EV3 Robotics›Level 4 · WRO Prep›Lesson 42
Level 4 · Lesson 42 · EV3-L04-4260 minutes · Block 6 of 6 · Mat: WRO 2026 — Robot Rockstars
Design the robot for this set — and justify every choice against the scoring sheet.
Every build lesson so far handed you a constraint. Build a quick-swap arm. Build a sorter. One attachment, two missions. A modular mount. Today there is no constraint at all, except that everything has to earn its place.
You may keep the robot you have. But you have to defend it item by item against yesterday’s requirements list, exactly as if you were proposing it new. A robot that survives that audit is a good robot and you now know why. A robot kept because taking it apart feels wasteful is one nobody can defend to a judge.
Read the requirements list from lesson 41 aloud — the verbs, not the attachment ideas. Then walk the mat with it and check nothing was missed.
That last point is the strongest design lead on this mat. Two neighbouring stations that need two different mechanisms turn a cheap corner into an expensive one.
You are not starting from nothing, whatever the lesson title says. You are starting from five blocks of measurements. These are not opinions and they are not up for rediscovery:
The audit question for every part: which line of the scoring table does this earn? If a component cannot be traced to points, it is weight. That includes decorative bracing, a sensor nothing reads, and the mechanism for a mission you cut yesterday.
Then check the port budget from lesson 41 against what you have drawn. If the design fits one Brick — four motors, four sensors — it is finished. If it does not, lessons 43 and 44 add a second Brick, and you should know the price first: another set of batteries, real weight, and slower commands to anything on it.
Draw before you build. Side and above, with the widest point, the furthest forward point, and where each port’s cable runs. Ten minutes of drawing saves an hour of rebuilding, and the drawing goes in the journal that lesson 48 submits.
Then build in this order, which is the order things become expensive to change:
Keep the ports as they have been all course unless you have a reason to change: drive on B and C, gyro on 2, colour on 3, ultrasonic on 4. Every My Block you own assumes it, and re-plugging is a whole evening of confusing faults.
A changed robot invalidates numbers, and the numbers do not announce themselves. Work through this list honestly.
Re-tune in the order from lesson 29. P to the edge and back off, D to damp, P again, I last and only if a steady gap remains. You are not starting over — you own the procedure, and that is exactly what it was for.
Then run your menu once on the bench and confirm every entry still dispatches to a mission that exists. A redesign that dropped a mechanism leaves a menu entry pointing at nothing.
Swap robots with another team. They audit yours, you audit theirs, and neither team gets to explain first.
Three questions each, answered from the design and not from memory:
Write down every question you could not answer. That list is more useful than the ones you could, and it is what lesson 47’s judge will ask.
Do not attempt the whole route today. Prove the rebuild is sound first, one piece at a time:
Four short tests. Each one isolates something the rebuild could have broken, which is why they are worth more today than one long run that fails for an unknown reason.
This entry is scored by a judge in lesson 48, so write it for one:
Last build lesson of the course. Lessons 43 and 44 are wiring, 45 is software, and 46, 47 and 48 are rounds. From here the robot is what it is — so anything you know is wrong today stays wrong.
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 2026 RoboMission Elementary — Robot Rockstars · 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.
Audit the robot you have against yesterday's requirements list, item by item, as if you were proposing it new. Point at any component and say which line of the scoring table it earns — if it cannot be traced to points, it is weight. Then draw the design, side and above, with the widest and furthest-forward points marked.
Build in the order things become expensive to change: drive base, sensors, Brick, mounting point, modules. Then work out honestly what the rebuild invalidated — wheel size or track width breaks every distance and turn, sensor height breaks the calibration, changed balance breaks your PID gains. Re-measure them.
Swap robots with another team and audit each other, neither team explaining first. Ask what each part earns, what the widest point will hit, and what a mechanism costs to carry when its mission is not in the round. Write down every question you could not answer — that is what lesson 47's judge will ask.
Prove the rebuild is sound one piece at a time rather than with one long run: follow a line for a couple of metres, turn ninety degrees each way, drive HOME to the concert stage at A and do the job, and drive past the plaza at E loaded to check nothing catches. Four short tests, each isolating something the rebuild could have broken. This is the last build lesson of the course.