fan exploded one day on the freeway in Los Angeles, CA
prompting a tense stay on the off ramp while waiting for
the tow truck to arrive, lest the engine overheat like the
creation of many a losing team on Junkyard Wars. We
ended up replacing the fan and motor assembly in toto
because you don’t just throw something away with an
origin story as death defying as that.
The fan motor itself is a little unusual in that it doesn’t
have a traditional shaft. It has a flat flange type thing that
would lock into the fan, and a large part of the fan casing
actually spun around with the flange. We still had
projectiles on the brain, and given our penchant for
medieval weaponry (our 30 pound combat robot is called
Twibill Trouble), our brains immediately focused on a more
old-school way to throw stuff around than an air cannon: a
catapult. Specifically, we were thinking of a mangonel.
A mangonel is a catapult that works through torsion.
Unlike a trebuchet — which depends on a falling
counterweight — the mangonel relies on twisted ropes or
springs. We thought that the fan motor could be used to
twist a torsion spring.
Another unusual aspect of the fan motor was that it
had a three-wire lead with some funky connectors. It would
take a little thinking to determine how best to get it to
work with the Victor speed controllers on Protobot, and as
we were scratching our heads over this very problem we
finally found our perfect inspiration staring us in the face.
The walls of Robot Central serve as a sort of shrine to
builds past, with various souvenirs we’ve collected watching
over our new endeavors. We’ve got side panels from old
FIRST robots (one signed by Dean Kamen), castoffs from
our own combat robots, and a few parts from other
combat robots — friend and foe. One of the more unique
entries in the menagerie is a panel of thin spring steel from
Agamemnon: one of the first bots built by combat robot
greats, Team Delta and a competitor in Robot Wars 1996.
Dan Danknick from Team Delta was one of the awesome
mentors for our FIRST Team, and the panel from a classic
combat bot has been one of the prized possessions of
Robot Central for years.
As we were thinking about medieval weaponry, the
idea of a crossbow (or perhaps ballista, given the scale we
were going for) did zip across our gray matter. Our concern
was that we didn’t have the proper material for the bow of
the crossbow — something flexible that could store and
effectively release enough energy to fire a bolt with enough
power to fight off hordes of sieging Vikings (or
shambling zombies, to borrow from more
current pop culture). However, a panel of thin
spring steel would be just about perfect.
Siege the Day
As with many engineering advances, the
crossbow replaced human skill with mechanical
reliability. Bows were essential to warfare in
medieval times and even earlier during classical
antiquity, but their effective use required years —
often lifetimes — of training. The crossbow —
invented in China around the 6th Century B.C. —
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