Monday, April 16, 2012

Final Machine & Bill of Materials

the evolution of our machine: February, March, April
     Our final car doesn't look too different from our original concepts. The biggest change, illustrated above in the center image, occurred when we decided to double the side pieces, sandwiching our transmission systems  in between, to keep the underside of the chassis clean and clear and to provide wheel stability.

     The machine is built on our original concept: a 4-wheeled vehicle with a 'waterwheel' device in front to continuously move balls under the car and a 'fence' assembly in the rear to extend and guide the balls to the goal. Our original strategy was to sit by the tower and chug away with the waterwheel, sending a large number of bars straight back to our goal, so that we spend a minimum amount of time moving and a maximum amount of time scoring. We were going for error-forgiving efficiency.

     When we knew how we wanted our car to look and function, we thought a lot about what material to use for each part. We went for sturdiness and ease of manufacturing.
     We used a rack and pinion for the fence because we wanted a lot of torque and we needed precision so that the fence would come out straight.
     To reduce unnecessary friction, we invested in extra ball bearings, using them in each wheel and the waterwheel.
     The simple 'waterwheel' is made of colored craft foam hot-glued onto a long axle. The foam is a very good material to grab and bend with ping-pong balls. After considering different numbers and shapes of spokes, its cross-section was carefully designed with two tightly curved sections to maximize space and to push on the balls below their center of gravity. To be as forgiving as possible, the transmission for the waterwheel is just a couple rubber bands.
     Our finalized bill of materials details every item we used to make our machine, especially trades and extra materials that we purchased.

     In the end, however, our 'fence' module was operational, but not smoothly so. In competition, we moved around more and herded balls without the fence extending, getting in our opponent's way when convenient. Additionally, one of the set screw holes that connected a wheel axle to a motor stripped out shortly before seeding, and is currently replaced with epoxy and electrical tape. Yes, that fix actually worked! Despite this and its size and weight, our machine was surprisingly mobile, thanks to well thought out gear-ratios.

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