C - Secure the Planet!

Make sure your robot is setup in the same way as the previous sections!

For the rest of this lesson, we need to be able to make the robot turn accurately.

Build the simple test program in the picture - it should make your robot spin on the spot for 1 second, and then stop.

There are 1000 milliseconds in 1 second - adjust the number until your robot turns by exactly 90 degrees.

Now you can turn by 90 degrees, write a program that makes your robot move in a square!

It should like something like the example in the picture but your 'delay' times will be different.

If you think about it, you only need to reverse 1 motor and then set it to forwards again to change direction - one motor can be going forward all the time.

Also, you don't necessarily need to stop after turning - just change the motor going in reverse to go forward again!

Making that last program took a while - and the robot was just doing the same things over and over again.

Say we wanted to drive in a square 10 times - that would take ages to program!

Driving in a square was doing the same thing 4 times:

Drive Forward

Delay

Turn

Delay

We can use a loop to get the computer to repeat these steps for us!

We're going to be using a type of loop called a while loop to repeat the steps.

A while loop works by checking something - this can be absolutely anything, for example if 1=1, if a switch is pressed, or if the program has been running for a certain length of time. This is called the condition.

If the condition is true, any code inside the while loop is run so long as the condition remains true.

Once the condition becomes false, the code inside the loop is no longer run, and the program moves to the next line.

In Python, we always put a colon (:) after the condition, and any code inside the while loop is indented from the margin.

Let's write some code using a while loop to drive forwards, stop, drive forwards, stop, forever.

To make sure the while loop runs forever, we just need to make the condition always true! The easiest way to do that is to simply use the line:

while True:

Easy right? Don't forget the capital 'T' - true and false in Python are always capitalised.

Inside the loop, we need some lines to drive forwards, wait, stop, and wait that will be repeated forever - add them in like the picture.

Don't forget to indent these lines of code (you can do it using the TAB key) - this means they are inside the while loop.

Change your program so that you only have lines of code in the loop, that make the robot:

Drive forwards

Turn 90 degrees

Check the picture for a hint if you need it - the program in the picture will drive forwards, then turn 90 degrees, but it will only do it once!

Now your robot can drive in a square using a loop, let's change the code so it will drive in a figure of 8, forever.

Have a look at the picture if you don't know what a figure of 8 is.

Try to split the shape up into 2 sections, and put it in a while loop to reduce the length of your program.

Make sure your robot drives in the figure of 8 properly, and ends up where it started !