Tutorial 2.2: Motors and Gears

Time: ~10 minutes Prerequisites: Tutorial 2.1: Brain and Controller

---

The V5 Smart Motor

The V5 Smart Motor is the most important component of your robot. It converts electrical power into rotational motion.

flowchart TB
    subgraph MOTOR["V5 SMART MOTOR"]
        direction TB
        subgraph CONNECTIONS["Connections"]
            direction LR
            PORT["PORT<br/>Smart cable connects here"]
            SHAFT["OUTPUT SHAFT<br/>Rotates"]
        end
        CARTRIDGE["GEAR CARTRIDGE SLOT<br/>(swap for different speeds/torque)"]
        subgraph INTERNAL["Internal Sensors"]
            direction LR
            ENC["Encoder<br/>(rotation sensor)"]
            TEMP["Temperature<br/>sensor"]
            CURR["Current<br/>sensor"]
        end
    end

Smart Features

Unlike simple motors, V5 Smart Motors have built-in sensors:

Sensor	What It Measures	Why It's Useful
Encoder	Rotation count	Know how far you've traveled
Temperature	Motor heat	Prevent overheating
Current	Power usage	Detect stalls/resistance
Velocity	Speed	Accurate speed control

Motor Configuration in Code

Let's look at src/robot_config.py:

# Left side motors (not reversed - standard mounting)
left_motor_front = Motor(Ports.PORT1, GearSetting.RATIO_18_1, False)
left_motor_back = Motor(Ports.PORT2, GearSetting.RATIO_18_1, False)

# Right side motors (reversed - mirror mounting spins opposite)
right_motor_front = Motor(Ports.PORT3, GearSetting.RATIO_18_1, True)
right_motor_back = Motor(Ports.PORT4, GearSetting.RATIO_18_1, True)

The Motor() Constructor

Motor(port, gear_setting, reversed)

Parameter	What It Means	Your Values
port	Which port on Brain	PORT1, PORT2, PORT3, PORT4
gear_setting	Cartridge type	RATIO_18_1 (green)
reversed	Spin direction	False (left), True (right)

Why Are Right Motors Reversed?

This is one of the most common questions! Look at how motors are mounted:

    TOP VIEW OF ROBOT:

         FRONT
           ↑
    ┌─────────────┐
    │             │
    │  LF     RF  │
    │  [→]   [←]  │  ← Motors face OUTWARD
    │             │
    │  LB     RB  │
    │  [→]   [←]  │
    │             │
    └─────────────┘

    Left motors:  Clockwise = Forward
    Right motors: Clockwise = BACKWARD (opposite!)

Solution: Tell the code to reverse right motors:

# Left: clockwise = forward (normal)
left_motor_front = Motor(Ports.PORT1, GearSetting.RATIO_18_1, False)

# Right: clockwise = backward, so REVERSE it!
right_motor_front = Motor(Ports.PORT3, GearSetting.RATIO_18_1, True)

Now when you tell both motors to spin "forward," they actually move the robot forward!

Motor Groups

Individual motors are useful, but for a drivetrain, we want to control multiple motors together:

# Group left motors together
left_motors = MotorGroup(left_motor_front, left_motor_back)

# Group right motors together
right_motors = MotorGroup(right_motor_front, right_motor_back)

Why Use Motor Groups?

# WITHOUT MotorGroup (tedious):
left_motor_front.spin(FORWARD, 50, PERCENT)
left_motor_back.spin(FORWARD, 50, PERCENT)

# WITH MotorGroup (simple):
left_motors.spin(FORWARD, 50, PERCENT)

One command controls both motors at once!

Common Motor Methods

Setting Velocity

# Set speed (doesn't start spinning yet)
motor.set_velocity(50, PERCENT)   # 50% of max speed

# Different units:
motor.set_velocity(200, RPM)      # 200 rotations per minute
motor.set_velocity(100, DPS)      # 100 degrees per second

Spinning the Motor

# Start spinning
motor.spin(FORWARD)               # Spin forward at set velocity
motor.spin(REVERSE)               # Spin backward

# Spin with specific velocity
motor.spin(FORWARD, 75, PERCENT)  # 75% speed forward

Stopping the Motor

motor.stop()                      # Stop with default mode

# Stop modes:
motor.set_stopping(COAST)         # Free-spin to stop
motor.set_stopping(BRAKE)         # Active braking
motor.set_stopping(HOLD)          # Hold position firmly

    COAST                BRAKE                HOLD

    ⟳ → ⟳ → ⟳ → stop     ⟳ → ⟳ → X           ⟳ → X (locked!)
    Slowly coasts        Quick stop           Resists movement

Reading Motor Values

motor.velocity(PERCENT)           # Current speed
motor.position(DEGREES)           # Total rotation in degrees
motor.temperature(FAHRENHEIT)     # Motor temperature
motor.current()                   # Current power draw

The DriveTrain Class

For easier autonomous movement, we wrap everything in a DriveTrain:

drivetrain = DriveTrain(
    left_motors,           # Left MotorGroup
    right_motors,          # Right MotorGroup
    WHEEL_TRAVEL_MM,       # Wheel circumference (319.19mm)
    TRACK_WIDTH_MM,        # Distance between wheels (295mm)
    WHEEL_BASE_MM,         # Front-to-back distance (200mm)
    MM,                    # Units
    EXTERNAL_GEAR_RATIO    # External gearing (1 = direct)
)

DriveTrain Methods

# Autonomous movements
drivetrain.drive_for(FORWARD, 500, MM)     # Drive 500mm forward
drivetrain.turn_for(RIGHT, 90, DEGREES)    # Turn 90° right

# Speed settings
drivetrain.set_drive_velocity(50, PERCENT)  # Set drive speed
drivetrain.set_turn_velocity(30, PERCENT)   # Set turn speed

# Stopping mode
drivetrain.set_stopping(BRAKE)

---

Motor Wiring Diagram

Here's how your robot is wired:

    V5 BRAIN PORTS:

    [1]──────┐     ┌──────[3]
    Left     │     │     Right
    Front    │     │     Front
             │     │     (reversed)
    [2]──────┤     ├──────[4]
    Left     │     │     Right
    Back     │     │     Back
             │     │     (reversed)
             ↓     ↓

         LEFT SIDE    RIGHT SIDE

         [LF] [LB]    [RF] [RB]
           ↓   ↓        ↓   ↓
         +--------+  +--------+
         |        |  |        |
         +--[O][O]+  +[O][O]--+

              ROBOT (top view)

---

Summary

Concept	Purpose	Code
Motor	Single motor object	Motor(port, gear, reversed)
Reversed	Flip direction	True for right side motors
MotorGroup	Control multiple	MotorGroup(motor1, motor2)
DriveTrain	High-level driving	drivetrain.drive_for()
spin()	Start motor	motor.spin(FORWARD)
stop()	Stop motor	motor.stop()

---

Exercise: Add a Fifth Motor

Goal: Add an intake motor to robot_config.py

Imagine you're adding a motor on Port 5 for an intake mechanism: - It should spin at high speed (use BLUE cartridge) - It doesn't need to be reversed

Write the code:

# Add this line to robot_config.py:
intake_motor = Motor(_____, GearSetting._____, _____)

Bonus: How would you make it spin forward when button R1 is pressed?

---

Answers

intake_motor = Motor(Ports.PORT5, GearSetting.RATIO_6_1, False)

Bonus - Button control:

# In driver_control.py, inside the while loop:
if controller.buttonR1.pressing():
    intake_motor.spin(FORWARD, 100, PERCENT)
else:
    intake_motor.stop()

---

← Previous: Brain and Controller | Next: Sensors Overview → | Review Q&A