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.

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 Harder Than It Looks

You already know how to make both wheels turn. Here is the part nobody warns you about: equal power does not mean equal speed.

Send 50 to both motors and your robot will drift. Every robot does. The reasons are physical, not programming mistakes:

• No two motors are built exactly alike.
• The wheels may not be mounted perfectly straight.
• One wheel has more friction than the other.
• Weight is not spread evenly across the robot.

Reverse is just a minus sign

Positive power drives forward. Put a minus in front of both numbers and the robot backs up along the same path.

// Forward
motor(0, 50);
motor(3, 50);

// Backward
motor(0, -50);
motor(3, -50);

Shape of the program

Every out-and-back run has the same five moves. Write it as pseudocode before you write it as code.

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

White space is free

Leave a blank line between each move. It costs nothing and makes the sections of your program obvious at a glance.

// Out
motor(0, 50);
motor(3, 50);
msleep(2000);

// Stop and hold
ao();
msleep(30);
msleep(3000);

// Back
motor(0, -50);
motor(3, -50);
msleep(2000);

// Stop in the box
ao();
msleep(30);

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

Create a new project called Waypoint. Put attribution comments at the top. Drive forward and stop — that is all for now.

Start with power 50 and guess a time. Run it. If you stopped short, add time. If you overshot, take time away.

• My robot stops IN THE ZONE

Step 3 — Fix the drift

Watch which way your robot pulls as it drives out. Then adjust one wheel’s power — small changes only.

Step 4 — Make the stop obvious

Add ao(); then msleep() so the robot sits still in the zone. The mission says stop — the judge needs to see it.

• A person watching can clearly tell my robot stopped

Step 5 — Come home

Now add the return trip. Same powers, both negative. Same drift correction — do not swap which wheel gets the smaller number.

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 time different from the forward time? 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 powers.

Can you do it again?

• I can place my robot in the same starting position every time
• I can change the msleep() value to change how far the robot goes
• I can tell which wheel to adjust when the robot drifts, and fix it
• I can drive the same path in reverse with the correction 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. It only knows how long to push. What could go wrong on competition day that would make your timing 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 use your straight-driving numbers as the starting point and learn the two ways to make a turn — and the three shapes a turn can have.

KIPR · Botball Explorer — Discovery Projects · © KISS Institute for Practical Robotics 1997–2026