Worksheet

3.6 Project: precision parking

Control · Robot club · about 25 min

What this lesson is about

Round a box and into a bay facing east, on the worst robot in the course.

• The plan
• Leg one as a function
• Leg two: sideways, holding two things
• Leg three: turn and hold
• Where next

Questions 6 marks in all

1. [1 mark]In hold_line(0, 67), what does x = 0 mean?

   1. AThe line the robot started on
   2. BThe left edge of the mat
   3. CThe middle of the box
   4. DThe parking bay

2. [1 mark]In slide_right, which part of the drive is the speed?

   drive((target_y - y) * 10, 70, wrapped(0 - heading()) * 4)

   1. AThe sideways part, 70
   2. BThe forward part, holding y
   3. CThe rotation part, holding the heading
   4. DThere is no speed, it uses distance

3. [1 mark]hold_heading(90) is running and the robot faces 60. What rotation does max(-60, min(60, error * 3)) ask for?

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

   def wrapped(h):
       return (h + 180) % 360 - 180
   
   target = 90
   for heading in [350, 80, 120]:
       error = wrapped(target - heading)
       print(heading, max(-60, min(60, error * 3)))

5. [1 mark]Put the parking program's main lines in order, after the functions have been defined.

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

   1. hold_line(0, 67)
   2. print("facing", round(heading(), 1))
   3. hold_heading(90)
   4. slide_right(67, 55)

6. [1 mark]Why does hold_heading loop while abs(error) > 2 instead of until the error is exactly 0?

   1. AThe heading is never exactly on target, so it would never stop
   2. Babs() cannot give 0
   3. CAn error of 2 is the same as 0
   4. DPython cannot compare with 0

The task: precision parking

Reach the bay without touching the box and finish facing 90, within 6 degrees.

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

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

def hold_line(target_x, until_y):
    while position()[1] < until_y:
        # where am I? (cm from where I started)
        x, y = position()
        # forward, sideways, rotation: -100 to 100 each, until the next command
        drive(70, (target_x - x) * 10, wrapped(0 - heading()) * 4)
        # pause 0.1 s (the robot keeps doing what it was told)
        wait(0.1)
    # all motors off
    stop()

hold_line(0, 67)

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

Do it on the robot
www.bugbotlab.com/learn/3-6-project-parking/
The simulator checks it and tells you when it passes. Nothing to install, no account.

Challenges

1. Park in under 10 seconds.
2. Go round the *right* of the box instead and arrive from below.
3. Write go_to(x, y) that drives to any point using math.atan2 for the heading and the two-loop line holder, and park with two calls to it.