Learning to Turn

Try It — Break the Straight Line

In Project 4 you worked hard to make your robot drive straight. Now you are going to ruin it on purpose — and pay close attention while you do.

Start a new project called Turns. Put in your straight-driving program from Project 4, but keep msleep(3000) the same for every single run.

Then change one wheel only. Leave the left wheel at your usual power. Change the right wheel to each value below, run it, and describe the path the robot took.

What did your data tell you?

At the end of Project 3 you predicted what a robot would do with one wheel forward and one wheel backward. Were you right?

Learn It — Two Knobs, Three Shapes

You only have two things to adjust, and they do completely different jobs.

The three shapes

Radius turn, where both wheels go the same direction at different speeds. The robot sweeps a wide arc, like a car going around a bend. Sharpness comes from how different the two numbers are.

motor(0, 50);
motor(3, 25);

One-wheel turn, where one wheel drives, the other sits still. The robot swings around the stopped wheel — like ring around the rosie. More power on the moving wheel means a faster swing, not a tighter one.

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

Zero radius turn, where the wheels go opposite directions. The robot spins in place without moving forward or backward at all. Also called a pivot or spin turn. This is what you use for precise angles.

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

Where you are headed

Do It — Learn to Aim

Step 1 — Drive a big circle

Create a new project called Circles. Put a chair in the middle of an open floor.

Write a program that drives your robot in one big circle all the way around the chair, without TOUCHING it. Use only one set of motor(), msleep(), and ao() — no stopping and restarting.

• One full circle around the chair, no contact

Step 2 — Drive a tight circle

Swap the chair for something small — a tissue box works. Circle that instead, same rule: one set of commands.

Compare your two sets of numbers. What did you change to make the circle smaller?

Step 3 — Try all three shapes

Run each one and record what the robot actually does.

Which of the three moved the robot the least distance across the floor? Why does that matter on a crowded field?

Step 4 — Build a 90° turn

Create a new project called Right Angle. Use a zero radius turn and find the msleep() that gives you a 90° turn.

Keep both powers the same the whole time. Change only the time.

Step 5 — Prove it with a square

Here is the honest test of a 90° turn: do it four times and see if you end up where you started, facing the way you started.

Drive forward, turn 90°. Repeat four times total.

• My robot came back close to its starting spot
• It ended up facing the same direction it started

If your robot did not close the square, was each turn too much or too little? How could you tell?

A small error in one turn becomes a big error after four. This is why turning by time is hard — and why Project 11 replaces it with counting.

Step 6 — Drive to the spilled cubes

Onto the field. New project called Approach 12.

Start in your starting box, exactly the way you decided in Project 4. Drive out, turn, and stop next to the spilled cube area — close enough and square enough that a claw could pick a cube up.

Write your plan as pseudocode first:

// 1. Drive forward out of the starting box
// 2. Turn toward the spilled cubes
// 3. Drive up to them
// 4. Stop

• My robot stops at the spilled cubes
• It is square to the cubes, not at an angle
• It did not knock any cubes out of the area on the way in

Step 7 — Run it five times

Same rule as Project 4. One good approach is luck.

Score It — Checkpoint

No points yet — Mission 12 does not score until something gets stacked. What you have built is the half of the mission that has to work before the other half matters.

My turning numbers

Every project from here uses these. Write them down properly.

You worked out 90° by testing. Did doubling it give you a good 180°? Did halving it give you a good 45°?

Match the turn to the job

Can you do it again?

• I can explain what happens when the two power numbers get closer together or further apart
• I can name all three turn types and write the code for each
• I know which knob changes the shape of the path and which changes how far along it I go
• I can make a repeatable 90° turn
• I can chain drive, turn, and drive into one run
• My robot reaches the spilled cubes in a workable position five times running

Think about it

Your square test almost certainly did not close perfectly. Where did the error come from — was the robot doing the wrong thing, or was your program asking for something it cannot deliver?

A teammate’s robot turns 90° perfectly on the carpet but overshoots on the field mat. Nothing in the program changed. What happened?

You now have a robot that gets to the right place and points the right way. What is the next thing it needs before Mission 12 can actually score?

Next

In Project 6 — Bulldoze Run, you put driving and turning together to score four missions at once — and you do it all without a claw, by pushing.

KIPR · Botball Explorer — Introductory Projects · © KISS Institute for Practical Robotics 1997–2027