Battery Buggy ’11Dennis Papesh

(papeshdr@holyangels.cc)Bro. Nigel

(bronigel@kellenberg.org)National Event Supervisors

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Disclaimer???

This presentation was prepared using draft rules. There may be some changes in the final copy of the rules. The rules which will be in your Coaches Manual and Student Manuals will be the official rules.

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Object:A battery powered vehicle travels a specific distance as quickly as possible around an object and stop as close as possible to the

Finish Dot.

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What???

Yes, this year, the vehicle must not only get to the finish as quickly as possible, it must go around an object to do so.

(It has to deliberately do the arc that some did unintentionally last year.)

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For several 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 5

‡But that was changed last year with the addition of speed!!

‡ YouTube - Battery Buggy v4 Practice: 9m

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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)No other electrical energy is permitted

have a wheelbase of 30.0 +/-2.0 cmMidpoints of front and rear axle

be started by actuating a switch of some sort with a pencil or similar objectThey CANNOT hold it when doing so!

Must be a vertical actioncome to a complete stop without any outside assistance.But braking system may NOT contact the floor. 7

aligning devices may be used 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.The most common item which puts the

vehicle in jeopardy of being lower tieredNOT have any electronic components at all. Only the electrical items listed in the rules may be used. Any “black boxes” should be easily opened to allow inspection.

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Testing:To achieve the maximum score, the vehicle should be thoroughly

tested. It should‡ be adjustable to travel 8 meters for

regional, from 6 to10 meters for state (in 1.00 meter intervals), and 6 to 10 meters for national tournaments (in 0.50 meter intervals)

‡ come to a complete stop with the vehicle’s fixed, pointed object (hereafter “fixed point”) as near as possible to the Finish Dot

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The Track

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8.0 meters

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The Start Dot and the Finish Dot are interchangeable to accommodate different venues and the direction of arc of the vehicle.

The TrackThe track will:‡ be on a smooth, level, and hard surface‡ have Starting Dot, a Finish Dot, and a 5

gallon bucket placed directly in the midpoint of the course.

‡ have “free space” to allow the buggy to stray from its path 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 Dot‡ 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.

The switch must be designed so the action to start it is either straight down or straight up.A ‘sideways’ switch will be considered a construction penalty.

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‡ may use non-electronic measuring devices to verify the track dimensions (but they cannot use the vehicle to do so)

‡ may place a target, which must be removed prior to starting each run, on the Finish Dot to aid in aligning the buggy

‡ may ask that the bucket be moved before each run in order to align and aim their vehicle

‡ MAY, between runs, remove/install/change any impounded parts, including batteries. 13

‡ 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.

‡ It is considered a run if the vehicle moves after the switch is actuated.

‡ Must wait behind the Starting Dot during the runs until called by the Event Supervisor

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Scoring - MeasurementsFor each run the judges will determine:‡ TIME SCORE: 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.

‡ DISTANCE SCORE: the Distance from the fixed point to the Finish Dot. This is a point to point (straight line) distance, measured in mm.

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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 25, e.g. if the time was 8.53 s, the Time Score would be 213.25213.25 points.

‡ Run Score = Distance Score + Time ScoreE.g. Run Score = 104.00 + 213.25E.g. Run Score = 104.00 + 213.25 Run Score = 317.25Run Score = 317.25

‡ 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 desired

path 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 axles to maintain their proper angles.”

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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. 21

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 22

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” 24

A great switch touse to start the

buggy.

A micro switch to

open the circuit at the end of the

run.25

Steering Mechanism‡ Adjusts buggy to travel in the desired

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 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. 29

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

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Big questions !!!

‡ How will your students design the front end to keep the vehicle going in a constant arc?

‡ How will your students align the vehicle at the Starting Dot with the proper angle to get to the Finish Dot after going around the bucket?

‡ Thinking time and time for you to contribute.

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‡OK – get thinking!!!

‡Give an idea and get an idea in return.

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Another disclaimer (mine)

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The following pictures are simply to give you ideas. They are not drawn to scale nor is their any attempt to make them professional. I am not even sure that they even make the rank of amateurish.

Some ideas ?

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The use of turnbuckles on the front axle will help to keep the turning radius constant.

Choice of the proper sized turnbuckles will allow a great range of adjustment to cover different course lengths.

Another general idea

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Have several indicators on the vehicle chassis to reset to different angles for different length tracks.

One way to align the vehicle ?

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Using a sighting device, the students can extend the direction to behind the Starting Dot.

After placing their fixed point on the Starting Dot, they can measure a pre-calculated distance from a spot market on the vehicle, thereby determining the proper angle.

Another way to align the vehicle

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Offset the front sighting post

Have several pre-calculated sighting positions (for different lengths) offset at the rear of the vehicle.

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Your students will come up with even more ingenious ideas for their vehicle.

Good luck to them all.