|Entry #||Driver Name||Car Name||Mass
|4||33||Guy Raz||Swales Flywheel Flyer||222||8||6.75||2.75||0.83||3.80|
Balloon car designer Guy Raz writes:
Having decided to enter the race a little over two weeks before the event, I did not have at my disposal the time and resources some of the more serious contestants decided to invest which, rumor has it, cost one his marriage and another his sanity (just kidding!).
My co-worker, John, and I decided to use as many off the shelf parts and materials we could find as we both had very little time to devote to the contest. After several dry-erase board and napkin sketches and brainstorming sessions, we concluded that our original concept - a car propelled by a balloon-actuated vaned flywheel, was impractical to design in the short amount of time we faced.
Instead, John and I visited a toy store by our office where we browsed for a vehicle that would be both readily modifiable and affordable. What we found was an Erector-brand motorcycle that consisted of stamped sheetmetal parts, socket-head screws, self-locking nuts, washers, plastic and rubber spacers, and plastic/rubber wheels.
A week before the race, with the holidays looming, John, pleading family commitments, bowed out of the contest and I spent the last week improvising 3-wheeled vehicle variations that would accommodate the two inflated regulation balloons as the source of propulsion. I decided that my best shot would be to minimize the mass of the vehicle and rely on both balloons for thrust. My enemies were instability and lack of traction, which I knew would compromise directional control. I knew that weight would overcome the stability and traction challenges, but would decrease the efficiency of the balloons as the source of thrust. I also knew that a wide wheel base with one large rubberized wheel and two minimal-contact wheels was a proven design that I could apply to the Swales Flyer.
Instead of using the kit-supplied rubber tires, which provided only tangential surface contact, I took a broad rubberband and cut it to fit the circumference of the plastic wheel rim, and then attached it using contact cement. I also killed three birds with one stone by attaching equal-length sections of heat-shrink tubing to the mouth of the balloons, which allowed easy inflatability, increased air explusion velocity, and directional thrust.
I used large office paper clips and aluminum tape to fabricate fore, port, and starboard supports to catch the deflating balloons, which I found were contacting the wheels and causing friction. Aluminum and duct tape were also used to secure the balloon/tube interface and attach them to the vehicle.
Lack of time and money were the most restricting factors in the design. As mentioned earlier, John and I had come up with a unique air-powered flywheel concept, but could not develop and test it in time for this particular race.
iThe unspectacular performance of the Swales Flyer, which only traveled 10 inches, can be attributed mainly to my decision not to test-run the vehicle under race conditions. My lack of time and commitment to the race are exemplified more than anything in this oversight. The surface the car successfully traversed during its development was a level, smooth indoor conference table. The actual race surface was pocked cement at a slight incline, outdoors. Since the rear wheels were 3/4" washers, the slightest surface imperfection could have stalled the vehicle, like a common pothole. And that is precisely what happened during the race. The car inched forward and suddenly stopped, while both balloons had yet to expel more than 2/3 or their air, to the sympathetic "awwws" from the crowd. My frustration and angst can be found aptly quoted in the December 19 Pasadena Star article that covered the race...
The race was an opportunity to stretch my creative muscles and work on something fun and different. It reinforced lessons I learned in the constant drive to improve my design skills as an engineer: in addition to a sound idea and design methodology, one must duplicate or approximate the actual performance conditions the vehicle or instrument will encounter once introduced into its operational environment. This maxim is true for unmanned spacecraft as well as for kitchen blenders.
This race also reminded me that logistic preparations, material and financial support, a coherent, practical timetable, and cooperation and dedication are essential for the success of any engineering endeavor. I look forward to participating in next year's race and applying these lessons with more conviction!