Answers

10.4 Trails and tight spots

Competing · Robot club · about 15 min

What this lesson is about

A mat that fills up: seeing trails, turning early, keeping to the outside, and turning without stopping.

• Seeing a trail
• Never drive into a dead end

Questions 6 marks in all

1. [1 mark]In Light Cycles you want a moment to think. What happens if you stop?

   1. AYou lose: sitting still is not allowed
   2. BNothing, the trails pause too
   3. CYour trail disappears
   4. DThe other robots stop as well
   Answer: A. Stopping to think is the same as losing. Turn while moving instead.

2. [1 mark]Which line turns a corner without stopping?

   1. Adrive(35, 0, 80)
   2. Bstop() then turn_right(40, angle=90)
   3. Cturn_right(40)
   4. Dbackward(30) then turn_left(40)
   Answer: A. drive(forward, sideways, turn) sets all three at once, so you keep moving forward while turning.

3. [1 mark]Which of these keep you alive longer in Light Cycles?

   Tick every answer that is true.

   1. ATurn early, when a trail is about 30 cm away
   2. BKeep to the outside of the mat
   3. CHead for the middle, where there is most space at the start
   4. DWait until a trail is 15 cm away before turning
   5. ENever stand still
   Answer: A, B, E. The middle fills up first, and a robot that turns at 15 cm needs space it may not have.

4. [1 mark]What does this program print?

   import math
   trail = [(0, 30), (10, 30), (20, 30)]
   x, y = 8, 12
   closest = min(math.hypot(px - x, py - y) for px, py in trail)
   print(round(closest, 1))

   Answer:

   18.1

   The point (10, 30) is 2 across and 18 up from (8, 12), about 18.1 cm. The other two points are farther.

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

   found = None
   print("line ahead?", bool(found))
   found = [200, 5]
   print("line ahead?", bool(found))

   Answer:

   line ahead? False
   line ahead? True

   None counts as false and a list with something in it counts as true, which is how if found: works.

6. [1 mark]Does info()['trails'] include your own trail?

   1. AYes, and touching your own trail puts you out too
   2. BNo, only the other robots' trails
   3. COnly the last 10 cm of it
   4. DOnly in team games
   Answer: A. Every robot leaves a trail, yours included, so the mat gets smaller for you as well.

The task: thread the gap

from bugbot import *
connect()

while position()[1] < 85:
    forward(45)
    wait(0.1)

stop()

from bugbot import *
connect()
def across(to_x):
    while abs(position()[0] - to_x) > 2:
        if position()[0] < to_x:
            right(45)
        else:
            left(45)
        wait(0.1)
    stop()
def up_to(y):
    while position()[1] < y:
        forward(45)
        wait(0.1)
    stop()
across(30)
up_to(41)
across(-30)
up_to(72)
across(20)
up_to(84)
stop()