Bulldoze Run

Try It — Sixteen Points Without a Claw

Your robot cannot pick anything up yet. It can only drive and turn.

That turns out to be enough for four whole missions, because those missions do not ask you to hold anything. They just ask you to get things off the black line.

What OFF actually means

Everything in this project depends on one word. Read it carefully.

Walk the field

Before you write anything, go look. Find each of these on the field and fill in the table.

Which two objects are closest together? Could one push move both?

Look at the front of your robot. How wide is the part that would do the pushing, and does that width help or hurt you?

Learn It — Pushing Is a Skill

Pushing looks like the easy version of picking something up. It is not — it is a different problem with its own rules.

Where you hit it decides where it goes

Push far enough, then a bit more

You cannot see the line edge from inside your program. Your robot pushes for a set time and stops, and whatever happened, happened.

So overshoot on purpose. If the object needs to travel four inches to clear the line, push it six. There is no penalty for being further OFF, and there is a big penalty for being one millimeter short.

SIMULTANEOUSLY — the trap in Mission 4

Mission 4’s bonus does not just ask for an orange pom OFF and a blue pom OFF. It asks for both SIMULTANEOUSLY — true at the same moment.

That last one is the whole problem. Clear one pom, come back, clear the other, and if the first one rolled back onto the line in between, you get the base and not the bonus.

The reliable answer is one push that takes both. That is a positioning problem, not a programming problem.

One run, four missions

Build each mission on its own first. Get it working. Then join them together.

The order matters — after every push, your robot is somewhere new, facing a new direction, and the next section has to start from there.

// ---- Mission 13: unstraight cubes ----
// drive, push, back off

// ---- Mission 14: cones ----
// turn, drive, push

// ---- Mission 2: red cubes ----
// ...

Use comment banners like these to mark each section. When one mission stops working, you will know exactly which block of code to look at.

Do It — Clear the Line

One mission at a time. New project for each, then a combined one at the end.

Step 1 — Mission 13 — Unstraight Cubes for 1 point

• All three Unstraight Cubes are OFF the black line

Step 2 — Mission 14 — Traffic Cones for3 points

• First cone is completely OFF
• Second cone is completely OFF

Did one push clear both cones, or did you need two moves? Describe what you did.

Step 3 — Mission 2 — Red Cubes for 4 points

Good news on the bonus: the small red cubes do not have to stay stacked. Knocking them apart is fine as long as both end up OFF.

• Large Red Cube is OFF
• The pallet is OFF too
• Both Small Red Cubes are OFF

Step 4 — Mission 4 — The Poms for 8 points

Get the base first: one orange pom, completely OFF. Then work out how to take a blue one with it in the same motion.

• An Orange Pom is completely OFF the line
• Orange and Blue are OFF at the same moment

Step 5 — Chain them into one run

Create a new project called Bulldoze. Copy your four working programs into it, one after another, with a comment banner above each section.

Now the hard part: the end of one section is the start of the next. After a push, your robot is not where it began — you need to drive it from wherever it ended up to wherever the next mission starts.

What order did you put the four missions in, and why that order?

• All four missions run from one program, one start

Step 6 — Run it five times and time it

Same standard as always. Reset the field between runs. Time each one with a stopwatch.

Which mission failed most often across your five runs, and what do you think caused it?

One last thing before the arm

You have been stopping with ao() — all off. It cuts power to every motor and lets them coast to a halt.

That has been fine so far. From the next project it will not be, because you are about to add an arm, and an arm changes where the weight sits. A robot that coasts is a robot that keeps creeping after you told it to stop.

Freezing instead of switching off

Setting a motor’s power to zero is not the same as switching it off. Zero power is still a command — the motor actively holds position instead of rolling free.

So from Project 7 onwards, every stop looks like this:

motor(0, 0);
motor(3, 0);
msleep(30);

Three lines instead of one. You still give it the thirty milliseconds to settle, because even a held motor takes a moment for the robot to stop rocking.

• I tested both kinds of stop and measured the difference
• I can explain why zero power is not the same as no power

Score It — Checkpoint

My best run

Fastest clean run

Can you do it again?

• I can state the OFF definition and judge whether an object satisfies it
• I can square my robot up to an object before pushing it
• I push past the line on purpose instead of stopping right at it
• I can explain why the Mission 4 bonus needs one motion, not two
• I can chain several missions into a single run that starts once
• My program uses comment banners so I can find each mission’s code
• I add one section at a time and test before adding the next

Think about it

Your program is getting long, and big chunks of it are nearly identical — drive, turn, drive, push, back off, over and over. What is annoying about that?

You change one msleep() near the start of the run. What happens to every mission that comes after it, and why?

A team at a tournament has a robot that scores 16 points in practice and 3 points in the actual match. Nothing about the program changed. Give two possible explanations.

Next

You have taken pushing about as far as it goes. Everything left on the field has to be lifted — and that needs a claw.

Before Project 7 — Your Robot’s Arm, go build one. The claw build lives in the Systems strand, and this is the one place where the two strands have to meet.

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