Overview The ControlModule class provides a unified interface for controlling all motors on the VEX IQ robotic arm. It manages four motors (base, shoulder, elbow, gripper) with methods for rotation control, current monitoring, and emergency stops.
Source: ~/workspace/source/arm_controller/src/main.py:219Constructor __init__()Initializes all motor hardware components with their port configurations.
control = ControlModule()
Initialized Motors: Rotates the entire arm base for horizontal scanning Port: Ports.PORT1Reversed: True (motor direction inverted)
Controls shoulder joint for vertical arm movement Port: Ports.PORT2Reversed: True
Controls elbow joint for reach extension Port: Ports.PORT3Reversed: True
Opens and closes gripper for object manipulation Port: Ports.PORT4Reversed: True
All motors are configured with reversed=True to standardize positive rotation direction across the arm.
Source: main.py:220Motor Rotation Methods rotate_motor_forward(motor: Motor, speed: int)Rotates specified motor in the forward direction at given speed.
# Rotate base motor for scanning control.rotate_motor_forward(control.base_motor, 20 ) # Raise shoulder control.rotate_motor_forward(control.shoulder_motor, 60 )
Motor object to rotate. Use one of:
control.base_motorcontrol.shoulder_motorcontrol.elbow_motorcontrol.gripper_motor Rotation speed in RPM (Revolutions Per Minute)
Range: 1-100 RPM (typical)Low speeds (1-30): Precise control, scanningMedium speeds (30-70): Normal operationHigh speeds (70-100): Rapid movement Motor continues rotating until stopped or reversed. Motor will run indefinitely at specified speed. Always call general_stop() or monitor safety conditions.
Source: main.py:227rotate_motor_reverse(motor: Motor, speed: int)Rotates specified motor in the reverse direction at given speed.
# Lower shoulder control.rotate_motor_reverse(control.shoulder_motor, 10 ) # Open gripper control.rotate_motor_reverse(control.gripper_motor, 20 )
Motor object to rotate (same as forward method)
Rotation speed in RPM (same range as forward)
Typical Reverse Operations:
Base: Counter-clockwise rotationShoulder: Lowering armElbow: Retracting armGripper: Opening claws
Source: main.py:230Motor Monitoring get_current_motor(motor: Motor)Reads the electrical current draw of the specified motor.
current = control.get_current_motor(control.gripper_motor) if current > 0.3 : print ( "Gripper has gripped object!" ) control.general_stop()
Current draw in amperes (A)
Idle: ~0.05ALight load: 0.1-0.2AHeavy load: 0.3-0.5AStall: 0.6A+ Use Cases: Show Gripper Object Detection
Monitor gripper current to detect when object is gripped: control.rotate_motor_forward(control.gripper_motor, 20 ) while control.get_current_motor(control.gripper_motor) < 0.3 : time.sleep( 0.05 ) control.general_stop() print ( "Object secured" )
Detect mechanical obstruction or end-of-travel: control.rotate_motor_forward(control.shoulder_motor, 40 ) current = control.get_current_motor(control.shoulder_motor) if current > 0.5 : control.general_stop() print ( "Mechanical limit reached" )
Estimate object weight or resistance: baseline = control.get_current_motor(control.elbow_motor) control.rotate_motor_forward(control.elbow_motor, 30 ) time.sleep( 0.5 ) loaded = control.get_current_motor(control.elbow_motor) load = loaded - baseline print ( f "Additional load: { load :.2f} A" )
Source: main.py:234Emergency Stop general_stop()Immediately stops all motors on the robotic arm.
# Emergency stop control.general_stop()
Critical safety method. Called in emergency situations, errors, or task completion.
Stopped Motors:
Base motor
Shoulder motor
Elbow motor
Gripper motor
Behavior:
Stops motors immediately (not gradual deceleration)
Motors enter brake mode (hold position)
No motor movement until new rotation command
Common Triggers:
Bumper sensor activation
Exception handling
Scan completion
Safety check failure
User stop command
Example Safety Pattern: try : # Perform operation control.rotate_motor_forward(control.base_motor, 20 ) # ... operation code ... except Exception as e: print ( f "Error: { e } " ) control.general_stop() # Emergency stop finally : control.general_stop() # Ensure stopped
Source: main.py:238Hardware Verification check_motors()Verifies that all motors are properly installed and responsive.
if control.check_motors(): print ( "All motors operational" ) else : print ( "ERROR: Motor installation issue" )
Returns True if all motors installed, False if any motor missing or unresponsive
Checked Motors:
Base motor (Port 1)
Shoulder motor (Port 2)
Elbow motor (Port 3)
Gripper motor (Port 4)
Use Before:
Starting any motor operations
System initialization
After physical maintenance
Source: main.py:244Port Configuration Summary Motor Port Direction Primary Function Base PORT1 Reversed Horizontal rotation for scanning Shoulder PORT2 Reversed Vertical arm positioning Elbow PORT3 Reversed Arm reach extension Gripper PORT4 Reversed Object grasping
Motor Speed Guidelines Base Motor (Scanning) # Slow scan (high precision) control.rotate_motor_forward(control.base_motor, 10 ) # Normal scan control.rotate_motor_forward(control.base_motor, 20 ) # Fast scan (lower precision) control.rotate_motor_forward(control.base_motor, 40 )
Recommended: 15-25 RPM for object detectionShoulder Motor (Safety Critical) # Safety check (with bumper monitoring) control.rotate_motor_forward(control.shoulder_motor, 60 ) # Slow recovery after bumper hit control.rotate_motor_reverse(control.shoulder_motor, 10 )
Recommended:
Normal: 40-60 RPM
Recovery: 5-15 RPM
Gripper Motor (Precision) # Close gripper with current monitoring control.rotate_motor_forward(control.gripper_motor, 20 ) while control.get_current_motor(control.gripper_motor) < 0.3 : time.sleep( 0.05 ) control.general_stop()
Recommended: 15-25 RPM to avoid crushing objectsComplete Usage Examples Initialization and Hardware Check from vex import * import time # Initialize control module control = ControlModule() # Verify all motors installed if not control.check_motors(): print ( "ERROR: Motors not installed properly" ) raise Exception ( "Hardware check failed" ) print ( "All motors operational" )
Environmental Scan def perform_scan ( control , sensor ): """Rotate base 360° for scanning""" # Start rotation control.rotate_motor_forward(control.base_motor, 20 ) start_angle = sensor.get_angle() accumulated_rotation = 0 last_angle = start_angle while accumulated_rotation < 360 : current_angle = sensor.get_angle() # Calculate delta with wraparound delta = current_angle - last_angle if delta > 180 : delta -= 360 elif delta < - 180 : delta += 360 accumulated_rotation += abs (delta) last_angle = current_angle time.sleep( 0.05 ) # 20Hz update # Stop when complete control.general_stop() print ( "Scan complete" )
Safety-Monitored Shoulder Movement def raise_shoulder_safely ( control , sensor ): """Raise shoulder with bumper monitoring""" control.rotate_motor_forward(control.shoulder_motor, 60 ) while True : # Check bumper every cycle if sensor.is_bumper_pressed(): # Emergency stop control.general_stop() sensor.set_color(( 255 , 0 , 0 )) # Red error # Reverse briefly control.rotate_motor_reverse(control.shoulder_motor, 10 ) time.sleep( 2 ) control.general_stop() print ( "Bumper collision detected" ) return False time.sleep( 0.02 ) # 50Hz safety check return True
Current-Monitored Gripper Control def close_gripper ( control ): """Close gripper until object gripped""" control.rotate_motor_forward(control.gripper_motor, 20 ) max_time = 5 # 5 second timeout start_time = time.time() while time.time() - start_time < max_time: current = control.get_current_motor(control.gripper_motor) if current > 0.3 : control.general_stop() print ( "Object gripped successfully" ) return True time.sleep( 0.05 ) # Timeout - no object control.general_stop() print ( "No object detected in gripper" ) return False def open_gripper ( control ): """Open gripper fully""" control.rotate_motor_reverse(control.gripper_motor, 20 ) time.sleep( 1.5 ) # Time to fully open control.general_stop()
Coordinated Multi-Motor Movement def position_arm ( control , base_angle , shoulder_angle , elbow_angle ): """Move multiple motors to target positions""" try : # Start all motors control.rotate_motor_forward(control.base_motor, 30 ) control.rotate_motor_forward(control.shoulder_motor, 40 ) control.rotate_motor_forward(control.elbow_motor, 30 ) # Wait for positioning (simplified) time.sleep( 2 ) # Stop all control.general_stop() print ( "Positioning complete" ) except Exception as e: print ( f "Error during positioning: { e } " ) control.general_stop() # Emergency stop raise
Safety Integration The ControlModule is used by SafetyModule for critical safety checks:
# From SafetyModule (main.py:254) class SafetyModule : def check_shoulder_safety ( self ) -> bool : if self .sensor_module.is_bumper_pressed(): self .control_module.general_stop() # Emergency stop self .control_module.rotate_motor_reverse( self .control_module.shoulder_motor, 10 ) time.sleep( 2 ) self .control_module.general_stop() return True return False def check_gripper_safety ( self ) -> bool : gripper_current = self .control_module.get_current_motor( self .control_module.gripper_motor ) self .control_module.rotate_motor_forward( self .control_module.gripper_motor, 20 ) if gripper_current > 0.3 : self .control_module.general_stop() return True return False