Presentation on theme: "Electric Vehicle 09 Dennis Papesh & Bro. Nigel National Event Supervisors"— Presentation transcript:
Electric Vehicle 09 Dennis Papesh & Bro. Nigel National Event Supervisors
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: cience%20olympiad%20electric%20vehicle&searc h=Search&sa=X&oi=spell&resnum=0&spell=1 cience%20olympiad%20electric%20vehicle&searc h=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 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. 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 tracks 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 vehicles 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 Distance 5-10 meters
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 (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 Competition During 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
Scoring For 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 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 vehicles 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.
RankTeam Name Pred. TimeRun Score Timeshort/overDist.(m)LaneFinishTimeDist.LaneFinishRun 1Fairport yes Islip yes Cicero N. Syracuse yes Brentwood yes Fayetteville Manlius yes Horace Greeley yes Red Creek yes Ballston Spa yes Kellenberg yes Columbia yes New York State Electric Vehicle Finals 08 Target 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 decision ELECTRONIC 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 DONT 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!
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 Drive Reduction Gear Worm Gear Planetary Gear Belt / 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 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
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 Dont 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 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. Electrical Type Use the drive motor as the brake – works best in direct drive transmission A 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 weve seen: HOME MADE: Circuit boards, ICs, some easy, some incredibly sophisticated LEGOs Mindstorm es/NXT%20Intelligent%20Brick.aspx es/NXT%20Intelligent%20Brick.aspx Vex Robotics
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 Brakes Some of the following is from here: 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 turns Vex Robotics is here: shaft-encoder-kit.shtmlhttp://www.vexrobotics.com/vex-robotics-optical- shaft-encoder-kit.shtml
Final suggestions Decide electronic or not early, then build! Calibrate, calibrate, calibrate Be as consistent as possible Record data, graph it, do more trials Did I say calibrate? MAKE sure that it goes straight – those 10 points could make a big difference Use alignment tools to help here Concentrate on the TIME predictions THE END!