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Rubber Fueled Dragster

Race Order	Entry #	Driver Name	Car Name	Mass (grams)	Length (inches)	Width (inches)	Height (inches)	Distance Traveled (feet)	Running Time (seconds)
24	5	Paul MacNeal	Rubber Fueled Dragster	265	26	12	4	0.67	5.00

Balloon car designer Paul MacNeal writes:

• Design approach taken - explain how it worked.

  I chose to utilize the balloon as a twisted rubber band.

• Unique or clever features embodied

  My best feature was the wheel and axle system. The wheels were constructed from thin cardstock. The circles were cutout and then shaped and glued into shallow cones. Two cones were glued edge-to-edge to complete the wheel. The axles were simply straws (Baskin Robbins straws seemed to be the best). I chose to have the wheels fixed to the straws with the axle freely rotating on a precision drilled, knife edge, plexiglass plate.

  To transmit the torsional torque of the balloon into a direct drive of the wheels, I chose a matched set of precision aluminum bevel gears.

  To reduce friction of untwisting while under a compression load, I used thrust bearings.

• Materials of construction (mention unique parts you used or fabricated)

  The entire body was made from 17 precision cut plexiglass pieces glued together.
  Axles were a combination of steel and plastic straws.
  Wheels were cardboard.
  Thrust bearings and washers were steel.
  Bevel gears were aluminum.
  Lots of epoxy was used, along with hot glue gun adhesive, rubber glue, duct tape, and acrylic cement.
  
  In total, 66 pieces.

• Reasons behind any significant design choices you had to make

  One of the most important discoveries was made during early testing. I noticed that the 2 balloon assembly, when twisted, would collapse (actually buckle) to a small diameter, which did not produce much torque. To improve the torque, I simply placed a straw down the middle of the balloon. this prevented the balloons from collapsing to a small diameter, and in fact they would collapse to the diameter of the straw. Subsequent testing showed that the balloons would actually crush the straws which eventually were replaced with wooden rods running the entire length of the balloon.

• Lessons learned (what you'd do differently next time)

  Twisted balloons do not produce much power. My vehicle just did not have a chance due to the method of energy storage that I chose. Clearly, a linear stretching of the balloon would have been better.

MB 1/9/99