Challenge 1
Find every black line on the mat and trace it with your finger. Write down how many separate lines there are and which stations each one connects.
The mission 4 min
Welcome to Level 4. For the next forty-eight lessons you are not building models — you are building one robot that has to survive a competition, and rebuilding it six times for six different game mats.
This block runs on the WRO 2021 RoboMission Elementary mat, themed POWERBOTS — Energy at Home. A house is drawn on the mat. Energy is being wasted in some rooms and generated in others, and the robot has to move energy modules to where they belong.
Today you will not touch a brick. That is deliberate. The fastest way to lose a WRO round is to build a beautiful robot that scores the wrong thing. Before anyone picks up a motor, the team has to be able to read the mat the way an engineer reads a drawing.
Why a whole lesson on reading? In a real round you get two minutes. There is no time to discover during the run that a module only counts when it is fully inside its zone, or that a line stops 10 cm short of the station you assumed it reached. Every one of those is written down somewhere before the round starts.
On the mat 6 min
Your branch has its own printed copy of this mat, and the picker at the bottom of this page shows the one you are standing next to. Every mat in the Hub carries named stations rather than measurements, because a challenge that says “drive 45 cm” is wrong on somebody else’s copy.
The 2021 mat has seven named positions:
| Station | What is there | Why it matters |
|---|---|---|
| HOME | Delivery yard, bottom left, outside the house | Every run starts and usually ends here |
| A | Battery bin, top left, outside | Furthest point on the mat — the expensive trip |
| B | Bathroom | Tight approach, close to the wall |
| C | Living room (the sofa) | Wide open — easy to reach, easy to overshoot |
| D | Bedroom | Middle of the mat, reachable from three directions |
| E | Kitchen (the hob) | On the main line, so a good first target |
| F | Solar panel, bottom edge | Closest to HOME — where energy is generated |
Say the letters out loud as a team. For the rest of the block, “go to E” has to mean the kitchen to everybody without anyone pointing.
The technique — reading a mat like an engineer 12 min
There are four passes. Do them in this order, and write as you go. Reading a mat is not looking at it.
Pass 1 — the lines
Trace every black line with a finger. Note where each line starts and stops, and where two lines cross. A junction is a decision the robot will have to make, and a line that stops short is a place where a line follower will drive off into nothing.
Pass 2 — the zones
Find every coloured square, circle and border. For each one ask the question that decides the points: does the object have to be touching, inside, or completely inside? Those are three different robots.
Pass 3 — the scoring table
Missions are not worth the same. Write them in points-per-second order, not points order — a 15-point mission that takes 20 seconds beats a 20-point mission that takes 60. That ranking is your route plan, and most teams never make it.
Pass 4 — the rules that are not on the mat
Starting area size, whether you may touch the robot mid-run (and what it costs), the time limit, and what counts as a restart. These live in the rulebook, not the artwork, and they change what a sensible route looks like.
The trap that catches every new team. A mission worth 20 points that you complete 60% of the time is worth 12 points on average. A mission worth 10 points that you complete every time is worth 10. But the 20-point mission also costs you the run when it jams. Reliability is a score, not a feeling.
Build it — on paper 10 min
The only thing built today is a route plan. Take a sheet of blank paper and draw the mat from memory — you will get it wrong, and the gaps are the useful part.
- Draw the outline and mark HOME.
- Add every station letter you can remember, roughly in place.
- Draw the lines you are confident about in solid pen.
- Draw the ones you are unsure about as dashes.
- Now compare with the real mat and correct it in a different colour.
Everything in the second colour is something you would have got wrong under competition pressure. Keep the sheet — it goes in the journal.
The program — in words first 10 min
No blocks today. Write the run as pseudocode: one line per action, in the order the robot will do them. EV3Lessons calls this step pseudocode and it is the single habit that most separates teams that finish from teams that debug.
when program starts :: events hat say [PSEUDOCODE ONLY - no blocks yet] :: display
A first attempt for the solar-panel run might read:
- Start with the robot square in the starting area at HOME.
- Drive forward until the Colour Sensor finds the line.
- Follow the line towards F.
- Stop when the front of the robot reaches the solar panel zone.
- Lower the collector.
- Reverse along the line back to HOME.
- Release inside the delivery yard.
Now read it back and mark every line that contains a word you cannot yet program — square, find the line, follow. Those marked lines are lessons 4, 5, 6 and 7 of this block. The plan is also the syllabus.
Tune it — cut the route down 8 min
Take your points-per-second ranking and your route plan, and answer three questions as a team:
- What would you drop? If the run had to fit in half the time, which mission goes first — and does dropping it cost fewer points than failing everything?
- What is on the way? Two missions that share a leg are nearly free. Two missions at opposite corners are not.
- Where does the robot end? A run that finishes at A, the far corner, has thrown away the trip home.
Rewrite the route once with those answers applied. Keep both versions — showing that you improved a plan is worth marks in the journal.
Run it — the walk-through 6 min
Put a robot from Level 3 — any driving base — on the mat at HOME. Nobody programs it. One student pushes it by hand along the route while another reads the pseudocode aloud, one line at a time.
Time it. A hand-pushed run is roughly as fast as a well-tuned robot, so if the walk-through busts the time limit, the plan does — and it is far cheaper to find that out now.
Watch for the pauses. Every time the person pushing hesitates about what to do next, the pseudocode has a gap. Mark it and fix the wording before the next lesson.
The journal 4 min
WRO judges score the engineering journal as well as the run. Start it today, on the first day, because a journal written at the end is fiction.
Entry 1 must contain:
- Your from-memory mat sketch, with the corrections in colour.
- The missions ranked by points per second.
- Version 1 and version 2 of the route plan.
- The hand-pushed walk-through time.
- One sentence: the thing we did not know about this mat before today.
What a judge is actually looking forThe journal is scored — here is what earns the marks.Show meHide
Not neatness. Judges look for evidence of decisions: a choice, the reason for it, what you measured, and what you changed as a result. A journal full of tidy photographs and no numbers scores badly. A scruffy one with three route versions and a table of times scores well.