Transcript Electric Vehicle `08

Battery Buggy ’10
Dennis Papesh ([email protected])
Bro. Nigel ([email protected])
National Event Supervisors
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Object:
A battery powered vehicle travels a
specific distance as quickly as possible
and stop as close as possible to the center
of the finish line.
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For the last couple of years…
‡ http://www.youtube.com/watch?v=fpQc3VQqvxg
‡ BTW, a good Coaches aid is You Tube, Google
Video, etc. Just type “Electric Vehicle Science
Olympiad” and search
Just like some of these:
http://www.youtube.com/results?search_qu
ery=science%20olympiad%20electric%20vehicl
e&search=Search&sa=X&oi=spell&resnum=0&
spell=1
‡ For pictures, go to the SO Student center:
http://www.scioly.org/phpBB3/index.php
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‡BUT THIS YEAR –
EXCITING CHANGES
ARE IN STORE!!!
‡ http://www.youtube.com/watch?v=tZEl8dRE4M&feature=related
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‡ The vehicle must:
be propelled ONLY by energy from a
maximum of 4 commercially available
batteries (each rated at 1.5 V or less) or one
battery pack (rated at 4.8 V or less)
have a wheelbase of 26.0 +/-2.0 cm and a
track of no more than 19.0 cm
be started by actuating a switch of some sort
with a pencil or similar object
They CANNOT hold it when doing so!
come to a complete stop without any outside
assistance.
But braking system may NOT contact the
floor.
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aligning devices may be used this year
which do NOT have to be permanently
attached in a fixed position
have a fixed, pointed object extending
beyond ALL other parts of the vehicle and
within 1 cm of the track’s surface to be used
as the reference point for all distance
measurements.
NOT have any electronic components at all.
Only the electrical items listed in the rules
may be used.
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Testing:
To achieve the maximum score, the vehicle should be thoroughly tested.
It should
‡ be adjustable to travel any distance from 5 to
10 meters (distance will be in 0.5 meter
intervals for regional, 10 centimeter for state,
and 1 centimeter for national tournaments)
‡ NOT stray from the centerline tape
‡ come to a complete stop with the vehicle’s
fixed, pointed object (hereafter “fixed point”)
as near to the point where the middle of the
center line tape intersects the finish line tape.
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The Track
Starting Line
Finish Line
Centerline
Tape
Target Distance
5-10 meters
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The Track
The track will:
‡ be on a smooth, level, and hard surface
‡ have Starting Line, Target Distance (finish line)
and track center marked with 1 inch tape on
the floor (“center line tape”).
‡ have “free space” to allow the buggy to stray
from the center line tape and past the finish
line
‡ If more than 1 track is used, contestants may
choose which track to use. Both runs for a
team will be on the same track.
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The Competition
During the competition the students:
‡ will place their buggy's fixed pointer on
the starting line
‡ will set the buggy in motion by
actuating some sort of electrical switch.
They may not touch it, but must use a
dowel-like device.
‡ may use non-electronic measuring
devices to verify the track dimensions
(but they cannot use the vehicle to do
so)
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‡ may place a target, which must be
removed prior to starting each run, on
the finish line to aid in aligning the
buggy
‡ MAY, between runs,
remove/install/change any impounded
parts, including batteries.
‡ will be allowed 10 minutes to adjust
their buggy and make up to 2 runs – if
the a run is started before the 10
minutes is up, that run may be
completed
‡ Must wait behind the start line during
the runs until called by the Event
Supervisor
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Scoring - Measurements
For each run the judges will determine:
‡ if the buggy strays from the Center Line
tape.
‡ the time the buggy takes to travel the
Target Distance. The time starts when the
vehicle begins forward motion and ends
when the buggy comes to a complete stop.
‡ the Distance from the fixed point to the
center of the finish line. This is a point to
point (straight line) distance.
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Scoring - Measurements
‡ If the vehicle goes in the wrong
direction, it will be considered a failed run
and count as a run.
‡ If the vehicle inadvertently begins a run,
it will also be considered a failed run and
count as a run.
‡ If the vehicle does not move upon
actuation of the switch, the students may
request another try and that attempt does
not count as a run.
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Scoring - Points
The Run Score is equal to the sum of the following. Remember that
LOW SCORE wins.
‡ The Distance Score – This is the Measured Distance converted to mm,
e.g. if the Distance was 10.4 cm, the Distance Score would be 104.00
points.
‡ The Time Score – This score component is the Measured Time x 20,
e.g. if the time was 8.53 s, the Time Score would be 170.60 points.
‡ The Center Line Score – If the center line tape remains between the
left and right outside edges of the vehicle’s widest axles wheels during
the run between the start and the finish line, 20 points will be
deducted (-20 points). The vehicle may cross the finish line and still
receive these points.
‡ Run Score = Distance Score + Time Score + Center Line Score
E.g. Run Score = 104.00 + 170.60 + -20
Run Score = 254.60
‡ Ties will be broken by….
1st: Lower Time Score of the Final Scored Run
2nd: Lower Distance Score of the Scored Run
The Final Score will be the lower score of the 2 Run
Scores.
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Batty Buggy Systems
Construction/Suggestions/Ideas
Possible ways to approach the
event - May be consolidated or
divided as necessary.
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First issue – Kinetic Energy
Do whatever you can to increase the speed
of the buggy!
Mass
Wheels – 3 vs. 4
Motor “strength”/torque/RPM
Efficiency of energy transfer
Reduce friction of the buggy
components
Battery decision – what will give you the
greater voltage and therefore the faster
motor.
Anything else you can think of!!??
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Body / Chassis
‡ Connects all of the other parts/systems
together
‡ Is probably the easiest to design and build
‡ “A matchbox car CANNOT travel a straight line
for a great distance.”
Therefore, make both the wheelbase AND the track
as wide as the rules allow!
Be careful, “No 2 rulers are alike!”
‡ Strongly consider some way to adjust the
steering of your vehicle – “It is difficult to get
the 2 axis parallel to each other.”
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Wheels and axles
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‡
‡
Axles may be part of the transmission or a separate system
Wheels are VERY difficult to make exactly round  SO DON’T MAKE THEM!
Large diameter Wheel
Revolves fewer times to travel a given distance.
Transmission must have a higher gear ratio.
Vehicle might travel faster
Heavier
‡
Small diameter wheel
Revolves more times to travel a given distance
Transmission can have lower gear ratio
Vehicle might travel slower
Lighter
‡
Optimum size is somewhere in between
Affected by motor power
Affected by transmission gear ratio
‡ Recommendation: Wide wheels tend not to drift as
much and, IMO, tend to force the vehicle to go
straighter!...but have greater mass.
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Motor
‡ May be part of electrical system or
transmission
‡ Must be close to total battery voltage
Will operate within a wide voltage range +/- 50% of rated voltage typical (but +/- 10%
better for the motor)
‡ RPM (speed) varies with load and battery
voltage
‡ Torque (power) varies with battery
voltage
‡ Few types available at reasonable cost
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Transmission
‡ Most difficult to design / build
‡ Reduces high RPM of motor to low speed for
driving wheels
‡ Several types possible
Direct Drive
Reduction Gear
Worm Gear
Planetary Gear
Belt / Pulley Drive (AVOID!)
‡ Expensive to buy
‡ Definitely a candidate for surplus / salvage
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Electrical System
Batteries
‡ Voltage should be suitable for motor
‡ Larger batteries last longer / weigh more
‡ Evaluate different types
‡ Holder can be part of chassis or separate component
Motor
‡ Terminals are almost always identified in some way.
e.g. + , square, notch
‡ If motor turns the wrong direction, reverse the wires
connected to its terminals
Start Switch
‡ Should be easy to operate
‡ Should be in an accessible location
‡ Can be “Home Made”
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A great switch to
use to start the
buggy.
A micro switch to
open the circuit at
the end of the run.
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Steering Mechanism
‡ Adjusts buggy to travel in a straight path.
‡ Adjustment need not be very large
‡ Should retain setting reliably
Distance measuring device
‡ Measures how far the buggy has traveled
‡ Turns off motor
‡ May apply brake
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Stop Switch
‡ Actuated by the distance measuring device
‡ May be the same as the Start switch
‡ Turns off motor to stop buggy
‡ Could be used to apply brake
Wires
‡ Almost any type of wire can be used
‡ Don’t use too large a size
‡ Stranded wire will flex more before breaking
‡ Solid wire holds its shape better
‡ For better reliability solder all connections
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Brakes
All methods must involve
either disconnecting the
transmission or
stopping/turning off the
drive motor!
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Brakes (cont.)
‡ None – Coast to a stop – Called the “Prayer”
method of braking!!
Easy to implement
Distance unreliable
‡ Mechanical Types (tend to be easier to make)
String and Axle
Wheel Jam
Wing nut and Axle (by far the most popular)
Best combination: Have the wing nut not only lock the
wheels but simultaneously turn off the motor with a mini
lever disconnect switch.
http://www.youtube.com/watch?v=RJwFtkFSuJM
‡ Electrical Type
Use the drive motor as the brake – works best in
direct drive transmission
A DC motor provides some dynamic braking when its
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terminals are shorted together.
‡ Final suggestions
Think LIGHT LIGHT LIGHT
Design and build early!
Calibrate, calibrate, calibrate
Be as consistent as possible
Practice at many different track lengths
Keep a record of data
Try different batteries, motors
Did I say calibrate?
MAKE sure that it goes straight – those -20 points
could make a big difference
Use alignment tools to help here
Will you use two different sets of batteries for the
two runs?
THE END!
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