canister with the lid on.
4. Cover the holes on the sides of the motor with electrical tape by wrapping electrical
tape around the motor two times.
5. Use hot glue to seal the holes in the top and bottom of the motor. Be careful to keep
the hot glue from dripping inside the motor.
6. Drill a hole in the inside of the film canister slightly larger than the diameter of the
motor shaft. For most shafts, a hole about 3/32” in diameter will do.
7. Place a thick dab of petroleum jelly on the shaft and bottom of the motor.
8. Place the motor inside the film canister and set them on the block of wood with the
hole in it. The shaft of the motor should fit snugly in the blocks hole.
9. Pour wax into the canister until the motor is entirely covered but leave enough space
so the knot can fit in the canister with the lid on.
10. After the wax has hardened connect the other end of the 20’ tether to a battery to
make sure the motors are still functional.
11. You will glue propellers on the thrusters after the thrusters are secured to the ROV
frame.
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Part 4 - Mounting the thrusters to the frame and testing
1. Mount your thrusters on the ROV so that it can go forwards, backwards, up and
down.
2. After mounting your motors place the ROV in the tank and notice how it is positioned
in the water. Does it float or sink?
3. If it sinks, which material in your kit should you use for buoyancy?
4. Where should the buoyancy material be placed on the ROV?
5. The uppermost part of the ROV should be positioned just below the surface of the
water (about 5 cm), if it is not, what do you think you should do? Look at the parts in
your kit, do you see anything that may help you to solve this problem?
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