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. 3
For the last couple of years… ‡http://www.youtube.com/watch?v=fpQc3VQqvxghttp://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 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 http://www.scioly.org/phpBB3/index.php 4
5 ‡B‡B‡B‡BUT THIS YEAR – EXCITING CHANGES ARE IN STORE!!! ‡h‡http://www.youtube.com/watch?v=tZEl8d- RE4M&feature=related
6 ‡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.
7 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. 8
The Track Starting Line Centerline Tape Finish Line Target Distance 5-10 meters 9
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. 10
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) 11
12 ‡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 - 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. 13
Scoring - Measurements 14 ‡ 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 - Points The Run Score is equal to the sum of the following. Remember that LOW SCORE wins. 104.00 ‡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. 170.60 ‡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. -20 ‡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 Run Score = 254.60 ‡Ties will be broken by…. 1 st : Lower Time Score of the Final Scored Run 2 nd : Lower Distance Score of the Scored Run The Final Score will be the lower score of the 2 Run Scores. 15
Batty Buggy Systems Construction/Suggestions/Ideas Possible ways to approach the event - May be consolidated or divided as necessary. 16
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!!?? 17
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.” 18
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 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. 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 Drive Reduction Gear Worm Gear Planetary Gear Belt / Pulley Drive (AVOID!) ‡Expensive to buy ‡Definitely a candidate for surplus / salvage 21
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” 22
23 A great switch to use to start the buggy. A micro switch to open the circuit at the end of the run.
24 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
25 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! 26
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 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 terminals are shorted together. 27
28 ‡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!