1. Gravity Vehicle SOSI 2012 Matt Chalker, Bro. Nigel Pratt, Dennis Papesh chalker7@gmail.com

2. 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

3. 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

4. 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

5. 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?

6. General tips Potential energy (u) = mgh Maximize mass and height – maximize energy – Get fewer points Minimize friction for speed

7. Vehicle Construction Major components – Chassis – Wheels – Braking mechanism – Axles – Bearings

8. 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

9. 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

10. Braking Mechanism Threaded rod and wing nut (or tapped block)

11. 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

12. 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

13. 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

14. 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

15. Sources for more obscure materials Wheels – R/C plane wheels, MPI www.maxxprod.com/mpi/mpi- 29.html, CD’swww.maxxprod.com/mpi/mpi- 29.html 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 www.lonestar-balsa.com