One Motor
=========

This example :ref:`code <code1motor>` shows how to precisely apply a time-based
excitation (in this case a sine wave) to a single motor. Keeping track of the
current execution time is the key to achieving that. The motor speed is
calculated as the derivative of the tacho angular position *output*.

.. image:: ../../images/Motor-Example-1A.png
.. image:: ../../images/Motor-Example-1B.png

.. _code1motor:

.. code-block:: python

    """ onemotor.py 

    Run one motor with a sinusoidal speed input.

    Setup:
        Connect one large motor to port 'A'

    """
    # Importing modules and classes
    import time
    import numpy as np
    from pyev3.utils import plot_line
    from pyev3.brick import LegoEV3
    from pyev3.devices import Motor

    # Defining parameters (for one motor)
    T = 2  # Period of sine wave (s)
    u0 = 80  # Motor speed amplitude (%)
    tstop = 2  # Sine wave duration (s)

    # Pre-allocating output arrays
    t = []
    theta = []

    # Creating LEGO EV3 objects
    ev3 = LegoEV3()
    motor = Motor(ev3, port='A')

    # Initializing motor
    motor.outputmode = 'speed'
    motor.output = 0
    motor.reset_angle()
    motor.start()

    # Initializing current time stamp and starting clock
    tcurr = 0
    tstart = time.perf_counter()
    # Running motor sine wave output
    while tcurr <= tstop:
        # Getting current time (s)
        tcurr = time.perf_counter() - tstart
        # Assigning current motor sinusoidal
        # output using the current time stamp
        motor.output = u0 * np.sin((2*np.pi/T) * tcurr)
        # Updating output arrays
        t.append(tcurr)
        theta.append(motor.angle)
    # Stopping motor and closing brick connection
    motor.stop()
    ev3.close()

    # Calculating motor angular velocity (rad/s)
    w = 2*np.pi/360 * np.gradient(theta, t)

    # Plotting results 
    plot_line([t], [theta], yname=['Angular Position (deg.)'], marker=True)
    plot_line([t], [w], yname=['Angular velocity (rad/s)'], marker=True)