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Let's Eat

Let's Eat Balloon Car

Race
Order
Entry
#
Driver Name Car Name Mass
(grams)
Length
(inches)
Width
(inches)
Height
(inches)
Distance Traveled
(feet)
Running Time
(seconds)
Awards
                     
9 8 Ken Erickson Let's Eat 232 27.5 7 10.5 70.42 21.36 2nd Farthest Distance & Longest Running Time


Balloon car designer Ken Erickson writes:

The balloon-powered car, "Let's Eat," was so named because of its use of 10.5 inch diameter paper plates as wheels. The car uses the elastic properties of two uninflated balloons connected in parallel to propel the car. One end of each balloon is connected to the car's balsa wood frame near the front of the car. The other end of each balloon is tied to a string. The other end of the string is wrapped around the rear axle of the car.

The rear axle is a 1/8 inch diameter steel rod that is rigidly connected to both rear wheels. Similarly the front axle is a 1/8 inch diameter steel rod which is rigidly connected to the both front wheels. The front and rear axles are each supported by bearings consisting of loops of bare copper wire. With the string wrapped around the rear axle, the balloons can be stretched by rolling the car backwards.

When the string is completely wrapped around the rear axle, the car is set down on the running surface, aimed and released. The string tension created by the stretched balloons causes the rear axle to spin, which in turn causes the car to move forward.

The unique feature of this car is its high gear ratio resulting from the use of a small diameter drive axle and large diameter wheels. It was important to keep the weight of the car as low as possible. For this reason, balsa wood was used as the car's frame and paper plates were used as the car's wheels.

Originally the car was much longer, used 3.5 inch diameter rubber wheels, aluminum pipes as bearings and was propelled by two balloons connected in series. It was determined that the cars range can be increased by increasing he wheel diameter, using copper wire as bearings, making the car shorter (to reduce weight) and to use two balloons connected in parallel. These changes were made progressively, rather than all at the same time.

One lesson learned is that pull testing of balloons should have been performed to determine how far they can be stretched before breaking. If this testing had been performed, it would have been determined that the balloons could be stretched 24 inches instead of 19 inches that my balloons were stretched. By stretching my balloons to 24 inches, the car would have traveled much farther.

The project was time consuming, but fun. The second place trophy that I was awarded and fun of competition certainly made it all worth while.


MB 1/9/99