Worksheet

6.5 Following a robot

Seeing more · Robot club · about 20 min

What this lesson is about

Two controllers that never finish: chase a moving tag at a set distance.

• Watch it go
• Two controllers, forever
• Corners
• Losing it

Questions 6 marks in all

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

   for dist in [50, 30, 20, 12]:
       speed = max(0, min(70, (dist - 20) * 4))
       print(dist, speed)

2. [1 mark]Why is the lowest speed in the follower 0, the max(0, ...)?

   1. ASo the robot stops when too close instead of reversing
   2. BSo it never goes faster than the leader
   3. CSo it keeps moving when the leader stops
   4. DBecause negative speeds are an error

3. [1 mark]With speed = max(0, min(70, (dist - 20) * 4)), what speed does the follower use when the leader is 26 cm away?

4. [1 mark]How is following a robot different from docking at a marker?

   1. AThe target keeps moving, so the loop never finishes
   2. BIt uses a different detector
   3. CIt needs no rotation controller
   4. DThe distance is measured in pixels

5. [1 mark]When the leader goes out of view, the lesson just turns right. What is a better recovery?

   1. ARemember the last bearing and turn that way
   2. BStop and wait for the leader to come back
   3. CDrive forward at full speed
   4. DSwitch to the line detector

6. [1 mark]The task starter always drives at 60 towards robot 101. What goes wrong?

   1. AIt rams the leader, because nothing slows it down as it gets close
   2. BIt never catches up
   3. CIt turns away from the leader
   4. DIt loses the leader immediately

The task: follow the leader

Stay 12 to 35 cm behind the green robot for at least 80% of the run, without touching it. The starter drives at the leader at a fixed speed and rams it. Add the distance controller.

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

# do this 390 times (tick counts from 0)
for tick in range(390):
    seen = [r for r in robots() if r[0] == "green"]
    if seen:
        # forward, sideways, rotation: -100 to 100 each, until the next command
        drive(60, 0, (seen[0][1] - 160) * 120 / 320 * 3)
    # 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/6-5-following-a-robot/
The simulator checks it and tells you when it passes. Nothing to install, no account.

Challenges

1. Hold 30 cm instead of 20. How far behind does it sit on the straight now, and does it still stay inside 12 to 35 cm?
2. Print your distance to the leader every second and see how steady it is.
3. Make the LED green while you can see the leader and red when you cannot.