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

  1. Remain furry throughout the contest.
  2. Occasionally make a "baa" sound.
  3. Push around balls on the table.
  4. 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-