Basic Motor Torque Control Application

In this application, you will learn how to control the torque (current) of a brushed DC motor using the Torque Mode of the SMD Red module. You will input a torque value between -100 and 100, and observe the motor’s response. This control mode is particularly useful for applications that require force feedback, current-limited motion, or haptic interaction.

About Tools and Materials:

SMD Red (Purchase Here)

SMD USB Gateway (Purchase Here)

Arduino Gateway Module (Purchase Here)

BDC Motor (Purchase Here)

Step 1: Hardware & Software Overview

Project Key Components

1. SMD Red: Drives the DC motor and manages current control via internal PID loop.

2. BDC Motor: Converts electrical energy into mechanical torque.

Project Key Features

1. Real-time torque input via command line

2. Bidirectional torque control (±100)

3. Live current measurement feedback

4. PID-based torque regulation

Step 2: Assemble

Getting Started

Hardware Setup

• Connect the SMD to the PC or Arduino board using USB Gateway Module or Arduino Gateway Module.

• Connect the 100 RPM BDC Motor with Encoder to the motor ports of the SMD Red.

• Make sure that the SMD is powered and all connections are correct.

Project Wiring Diagram

Step 3: Run & Test

Run the Script

You will be prompted to enter a torque value in the range of -100 to 100. The motor will apply the specified current, and the system will print both the target and actual measured torque.

Codes

Python Code

from smd.red import *  # Import the SMD Red Python library
from serial.tools.list_ports import comports  # Used to detect available serial (COM) ports
from platform import system  # Used to identify the current operating system
import time  # For time delays

# Function to automatically detect the correct USB port where SMD Red is connected
def USB_Port():
    ports = list(comports())  # Get list of all serial ports
    usb_names = {
        "Windows": ["USB Serial Port"],
        "Linux": ["/dev/ttyUSB"],
        "Darwin": ["/dev/cu."]  # macOS serial devices typically start with /dev/cu.
    }
    os_name = system()
    for port, desc, _ in ports:
        # Return the first matching port based on platform-specific device names
        if any(name in port or name in desc for name in usb_names.get(os_name, [])):
            return port
    return None  # If no matching port is found, return None

# Main function that sets up and runs the torque control loop
def main():
    port = USB_Port()
    if not port:
        print("No port found.")  # Exit if no SMD Red is detected
        return

    master = Master(port)  # Create a Master object to communicate with the SMD Red
    motor_id = 1  # Set the motor ID (default is 1)

    # Attach the SMD Red module and configure it
    master.attach(Red(motor_id))  # Attach the motor
    master.set_shaft_cpr(motor_id, 6533)  # Set encoder resolution (not used in torque mode, but good practice)
    master.set_shaft_rpm(motor_id, 100)  # Set motor's nominal speed (not critical for torque mode)
    
    # Set torque control parameters (PID: P=3.0, I=0.1, D=0.0)
    master.set_control_parameters_torque(motor_id, 3.0, 0.1, 0.0)

    # Enable Torque mode
    master.set_operation_mode(motor_id, OperationMode.Torque)

    # Enable the motor torque output
    master.enable_torque(motor_id, True)

    # Loop to continuously read user input and set torque
    while True:
        try:
            # Read torque input from user
            current = float(input("Enter desired torque current (-100 to 100): "))
            
            # Send torque value to the motor
            master.set_torque(motor_id, current)

            # Read and print actual measured current from the motor
            measured = master.get_torque(motor_id)
            print(f"Set: {current:.2f}, Measured: {measured:.2f}\n")

            time.sleep(0.2)  # Small delay for stability
        except KeyboardInterrupt:
            # On Ctrl+C, safely disable torque and exit the loop
            master.enable_torque(motor_id, False)
            break

# Entry point of the script
if __name__ == "__main__":
    main()

Arduino Code