Make a Gravity Racer

A gravity racer, also called a hill trolley in Australia, is a motorless vehicle usually made of wood and used for competition racing. To steer it you have to use both feet and both hands at the same time. And of course you need a hill. The best hills are those that are not too steep and will let you ride for a long distance.

Steps

Design It Yourself, For Fun

1. Gather the needed materials. You'll find the complete list in the "Things You'll Need" section.
2. Cut the chassis plank to size. This plank is the longest and will support the rear axle and seat at one end and the steering axle plank at the other end.
   • The length will depend on your height. Cars are typically between 48 and 72 inches (120 to 200 cm) in length.
   • The width will depend on the width of your bottom. Cars are typically 24 to 36 inches (60 to 100 cm) wide.
3. Cut the axle planks to length. These need to be longer than your chassis plank is wide, plus enough to allow the wheels to turn about 30 degrees in either direction.
4. Make the pivot. Drill a hole through the front end of the chassis and the middle of the front axle plank to make the pivot point for the steering plank.
   • Fix the steering plank to the chassis plank Using the bolt.
5. Attach the rear axle plank. Fix the middle of the rear axle plank square to the chassis at the back end.
6. Fix the axle bars to the axle planks. Secure them well with four or more U-brackets spaced evenly across the axle.
7. Add the seat. Fix it to the chassis and rear axle plank. The rear axle plank should be underneath the chassis.
8. Build the steering. Drill a hole through the chassis behind the left and right sides of the steering plank, and slip the rope ends through. Attach to the steering plank near the left and right ends of the plank for maximum efficiency.
   • Make the rope loop a comfortable length for the driver when he is seated.
9. Slide the wheels onto the axles and secure them.
10. Have fun driving your gravity racer! Wear a helmet, and try not to crash!

Buy It For Official Competition

1. Determine your racing division. The AASBD (All-American Soap Box Derby) organization has specific requirements and limitations that you and your gravity racer will need to meet. The divisions are:
   • The Stock Division, designed for participants aged 7 to 13. The combined weight of car and driver may not exceed 200 pounds.
   • The Super Stock Division is open to participants between the ages of 10 and 17, and the combined weight of car and driver not to exceed 240 pounds.
   • The Masters Division is open to participants between the ages of 10 and 17. Car and driver may not exceed 255 pounds.
2. Purchase the kit. All competition kits must be purchased through the AASBD. They are available online at here.
3. Download the plans. They are available at www.aasbd.org.
4. Build it!

Tips

• The main thing is to align the axles because this will give you a lot more of stability.

Warnings

• Be careful with the wheels, check that they are properly aligned.
• A hill trolley at speed can chuck you off and forever change your life. Wear a helmet, stay off busy streets and enjoy the experience.
• By limiting the turn radius, you will minimize the chance of flipping your car.

Things You'll Need

• Hammer
• Screwdriver
• Wood saw
• Nails
• Screws
• Rope
• Wood planks
• A bolt for the steering pivot
• 4 wheels with axle bars
• A ready-made seat for the driver's seat

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