Line Follower III — Scratch L2 Lesson 19

Learnt28 min · sliders, tuning, marker pads, the timer
Basic24 min · tune, stop, time
Challenge 1–327 min · fastest settings, four trips, a three-lap race
Extrabonus · careful on the bends

WHAT IT SHOULD LOOK LIKE

Today the robot gets two numbers you can change while it runs, two new pads, and a stopwatch for every lap.

tune it

time it

panels run left to right

Review — where we got to 5 min

<color [#FF00D4] is touching [#23262D]?> asks about the pink dot only.
Pink sees the line: turn left. Sky blue: turn right. Neither: move.
Changing forever to repeat until <> gives the robot somewhere to stop.

Quick-fire

Your robot is too slow. You change move (3) steps to 6. What did you have to do first?

Reveal the answer

Stop the project, find the block, type, and start again. Every single time. Today the numbers become sliders, so you tune while it runs.

Today’s Topic 3 min

(speed) and (turn) as variables
A variable shown as a slider on the Stage
Marker pads: blue means stop, yellow means turn round
(timer) and reset timer — a lap timer

Learning outcome

By the end of this lesson you will be able to:

Turn a number in a script into a variable you can change on the Stage.
Tune two numbers to make a robot fast and safe.
Time something with Scratch’s own clock.

Learnt — tune it, signal it, time it 28 min

1 · Numbers become variables

The follower has two numbers that matter: how far it moves, and how far it turns.

In Variables, make speed and turn, for all sprites.
Drop (turn) into both turn blocks.
Drop (speed) into the move block.


when flag clicked
go to x: (-46) y: (97)
point in direction (132)
forever
  if <color [#FF00D4] is touching [#23262D]?> then
    turn ccw (turn) degrees
  else
    if <color [#00E0FF] is touching [#23262D]?> then
      turn cw (turn) degrees
    else
      move (speed) steps
    end
  end
end

No set [speed v] to (3) under the flag. The slider owns the number now, and the flag must not undo it.

2 · A slider on the Stage

Tick the box next to each variable, so it shows on the Stage.
Right-click the speed box on the Stage. Choose slider.
Right-click it again. Choose change slider range. Type 1 and 30.
Do the same for turn, from 1 to 30.
Press the flag. Drag the sliders while the robot runs.

3 · Tuning

Tuning means changing numbers until something works well. Every real robot is tuned. Try these:

You change	What happens on the Wave
speed 3, turn 5	Safe and slow.
speed 12, turn 5	Much faster, still safe.
speed 3, turn 30	Swings past the line on a bend. Left, right, left — stuck.
speed 30, turn 5	The dots jump over the line on a bend. It flies off.

WHAT IT SHOULD LOOK LIKE

Speed too big and the dots jump right over the line on a bend. Turn too big and the robot swings past the line and back, for ever.

speed 30 on the Wave

turn 30 on the Wave

panels run left to right

In this demo, the Stage moves the numbers for you, like a hand on each slider. Before each bad setting it sends the robot back to the start, so both meet the same bend.


when flag clicked
set [speed v] to (3)
set [turn v] to (5)
broadcast [go v]
wait (4) seconds
set [speed v] to (12)
wait (4) seconds
set [speed v] to (3)
set [turn v] to (30)
broadcast [go v]
wait (4) seconds
set [turn v] to (5)
set [speed v] to (30)
broadcast [go v]

The tester, on the Stage.


when I receive [go v]
go to x: (-46) y: (97)
point in direction (132)
forever
  if <color [#FF00D4] is touching [#23262D]?> then
    turn ccw (turn) degrees
  else
    if <color [#00E0FF] is touching [#23262D]?> then
      turn cw (turn) degrees
    else
      move (speed) steps
    end
  end
end

The robot: the follower above, started by a message.

Runs here in the page. Nothing to install.

How to use this: Click the green flag and watch for about 15 seconds. Nothing to press — the Stage changes speed and turn for you.

Slow, then fast. Then turn 30: stuck wobbling at the first bend. Then speed 30: it shoots off the bends.

4 · Marker pads

Real warehouse robots read marks on the floor. We add two.

A blue stop line across the line: wait one second, then go on.
A yellow pad over the end of the line: turn round.

The pink dot is at the front, so it finds a pad first. We ask about the pink dot, not the whole robot.


if <color [#FF00D4] is touching [#3B82F6]?> then
  wait (1) seconds
  repeat until <not <color [#FF00D4] is touching [#3B82F6]?>>
    move (speed) steps
  end
end
if <color [#FF00D4] is touching [#FACC15]?> then
  turn cw (180) degrees
end

Both go at the bottom of the follower’s forever loop, under the steering.

WHAT IT SHOULD LOOK LIKE

Blue stop line: wait one second, then drive on. Yellow pad at the end: turn round. The robot shuttles back and forth for ever.

at the blue line

at the yellow pad

panels run left to right

Runs here in the page. Nothing to install.

How to use this: Click the green flag to start it. Nothing else to press — the robot drives itself back and forth.

A one-second stop at the blue line each way, and a turn at each yellow end.

5 · A lap timer

Scratch has a clock that is always running: (timer). It counts seconds. reset timer puts it back to 0.

Make a variable called lap time.
Add a second script to the robot, with the blocks below.
Tick (timer) in Sensing to watch it count.


when flag clicked
reset timer
forever
  wait until <touching color [#FFFFFF]?>
  set [lap time v] to (timer)
  reset timer
  wait until <not <touching color [#FFFFFF]?>>
end

It waits for the white squares of the finish strip, saves the time, and starts again.

WHAT IT SHOULD LOOK LIKE

The timer counts up by itself. Each time the robot crosses the chequered strip, we copy the timer into lap time and start it again.

halfway round

over the strip

panels run left to right

Runs here in the page. Nothing to install.

How to use this: Click the green flag to start it. Nothing else to press — watch lap time fill in each time the robot crosses the chequered strip.

Speed 8 on the Loop: about seven seconds a lap. The timer box drops to 0 at every crossing.

Basic — tune, stop, time 24 min

Open your follower from last lesson.

Step 1 — two variables

Make speed and turn.
Put them in the move block and both turn blocks.
Show them as sliders, from 1 to 30.

Step 2 — tune it

Drag the sliders while it runs. Find a speed that is fast and still safe.

Step 3 — a finish strip

Paint a short chequered strip of white and grey across your line. Move the robot’s start just past it.

Step 4 — the lap timer

Build the lap timer script. Check lap time changes once per lap.

Step 5 — a stop line

Paint a short blue stripe across a straight part of your line.
Add the blue stop if at the bottom of the loop.
Pick the pink from your dot, and the blue from your stripe.


when flag clicked
go to x: (-17) y: (118)
point in direction (90)
forever
  if <color [#FF00D4] is touching [#23262D]?> then
    turn ccw (turn) degrees
  else
    if <color [#00E0FF] is touching [#23262D]?> then
      turn cw (turn) degrees
    else
      move (speed) steps
    end
  end
  if <color [#FF00D4] is touching [#3B82F6]?> then
    wait (1) seconds
    repeat until <not <color [#FF00D4] is touching [#3B82F6]?>>
      move (speed) steps
    end
  end
end

Your follower after Step 5. The lap timer is its own script beside it.

My sliders go back to the same number every time I press the flag.

There is a set [speed v] to (3) under the flag. Take it out. The slider keeps its number between runs.

The robot stops at the blue line and never goes again.

The repeat until is missing, or it asks about a different colour. After the wait, it must drive until the pink dot is off the blue.

Lap time is always 0.

The robot starts on the finish strip, so the first crossing happens at once. Start it further along.

CHALLENGE 1 · L2-19-M1🪙 30 Adcoins8 min

The fastest safe settings

Find the speed and turn that give the best lap time on a wavy track.

The robot must finish three laps in a row without getting stuck or flying off.
Write down your speed, your turn and your best lap time.
Then try to beat your own time by changing one number.

WHAT IT SHOULD LOOK LIKE

Challenge 1 — the fastest numbers that still get round the Wave.

tuned

Runs here in the page. Nothing to install.

How to use this: Click the green flag to start it. Nothing else to press — watch lap time.

Speed 20 and turn 8 on the Wave: about four seconds a lap. Can your robot beat it?

Done when: you have three clean laps in a row, and a written note of the numbers that gave your best time.

Teacher note

Pupils usually push speed first and forget turn. A slightly bigger turn lets a faster robot get round bends it would otherwise fly off. Ask them to change one number at a time — that habit is the real lesson.

CHALLENGE 2 · L2-19-M2🪙 50 Adcoins9 min

Four trips, then park

A shuttle robot carries things back and forth. Make it count its trips.

Paint a line with two ends and a yellow pad on each end.
Each turn at a yellow pad adds one to trips.
After four trips, the robot stops and says “Four trips. Done!”.

WHAT IT SHOULD LOOK LIKE

Challenge 2 — count the trips, and park after four.

turning at the end

done

panels run left to right

Runs here in the page. Nothing to install.

How to use this: Click the green flag to start it. Nothing else to press — watch the trips box count to 4.

Back and forth four times, with a stop at the blue line every pass, then it parks.

Done when: trips counts 1, 2, 3, 4 — once per turn — and the robot stops on the fourth.

Teacher reveal


when flag clicked
go to x: (-114) y: (-20)
point in direction (55)
set [trips v] to (0)
repeat until <(trips) = (4)>
  if <color [#FF00D4] is touching [#23262D]?> then
    turn ccw (turn) degrees
  else
    if <color [#00E0FF] is touching [#23262D]?> then
      turn cw (turn) degrees
    else
      move (speed) steps
    end
  end
  if <color [#FF00D4] is touching [#3B82F6]?> then
    wait (1) seconds
    repeat until <not <color [#FF00D4] is touching [#3B82F6]?>>
      move (speed) steps
    end
  end
  if <color [#FF00D4] is touching [#FACC15]?> then
    turn cw (180) degrees
    change [trips v] by (1)
  end
end
say [Four trips. Done!]

The forever becomes repeat until <(trips) = (4)>, as the route did last lesson. The count goes where the turn happens. The demo runs at speed 6.

CHALLENGE 3 · L2-19-M3🪙 70 Adcoins10 min

A three-lap race

Turn the lap timer into a race.

A variable laps counts each crossing of the finish strip.
After three laps, the robot stops.
It says the total time, like “3 laps in 17.9”.

WHAT IT SHOULD LOOK LIKE

Challenge 3 — a three-lap race against the clock.

after three laps

Runs here in the page. Nothing to install.

How to use this: Click the green flag to start it. Nothing else to press — watch it through, about 20 seconds.

Speed 12 on the Loop. Three laps, then it stops and says its time.

Done when: the robot stops by itself after exactly three laps and says a time that matches the timer box.

Teacher reveal — no reset this time


when flag clicked
set [laps v] to (0)
reset timer
repeat until <(laps) = (3)>
  wait until <touching color [#FFFFFF]?>
  change [laps v] by (1)
  wait until <not <touching color [#FFFFFF]?>>
end
say (join [3 laps in ] (timer))
stop [other scripts in sprite v]

The timer is reset once, at the start, so at the end it holds the whole race. stop [other scripts in sprite v] stops the follower, so the robot stands still with its bubble.

EXTRA MISSION · L2-19-MX🪙 100 Adcoinsbonus

Careful on the bends

Speed 30 flies off the Wave. Make a robot that goes fast on straights and slow on bends.

Every time the robot turns, it remembers: “I am on a bend”.
For the next ten moves, it only moves 3 steps.
After that, it moves at full speed again.

WHAT IT SHOULD LOOK LIKE

Extra — speed 30, but slow for ten moves after every turn. The robot that flew off the Wave now gets round it.

on a straight

just after a turn

panels run left to right

Runs here in the page. Nothing to install.

How to use this: Click the green flag to start it. Nothing else to press — watch the bend box jump to 10 on every turn.

Speed 30, and it still gets round. Fast on the straights, careful after every turn.

Teacher reveal


when flag clicked
go to x: (-46) y: (97)
point in direction (132)
set [bend v] to (10)
forever
  if <color [#FF00D4] is touching [#23262D]?> then
    turn ccw (turn) degrees
    set [bend v] to (10)
  else
    if <color [#00E0FF] is touching [#23262D]?> then
      turn cw (turn) degrees
      set [bend v] to (10)
    else
      if <(bend) > (0)> then
        move (3) steps
        change [bend v] by (-1)
      else
        move (speed) steps
      end
    end
  end
end

The set [bend v] to (10) under the flag matters: without it, the robot starts at full speed and flies off the first bend before it has turned once.

Summary 5 min

A number in a script can become a variable, and a variable can be a slider.
Tuning: change one number, watch, change it again.
Too much speed flies off. Too much turn wobbles and sticks.
Marker pads give orders. The front sensor finds them first.
(timer) counts seconds by itself. reset timer starts it again.

Slider: A variable box on the Stage you can drag to change its number.
Tuning: Changing numbers, one at a time, until something works well.
Marker: A mark on the floor that tells a robot to do something.
Timer: Scratch’s own clock. It counts seconds from the last reset.

Hand in

Save your tuned robot and write your best lap time in the project notes. Next lesson: three tracks, a menu, and a best lap for each.

Learnt28 min · sliders, tuning, marker pads, the timer
Basic24 min · tune, stop, time
Challenge 1–327 min · fastest settings, four trips, a three-lap race
Extrabonus · careful on the bends

WHAT IT SHOULD LOOK LIKE

Today the robot gets two numbers you can change while it runs, two new pads, and a stopwatch for every lap.

tune it

time it

panels run left to right

Review — where we got to 5 min

<color [#FF00D4] is touching [#23262D]?> asks about the pink dot only.
Pink sees the line: turn left. Sky blue: turn right. Neither: move.
Changing forever to repeat until <> gives the robot somewhere to stop.

Quick-fire

Your robot is too slow. You change move (3) steps to 6. What did you have to do first?

Reveal the answer

Stop the project, find the block, type, and start again. Every single time. Today the numbers become sliders, so you tune while it runs.

Today’s Topic 3 min

(speed) and (turn) as variables
A variable shown as a slider on the Stage
Marker pads: blue means stop, yellow means turn round
(timer) and reset timer — a lap timer

Learning outcome

By the end of this lesson you will be able to:

Turn a number in a script into a variable you can change on the Stage.
Tune two numbers to make a robot fast and safe.
Time something with Scratch’s own clock.

Learnt — tune it, signal it, time it 28 min

1 · Numbers become variables

The follower has two numbers that matter: how far it moves, and how far it turns.

In Variables, make speed and turn, for all sprites.
Drop (turn) into both turn blocks.
Drop (speed) into the move block.


when flag clicked
go to x: (-46) y: (97)
point in direction (132)
forever
  if <color [#FF00D4] is touching [#23262D]?> then
    turn ccw (turn) degrees
  else
    if <color [#00E0FF] is touching [#23262D]?> then
      turn cw (turn) degrees
    else
      move (speed) steps
    end
  end
end

No set [speed v] to (3) under the flag. The slider owns the number now, and the flag must not undo it.

2 · A slider on the Stage

Tick the box next to each variable, so it shows on the Stage.
Right-click the speed box on the Stage. Choose slider.
Right-click it again. Choose change slider range. Type 1 and 30.
Do the same for turn, from 1 to 30.
Press the flag. Drag the sliders while the robot runs.

3 · Tuning

Tuning means changing numbers until something works well. Every real robot is tuned. Try these:

You change	What happens on the Wave
speed 3, turn 5	Safe and slow.
speed 12, turn 5	Much faster, still safe.
speed 3, turn 30	Swings past the line on a bend. Left, right, left — stuck.
speed 30, turn 5	The dots jump over the line on a bend. It flies off.

WHAT IT SHOULD LOOK LIKE

Speed too big and the dots jump right over the line on a bend. Turn too big and the robot swings past the line and back, for ever.

speed 30 on the Wave

turn 30 on the Wave

panels run left to right

In this demo, the Stage moves the numbers for you, like a hand on each slider. Before each bad setting it sends the robot back to the start, so both meet the same bend.


when flag clicked
set [speed v] to (3)
set [turn v] to (5)
broadcast [go v]
wait (4) seconds
set [speed v] to (12)
wait (4) seconds
set [speed v] to (3)
set [turn v] to (30)
broadcast [go v]
wait (4) seconds
set [turn v] to (5)
set [speed v] to (30)
broadcast [go v]

The tester, on the Stage.


when I receive [go v]
go to x: (-46) y: (97)
point in direction (132)
forever
  if <color [#FF00D4] is touching [#23262D]?> then
    turn ccw (turn) degrees
  else
    if <color [#00E0FF] is touching [#23262D]?> then
      turn cw (turn) degrees
    else
      move (speed) steps
    end
  end
end

The robot: the follower above, started by a message.

Runs here in the page. Nothing to install.

How to use this: Click the green flag and watch for about 15 seconds. Nothing to press — the Stage changes speed and turn for you.

Slow, then fast. Then turn 30: stuck wobbling at the first bend. Then speed 30: it shoots off the bends.

4 · Marker pads

Real warehouse robots read marks on the floor. We add two.

A blue stop line across the line: wait one second, then go on.
A yellow pad over the end of the line: turn round.

The pink dot is at the front, so it finds a pad first. We ask about the pink dot, not the whole robot.


if <color [#FF00D4] is touching [#3B82F6]?> then
  wait (1) seconds
  repeat until <not <color [#FF00D4] is touching [#3B82F6]?>>
    move (speed) steps
  end
end
if <color [#FF00D4] is touching [#FACC15]?> then
  turn cw (180) degrees
end

Both go at the bottom of the follower’s forever loop, under the steering.

WHAT IT SHOULD LOOK LIKE

Blue stop line: wait one second, then drive on. Yellow pad at the end: turn round. The robot shuttles back and forth for ever.

at the blue line

at the yellow pad

panels run left to right

Runs here in the page. Nothing to install.

How to use this: Click the green flag to start it. Nothing else to press — the robot drives itself back and forth.

A one-second stop at the blue line each way, and a turn at each yellow end.

5 · A lap timer

Scratch has a clock that is always running: (timer). It counts seconds. reset timer puts it back to 0.

Make a variable called lap time.
Add a second script to the robot, with the blocks below.
Tick (timer) in Sensing to watch it count.


when flag clicked
reset timer
forever
  wait until <touching color [#FFFFFF]?>
  set [lap time v] to (timer)
  reset timer
  wait until <not <touching color [#FFFFFF]?>>
end

It waits for the white squares of the finish strip, saves the time, and starts again.

WHAT IT SHOULD LOOK LIKE

The timer counts up by itself. Each time the robot crosses the chequered strip, we copy the timer into lap time and start it again.

halfway round

over the strip

panels run left to right

Runs here in the page. Nothing to install.

How to use this: Click the green flag to start it. Nothing else to press — watch lap time fill in each time the robot crosses the chequered strip.

Speed 8 on the Loop: about seven seconds a lap. The timer box drops to 0 at every crossing.

Basic — tune, stop, time 24 min

Open your follower from last lesson.

Step 1 — two variables

Make speed and turn.
Put them in the move block and both turn blocks.
Show them as sliders, from 1 to 30.

Step 2 — tune it

Drag the sliders while it runs. Find a speed that is fast and still safe.

Step 3 — a finish strip

Paint a short chequered strip of white and grey across your line. Move the robot’s start just past it.

Step 4 — the lap timer

Build the lap timer script. Check lap time changes once per lap.

Step 5 — a stop line

Paint a short blue stripe across a straight part of your line.
Add the blue stop if at the bottom of the loop.
Pick the pink from your dot, and the blue from your stripe.


when flag clicked
go to x: (-17) y: (118)
point in direction (90)
forever
  if <color [#FF00D4] is touching [#23262D]?> then
    turn ccw (turn) degrees
  else
    if <color [#00E0FF] is touching [#23262D]?> then
      turn cw (turn) degrees
    else
      move (speed) steps
    end
  end
  if <color [#FF00D4] is touching [#3B82F6]?> then
    wait (1) seconds
    repeat until <not <color [#FF00D4] is touching [#3B82F6]?>>
      move (speed) steps
    end
  end
end

Your follower after Step 5. The lap timer is its own script beside it.

My sliders go back to the same number every time I press the flag.

There is a set [speed v] to (3) under the flag. Take it out. The slider keeps its number between runs.

The robot stops at the blue line and never goes again.

The repeat until is missing, or it asks about a different colour. After the wait, it must drive until the pink dot is off the blue.

Lap time is always 0.

The robot starts on the finish strip, so the first crossing happens at once. Start it further along.

CHALLENGE 1 · L2-19-M1🪙 30 Adcoins8 min

The fastest safe settings

Find the speed and turn that give the best lap time on a wavy track.

The robot must finish three laps in a row without getting stuck or flying off.
Write down your speed, your turn and your best lap time.
Then try to beat your own time by changing one number.

WHAT IT SHOULD LOOK LIKE

Challenge 1 — the fastest numbers that still get round the Wave.

tuned

Runs here in the page. Nothing to install.

How to use this: Click the green flag to start it. Nothing else to press — watch lap time.

Speed 20 and turn 8 on the Wave: about four seconds a lap. Can your robot beat it?

Done when: you have three clean laps in a row, and a written note of the numbers that gave your best time.

Teacher note

CHALLENGE 2 · L2-19-M2🪙 50 Adcoins9 min

Four trips, then park

A shuttle robot carries things back and forth. Make it count its trips.

Paint a line with two ends and a yellow pad on each end.
Each turn at a yellow pad adds one to trips.
After four trips, the robot stops and says “Four trips. Done!”.

WHAT IT SHOULD LOOK LIKE

Challenge 2 — count the trips, and park after four.

turning at the end

done

panels run left to right

Runs here in the page. Nothing to install.

How to use this: Click the green flag to start it. Nothing else to press — watch the trips box count to 4.

Back and forth four times, with a stop at the blue line every pass, then it parks.

Done when: trips counts 1, 2, 3, 4 — once per turn — and the robot stops on the fourth.

Teacher reveal


when flag clicked
go to x: (-114) y: (-20)
point in direction (55)
set [trips v] to (0)
repeat until <(trips) = (4)>
  if <color [#FF00D4] is touching [#23262D]?> then
    turn ccw (turn) degrees
  else
    if <color [#00E0FF] is touching [#23262D]?> then
      turn cw (turn) degrees
    else
      move (speed) steps
    end
  end
  if <color [#FF00D4] is touching [#3B82F6]?> then
    wait (1) seconds
    repeat until <not <color [#FF00D4] is touching [#3B82F6]?>>
      move (speed) steps
    end
  end
  if <color [#FF00D4] is touching [#FACC15]?> then
    turn cw (180) degrees
    change [trips v] by (1)
  end
end
say [Four trips. Done!]

The forever becomes repeat until <(trips) = (4)>, as the route did last lesson. The count goes where the turn happens. The demo runs at speed 6.

CHALLENGE 3 · L2-19-M3🪙 70 Adcoins10 min

A three-lap race

Turn the lap timer into a race.

A variable laps counts each crossing of the finish strip.
After three laps, the robot stops.
It says the total time, like “3 laps in 17.9”.

WHAT IT SHOULD LOOK LIKE

Challenge 3 — a three-lap race against the clock.

after three laps

Runs here in the page. Nothing to install.

How to use this: Click the green flag to start it. Nothing else to press — watch it through, about 20 seconds.

Speed 12 on the Loop. Three laps, then it stops and says its time.

Done when: the robot stops by itself after exactly three laps and says a time that matches the timer box.

Teacher reveal — no reset this time


when flag clicked
set [laps v] to (0)
reset timer
repeat until <(laps) = (3)>
  wait until <touching color [#FFFFFF]?>
  change [laps v] by (1)
  wait until <not <touching color [#FFFFFF]?>>
end
say (join [3 laps in ] (timer))
stop [other scripts in sprite v]

The timer is reset once, at the start, so at the end it holds the whole race. stop [other scripts in sprite v] stops the follower, so the robot stands still with its bubble.

EXTRA MISSION · L2-19-MX🪙 100 Adcoinsbonus

Careful on the bends

Speed 30 flies off the Wave. Make a robot that goes fast on straights and slow on bends.

Every time the robot turns, it remembers: “I am on a bend”.
For the next ten moves, it only moves 3 steps.
After that, it moves at full speed again.

WHAT IT SHOULD LOOK LIKE

Extra — speed 30, but slow for ten moves after every turn. The robot that flew off the Wave now gets round it.

on a straight

just after a turn

panels run left to right

Runs here in the page. Nothing to install.

How to use this: Click the green flag to start it. Nothing else to press — watch the bend box jump to 10 on every turn.

Speed 30, and it still gets round. Fast on the straights, careful after every turn.

Teacher reveal


when flag clicked
go to x: (-46) y: (97)
point in direction (132)
set [bend v] to (10)
forever
  if <color [#FF00D4] is touching [#23262D]?> then
    turn ccw (turn) degrees
    set [bend v] to (10)
  else
    if <color [#00E0FF] is touching [#23262D]?> then
      turn cw (turn) degrees
      set [bend v] to (10)
    else
      if <(bend) > (0)> then
        move (3) steps
        change [bend v] by (-1)
      else
        move (speed) steps
      end
    end
  end
end

The set [bend v] to (10) under the flag matters: without it, the robot starts at full speed and flies off the first bend before it has turned once.

Summary 5 min

A number in a script can become a variable, and a variable can be a slider.
Tuning: change one number, watch, change it again.
Too much speed flies off. Too much turn wobbles and sticks.
Marker pads give orders. The front sensor finds them first.
(timer) counts seconds by itself. reset timer starts it again.

Slider: A variable box on the Stage you can drag to change its number.
Tuning: Changing numbers, one at a time, until something works well.
Marker: A mark on the floor that tells a robot to do something.
Timer: Scratch’s own clock. It counts seconds from the last reset.

Hand in

Save your tuned robot and write your best lap time in the project notes. Next lesson: three tracks, a menu, and a best lap for each.