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Battery Buggy ’10Dennis Papesh

(papeshdr@holyangels.cc)Bro. Nigel

(bronigel@kellenberg.org)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_query=science%20olympiad%20electric%20vehicle&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 4

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‡BUT THIS YEAR – BUT THIS YEAR – EXCITING EXCITING CHANGES ARE IN CHANGES ARE IN STORE!!!STORE!!!

‡ http://www.youtube.com/watch?v=tZEl8d-RE4M&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 cmbe started by actuating a switch of some sort with a pencil or similar objectThey 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.

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

Centerline Tape

Finish Line

Target Distance5-10 meters

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The TrackThe 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 CompetitionDuring 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) 11

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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

Scoring - MeasurementsFor 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

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‡ 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.

Scoring - PointsThe 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 104.00104.00 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 170.60170.60 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 -20 points). The vehicle may cross the finish line and still receive these points.

‡ Run Score = Distance Score + Time Score + Center Line ScoreE.g. Run Score = 104.00 + 170.60 + -20E.g. Run Score = 104.00 + 170.60 + -20 Run Score = 254.60Run Score = 254.60

‡ Ties will be broken by….1st: Lower Time Score of the Final Scored Run2nd: 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 EnergyDo whatever you can to increase the

speed of the buggy!MassWheels – 3 vs. 4Motor “strength”/torque/RPMEfficiency of energy transferReduce friction of the buggy componentsBattery decision – what will give you the greater voltage and therefore the faster motor. Anything else you can think of!!??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‡ 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 fasterHeavier

‡ Small diameter wheelRevolves more times to travel a given distanceTransmission can have lower gear ratioVehicle might travel slowerLighter

‡ Optimum size is somewhere in betweenAffected by motor powerAffected 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. 19

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 20

Transmission

‡ Most difficult to design / build‡ Reduces high RPM of motor to low speed

for driving wheels‡ Several types possible

Direct DriveReduction GearWorm GearPlanetary GearBelt / 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

componentMotor‡ Terminals are almost always identified in some

way. e.g. + , square, notch‡ If motor turns the wrong direction, reverse the

wires connected to its terminalsStart Switch‡ Should be easy to operate‡ Should be in an accessible location ‡ Can be “Home Made” 22

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A great switch touse 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

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 implementDistance unreliable

‡ Mechanical Types (tend to be easier to make)

String and AxleWheel JamWing 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 TypeUse the drive motor as the brake – works best in direct drive transmissionA DC motor provides some dynamic braking when its terminals are shorted together. 27

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‡ Final suggestionsThink LIGHT LIGHT LIGHTDesign and build early!Calibrate, calibrate, calibrateBe as consistent as possiblePractice at many different track lengthsKeep a record of dataTry different batteries, motorsDid I say calibrate?MAKE sure that it goes straight – those -20 points could make a big differenceUse alignment tools to help here

Will you use two different sets of batteries for the two runs?

THE END!