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
Park-flyer style
Aluminum hubbed MPI wheels
• 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/mpi29.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