Basic Motor Position Control Application
In this application, you will learn how to control a DC motor’s exact position in degrees using the Position Mode of the SMD Red module. You will enter a target angle between 0
and 360
, and the motor will rotate precisely to that point using encoder feedback.
About Tools and Materials:
SMD USB Gateway (Purchase Here)
Arduino Gateway Module (Purchase Here)
Step 1: Hardware & Software Overview
Project Key Components
SMD Red: Controls the brushed DC motor and reads encoder feedback for accurate position control.
BDC Motor: Converts electrical energy to mechanical rotation and provides position feedback via encoder signals.
Project Key Features
Precise angle-based control: Move the motor shaft to an exact angle between 0° and 360°.
Real-time encoder feedback: Monitor actual shaft position with high-resolution encoder data.
Tunable PID position control: Customize responsiveness and stability using:
set_control_parameters_position
Encoder-integrated control loop: Closed-loop control ensures accurate positioning over time.
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
After launching the script, you will be prompted to enter a desired angle between 0
and 360
degrees.
The motor will rotate to the target position using encoder feedback and stop.
Codes
from smd.red import * # Import SMD Red control library
from serial.tools.list_ports import comports # For listing available serial ports
from platform import system # To detect the operating system
import time # For sleep/delay
import math # For mathematical operations
# Automatically detect and return the correct USB port connected to SMD Red
def USB_Port():
ports = list(comports())
usb_names = {
"Windows": ["USB Serial Port"],
"Linux": ["/dev/ttyUSB"],
"Darwin": ["/dev/cu."] # macOS ports usually start with /dev/cu.
}
os_name = system()
for port, desc, _ in ports:
if any(name in port or name in desc for name in usb_names.get(os_name, [])):
return port
return None
def main():
port = USB_Port()
if not port:
print("No port found.") # If no port is found, exit the program
return
master = Master(port) # Create a Master object to control SMD Red
motor_id = 1 # ID of the connected motor
CPR = 6533 # Encoder Counts Per Revolution
# Attach the motor and configure its basic parameters
master.attach(Red(motor_id))
master.set_shaft_cpr(motor_id, CPR) # Set encoder resolution
master.set_shaft_rpm(motor_id, 100) # Set nominal RPM
master.set_control_parameters_position(motor_id, 0.5, 0.0, 20.0) # Set PID gains for position control
master.set_operation_mode(motor_id, OperationMode.Position) # Enable position control mode
master.enable_torque(motor_id, True) # Enable torque so the motor can move
while True:
try:
# Get target angle from user input and keep it in [0, 360) range
angle = float(input("Enter target angle (0-360°): ")) % 360
# Convert angle in degrees to encoder counts
target = angle * (CPR / 360)
# Send position command to the motor
master.set_position(motor_id, target)
# Wait for movement to complete
time.sleep(0.5)
# Read actual encoder position
current = master.get_position(motor_id)
# Convert encoder counts back to degrees
actual = current * (360 / CPR)
# Print both target and actual angles
print(f"Target: {angle:.2f}°, Actual: {actual:.2f}°\n")
except KeyboardInterrupt:
# On user interrupt (Ctrl+C), disable torque and stop the motor
master.enable_torque(motor_id, False)
break
# Entry point of the script
if __name__ == "__main__":
main()
Last updated