Answers

5.5 Brains

Behaviours · Robot club · about 20 min

What this lesson is about

From a loop to think(me) and me.memory, with a practice arena.

• The loop is outside
• Escape, as a loop
• The same thing as a brain

Questions 6 marks in all

1. [1 mark]How often does the arena call your think(me) function?

   1. ATen times a second
   2. BOnce, at the start of the game
   3. COnly when another robot comes close
   4. DAs fast as the computer can
   Answer: A. The arena owns the loop and the waiting. think is the body of the loop, run ten times a second.

2. [1 mark]Why does a brain keep its state in me.memory rather than in a normal variable?

   1. ALocal variables are forgotten when the function returns
   2. Bme.memory is faster
   3. CNormal variables cannot hold words
   4. DThe arena reads me.memory to score you
   Answer: A. Each call starts fresh. Anything that has to survive to the next tick goes in me.memory.

3. [1 mark]What does this program print?

   class Me:
       def __init__(self):
           self.memory = {}
   
   def think(me):
       count = me.memory.get("count", 0)
       me.memory["count"] = count + 1
   
   def forgetful(me):
       count = 0
       count += 1
       return count
   
   me = Me()
   for i in range(3):
       think(me)
       n = forgetful(me)
   print(me.memory["count"])
   print(n)

   Answer:

   3
   1

   think saves its count in memory, so it reaches 3. forgetful starts from 0 every call, so it is always 1.

4. [1 mark]On the very first tick, me.memory is empty. What does me.memory.get("state", "go") give?

   1. A"go", the default
   2. BNone
   3. CAn error, because the key is missing
   4. DAn empty string
   Answer: A. get returns the second argument when the key is not there yet, which is how the machine picks its starting state.

5. [1 mark]What does this program print?

   samples = [(20, 0), (25, 45), (60, 90), (80, 135), (70, 180), (30, 225), (20, 270)]
   opens = [h for d, h in samples if d > 40]
   target = opens[len(opens) // 2]
   print(opens, target)

   Answer:

   [90, 135, 180] 135

   Headings with a reading over 40 cm are the gap. The middle one of those is 135, the centre of the opening.

6. [1 mark]The escape program aims at the middle of the open headings, not the single longest reading. Why?

   1. AThe longest reading points at a corner of the opening
   2. BThe longest reading is always wrong
   3. CThe middle is quicker to work out
   4. DThe distance sensor cannot read long distances
   Answer: A. Through a gap, the furthest thing seen is usually past one edge. Aiming at the middle keeps you clear of both sides.

The task: escape the box

# the two lines every program starts with: the commands, then the robot
from bugbot import *
connect()

# as long as the thing ahead is further than 15 cm
while distance() > 15:
    # drive forward at 50 (keeps going until the next command)
    forward(50)
    # pause 0.1 s (the robot keeps doing what it was told)
    wait(0.1)
# all motors off
stop()
print("wall at", distance())

from bugbot import *
connect()
def wrapped(h):
    return (h + 180) % 360 - 180
state = "look"
samples = []
for tick in range(290):
    if state == "look":
        samples.append((distance(), heading()))   # a full turn of readings
        turn_right(50)
        if len(samples) >= 65:
            opens = [h for d, h in samples if d > 40]   # headings with room: the gap
            target = opens[len(opens) // 2]              # the middle of the gap, not the longest ray
            state = "turn"
    elif state == "turn":
        error = wrapped(target - heading())
        if abs(error) < 4:
            state = "go"
        else:
            drive(0, 0, max(-40, min(40, error * 3)))
    elif state == "go":
        x, y = position()
        if y < -32:
            break
        drive(60, 0, wrapped(target - heading()) * 3)
    wait(0.1)
stop()