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• Goal: Construct a gravity powered vehicle and ramp to move the vehicle down a track as quickly and accurately as possible (in draft rules)– Two components• Vehicle• Ramp
Competition
• Track 5 – 10 m– 50 cm interval regionals– 10 cm at state– 1 cm at nationals
• 50 cm x 50 cm square start box
• Start Dot at center of box• Finish Dot perpendicular
Scoring• Four components – Low Score Wins• Distance Score – Distance from the fixed point to the Target Point in
millimeters • Time Score– 25 * (Run Time).
• Predicted Time Score– 25*abs(Predicted Time-Travel Time)
• Height Score – NEW THIS YEAR– 2*Highest point of vehicle in cm in ready to launch
position
Construction rules
• Vehicle– Less than 2.5 kg– Bent paperclip as a fixed point– Only wheels contact floor – Automated braking mechanism
• Ramp– With vehicle loaded fit within 50cm x 75cm box– Release mechanism activated by unsharpened #2
pencil– Padding on base?
General tips
• Potential energy (u) = mgh• Maximize mass and height – maximize energy– Get fewer points
• Minimize friction for speed
Vehicle Construction
• Major components– Chassis – Wheels– Braking mechanism– Axles– Bearings
Chassis
• Stiffness critical– Pay attention to joints– Carbon Rods (from arrows)– Wood
• Good place to add weight• Design with braking mechanism in mind• Adjustable axle/bearing mounts– Steering
Wheels
Aluminum hubbed MPI wheelsPark-flyer style
• Thinner better for speed• More difficult to mount• Difficult to align
• CD’s useful• Require special adapters for mounting• Rubber bands/balloons for traction
Braking Mechanism
• Threaded rod and wing nut (or tapped block)
Axles• Critical Qualities
– Stiffness, weight, ability to hold wheels/braking mechanism• Carbon Fiber Rods (From Arrows)
– Smooth, light, stiff• Steel Threaded Rod
– Easy to find, cheap, braking mechanisms, heavy• Aluminum Threaded Rod
– Difficult to find, light, weak• Titanium Threaded Rod
– Expensive (order online), stiff!, light
Bearings
• Simple or complicated• Tubes– Easy, cheap, use graphite, functional
• Ball bearings– Reduce friction drastically, can get expensive– Ceramic hybrid best if willing to spend– May require some breaking in
Ramp
• Straight– Much easier to construct– Easier to transport– Not as efficient, – floor/ramp interface issues
• Curved– Delivers energy much better– Winning team at Nationals will have one– Interesting math problem– http://en.wikipedia.org/wiki/Brachistochrone_curve
Ramp materials
• Frame– PVC pipes• Easy disassembly• Difficult to make curved ramp
– Plywood/other wood• Heavy, difficult transportation
• Surface– Particleboard, Masonite, others?
• Lots of Skateboard ramp references online
Sources for more obscure materials
• Wheels– R/C plane wheels, MPI www.maxxprod.com/mpi/mpi-
29.html, CD’s• Bearings– www.bocabearings.com , online, hobby shops, etc
• Carbon fiber– Arrows, hobby shops, etc
• Titanium – Amazon, smallparts.com, etc
• Balsa– www.lonestar-balsa.com, hobby shops, etc
