epmc-serial 1.1.0

Python serial interface for the Easy PID Motor Controller (EPMC)

Easy PID Motor Controller (EPMC) Python Library

Python serial interface for the Easy PID Motor Controller (EPMC).

you can use it in your microcomputer robotics project (e.g Raspberry Pi, PC, etc.)

Install

• you'll need to pip install the pyserial library

    pip3 install epmc-serial   //linux or mac
    pip install epmc-serial  //windows
  

Uninstall

• you'll need to pip install the pyserial library

    pip3 uninstall epmc-serial   //linux or mac
    pip uninstall epmc-serial  //windows
  

How to Use the Library

• Ensure you have the EPMC MODULE interfaced with your preferred motors

• Ensure you've already setup the encoder and PID parameters with the epmc_setup_application.

• check the serial port the driver is connected to:

  ls /dev/ttyA*
  

  you should see /dev/ttyACM0 or /dev/ttyACM1 and so on

• use the serial port in your code

• A simple way to get started is simply to try out the example code below

Basic Library functions and usage

• connect to EPMC module

  controller = EPMCSerialClient()

  controller.connect("port_name or port_path")

• clear speed, position, e.t.c data buffer on the EPMC module

  controller.clearDataBuffer() # returns bool -> success

• send target angular velocity command

  controller.writeSpeed(motor0_TargetVel, motor1_TargetVel)

• send PWM command

  controller.writePWM(motor0_PWM, motor1_PWM)

• set motor command timeout

  controller.setCmdTimeout(timeout_ms)

• get motor command timeout

  controller.getCmdTimeout() # returns tuple -> (success, motor_command_timeout_ms): bool, float

• read motors angular position and angular velocity

  controller.readMotorData() # returns tuple -> (success, angPos0, angPos1, angVel0, angVel1): bool, float, float, float, float

• read motors angular position

  controller.readPos() # returns tuple -> (success, angPos0, angPos1): bool, float, float

• read motors angular velocity

  controller.readVel() # returns tuple -> (success, angVel0, angVel1): bool, float, float

• read motor maximum commandable angular velocity

  controller.getMaxVel(motor_no) # returns tuple -> (success, max_vel): bool, float, float maxVel0 or maxVel1 based on the specified motor number

• while these function above help communicate with the already configure EPMC module, more examples of advanced funtions usage for parameter tuning can be found in the epmc_setup_application source code

example code

from epmc_serial import EPMCSerialClient
import time

controller = EPMCSerialClient()

# variable for communication
pos0=0.0; pos1=0.0; pos2=0.0; pos3=0.0
vel0=0.0; vel1=0.0; vel2=0.0; vel3=0.0

# [4 rev/sec, 2 rev/sec, 1 rev/sec, 0.5 rev/sec]
targetVel = [1.571, 3.142, 6.284, 12.568]
vel = targetVel[1]
v = 0.0

readTime = None
readTimeInterval = 0.02 # 50Hz

cmdTime = None
cmdTimeInterval = 5.0

# 50Hz comm setup
serial_port = '/dev/ttyACM0'
serial_baudrate = 115200
serial_timeout = 0.018 #value < 0.02 (for 50Hz comm)

controller.connect(serial_port, serial_baudrate, serial_timeout)

#wait for the controller to fully setup
for i in range(4):
  time.sleep(1.0)
  print(f'waiting for the EPMC controller: {i+1} sec')

success = controller.clearDataBuffer()
controller.writeSpeed(v, v)
print('configuration complete')

timeout_ms = 10000
controller.setCmdTimeout(timeout_ms)
success, val0 = controller.getCmdTimeout()
if success: # only update if read was successfull
  timeout_ms = val0
  print("command timeout in ms: ", timeout_ms)
else:
  print("ERROR: could not read motor command timeout")

sendHigh = True

readTime = time.time()
cmdTime = time.time()

while True:
  if time.time() - cmdTime > cmdTimeInterval:
    if sendHigh:
      # print("command high")
      v = vel
      controller.writeSpeed(v, v)
      vel = vel*-1
      sendHigh = False
    else:
      # print("command low")
      v = 0.0
      controller.writeSpeed(v, v)
      sendHigh = True
    
    
    cmdTime = time.time()



  if time.time() - readTime > readTimeInterval:
    try:
      # controller.writeSpeed(v, v)
      success, val0, val1, val2, val3 = controller.readMotorData()
      if success: # only update if read was successfull
        pos0 = val0
        pos1 = val1
        vel0 = val2
        vel1 = val3

      print(f"motor0_readings: [{pos0}, {vel0}]")
      print(f"motor1_readings: [{pos1}, {vel1}]")
      print("")
    except:
      pass
    
    readTime = time.time()