Worksheet

U10.7 Project: drive the route

Following a trajectory · University · about 50 min

What this lesson is about

A full route through waypoints, marked on how closely it was followed and how long it took.

• The route
• The structure
• Slowing down for what matters
• Where to look when it fails
• What comes next

Questions 6 marks in all

1. [1 mark]What does this print for the project's route?

   import math
   PATH = [(30.0, 30.0), (30.0, 150.0), (120.0, 150.0), (120.0, 60.0), (170.0, 60.0)]
   cum = [0.0]
   for (ax, ay), (bx, by) in zip(PATH, PATH[1:]):
       cum.append(cum[-1] + math.hypot(bx - ax, by - ay))
   print(cum)
   print(round(cum[-1] / 13.0, 1))

2. [1 mark]The speed rule is cruise x max(0.45, 1 - off / 14) with a cruise of 13 cm/s. What speed does it give when the robot is 10 cm off the path, in cm/s to 2 decimal places?

3. [1 mark]Why is slowing down when off the path self correcting?

   1. ADrifting wide costs speed, which gives the correction time to work, which brings the speed back
   2. BLower speed shortens the look-ahead distance
   3. CThe dead band disappears at low speed
   4. DSlowing down removes the drive lag

4. [1 mark]off path is small on the straights but spikes at every corner, and the robot clips the crate. Where should you look?

   1. AThe look-ahead cutting the corners: reduce L, slow down for the bend, or both
   2. BThe cross-track sign convention
   3. CThe cruise speed is too low to finish in time
   4. DThe path itself goes through the crate

5. [1 mark]A follower that points its velocity at the look-ahead point stays within 1.3 cm of this route at L = 3. A classmate's robot turns to face the look-ahead point and drives forwards only, and it weaves along the straights. What is the likely cause?

   1. ASteering through the heading with a look-ahead too small for the speed
   2. BThe look-ahead is too large
   3. CThe corner speed rule is too cautious
   4. DThe route is longer than 350 cm

6. [1 mark]The corner rule reduces speed in proportion to the angle between the path direction at the projection and at the look-ahead point. What idea is that?

   1. AThe preview idea of pure pursuit, applied to the throttle instead of the steering
   2. BFeedforward of the reference speed
   3. CA dead band inverse on the speed
   4. DTime scaling from the tracking error

The task: drive the route

Follow the tape from (30, 30) round to the green finish, within 10 cm of it for at least 85 percent of the run, without touching the crate, inside 90 seconds. Plot off path and speed, and print drove:, how far the robot actually travelled.

from bugbot import *
import math
connect()

DT = 0.1
START = (30.0, 30.0)
PATH = [(30.0, 30.0), (30.0, 150.0), (120.0, 150.0), (120.0, 60.0), (170.0, 60.0)]
CRUISE, LOOK = 13.0, 16.0

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

Do it on the robot
www.bugbotlab.com/learn/u10-7-project-drive-the-route/
The simulator checks it and tells you when it passes. Nothing to install, no account.

Challenges

1. Round the corners in the path itself with short arcs, and follow that instead. Does the run get faster, tighter, or both?
2. Run it with a fixed speed and no corner rule, and compare the worst off path value.
3. Put the route on a clock as in U10.6, and report how many seconds behind its own plan the robot finished.