Electric Vehicle ’09Dennis Papesh & Bro. NigelNational Event Supervisorsbronigel@kellenberg.org

Object:A battery powered vehicle travels a specific 5-10 m distance chosen

by the supervisor as near as possible to a time (<45 s)

predicted by the students.

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

‡ 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)Problems last year!!!

have a wheelbase of 30 +/-2 cm and a track of no more than 20 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.

aligning devices may be used this year which do NOT have to be permanently attached in a fixed position have a stationary 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.

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)

‡ travel at a predictable rate of speed to allow accurate time estimations.

At Nationals, where the Predicted Time is chosen by the Event Supervisor, have the ability to adjust/vary its speed.

‡ NOT stray from the centerline tape‡ come to a complete stop with the vehicle’s

stationary pointed object (hereafter “fixed point”) as near to the point where the middle of the centerline tape intersects the finish line tape.

The Track

Starting Line

Centerline Tape

Finish Line

Target Distance5-10 meters

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 (“centerline tape”).

‡ have “free space” to allow the buggy to stray from the centerline 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.

The CompetitionDuring the competition the students:‡ may use any type of electronic calculating (not measuring)

devices to determine time prediction, including computers. These do NOT have to be impounded.

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

‡ will predict the time required to travel the Target Distance – the same prediction and distance will be used for both runs.

As mentioned, at Nationals, Event Supervisor will choose time.‡ 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

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

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

‡ will place their buggy's fixed pointer on the starting line‡ will set the buggy in motion by actuating some sort of

electrical switch

ScoringFor each run the judges will determine:‡ if the buggy strays from the centerline tape. (10

pts)‡ the time the buggy takes to travel the Target

Distance. The time starts when the switch is actuated and ends the FIRST time the buggy stops or when the marked point crosses the finish line. (up to 50 pts)

‡ the distance the fixed point travels from the starting line. The distance will be measured perpendicular to the starting line to where the fixed point stops. This is a point to line distance. (up to 100 pts)

‡ the distance from where the fixed point stopped to the center of the finish line. This is a point to point (straight line) distance. (up to 40 pts)

‡ BRAND NEW: Whether the device used any electronic components (if not, worth additional Bonus pts)

Scoring (cont.)Up to 200 points (maybe*) may be awarded for each run. This is called the

Run Score. It is equal to the total of:‡ The Distance Score – This is a percentage of correctness score. 100

points maximum, e.g. If the required distance is 10 meters and the distance traveled is 9 or 11 meters, the score will be 90 points.

‡ The Time Score – This score component is the percent of correctness divided by 2. 50 points maximum, e.g. If the predicted time is 5 seconds and the actual time is 4 or 6 seconds, the score will be 40 points.

‡ The Center Line Score – If the centerline tape remains between the left and right outside edges of the vehicle’s wheels during the entire run, 10 points will be awarded. The vehicle may cross the finish line and still receive these points.

‡ The Finish Line Score – From 0 to 40 bonus points will awarded depending on how far the fixed point stops from the center of the finish line. These are awarded regardless of whether the vehicle stops before or after the finish line. e.g. distance from fixed point to center of finish line is 13.7 cm, 26.3 (40 – 13.7) points are awarded.

‡ The Bonus Score – If the device is built with NO electronic components, then a bonus of 1/3 the difference between 200 and the sum of the previous 4 scores will be awarded.

‡ HOLD INTENSE DISCUSSION HERE!!

The final score will be the higher score of the 2 Run Scores.

Rank Team Name Pred. Time Run         Score        

      Time short/over Dist.(m) Lane Finish Time Dist. Lane Finish Run

1 Fairport 15.6 14.92 0.05 5.5995 yes 0.05 47.8205 99.9911 10 39.95 197.7616

2 Islip 11.76 12.13 1.10 5.5890 yes 1.10 48.4269 99.8036 10 38.90 197.1304

3 Cicero N. Syracuse 22.9 23.53 0.90 5.6090 yes 1.40 48.6245 99.8393 10 38.60 197.0637

4 Brentwood 6.09 6.21 1.40 5.6140 yes 1.80 49.0148 99.7500 10 38.20 196.9648

5 Fayetteville Manlius 11.74 11.41 0.30 5.5970 yes 4.50 48.5945 99.9464 10 35.50 194.0410

6 Horace Greeley 14.77 15.28 3.60 5.6360 yes 4.80 48.2735 99.3571 10 35.20 192.8307

7 Red Creek 9.1 10.00 1.10 5.5890 yes 2.40 45.0549 99.8036 10 37.60 192.4585

8 Ballston Spa 7.99 7.12 2.20 5.6220 yes 2.30 44.5557 99.6071 10 37.70 191.8628

9 Kellenberg 5.06 5.59 2.20 5.6220 yes 3.00 44.7628 99.6071 10 37.00 191.3700

10 Columbia 5.62 6.17 0.80 5.5920 yes 3.70 45.1068 99.8571 10 36.30 191.2639

New York State Electric Vehicle Finals ’08Target Distance: 5.60 m

Electric Vehicle Systems Construction/Suggestions/

Ideas Possible ways to approach the event - May be consolidated

or divided as necessary.

First – A BIG decisionELECTRONIC OR NOT?

- Pros and cons- What are the capabilities of your students?- Do you want to lose those Bonus pts.?- Accuracy vs. Easiness?- Do you want this to be an entry level event?- Cost concerns!- What science do you want your students to learn? Mechanics, basic electricity, programming, robotics?- Consistency

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.”

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!

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

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

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”

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

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!

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.

‡ 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.

Brakes (cont.) And Electronic ideas

‡ Electronic‡ If you decide to go electronic, then

basically 3 ways we’ve seen:HOME MADE: Circuit boards, IC’s, some easy, some incredibly sophisticatedLEGO’s Mindstormhttp://mindstorms.lego.com/Products/

Accessories/NXT%20Intelligent%20Brick.aspx

Vex Roboticshttp://www.vexrobotics.com/

‡ Some require that you attach your vehicle to a laptop or similar device, some not.

‡ Some had problems with time limits and getting the data downloaded in time

‡ At least one team at Nationals had their laptop battery die – and couldn't run their vehicle

‡ NO EXTERNAL Sensors allowed‡ Can be VERY accurate – since it is a

relatively easy robotic task.

‡ Options for Electronic BrakesSome of the following is from here:http://scioly.org/wiki/Electric_Vehicle

Timer: The motor is turned on for an adjustable amount of time and then stopped. This can be done with a microcontroller or a one-shot 555 timer.Wheel/shaft counter: A sensor counts how many revolutions your axle makes and can stop the motor after determined # of turnsVex Robotics is here:

●http://www.vexrobotics.com/vex-robotics-optical-shaft-encoder-kit.shtml

‡ Final suggestionsDecide electronic or not early, then build!Calibrate, calibrate, calibrateBe as consistent as possibleRecord data, graph it, do more trialsDid I say calibrate?MAKE sure that it goes straight – those 10 points could make a big differenceUse alignment tools to help here

Concentrate on the TIME predictions

THE END!