Inaugural Contest: Tree Climbing Machines

The inaugural contest was to build a machine that could climb a tree. Since we all thought the contest would be too easy, we decided to require each team to not only climb the tree, but to somehow haul a 200 lb anchor chain up with them. We used a limbed tree, but this was no telephone pole. A big gnarly cedar, it had an irregular, tapering cross section, and a thick skin of shaggy, stringy bark.

Any fears the JAC had entertained of converging designs were erased as the entries started to take shape. The Fish guys built a whimsical device, using a four-limbed humanoid climber to climb the tree and then clamp on. A beefy winch consisting of a converted car engine would then haul up the chain. The Zaber team also built a "climb and haul" design, but the lightweight climber consisted of a pair of circular saw blades clamped against the trunk with a spring loaded frame. The speed of each sawblade was independently controlled at a console on the ground. A strap of webbing would clamp to the tree when the climber was high enough, to anchor the winch. The Blue team had a completely different idea. A chain was to wrap in a helix around the tree trunk, and, driven by a high torque motor and chain sprockets, would wind the machine up the tree. The machine would need to be actuated by remote control, since any control cord would get wound around the tree.

Construction took place in a dilapidated warehouse, the only place we could rent for a weekend where constructing large machines out of junk would be tolerated. The building next door was all boarded up, but there were power cables snaking under the doors, and a barbeque set up near one of the doors. It glowed with an eerie light at night.

On contest day, the Fish guys went first, and their humanoid climber Joe flailed away at the tree for a long time. He looked impressively like a man climbing with a robot-like determination as his flailing feet stripped the bark off of a sizeable patch of trunk, but unfortunately, he didn’t move upward on the tree. The judge allowed a separate demonstration of their winch, which worked flawlessly, hauling Joe and the 200 lb chain at least 50 feet up the tree.

Team Zaber then installed their climber on the tree. The climber made slow progress, but actually climbed the tree. Unfortunately the circular sawblades, which had worked so well when the climber was tested on a telephone pole, had trouble getting a purchase on the soft bark of the cedar tree. They would alternate between gripping, which permitted a slow ascent, and spinning, which would simply dig the blade farther into the bark, much like a truck spinning its wheels into mud or snow. Progress stalled when the climber had clawed its way up a few feet from its starting point. The team opted to make their play. The anchor was successfully deployed, and the winch hauled the chain up to the climber.

The Blue team was up last. As they installed their bizarre contraption at the base of the tree, the audience puzzled about how it worked. "It won’t go up, it'll just go around..." observed one child. As the motor wound the chain tighter, the machine started to move, around the tree, but also upwards, in the helical path layed out by the chain. But every so often it would also drop down a few inches. A dozen mechanical engineers and mechanics stood around the tree, trying to figure out whether or not it would go up, even in principle, let alone in practice. In the end, no one was sure, and the debate continues to this day. After several revolutions around the tree, the payload had not been raised significantly above its starting point, and the judge called and end to the attempt.

In a controversial decision, first prize was awarded to the Fish guys, as the judge deemed that half of their machine had worked very well. The letter of the contest rules would have awarded first prize to Zaber, as theirs was the only entry to complete the entire task as stated. However, the rules also state that all decisions of the judge are final, and so the were.