Placebo: The Sheepbot
story
At the beginning of 6.270,
Cynthia and
Paul had a lot of
LEGO and a very capable
controller, but didn't know
what kind of robot to build with all of it. They talked over many
different ideas;
technically challenging, simple, pointless, able to win the
contest, and so forth. However, Cynthia and Paul realized that they
were not LEGO masters, and decided not to try to build something too
difficult. They listened well to the organizers' command, "thou shalt
build a placebo: a robot that tries not to score points," and decided
not to build something that would crush robots of the students: robots
designed without the benefit of years of experience. After tossing
out a few more ideas, one remained, and Cynthia and Paul began to
realize that it was the best of all.
They decided at last to build something furry.
Cynthia and Paul lived in the big
city, and nothing furry with which one could make a decent furry
placebo was readily available. After many frustrating attempts to
locate supplies, Cynthia told Paul, "let me go back
home to where such things are
abundant. I will find something for our robot and send it to you."
Paul did not want to let her go, but he realized how necessary it
was. Concealing his sadness, he bid her goodbye, then returned to his
room and cried for a whole night. No progress was made on the robot
for a few days.
Soon, however, a package arrived from the West.
Indeed, it contained something furry: sheep's wool, enough for a whole
robot-sheep, was rolled up inside! Within the folds of wool, Paul
found one more item; a strange object which made a beautiful
sheep-sound when turned over in one's hand. Being from the West
himself, Paul had seen such things before, and was not taken by surprise.
He knew how to use the resources he had, and quickly drew up a
multi-faceted strategy for his robot.
strategy
- Remain furry throughout the contest.
- Occasionally make a "baa" sound.
- Push around balls on the table.
- Generally act cute and sheep-like.
After writing down the fourth and final part of his strategy, Paul
realized that the first three were redundant. He chose, however, to
leave them in the plans, so that his goals would remain clear.
results
The sheepbot, as Paul decided to name it, turned out the way he had
been hoping from the beginning. To allow it to move around on the
smooth table, Paul gave the sheep a tank-like tread-based drive. This
drive does not remind one immediately of a sheep's four feet, but it
allows many sheep-like actions, such as turning in place and driving
forward.
The tail of the sheepbot is key to the implementation of part two of
Paul's strategy. It is mounted on a servo, so that it can wag at
appropriate times. This is, by itself, fairly cute, but the
sound-maker is concealed within the tail, so that the sheepbot makes a
"baa" sound whenever his tail wags. One additional servo for the head
was enough to give the sheepbot as much mobility and expressive ability as
an average real sheep.
Two sensors allow the sheep to navigate through a complex
environment. First, a reflectance sensor made from a phototransistor
and an overpowered blinking LED allows the sheep to measure the color
of the table beneath it. Using this sensor, the sheepbot can orient,
find the line, and follow it, quickly and reliably. Second, a
distance sensor gives the sheepbot a sense of what objects are around him.
He uses this sensor both for turning away from walls and for locating
obstacles elsewhere on the table. By examining either side of an
obstacle, the sheepbot can determine whether it is a ball (in which
case the sheepbot pushes it with his nose) or a wall (in which case he
looks over the edge).
View the sheepbot's contest code.
performance and conclusion
The sheepbot had only a few chances to compete on contest day. He was
scared by the bright lights and false-started once, but managed to
recover in time for a very successful round in which he executed his
complete strategy. Near the end of the competition, the sheepbot
competed against robot 14, Maximus. The sheepbot displayed rare
aggressive behavior in this round, trying hard to ram his opponent and
saying "baa" far more often than usual.
It seems that the shy sheepbot was not immune to the effects of the
bright lights and the huge crowd in 26-100. Luckily for him, he will
probably spend the rest of his days in quieter, more comfortable
conditions.
-pdg-
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