Step 1

Driving Decisions

When we walk around, we are always sensing our environment. We need to be able to sense obstacles that might have come up along the way. This is a problem for Zumi with the forward() function. With forward(), Zumi cannot check her sensors or her surroundings while driving. Imagine walking around with your eyes closed, and only opening your eyes when you have stopped moving to decide your next move. In this lesson, you will learn how to use a new function that will let Zumi multitask. You will be able to drive and check sensors to make decisions.

Include libraries

In [ ]:

from zumi.zumi import Zumi
import time
import IPython.display
zumi = Zumi()

Step 2

forward()

Run the following code and pick up Zumi as she’s driving. What happens?

In [ ]:

zumi.forward(duration=5)

Step 3

go_straight()

When you are walking, what actions are being repeated? Right foot, left foot, right foot, left foot… Zumi can also take “steps” forward. When these small steps are put in a loop, Zumi will drive forward. The driving function for a small step is zumi.go_straight(). Unlike forward(), parameters are not optional. Zumi needs to know speed and heading, or direction. In the image below, what is Zumi’s heading?

Run the code below to see the code for this driving pattern using go_straight().

In [ ]:

zumi.reset_gyro() # Resetting all angles to zero at the start

for x in range(40): # Take 40 steps
    zumi.go_straight(40, -30) # Drive at speed 40 at heading -30
    
zumi.stop() # Don't forget to stop!

The stop() at the end of the program is really important! Since go_straight() allows for smooth driving without stops in between, there is nothing to stop Zumi from driving forever (or until the battery dies). After a for loop completes, the code will continue to the next line. Any code that is not part of the for loop should not be indented.

Practice using for loops and this new method of driving straight. Try changing the second heading parameter and estimate how many times it takes to drive a certain number of iterations.

Step 4

Conditionals

Self-driving cars are always making decisions based on sensory input. In this section, you will learn how to write a program that stop Zumi from driving if she is upside down!

Orientation

To know if Zumi is upside down, you are going to learn about a new function: get_orientation(). There are six states that Zumi can be facing:

Use the code below to verify the six different states. If you see a 0,-1, or 7, Zumi is between states or the state is unknown.

In [ ]:

for i in range(80):
    zumi.update_angles()
    orientation = zumi.get_orientation() # Save this value in a variable so that you can use it later...
    print(orientation)
    time.sleep(0.1)
    IPython.display.clear_output(wait=True) 
print("Done!")

Step 5

Pseudocode

Your goal is to write code that will only allow Zumi to drive while she is flat on the ground. In other words, Zumi will only drive if get_orientation is in state 5. Before writing the code in Python, it is helpful to write pseudocode, which is a program that’s written in plain language that a human can understand. Look at the pseudocode below to see what we mean:

check orientation
if orientation is 5, drive
else if orientation is not 5, stop
repeat for 100 iterations

Step 6

If statements

Most of the pseudocode should be familiar except for the two middle lines where Zumi makes a decision based on the orientation. If statements, or conditionals, are used to make decisions within code. You actually use conditionals every day!

The alarm is the condition that needs to be true to wake up. Else, if the condition is false, the program will execute something different. In Python, if statements follow a format similar to this one:

if alarm goes off:
I will wake up
else:
I will stay asleep

Before running the code below, see the values of variables x and y. Can you predict what the output will be?

In [ ]:

x = 10
y = 30 

if x > y:
    print("x is greater than y")
elif x == y:
    print("x is equal to y")
else:
    print("x is less than y")

Notice the double equal signs == for checking if two values are equal. This is the comparator you will be using to compare the value of the orientation to the values that you choose. Using your knowledge of for loops, go_straight(), and get_orientation(), fill in the code below to have Zumi drive forward for 200 steps unless Zumi’s orientation is upside down. Don’t forget to put a stop() at the end of the for loop!

# TODO: Reset angles to zero

for x in range("CHANGE ME!"):
    zumi.update_angles()
    orientation = zumi.get_orientation() 
    
    # TODO Check if orientation is equal to 5 and go straight if true
    # TODO Else, stop.
    
# TODO Add one more stop here

1.8: Driving Decisions

This lesson uses:

Grade level:

Approx. time required:

Driving Decisions

Include libraries

forward()

go_straight()

Conditionals

Orientation

Pseudocode

If statements