mBot Kit Components

Components

• Complete parts list is included in the mBot kit.

Electrical Components

• Mainboard mCore is the primary programmable controller, connecting and managing all components.
• Ultrasonic Sensor measures distance using sound waves.
• Line-follower Sensor detects line contrast for black or white tracks.
• Motor (2) drives the mBot's wheels for movement.
• RJ25 Cable (2) connects sensors and modules to the mCore.
• USB Cable is for uploading programs and charging the mBot.
• Infrared Remote Controller allows wireless control.
• AA Battery Holder powers the mBot with AA batteries.

Mechanical Components

• Chassis provides the frame which holds all components.
• Mini Wheel stabilizes the robot with a small, free-rolling design.
• Wheel (2) are the main wheels that connects to the motors for movement.
• Screwdriver assembles and disassembles mBot parts.
• M4*25mm Brass Stud (4) are used as brass spacers to mount components.
• M3*25mm Screw (6) fastens parts together.
• M4*8mm Screw (15) are for general assembly purposes.
• M2.2*9mm Self-drilling Screw (4) mounts motors or plastic parts.
• M3 Nut (8) secures M3 screws in place.
• Line-follower Map is a pre-printed track to test the line-following function.
• Velcro sticker pad (2) helps attach components.
• Mini Screwdriver is a small tool to do fine adjustments.

Movement

• mBot utilizes two motors connected to M1 and M2 ports on the mCore board.
• The left motor connects to M1, while the right motor connects to M2.
• Incorrect motor connections invert movements if motor values are set to 255.
• Setting both motors to 255 is the fastest forward speed.
• Setting them both to -255 is the fastest backward speed.
• Setting them both to 0 makes the robot stop.

Movement Pseudocode

• Go Forward: set M1 speed to 255, set M2 speed to 255.
• Go Backward: set M1 speed to -255, set M2 speed to -255.
• Stop: set M1 speed to 0, set M2 speed to 0.
• Turn Left: set M1 speed to 0, set M2 speed to 255, invert logic to turn right.
• Rotate Left: set M1 speed to -255, set M2 speed to 255.
• Rotate Right: set M1 speed to 255, set M2 speed to -255.
• Curve Left: set M1 speed to 100, set M2 speed to 200.
• Curve Right: set M1 speed to 200, set M2 speed to 100.
• Add a delay after setting motor speeds and then set motors to 0 with a short delay (0.1 seconds) for consistent results.

Light Sensor Applications

• The light sensor is integrated into the mCore board and is not connected through motor or sensor ports.
• Measures light brightness from 0 (minimum) to 1023 (maximum).
• Maximum motor speed is 255.
• Brightness to speed mapping: speed = light / 4
• Allows the robot to move faster in brighter environments and slower in darker ones.

Ultrasonic Sensor

• The ultrasonic sensor connects to port 3 on the mCore board using an RJ25 cable.
• The sensor measures distances from 3 cm to 400 cm, in whole number values.
• Values below 3 cm distances are unreliable due to the sensor's physical placement on the chassis.

Obstacle Avoidance

• Ultrasonic sensor's primary function is obstacle avoidance.
• Pressing the button on the mCore board activates a pre-developed obstacle avoidance mode.
• Two green LEDs light up on the mCore board when active.

Basic Obstacle Avoidance Version

• The robot moves forward if the ultrasonic sensor detects a distance greater than a defined threshold (10 cm to 20 cm).
• It turns left or right briefly if the distance drops below the threshold.

Basic Obstacle Avoidance Pseudocode

• Repeat forever: move forward; wait until distance is less than 15; turn left or right 90 degrees; delay.

Advanced Obstacle Avoidance Version

• Checks left and right of robot for a clear path.
• If its a dead end the robot turns all the way back.
• Every time the robot faces an obstacle it checks in three directions: front, left, and right, or front, right, left.
• The robot picks one of the two approaches randomly, or if all three directions are blocked, it then turns around and goes back.

Advanced Obstacle Avoidance Pseudocode

• The code placed in the "else" statement is symmetrical to the first half.
• If rotation to the left 90 degrees, then right 180 degrees, then right 90 degrees, the robot instead will rotate right 90 degrees, then left 180 degrees, then left 90 degrees every time the robot is facing a wall or obstacle.

Factors Affecting Rotation

• Combined values of x and y result in rotation.
• Battery type, battery charge level, ground surface, dirt on wheels, and improperly fixed motors/wheels can influence the achieved angle.
• Developing the program in a computer system, installing it on the mCore board via USB, and adjusting parameters like x and y can remove runtime inconsistencies.

Line-Follower Sensor

• The line-follower sensor mounts under the front of the mBot.
• Connects to port 2 on the mCore board with an RJ25 cable.
• It has two detectors: left and right, and is designed to follow a black line on a white surface.
• Pressing the mCore button twice activates the pre-developed black line following mode.
• Two blue LEDs light up when active and obstacle avoidance is active.
• The logic can be inverted to follow a white line on a black surface.
• Returns four values:
  • 0: Both sensors see black
  • 1: Left sensor sees black, right sees white
  • 2: Left sensor sees white, right sees black
  • 3: Both sensors see white

Black Line Following Pseudocode

• Initiate lastCurve = 0
• Loop (forever)
• Read sensor value from line
• If the sensor detects 0 (black) then move forward
• Else if the sensor detects one (left)
  • Curve left
  • Then set the last curve to the left, else if the sensor detects two (right)
    • Curve right
    • Then set the last curve right - Else if the censor detects three go backwards.

Line Following Logic

• In sharper turns the robot may exit the line.
• It is essential to come up with a technique for the robot to follow the black line again.
• Make the mBot turn instead of curving in the same direction it was curving last until it can find the line.
• To follow a white line, invert the logic: move forward when the value is 3, and adjust accordingly.