Out and Back

Try It — Read the Mission First

You are about to score real points. Before you write a single line of code, find out exactly what the judge is looking for.

Mission 10 — Waypoint Bravo is the same mission on the other side: the zone next to the right starting box. Everything you learn here works for both.

What scores and what does not

Walk it first

Do not program yet. Put your robot in the starting box, then push it by hand through the whole mission — out to the zone, stop, back into the box.

Now measure and write down what you just did.

Look at the zone depth and your robot’s length. How much room for error do you actually have?

Learn It — Straight Is (Still) Not Automatic

In the EV3 Classroom app you do not drive each wheel on its own. A movement block drives both wheels together as one matched pair — the brick keeps the two motors in step for you.

Meet the blocks

Every driving program in this project starts the same way: a hat block that starts the program, one block that tells the brick which two motors are the wheels, and one that sets how fast they go.

The colors match the EV3 Classroom app, so you can find each block by its color: yellow = Events, pink = Movement, orange = Control.

The move block

One block does the driving. It has three parts, and you will use all three today:

• The dial is the steering number. 0 means straight. Positive numbers bend the path to the right, negative numbers bend it to the left.
• The middle number is how far to go.
• The last part is the unit. The dropdown offers rotations, degrees, and seconds. We will use rotations — one rotation means each wheel turns all the way around once.

Steering 0 should mean perfectly straight. Here is the part nobody warns you about: on a real robot, it usually almost does — but not quite. The brick keeps the motors matched, but it cannot fix things that are not motors:

• The wheels may not be mounted perfectly straight.
• One wheel has more friction than the other.
• Weight is not spread evenly across the robot.
• A tire that is dusty or worn grips differently than a clean one.

Change the steering by 1 or 2 at a time. Big jumps overshoot and you end up chasing it.

Reverse is just a minus sign

A positive distance drives forward. Put a minus in front of the distance and the robot backs up along the same path.

Shape of the program

Every out-and-back run has the same five moves. Write it as pseudocode before you build it from blocks.

Five moves — but only three blocks. A move for block does its own stopping when it finishes. What it does not do is wait around afterward. That is the wait block’s job.

Why does step 3 exist? What happens to your score without it?

Read it top to bottom

Blocks snap into one stack, and the robot runs them from the top down. Here is the whole mission:

Your numbers will not be 3.5 — they will come from your field measurements and your inches-per-rotation. That is what the next phase is for.

Do It — Drive the Mission

Step 1 — Mark your starting position

Your robot must start in the same spot every single run, or nothing you measure means anything. Put it in the starting box and decide exactly how you will place it — against a wall, on a mark, lined up with a corner.

Describe how you place your robot so it starts identically every time:

Step 2 — Get out to the zone

New project called Waypoint, with your names in the project name — that is your attribution. Drive forward and stop — that is all for now.

Start from your tape measure: turn your measured distance into rotations (inches ÷ your inches-per-rotation) and put that into the move block. Run it. Watch where the robot really stops. Short? Add a little. Past the zone? Take a little away. A quarter rotation is a good-sized nudge.

• My robot stops IN THE ZONE

Step 3 — Fix the drift

Movement blocks keep the wheels matched, so your robot drifts less than most — but less is not never. Watch which way your robot pulls as it drives out. Then nudge the steering number — 1 or 2 at a time, no more.

My final straight-driving steering value is:

Step 4 — Make the stop obvious

Your move block stops the robot on its own — but it does not make it sit there. Add a wait block after it so the robot holds still in the zone. The mission says stop — the judge needs to see it.

• A person watching can clearly tell my robot stopped

Test it on a person. Have a teammate watch a run and ask them, without warning, whether the robot stopped. If they hesitate, it is not long enough.

Step 5 — Come home

Now add the return trip: one more move block, with a minus sign on the rotations. Keep the same steering number — the minus goes on the rotations, never on the steering.

The robot must end FULLY WITHIN the starting box. Not TOUCHING the line. Not hanging over the edge. Every part inside.

• My robot returns FULLY WITHIN the starting box and stops
• No part of the robot touches or crosses the box line

Did you have to make the backward rotations different from the forward rotations? Why might that happen?

Step 6 — Run it five times

One good run is luck. Five good runs is a program. Run the whole mission five times without changing anything and record what happens.

Did all five runs come out the same? If not, what changed between them?

Step 7 — Do the other side

Copy your program into a new project called Waypoint Bravo and run Mission 10 from the right starting box.

Remember the rule: each mission needs its own out-and-back. You cannot score both bonuses with one trip home.

• Mission 10 scores too

Did the same numbers work on the other side, or did you have to change them? Why do you think that is?

Score It — Checkpoint

My score

My numbers

Keep these. Project 5 starts from your straight-driving steering value.

Can you do it again?

• I can place my robot in the same starting position every time
• I can change the distance in the move block to change how far the robot goes
• I can tell which way to nudge the steering number when the robot drifts, and fix it
• I can drive the same path in reverse with the steering still right
• I can make a stop that a judge can clearly see
• I can read a mission and say exactly what has to happen to score it
• My program scored on five runs in a row

Think about it

Your robot scored, but nothing in your program knows where the robot actually is on the field. It only knows how far to spin its wheels — and wheels can slip. What could go wrong on competition day that would make your distances wrong?

A teammate’s robot stops just past the zone line every time. Name two different things they could change, and say which one you would try first.

Which was harder — getting the robot to the right place, or getting it to do the same thing five times? What does that tell you?

Next

In Project 5 — Learning to Turn, the robot stops going in straight lines. You will crank the steering dial past a gentle nudge — all the way to a one-wheel turn and a spin in place — and learn the three shapes a turn can have.