Added example library

examples/Robot.py

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+# Simple two DC motor robot class.  Exposes a simple LOGO turtle-like API for
+# moving a robot forward, backward, and turning.  See RobotTest.py for an
+# example of using this class.
+# Author2: Tony DiCola, Chris Anderson
+# License: MIT License https://opensource.org/licenses/MIT
+
+
+# This assumes the Left motor is on Motor 1 and the Right motor is on Motor 2
+
+
+
+import time
+import atexit
+from adafruit_motorkit import MotorKit
+
+kit = MotorKit()
+
+class Robot(object):
+    def __init__(self, left_trim=0, right_trim=0, stop_at_exit=True):
+        """Create an instance of the robot.  Can specify the following optional
+        parameter
+         - left_trim: Amount to offset the speed of the left motor, can be positive
+                      or negative and use useful for matching the speed of both
+                      motors.  Default is 0.
+         - right_trim: Amount to offset the speed of the right motor (see above).
+         - stop_at_exit: Boolean to indicate if the motors should stop on program
+                         exit.  Default is True (highly recommended to keep this
+                         value to prevent damage to the bot on program crash!).
+        """
+
+        self._left_trim = left_trim
+        self._right_trim = right_trim
+        if stop_at_exit:
+            atexit.register(self.stop)
+
+    def _left_speed(self, speed):
+        """Set the speed of the left motor, taking into account its trim offset.
+        """
+        assert -1 <= speed <= 1, 'Speed must be a value between -1 to 1 inclusive!'
+        speed += self._left_trim
+        speed = max(-1, min(1, speed))  # Constrain speed to 0-255 after trimming.
+        kit.motor1.throttle = speed
+
+    def _right_speed(self, speed):
+        """Set the speed of the right motor, taking into account its trim offset.
+        """
+        assert -1 <= speed <= 1, 'Speed must be a value between -1 to 1 inclusive!'
+        speed += self._right_trim
+        speed = max(-1, min(1, speed))  # Constrain speed to 0-255 after trimming.
+        kit.motor2.throttle = speed
+
+    @staticmethod
+    def stop():
+        """Stop all movement."""
+        kit.motor1.throttle = 0
+        kit.motor2.throttle = 0
+
+    def forward(self, speed, seconds=None):
+        """Move forward at the specified speed (0-255).  Will start moving
+        forward and return unless a seconds value is specified, in which
+        case the robot will move forward for that amount of time and then stop.
+        """
+        # Set motor speed and move both forward.
+        self._left_speed(speed)
+        self._right_speed(speed)
+        # If an amount of time is specified, move for that time and then stop.
+        if seconds is not None:
+            time.sleep(seconds)
+            self.stop()
+
+    def steer(self, speed, direction):
+        # Move forward at the specified speed (0- 1).  Direction is +- 1.
+        # Full left is -1, Full right is +1
+        if (speed + direction/2) > 1:
+            speed = speed - direction/2 # calibrate so total motor output never goes above 1
+        left = speed + direction/2
+        right = speed - direction/2
+        self._left_speed(left)
+        self._right_speed(right)
+
+    def backward(self, speed, seconds=None):
+        """Move backward at the specified speed (0-255).  Will start moving
+        backward and return unless a seconds value is specified, in which
+        case the robot will move backward for that amount of time and then stop.
+        """
+        # Set motor speed and move both backward.
+        self._left_speed(-1*speed)
+        self._right_speed(-1*speed)
+        # If an amount of time is specified, move for that time and then stop.
+        if seconds is not None:
+            time.sleep(seconds)
+            self.stop()
+
+
+    def right(self, speed, seconds=None):
+        """Spin to the right at the specified speed.  Will start spinning and
+        return unless a seconds value is specified, in which case the robot will
+        spin for that amount of time and then stop.
+        """
+        # Set motor speed and move both forward.
+        self._left_speed(speed)
+        self._right_speed(0)
+        # If an amount of time is specified, move for that time and then stop.
+        if seconds is not None:
+            time.sleep(seconds)
+            self.stop()
+
+    def left(self, speed, seconds=None):
+        """Spin to the left at the specified speed.  Will start spinning and
+        return unless a seconds value is specified, in which case the robot will
+        spin for that amount of time and then stop.
+        """
+        # Set motor speed and move both forward.
+        self._left_speed(0)
+        self._right_speed(speed)
+        # If an amount of time is specified, move for that time and then stop.
+        if seconds is not None:
+            time.sleep(seconds)
+            self.stop()

examples/RobotTest.py

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+# Simple two DC motor robot class usage example.
+# Author: Tony DiCola, Chris Anderron
+# License: MIT License https://opensource.org/licenses/MIT
+import time
+
+# Import the Robot.py file (must be in the same directory as this file!).
+import Robot
+
+
+# Set the trim offset for each motor (left and right).  This is a value that
+# will offset the speed of movement of each motor in order to make them both
+# move at the same desired speed.  Because there's no feedback the robot doesn't
+# know how fast each motor is spinning and the robot can pull to a side if one
+# motor spins faster than the other motor.  To determine the trim values move the
+# robot forward slowly (around 100 speed) and watch if it veers to the left or
+# right.  If it veers left then the _right_ motor is spinning faster so try
+# setting RIGHT_TRIM to a small negative value, like -0.05, to slow down the right
+# motor.  Likewise if it veers right then adjust the _left_ motor trim to a small
+# negative value.  Increase or decrease the trim value until the bot moves
+# straight forward/backward.
+LEFT_TRIM   = 0
+RIGHT_TRIM  = 0
+
+
+# Create an instance of the robot with the specified trim values.
+
+robot = Robot.Robot(left_trim=LEFT_TRIM, right_trim=RIGHT_TRIM)
+
+# Now move the robot around!
+# Each call below takes two parameters:
+#  - speed: The speed of the movement, a value from -1.0 to +1.0.  The higher the value
+#           the faster the movement.  You need to start with a value around 0.10
+#           to get enough torque to move the robot.
+#  - time (seconds):  Amount of time to perform the movement.  After moving for
+#                     this amount of seconds the robot will stop.  This parameter
+#                     is optional and if not specified the robot will start moving
+#                     forever.
+
+robot.left(0.5,1)
+robot.right(0.5,1)
+robot.steer(0.5,0.2)
+time.sleep(3)
+robot.stop()      # Stop the robot from moving.
+
+
+# That's it!  Note that on exit the robot will automatically stop moving.