Set your YetiBorg v2 to move in a preset sequence

Robots such as BigTrak and Turtles work by having a sequence of moves programmed into them. Most of them use a set of commands based on the Logo programming language.

In this example we will turn our YetiBorg v2 into a turtle robot, just without the pen :)

Parts

All we need for this example is the YetiBorg v2 itself, no other bits are necessary :)

Get the example

The example is part of the standard set of YetiBorg v2 examples installed during the getting started instructions: bash <(curl https://www.piborg.org/installer/install-yetiborgv2.txt)

Run once

Before running make sure your YetiBorg v2 has plenty of room to move, we do not want it to fall of a table! When it is running keep and eye on where he is in case you need to rescue him from disaster. Go to the YetiBorg v2 code directory: cd ~/yetiborgv2 and run the script: ./yeti2Sequence.py The standard example should move roughly like this:

1. Draw a 40 cm sized square
2. Move to the center of the square
3. Spin around in both directions
4. Return to where we started

Tuning your YetiBorg v2

As you may have noticed, the moves are not 100% perfect because the YetiBorg v2 is driving without looking where he is going! If the moves are very wrong you probably need to tune the amount of time he spends moving. Start by opening the script in an editor, such as nano: nano yeti2Sequence.py then move down until you find the movement settings:

# Movement settings (worked out from our YetiBorg on a smooth surface)
timeForward1m = 5.7   # Number of seconds needed to move about 1 meter
timeSpin360   = 4.8   # Number of seconds needed to make a full left...
testMode = False      # True to run the motion tests, False to run...

Change testMode to True, then save and exit. After that re-run the script to run in test mode. While in test mode the YetiBorg v2 will perform some simple moves one at a time:

1. Forward for 50 cm
2. Backward for 50 cm
3. Spin left 360°
4. Spin right 360°

If the movement is too long or too short you can correct it by changing the values in the script:

• Forward / backward too long → Make timeForward1m smaller
• Forward / backward too short → Make timeForward1m larger
• Left / right spinning too long → Make timeSpin360 smaller
• Left / right spinning too short → Make timeSpin360 larger

When all the movements are roughly correct change testMode back to False to get YetiBorg v2 to run the sequence again.

Programming a new sequence

The sequence of moves are all towards the bottom of the script:

### Our sequence of motion goes here ###

# Draw a 40cm square
for i in range(4):
    PerformDrive(+0.4)
    PerformSpin(+90)

# Move to the middle of the square
PerformSpin(+45)
distanceToOtherCorner = math.sqrt(0.4**2 + 0.4**2) # Pythagorean theorem
PerformDrive(distanceToOtherCorner / 2.0)
PerformSpin(-45)

# Spin each way inside the square
PerformSpin(+360)
PerformSpin(-360)

# Return to the starting point
PerformDrive(-0.2)
PerformSpin(+90)
PerformDrive(-0.2)
PerformSpin(-90)

There are two commands provided for moving the YetiBorg v2:

• PerformDrive takes a distance in meters to move. Positive values move forward, negative values move backward
• PerformSpin takes an angle in degrees to spin. Positive values spin right, negative values spin left

You can use any normal python code with these functions, such as loops or maths to decide how many times to do something or how far to travel. You can make awesome patterns using these moves so have fun and experiment away :)

Run at startup

Once your sequence is ready you can make YetiBorg v2 perform the sequence when he is powered on all by himself. Open /etc/rc.local to make an addition using: sudo nano /etc/rc.local Then add this line just above the exit 0 line: /home/pi/yetiborgv2/yeti2Sequence.py & Finally press CTRL+O, ENTER to save the file followed by CTRL+X to exit nano. Next time you power up the Raspberry Pi it should start the script for you :)

Full code listing - yeti2Sequence.py

#!/usr/bin/env python
# coding: Latin-1

# Simple example of a motor sequence script

# Import library functions we need
import ZeroBorg
import time
import math
import sys

# Setup the ZeroBorg
ZB = ZeroBorg.ZeroBorg()
#ZB.i2cAddress = 0x44                  # Uncomment and change the value if you have changed the board address
ZB.Init()
if not ZB.foundChip:
    boards = ZeroBorg.ScanForZeroBorg()
    if len(boards) == 0:
        print 'No ZeroBorg found, check you are attached :)'
    else:
        print 'No ZeroBorg at address %02X, but we did find boards:' % (ZB.i2cAddress)
        for board in boards:
            print '    %02X (%d)' % (board, board)
        print 'If you need to change the I²C address change the setup line so it is correct, e.g.'
        print 'ZB.i2cAddress = 0x%02X' % (boards[0])
    sys.exit()
#ZB.SetEpoIgnore(True)                 # Uncomment to disable EPO latch, needed if you do not have a switch / jumper
ZB.SetCommsFailsafe(False)             # Disable the communications failsafe
ZB.ResetEpo()

# Movement settings (worked out from our YetiBorg v2 on a smooth surface)
timeForward1m = 5.7                     # Number of seconds needed to move about 1 meter
timeSpin360   = 4.8                     # Number of seconds needed to make a full left / right spin
testMode = False                        # True to run the motion tests, False to run the normal sequence

# Power settings
voltageIn = 8.4                         # Total battery voltage to the ZeroBorg (change to 9V if using a non-rechargeable battery)
voltageOut = 6.0                        # Maximum motor voltage

# Setup the power limits
if voltageOut > voltageIn:
    maxPower = 1.0
else:
    maxPower = voltageOut / float(voltageIn)

# Function to perform a general movement
def PerformMove(driveLeft, driveRight, numSeconds):
    # Set the motors running
    ZB.SetMotor1(-driveRight * maxPower) # Rear right
    ZB.SetMotor2(-driveRight * maxPower) # Front right
    ZB.SetMotor3(-driveLeft  * maxPower) # Front left
    ZB.SetMotor4(-driveLeft  * maxPower) # Rear left
    # Wait for the time
    time.sleep(numSeconds)
    # Turn the motors off
    ZB.MotorsOff()

# Function to spin an angle in degrees
def PerformSpin(angle):
    if angle < 0.0:
        # Left turn
        driveLeft  = -1.0
        driveRight = +1.0
        angle *= -1
    else:
        # Right turn
        driveLeft  = +1.0
        driveRight = -1.0
    # Calculate the required time delay
    numSeconds = (angle / 360.0) * timeSpin360
    # Perform the motion
    PerformMove(driveLeft, driveRight, numSeconds)

# Function to drive a distance in meters
def PerformDrive(meters):
    if meters < 0.0:
        # Reverse drive
        driveLeft  = -1.0
        driveRight = -1.0
        meters *= -1
    else:
        # Forward drive
        driveLeft  = +1.0
        driveRight = +1.0
    # Calculate the required time delay
    numSeconds = meters * timeForward1m
    # Perform the motion
    PerformMove(driveLeft, driveRight, numSeconds)

# Run test mode if required
if testMode:
    # Show settings
    print 'Current settings are:'
    print '    timeForward1m = %f' % (timeForward1m)
    print '    timeSpin360 = %f' % (timeSpin360)
    # Check distance
    raw_input('Check distance, Press ENTER to start')
    print 'Drive forward 30cm'
    PerformDrive(+0.3)
    raw_input('Press ENTER to continue')
    print 'Drive reverse 30cm'
    PerformDrive(-0.3)
    # Check spinning
    raw_input('Check spinning, Press ENTER to continue')
    print 'Spinning left'
    PerformSpin(-360)
    raw_input('Press ENTER to continue')
    print 'Spinning Right'
    PerformSpin(+360)
    print 'Update the settings as needed, then test again or disable test mode'
    sys.exit(0)

### Our sequence of motion goes here ###

# Draw a 40cm square
for i in range(4):
    PerformDrive(+0.4)
    PerformSpin(+90)

# Move to the middle of the square
PerformSpin(+45)
distanceToOtherCorner = math.sqrt(0.4**2 + 0.4**2) # Pythagorean theorem
PerformDrive(distanceToOtherCorner / 2.0)
PerformSpin(-45)

# Spin each way inside the square
PerformSpin(+360)
PerformSpin(-360)

# Return to the starting point
PerformDrive(-0.2)
PerformSpin(+90)
PerformDrive(-0.2)
PerformSpin(-90)