EV3 Robotics›Level 4 · WRO Prep›Lesson 39
Level 4 · Lesson 39 · EV3-L04-3960 minutes · Block 5 of 6 · Mat: WRO 2025 — The Future of Robots
One program whose menu can run any mission in the set.
Everything exists. The menu chooses, the window lets the list grow, the log records what happened, the helper beam moves the module during the drive. Today they become one thing, and the claim is tested properly.
Nothing new is taught today. If something is missing, this is where you find out — and finding out here is much cheaper than finding out in tomorrow’s round.
All of it is live: the three launch pads at A, B and C, the launch gantry at D, and the satellite row at E, from HOME and back.
Your menu from lesson 36 should already offer these as entries. If an entry on that list has no working mission behind it, either build it today or take it off the menu — an entry that does nothing is worse than a shorter list, because somebody will choose it under pressure.
The satellite entry needs the satellite module fitted, which the program cannot check. That is a configuration-card question from lesson 34, and today is when the card gets used for real.
Before assembling anything, draw the whole program on one page. Five parts, in this order, and every block you own belongs to exactly one of them:
Part one is where this block’s bugs live. The stale menu choice in lesson 35, the log holding last round’s stops in lesson 37, the synch flag left true in lesson 38 — three lessons, three bugs, one cause: state that outlived the run that made it. Put every initialisation in one visible group at the top where you can count them.
The canvas should now read as those five parts from left to right. If it does not — if the log emptying is buried inside a mission case, or the gyro calibration sits after the menu — move things until it does. A program you can read is a program you can fix in the two minutes between rounds.
Assemble the five parts, then count your initialisations against the list before running anything.
Six things. Count them on the canvas. Every one of them worked fine in its own lesson and every one of them is a live bug once the program runs twice in a row.
Then check the dispatch Switch has a case for every menu entry, and that the numbers line up. An off-by-one between the menu list and the Switch cases makes every choice run the mission next to the one you picked — which is a confusing bug because everything works, just wrongly.
This is the test that defines the milestone, and it is the only one that catches what this block is actually about.
Three different missions, chosen from the menu, run one after another, without touching the computer. Not three separate runs with a reload in between — those all pass even when the program is broken.
After each run, check three things before starting the next:
When it fails, look at the top of the program. The routes were proved in Block 4 and the missions worked in isolation five minutes ago. A back-to-back sequence that misbehaves is almost never a route problem — it is something that was not reset.
Now attack your own program. Fifteen minutes here is worth more than any other fifteen in this block.
The declared run: three missions from the menu, back to back, no reloading, each doing what was chosen and each reporting a correct summary.
Have another team watch and confirm nobody touched the computer between runs. That is the part it is easy to be generous with yourself about.
Then run the same three again in a different order. Passing once can be luck about which order happened to hide a stale value; passing in two different orders is a much stronger claim.
The milestone entry:
Tomorrow the mission is drawn at random. The Block 5 mock round tells you which mission to run shortly before each round starts, the way a real one does. That is the whole point of this block, and tomorrow is the first time the menu is used for the reason it was built.
This model drives, so its challenges are run on a mat. Mats differ between branches — check you are looking at the one in your room.
WRO 2025 RoboMission Elementary — The Future of Robots · official WRO game mat, 2362 × 1143 mm
The challenges name these places rather than distances, so the same challenge works on any mat:
Switch mats above and every route below is redrawn on the mat you chose.
Work through the challenges in order — each is harder than the last. The mission comes after all three, and it is meant to make you plan before you build.
Draw the whole program on one page as five parts — initialise, choose, dispatch, run, report — then count your initialisations on the canvas: both log lists emptied, menu choice set, window start set, synch flag false, gyro calibrated. Six things, every one of which worked fine in its own lesson.
The test that defines the milestone: three different missions from the menu, one after another, WITHOUT touching the computer. Not three runs with a reload between — those pass even when the program is broken. After each, check the robot did what the menu said, the summary covers only this run, and the menu opened where it should.
Now attack it. Choose the entry furthest from the last one. Press centre without moving the selection. Scroll to the last entry and run it. Stop a run part-way and immediately start another. Run the satellite entry with the wrong module fitted, to find out what happens and whether your configuration card would have caught it.
Deliver one program whose menu can run any mission in the set: three missions back to back with nobody touching the computer, then the same three again in a different order. When it fails, look at the top of the program — the routes were proved in Block 4, and the stale menu choice, the log holding last round's stops and the flag left true are the same bug three times.