Vehicle Control

Module Goal: learn to make Robby go left & right.

Let’s learn how to turn Robby left and right.

Stop & Turn

When you have a two-wheeled drive system like Robby, the wheels provide both the drive motion of the vehicle and also the steering control. How is that? Think of a tank. It only has tracks and yet it goes forward, backward, left, and right. Why? Because it can make the two tracks turn opposite directions from each other.

Robby can do the same thing with its wheels!

In the python language we’re using, we have some commands that will help us do this:

• stop() will make the wheels stop spinning;
• sleep() will make the current motion continue for some amount of time;
• left() will make Robby turn left;
• right() will make Robby turn right.

Time to try it out. In code-oss, create a new file and add this:

#!/bin/python3

# our team's left turn module
from gpiozero import Robot
import time

# Students: you may need to modify the left/right numbers
#           based on your wiring choices!
robby = Robot(left=(7, 8), right=(9, 10))

robby.left()
time.sleep(1.0)
robby.stop()

Make sure you save it: turn_left.py.

Then run it. In the terminal :

• If you need to, change directories by typing cd cca_robotics and then Enter
• python3 turn_left.py and then Enter

Robby should have turned left by some amount. Maybe not much, maybe a lot. Discuss what happened.

Challenge: what can you do to make Robby turns a precise 90-degrees? Make it happen!

Turn Right

To turn right, just change one line of code. I bet you can guess which one :grin:

Change robby.left() to robby.right()!

Turning While Going Forward

Now, the code you’ve written so far makes Robby stop before turning. But, that’s not super practical. Let’s make Robby turn while driving forward.

Modify the code above to this:

robby.forward(curve_right=1)

Or, you can use curve_left. But, you can’t use them both at the same time :grin:

Challenge: what can you do to make Robby turns in a circle (left or right)? Make it happen!

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Module Complete