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Design Squad Poses Gravity Bike Challenge to Young Engineers
Sean Snyder, Associate Editor -- Design News, July 31, 2007
Learn more about Design Squad on our coverage page.
Podcasts, video and image gallery included.
Design Squad, a new show on PBS that poses real-world engineering challenges to young engineers, recently produced an episode that challenged the cast to design, build and test a gravity bike in a head-to-head race.
Gravity biking is the “x-treme” sport activity of riding a peddleless, gearless bike down a hill propelled by foot pushes and Newton’s trademark discovery. The bikes have to be low to the ground and have to fit within a specified weight range. The heavier the bike is, the farther and faster it goes. The bikes have the potential to reach 70 miles an hour and above through gravity, good design and skillful racing.
Design Squad poses the challenge as a real-world engineering assignment, where a client has a job to be done and the designers execute that task within the framework of the assignment. The client for the gravity bike is Tom Walen, a competitive gravity bike racer. “We had given them the rules, the basic limitations of what you can get on your bikes and the idea that you have to push the rules as far as you can,” says Walen. “I definitely think both teams ran with it pretty well.”
From concept to crossing the finish line, the kids were given a total of three days to complete and race the bikes using a number of materials the show provides. Both teams, Green and Purple, were given the same list of materials, which includes brake pads, cables and adapters, slick road tires, wheels, inner tubes, metal and PVC pipes and tubing, sheet metal and tools. Each team was also given three BMX bikes to strip down and use.
The Purple team lengthened one of the BMX bike frames with tubing and changed the rake angle of the head tube, which lengthened the wheel base and added stability for higher speeds. They reassembled their new frame using a mig welder, which they had been trained to use. Their design for the frame modification kept it low to the ground and focused on providing good balance.
The Green team, on the other hand, chose to design and build their frame from scratch. “They knew it was going to be a lot harder to do from scratch but they did it for aesthetic reasons and because they figured that if they were modifying a bike frame anyway, they could do it exactly how they wanted,” says Nate Ball, a mechanical engineer and host of Design Squad. They used square steel stock, which they rolled in a pipe bender into the shape they wanted, and attached an existing head tube and dropout from the BMX bikes, and welded them all together also using a mig welder.
| Gravity Bike Materials List |
| 6 BMX bikes (three for each team) 2 mig welders (one for each team) 1 bike pump 2 bathroom scales (one for each team) 4-ft x8-ft piece of steel sheet (1/16 inch thick) Some 3/4-inch pipe (about 8 feet ) Thin walled steel tubing and square steel stock (1/2-inch, 3/4-inch, 1-inch, 1.5-inch, and 2-inch diameters, two 12-inch pieces of each) Foam padding (bed padding) Pipe insulation Brake kits 4V brake adapter kits (2 for each team) 4 packs of brake pads (2 for each team) 8 brake cables (4 for each team) 4 slick road tires 4 wheels 10 inner tubes 4 sheet metal pliers Sand Steel weights (2.5 lbs and 7 lbs, 4 of each weight for each team) PVC pipe, left over from previous challenges U-bolts |
The mig welder was chosen for the cast because “it’s quite easy to learn and use; you can get pretty good at it pretty fast as long as you have the patience,” says Ball. “Other types of welding are more versatile and can produce better quality, but as far as bang for your buck, mig welding is the way to go for a situation like this.”
Both teams used new wheels, slick road tires and tubes for their bikes instead of the wheels and tires from the BMX bikes. “It was clearly apparent to them that the BMX tires that we gave them were not for road, but they were for dirt,” says Ball. “I did come in and explain the difference in mountain bike tires and road tires and how you want to run road tires at a higher pressure. You want to decrease the road resistance as much as possible so you can get maximum speed.” Each team ran their tires at about 110 psi.
Each bike had pegs built on both the left and right side of the frame where the racers could add or remove steel weights to increase or decrease the weight of the bike within the parameters of the project. After the bikes were built, both teams had a couple of chances to test them on the actual course before the head-to-head competition. The racers, one from each team, found that the weight they had added to their bikes to make them faster also made them harder to start. So after a test run, both racers decided to remove most of the extra weight. In the case of the Green team, they found that after a second test run without the weight, the bike was less stable, so they added some back on.
According to Ball, some of the challenges involved in designing and building the bikes were understanding the brake systems and being able to assemble them, knowing how to make the frames appropriate for a gravity bike, understanding the functions of the different types of tires, understanding how the weight of the bike affects the race and getting the riding position as low and tucked as possible. Ball and the show’s advisory staff are around to help the cast with any difficulties but avoid telling the kids what to do. “What I try to make sure that I’m doing is never feeding them ideas, but helping them implement some things that they’ve conceived but don’t quite have the technical know-how to do all by themselves,” he says.
For Design Squad’s producers, the show has a serious social mission beyond pure entertainment. “There is a real dearth of engineers in the world right now, and we’ve got a major pipeline issue,” says Marisa Wolsky, executive producer of Design Squad. “Kids don’t know what engineers do, they don’t understand the need for engineers, and we keep outsourcing our engineering work to the rest of the world. We’re going to start losing our competitive edge in the U.S. so we really need engineers to fill the pipeline.”
Through the production of this episode the kids learned about all the parts of a bicycle, how to design a bike frame, how to build a braking system and how to race fast. But the show also aims to teach children how to approach the design process, how to think for themselves and to have confidence in their ideas. “Young people that get into technology fields will not do value added by analyzing problems that other people define,” says Dr Woodie Flowers, MIT professor and Design Squad advisor. “I think you learn intuitive, creative thinking through hands-on experience working with mentors that are working with you as opposed to telling you what to do.”
To find out which team won the head-to-head challenge, watch the Gravity Bike episode of Design Squad in spring 2008 on PBS.
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