Answers

1.4 Sideways

Driving · Robot club · about 15 min

What this lesson is about

Strafing: moving without turning, the thing wheels cannot do.

• left and right
• Why it matters
• Diagonals
• A gentle curve
• Sideways by distance, with a sensor

Questions 7 marks in all

1. [1 mark]What is strafing?

   1. ASliding sideways or diagonally while facing the same way
   2. BTurning on the spot
   3. CDriving backwards
   4. DDriving in a curve
   Answer: A. BugBot's feet can push it sideways without turning, so it keeps the heading it had.

2. [1 mark]What does this program make the robot do?

   forward(60, distance=20)
   right(60, distance=20)
   backward(60, distance=20)
   left(60, distance=20)

   1. ADrive a square, facing the same way the whole time
   2. BDrive a square, turning at each corner
   3. CDrive forward 40 cm
   4. DStay exactly where it is
   Answer: A. Forward, right, back, left is a square, and none of those commands turn the robot, so its nose never changes direction.

3. [1 mark]Why is strafing useful? Choose all that apply.

   Tick every answer that is true.

   1. AIt keeps the heading, so no turning error is added
   2. BThe camera and distance sensor can stay pointed at something while the robot moves
   3. CIt makes the robot drive perfectly straight
   4. DIt uses no power
   Answer: A, B. Every turn is a little off, and strafing avoids turning. The sensors on the front keep looking where you want. It still drifts like any drive.

4. [1 mark]What does drive(60, -60, 0) do?

   1. ADrives diagonally forward and to the left
   2. BDrives diagonally forward and to the right
   3. CDrives forward and turns left
   4. DStays still, because 60 and -60 cancel out
   Answer: A. The three numbers are forward, sideways and rotation. Negative sideways is left, so forward plus left is a diagonal.

5. [1 mark]Why does drive need a wait and a stop around it?

   1. AIt returns at once and takes no distance
   2. BIt only works inside a loop
   3. CIt drives for exactly one second
   4. Dwait and stop set its speed
   Answer: A. drive is the raw command the others are built from. It starts the motors and returns, like forward(speed) with no distance.

6. [1 mark]What does this program print?

   p = (12.5, 30.0)
   print("moved right to x =", p[0])

   Answer:

   moved right to x = 12.5

   Like a list, [0] picks the first item, which for a position is x. [1] would be y.

7. [1 mark]What does drive(60, 0, 20) with a wait(3) make the robot do?

   1. ADrive forward in a gentle curve
   2. BSlide sideways
   3. CSpin on the spot without moving forward
   4. DDrive dead straight
   Answer: A. Forward plus a little rotation means it turns slowly as it goes, which draws a curve.

The task: reach the green square

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

# drive forward at 60 for 20 cm, then stop
forward(60, distance=20)
# your turn: go round the wall and into the square

from bugbot import *
connect()
forward(60, distance=20)
right(60, distance=25)
forward(60, distance=45)
left(60, distance=25)