reactive_encoder.py

import time
from inventorhatmini import InventorHATMini, MOTOR_A, NUM_LEDS
from ioexpander.common import PID, NORMAL_DIR  # , REVERSED_DIR

"""
A demonstration of how a motor with an encoder can be used
as a programmable rotary encoder for user input, with
force-feedback for arbitrary detents and end stops.

Press "User" to exit the program.
"""

# Constants
GEAR_RATIO = 50                         # The gear ratio of the motor
DIRECTION = NORMAL_DIR                  # The direction to spin the motor in. NORMAL_DIR (0), REVERSED_DIR (1)
SPEED_SCALE = 5.4                       # The scaling to apply to the motor's speed to match its real-world speed

UPDATES = 100                           # How many times to update the motor per second
UPDATE_RATE = 1 / UPDATES

DETENT_SIZE = 20                        # The size (in degrees) of each detent region
MIN_DETENT = 0                          # The minimum detent that can be counted to
MAX_DETENT = NUM_LEDS - 1               # The maximum detent that can be counted to
MAX_DRIVE_PERCENT = 0.5                 # The maximum drive force (as a percent) to apply when crossing detents

BRIGHTNESS = 0.4                        # The brightness of the RGB LED
USE_LEDS = True                         # Whether to show the encoder position on the LEDs (requires code to run with sudo)

# PID values
POS_KP = 0.14                           # Position proportional (P) gain
POS_KI = 0.0                            # Position integral (I) gain
POS_KD = 0.0022                         # Position derivative (D) gain


# Create a new InventorHATMini and get a motor and encoder from it
board = InventorHATMini(motor_gear_ratio=GEAR_RATIO, init_leds=USE_LEDS)
m = board.motors[MOTOR_A]
enc = board.encoders[MOTOR_A]

# Set the motor's speed scale
m.speed_scale(SPEED_SCALE)

# Set the motor and encoder's direction
m.direction(DIRECTION)
enc.direction(DIRECTION)

# Create PID object for position control
pos_pid = PID(POS_KP, POS_KI, POS_KD, UPDATE_RATE)

# Enable the motor to get started
m.enable()


current_detent = 0


# Function to deal with a detent change
def detent_change(change):
    global current_detent

    # Update the current detent and pid setpoint
    current_detent += change
    pos_pid.setpoint = (current_detent * DETENT_SIZE)     # Update the motor position setpoint
    print("Detent =", current_detent)

    # Convert the current detent to a hue and set the onboard led to it
    hue = (current_detent - MIN_DETENT) / (MAX_DETENT - MIN_DETENT)
    for i in range(NUM_LEDS):
        if current_detent == i:
            board.leds.set_hsv(i, hue, 1.0, BRIGHTNESS)
        else:
            board.leds.set_hsv(i, hue, 1.0, 0.0)


# Call the function once to set the setpoint and print the value
detent_change(0)


# Sleep until a specific time in the future. Use this instead of time.sleep() to correct for
# inconsistent timings when dealing with complex operations or external communication
def sleep_until(end_time):
    time_to_sleep = end_time - time.monotonic()
    if time_to_sleep > 0.0:
        time.sleep(time_to_sleep)


# Continually move the motor until the user button is pressed
while not board.switch_pressed():

    # Record the start time of this loop
    start_time = time.monotonic()

    # Capture the state of the encoder
    capture = enc.capture()

    # Get the current detent's centre angle
    detent_angle = (current_detent * DETENT_SIZE)

    # Is the current angle above the region of this detent?
    if capture.degrees > detent_angle + (DETENT_SIZE / 2):
        # Is there another detent we can move to?
        if current_detent < MAX_DETENT:
            detent_change(1)    # Increment to the next detent

    # Is the current angle below the region of this detent?
    elif capture.degrees < detent_angle - (DETENT_SIZE / 2):
        # Is there another detent we can move to?
        if current_detent > MIN_DETENT:
            detent_change(-1)    # Decrement to the next detent

    # Calculate the velocity to move the motor closer to the position setpoint
    vel = pos_pid.calculate(capture.degrees, capture.degrees_per_second)

    # If the current angle is within the detent range, limit the max vel
    # (aka feedback force) that the user will feel when turning the motor between detents
    if (capture.degrees >= MIN_DETENT * DETENT_SIZE) and (capture.degrees <= MAX_DETENT * DETENT_SIZE):
        vel = max(min(vel, MAX_DRIVE_PERCENT), -MAX_DRIVE_PERCENT)

    # Set the new motor driving speed
    m.speed(vel)

    # Sleep until the next update, accounting for how long the above operations took to perform
    sleep_until(start_time + UPDATE_RATE)

# Disable the motor
m.disable()

# Turn off the LEDs
board.leds.clear()