Buggy, Design Contradictions, and TRIZ (now ARIZ)

A Tuesday session of the Project Summit / Business Analyst World conference (June 20th), featured an interesting talk by the New Jersey Department of Health’s Victoria Roza. She described methods of design and creativity coming out of a practice called TRIZ, which I originally encountered during my Lean Six Sigma training. That training only discussed the idea in terms of the contradiction matrix that was the original innovation of the practice, but Ms. Roza described how the practice has been greatly expanded and generalized since then. The expanded practice is known as ARIZ. (Both acronyms reflect their Russian origins. The “T” is for “theory” while the “A” is for “algorithmic.”)

I look forward to doing more reading on these subjects but for now I want to take the opportunity, for Ms. Roza’s benefit and others, to describe an engineering/athletic competition that is a major tradition at Carnegie Mellon University. Officially known as Sweepstakes, the competition is a combination soapbox derby and relay race, where two pushers relay their buggies up the front hills, release them to “freeroll” down a long, winding road to a high-speed right turn (called the chute), after which three more pushers relay the buggies up the back hills to the finish line. The course is about 0.8 miles long and the record time as of 2017 is 2:02.16. This is not quite ten seconds faster than the record set my first spring on campus in 1981.

Here are some nice introductions to the subject from YouTube.

A buggy team consists of five pushers and a driver, and organizations that want to enter buggies into competition must provide other kinds of support to the event. Separate competitions are run for push teams of men, women, and alumni.

  • Driver: Small, light, probably female, nerves of steel, probably a screw loose.
  • Hill 1 pusher: Typically the strongest pusher, gives the buggy its initial momentum up the steepest hill.
  • Hill 2 pusher: Can be the slowest runner, but needs to push like a beast when releasing to freeroll.
  • Hill 3 pusher: On the teams with the best buggies this pusher may only run a few yards. On weaker teams it doesn’t matter.
  • Hill 4 pusher: Requires a combination of strength and speed to crest the final slope.
  • Hill 5 pusher: “Hill” 5 is actually flat, so this pusher should be the fastest runner but doesn’t need to be the strongest. My senior year I pushed hill 5 for our B-team, a sure indication that most of the guys in our fraternity were on the slower side. We finished in 2:47, at least twenty seconds behind the other buggies in our heat, but tying our extant record until our A-team lowered it to 2:37 about an hour later.
  • Buggy Chairperson: One representative per organization who attends meetings, coordinates activities, and ensures all duties are performed. Usually the chief designer and builder of the buggy.
  • Mechanics: Any individuals who assist the chief designer.
  • Guide Flagger: One or more people who provide targets to help the driver take the ideal line in freeroll.
  • Sweepers and Flaggers: Organizations entering buggies must provide help to sweep the course before practices and races, and flaggers to control traffic access to the course. Practices were often early in the mornings on weekends, following mixers that ran late into the night. It wasn’t uncommon for sweepers to sleep on the floor in the hallway outside the chairman’s door, so the chairman would wake the individual up while tripping over him, and make sure he got out to fulfill his duties.

As you can see from the fourth video above, the buggies themselves have gotten smaller, faster, and simpler over the years in many ways, while some aspects of the wheels and bearings have undoubtedly gone increasingly high-tech.

Buggy is a classic constrained optimization problem. Here are some of the contradictions.

  • A heavier buggy might roll downhill faster and might gain better traction in the chute but a lighter buggy is easier to push uphill. Buggies doubtless get lighter and lighter every year. The benefits of improving (sideways) traction in other ways, plus requiring less traction for lighter buggies in the chute, definitely skew the buggies towards smaller size and lighter materials. Additionally, buggies cannot change weight during the run, so they can’t, for example, drop a heavy weight at the bottom of the hill.
  • The pushbar needs to stick out to allow the pushers to move the buggies, but they generate drag at higher speeds. Builders have experimented with many different cross-sections of pushbar, but the most extreme designs involve having the pushbar fold down to a horizontal position during the freeroll. This innovation was first adopted in 1983 or 1984 with a pushbar that lowered backward so it extended out behind the vehicle. This was later seen as a safety hazard (to following buggies) so subsequent pushbars folded forward into the main body of the buggy. The question then becomes whether the drag saved is worth the weight and complexity of the (driver-powered since there can be no energy storage, if I understand correctly) folding mechanism.
  • The crossbar on the pushbar can take different forms. A wide pushbar would create more drag but allow for a more powerful pushoff with a widely spread hands (think bench press) and would in general be easier to grasp. A shorter crossbar would create less drag and possibly allow a push-off to be weaker but longer if the hands are closer together, and would be a bit harder to grasp in general. I think I’ve seen pushbars eliminated entirely to be replaced by a tennis ball, but that’s very hard to control and all but impossible to get two hands on. It didn’t catch on.
  • Larger wheels allow for greater contact with the road and lower speeds at the bearings near the axle and hence lower friction, but smaller wheels are easier to spin up (less rotational inertia) and present a smaller cross-sectional area for reduced drag. I don’t know whether smaller wheels are easier or more difficult to balance (classic soapbox derby wheels can spin for thirty minutes) but with lower rotational inertia perhaps it matters less.
  • Drivers were traditionally males but over time became all but exclusively female. Older analyses (men are stronger, more coordinated, more willing to risk injury) are no longer applied and 80-pound, four-foot-nine, fifteen-year-olds who somehow materialize on campus (this happened when I was there) are recruited heavily by the most aggressive and successful competitors. Smaller drivers mean lighter buggies with smaller cross-sectional areas.
  • Having the drivers drive feet-first is safer but orienting them head-first makes for a smaller cross-sectional area. Safety is a huge concern. Ambulances have been known to take the entire buggy to the emergency room so the driver can be extracted under the best possible circumstances. I heard about a bad, head-on crash before my time on campus and was standing about 20 feet from a similar occurrence in 2014, I think. The safety harnesses and forward protection in modern buggies is good, but a sudden deceleration when hitting hay bales head-on at over forty miles an hours is always going to be a problem. I don’t know why the driver didn’t make the turn (perhaps the steering failed?) but it was a scary and heart-rending event to witness.
  • Steering with hands in front of the driver makes for a less comfortable setup for the driver and a potentially more limited field of view, but steering with hands at the driver’s sides makes for a wider buggy with a larger cross-sectional area.
  • Wheels with soft rubber surfaces will grip better than a harder surface for better traction through the chute but will generate more rolling friction over the rest of the course. Designers have addressed this problem in many ways and I’ve seen a lot of crazy wheel configurations since 1981, including one that didn’t survive its first power-slide through the chute during practice rolls one winter weekend. An interesting solution is to use two larger, softer wheels inside the buggy’s body and one smaller, harder one outside it. I know that rolling surface designs have been a huge point of experimentation over the years and I was always amused when spectators rushed over the hay bales at the bottom of the course to retrieve sections of tires that scuff off in the turn. They would all sniff the rubber bits and make knowing pronouncements on the chemical treatments that must have been applied. I suggested in a class assignment that buggies use a tire with a hard, narrow band in the middle or to one side and softer surface to either side. The wheels would be arranged so they would tilt in a turn, which would bring the softer sections in contact with the ground. This wouldn’t be hard to do with a single front or rear wheel mounted at an angle, but would be harder to do for pairs of wheels on a fixed axle on in a classic, two-wheeled steering arrangement.
  • Speaking of wheel arrangements, classic four-wheel setups presumably offer greater stability and traction in the chute but at the cost of weight, drag, and complexity. Three-wheel arrangements offer a lot more flexibility and are typically simpler and lighter. Two-wheeled arrangements were employed in the 60s (using modified bicycle frames without fairings, which would never fly today) and again briefly in the 80s, briefly holding the course record (not bad for a fraternity that was traditionally terrible at buggy!). The biggest problem with four-wheeled buggies was getting the caster and camber of the wheels right. Using three wheels and steering with one greatly mitigates this problem. Two-wheeled buggies were outlawed (supposedly) for safety reasons. Interestingly, they used a pair of retractable training wheels for stability when being pushed at lower speeds, and only ran on two wheels during the freeroll section of the course (including the chute).
  • Smoother bodies that cover more components prove to be more aerodynamic than the wider variety of designs that have been employed throughout the event’s history, at the cost of added weight, cost, and complexity. Experience has demonstrated the value of smaller, faired bodies, to the point where the macro design of most buggies has converged, leaving differences only in the small mechanical details, the fitness of the pushers, and the skill of the drivers.

Doubtless there are other considerations, but those are the main ones I remember thinking about back in the day. Our fraternity did better at Booth and Greek Sing, the other two legs of the “Triple Crown,” than we ever did at buggy, but we had loads of fun doing all of it.

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