Gravity Vehicle

Disclaimer

This PowerPoint is based on the DRAFT rules for Gravity Vehicle 2013.

The rules may have changed. The rules and parameters in the 2013

Rules Manual is the final say.

Goal: Construct a gravity powered vehicle and ramp to move the vehicle down a track as quickly, as accurately and as close to their predicted time as possible.– Two components• Vehicle• Ramp

Competition

• Track 5 – 10 m– 50 cm interval regionals– 10 cm at state– 1 cm at nationals

• 50 cm wide x 75 cm deep x 200.0 cm high rectangular 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. This is a point-to-point measurement.• Time Score– 25 * (Run Time).

• Predicted Time Score– 50* (Predicted Time-Travel Time)

• Height Score – NEW THIS YEAR– 400* Vehicle Height in cm/ (300 cm – Vehicle Height

in cm)

Construction rules• Vehicle

– Total mass must not exceed 1.500 kg.– Bent paperclip as a fixed point (measurement point) on either

the leftmost or the rightmost edge/face of vehicle between front and rear axles extending down to within 1.0 cm of track surface

– Only wheels contact floor – Automated braking mechanism

• Ramp– With vehicle loaded fit within 50 cm wide x 75 cm deep x 200

cm high box– Release mechanism activated by unsharpened #2 pencil

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