5.6 Project: rescue worksheet

Questions 7 marks in all

[1 mark]Put the rescue states in the order the robot goes through them.

Number the lines 1 to 4 to put them in the right order.

home
done
search
approach

[1 mark]Which condition moves the machine from search to approach?

ATag 9 is in view
BThe robot is closer than 12 cm
CThe robot is near the start
DThe loop has run 300 ticks

[1 mark]Why does the code say if tags and tags[0][3] < 12 rather than just if tags[0][3] < 12?

AIf the list is empty, tags[0] would be an error, and and stops before reading it
Band makes the test run faster
CIt checks the tag is number 9
DWithout it the robot would never stop

[1 mark]What does this program print?

def step(state, tag_dist, at_home):
    if state == "search" and tag_dist is not None:
        return "approach"
    if state == "approach" and tag_dist is not None and tag_dist < 12:
        return "home"
    if state == "home" and at_home:
        return "done"
    return state

state = "search"
for tag_dist, at_home in [(None, False), (60, False), (30, False), (11, False), (None, False), (None, True)]:
    state = step(state, tag_dist, at_home)
    print(state)

[1 mark]How does the home state know where home is?

APositions are relative to the start, so home is (0, 0)
BIt searches for a home tag
CIt reverses every move it made
DIt follows the distance sensor back

[1 mark]The task starter stops at the marker with break. What turns it into the full rescue?

ASet state = "home" instead of breaking, and add an elif state == "home": branch
BAdd a second loop after the first one that searches again
CChange the 12 to 0
DCall set_cv("apriltag") again at the marker

[1 mark]The rescue ends with print("home:", position(), "after", tick / 10, "seconds"). If the loop ended on tick 437, how many seconds does it print? Give the exact number.

The task: rescue

Find marker 9, print found 9, drive to it, and return home, without touching the box.

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

# maths: atan2, hypot, sin, cos, radians
import math

def wrapped(h):
    return (h + 180) % 360 - 180

def go_to(x, y, speed=70):
    # where am I?
    px, py = position()
    a = math.radians(wrapped(math.degrees(math.atan2(x - px, y - py)) - heading()))
    # forward, sideways, rotation: -100 to 100 each, until the next command
    drive(speed * math.cos(a), speed * math.sin(a), wrapped(0 - heading()) * 3)

def near(x, y, cm=6):
    # where am I?
    px, py = position()
    return math.hypot(x - px, y - py) < cm

def bearing_of(cx):
    return (cx - 160) * 120 / 320

# camera: the tag detector
set_cv('apriltag')
state = 'search'
# do this 590 times (tick counts from 0)
for tick in range(590):
    tags = [t for t in apriltags() if t[0] == 9]
    if state == 'search':
        if tags:
            print('found 9')
            state = 'approach'
        else:
            # spin clockwise on the spot at 40
            turn_right(40)
    elif state == 'approach':
        if tags and tags[0][3] < 12:
            # leave the loop
            break
        elif tags:
            # forward, sideways, rotation: -100 to 100 each, until the next command
            drive(60, 0, bearing_of(tags[0][1]) * 3)
        else:
            # spin clockwise on the spot at 30
            turn_right(30)
    # pause 0.1 s (the robot keeps doing what it was told)
    wait(0.1)
# all motors off
stop()

Plan your program here, then type it in and press Run.

Do it on the robot
www.bugbotlab.com/learn/5-6-project-rescue/
The simulator checks it and tells you when it passes. Nothing to install, no account.

5.6 Project: rescue

What this lesson is about

Questions 7 marks in all

The task: rescue

Challenges