Remote-controlled Mini Loader

Python code and building instructions for the LEGO MINDSTORMS Robot Inventor Other Fan Creations (51515).

Remote-controlled Mini Loader

Mini Loader controlled with LEGO Bluetooth Remote


This Mini Loader has four motors to allow it to drive, steer, lift, and dump. The program connects to the LEGO Bluetooth Remote and uses the remote’s buttons in several ways to implement a variety of control features.


Twist the controls on the remote to make the left side vertical with + on top, and the right side horizontal with + on the right.

Establish the connection between the hub and remote using these steps:

  1. Download the Pybricks program to the hub.
  2. If the program is running (display animating), press the hub button to stop it.
  3. Press the green center button on the Remote (light flashes white).
  4. Immediately press the Inventor hub button to run the program.
  5. If the connection is successful, both the remote and hub lights turn green.

The remote has two modes, which you toggle between using the green center button on the remote. The modes are indicated by both the remote and hub lights. Use Drive mode (green) to drive and steer, and Lift mode (Orange) to control the lift.

Drive Mode (Green light)

Use the left side buttons to control the drive direction and the right side buttons to steer. You can drive and steer at the same time, or just steer to pivot in place.

By holding down either of the two red buttons, you can reduce both the driving and steering speed for more precise positioning. You can do this either by holding a red button with one thumb (like a shift key) while using +/- controls with your other thumb, or with a single thumb, you can roll between pressing both Center and +/- at the same time (slow) or just +/- (fast).

Lift Mode (Orange Light)

Tap the three left side buttons to make the lift and scoop move together to three preset positions: Carrying High, Carrying Middle, or Ready Low.

Tap -/+ on the right side to dump/undump the scoop without moving the lift.

The red right center button runs a special feature to help position the mini loader to prepare to dump. Pressing and holding this button will make the robot drive straight forward until the distance sensor measures 5 cm (or until you release the button to cancel). The lights on the ultrasonic sensor are turned on when the robot is using them, so a fun side effect is that quickly tapping the right center button just flashes the sensor lights.


from pybricks.hubs import InventorHub
from pybricks.pupdevices import Motor, UltrasonicSensor, Remote
from pybricks.parameters import Button, Color, Direction, Port, Stop
from pybricks.robotics import DriveBase
from import wait, StopWatch

# Define objects that correspond to the design of the Mini Loader 
hub = InventorHub()
left_motor = Motor(Port.F, positive_direction=Direction.COUNTERCLOCKWISE)
right_motor = Motor(Port.E, positive_direction=Direction.CLOCKWISE)
drive_base = DriveBase(left_motor, right_motor, wheel_diameter=56, axle_track=80)
lift_motor = Motor(Port.D)
scoop_motor = Motor(Port.C)
eyes = UltrasonicSensor(Port.A)

# Motor speeds
DRIVE_SPEED = 150     # straight driving speed in mm/sec
TURN_RATE = 150       # turning speed in deg/sec
LIFT_SPEED = 200      # deg/sec
SCOOP_SPEED = 200     # deg/sec

# Preset lift and scoop positions (degrees relative to starting ready position)

# Connect to the remote (will stop the program if unsuccessful)
rc = Remote()

# Get the set of buttons on the remote that start out pressed 
pressed = rc.buttons.pressed()
was_pressed = pressed   # remembers which buttons were previously pressed

# Return True if the specified button is newly pressed (not held down)
def new_press(button):
    return (button in pressed) and not (button in was_pressed)

# This function controls the robot in drive mode
def drive_mode():
    # Pressing and holding either the left or right center button
    # reduces both the drive and steering speed.
    speed = DRIVE_SPEED
    steering = TURN_RATE    
    if (Button.LEFT in pressed) or (Button.RIGHT in pressed):
        speed *= 0.3
        steering *= 0.3    

    # Determine what speed and steering to use.
    # The left side controls drive direction, and the right side steers. 
    current_speed = 0
    current_steering = 0
    if (Button.LEFT_PLUS in pressed):
        current_speed += speed
    if (Button.LEFT_MINUS in pressed):
        current_speed -= speed
    if (Button.RIGHT_PLUS in pressed):
        current_steering += steering
    if (Button.RIGHT_MINUS in pressed):
        current_steering -= steering, current_steering)

# This function controls the robot in lift mode
def lift_mode():
    # The three left side buttons set the lift height (high, middle, or low)
    # and automatically adjust the scoop as appropriate.
    if new_press(Button.LEFT_PLUS):
        scoop_motor.run_target(SCOOP_SPEED, SCOOP_CARRY_POS, wait=False)
        lift_motor.run_target(LIFT_SPEED, LIFT_HIGH_POS)
    elif new_press(Button.LEFT):
        scoop_motor.run_target(SCOOP_SPEED, SCOOP_CARRY_POS, wait=False)
        lift_motor.run_target(LIFT_SPEED, LIFT_MIDDLE_POS)
    elif new_press(Button.LEFT_MINUS):
        scoop_motor.run_target(SCOOP_SPEED, SCOOP_READY_POS, wait=False)
        lift_motor.run_target(LIFT_SPEED, LIFT_LOW_POS)
    # Right side -/+ buttons dump/undump the scoop
    if new_press(Button.RIGHT_MINUS):
        scoop_motor.run_target(SCOOP_SPEED, SCOOP_DUMP_POS)
    if new_press(Button.RIGHT_PLUS):
        if lift_motor.angle() > LIFT_MIDDLE_POS / 2:    # can't carry if low
            scoop_motor.run_target(SCOOP_SPEED, SCOOP_CARRY_POS)

    # Holding Right Center drives straight forward until the distance sensor
    # is at 5 cm, or until the button is released.
    if new_press(Button.RIGHT):
        while (eyes.distance() > 50) and (Button.RIGHT in rc.buttons.pressed()):
  , 0)

# The remote has multiple modes, selected by the center button.
# This table lists the different mode functions and which color they show.
modes = (
    (drive_mode, Color.GREEN),
    (lift_mode, Color.ORANGE),
mode = 0    # index of current mode

# Set the mode to new_mode and update both the remote and hub status lights
def set_mode(new_mode):
    global mode
    mode = new_mode 
    color = modes[mode][1]

# Set the initial mode

# The main loop repeatedly tests the remote buttons and reacts
while True:
    # Update the set of buttons that are currently pressed,
    # and also remember which ones were pressed the last time we looked.
    was_pressed = pressed
    pressed = rc.buttons.pressed()

    # The green center button changes modes
    if new_press(Button.CENTER):
        set_mode((mode + 1) % len(modes))   # next mode and wrap around

    # Execute the current mode

This project was submitted by Dave Parker.