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Python Bulk Read Protocol 1.0

Sample code Parts

import os

if os.name == 'nt':
    import msvcrt
    def getch():
        return msvcrt.getch().decode()
else:
    import sys, tty, termios
    fd = sys.stdin.fileno()
    old_settings = termios.tcgetattr(fd)
    def getch():
        try:
            tty.setraw(sys.stdin.fileno())
            ch = sys.stdin.read(1)
        finally:
            termios.tcsetattr(fd, termios.TCSADRAIN, old_settings)
        return ch

from dynamixel_sdk import *                    # Uses Dynamixel SDK library

# Control table address
ADDR_MX_TORQUE_ENABLE       = 64               # Control table address is different in Dynamixel model
ADDR_MX_GOAL_POSITION       = 116
ADDR_MX_PRESENT_POSITION    = 132
ADDR_MX_MOVING              = 122

# Data Byte Length
LEN_MX_GOAL_POSITION        = 4
LEN_MX_PRESENT_POSITION     = 4
LEN_MX_MOVING               = 1

# Protocol version
PROTOCOL_VERSION            = 1.0               # See which protocol version is used in the Dynamixel

# Default setting
DXL1_ID                     = 1                 # Dynamixel#1 ID : 1
DXL2_ID                     = 2                 # Dynamixel#1 ID : 2
BAUDRATE                    = 57600             # Dynamixel default baudrate : 57600
DEVICENAME                  = '/dev/ttyUSB0'    # Check which port is being used on your controller
                                                # ex) Windows: "COM1"   Linux: "/dev/ttyUSB0" Mac: "/dev/tty.usbserial-*"

TORQUE_ENABLE               = 1                 # Value for enabling the torque
TORQUE_DISABLE              = 0                 # Value for disabling the torque
DXL_MINIMUM_POSITION_VALUE  = 100           # Dynamixel will rotate between this value
DXL_MAXIMUM_POSITION_VALUE  = 4000            # and this value (note that the Dynamixel would not move when the position value is out of movable range. Check e-manual about the range of the Dynamixel you use.)
DXL_MOVING_STATUS_THRESHOLD = 20                # Dynamixel moving status threshold

index = 0
dxl_goal_position = [DXL_MINIMUM_POSITION_VALUE, DXL_MAXIMUM_POSITION_VALUE]        # Goal position

# Initialize PortHandler instance
# Set the port path
# Get methods and members of PortHandlerLinux or PortHandlerWindows
portHandler = PortHandler(DEVICENAME)

# Initialize PacketHandler instance
# Set the protocol version
# Get methods and members of Protocol1PacketHandler or Protocol2PacketHandler
packetHandler = PacketHandler(PROTOCOL_VERSION)

# Initialize GroupBulkRead instace for Present Position
groupBulkRead = GroupBulkRead(portHandler, packetHandler)

# Open port
if portHandler.openPort():
    print("Succeeded to open the port")
else:
    print("Failed to open the port")
    print("Press any key to terminate...")
    getch()
    quit()


# Set port baudrate
if portHandler.setBaudRate(BAUDRATE):
    print("Succeeded to change the baudrate")
else:
    print("Failed to change the baudrate")
    print("Press any key to terminate...")
    getch()
    quit()


# Enable Dynamixel#1 Torque
dxl_comm_result, dxl_error = packetHandler.write1ByteTxRx(portHandler, DXL1_ID, ADDR_MX_TORQUE_ENABLE, TORQUE_ENABLE)
if dxl_comm_result != COMM_SUCCESS:
    print("%s" % packetHandler.getTxRxResult(dxl_comm_result))
elif dxl_error != 0:
    print("%s" % packetHandler.getRxPacketError(dxl_error))
else:
    print("Dynamixel#%d has been successfully connected" % DXL1_ID)

# Enable Dynamixel#1 Torque
dxl_comm_result, dxl_error = packetHandler.write1ByteTxRx(portHandler, DXL2_ID, ADDR_MX_TORQUE_ENABLE, TORQUE_ENABLE)
if dxl_comm_result != COMM_SUCCESS:
    print("%s" % packetHandler.getTxRxResult(dxl_comm_result))
elif dxl_error != 0:
    print("%s" % packetHandler.getRxPacketError(dxl_error))
else:
    print("Dynamixel#%d has been successfully connected" % DXL2_ID)

# Add parameter storage for Dynamixel#1 present position
dxl_addparam_result = groupBulkRead.addParam(DXL1_ID, ADDR_MX_PRESENT_POSITION, LEN_MX_PRESENT_POSITION)
if dxl_addparam_result != True:
    print("[ID:%03d] groupBulkRead addparam failed" % DXL1_ID)
    quit()

# Add parameter storage for Dynamixel#2 moving value
dxl_addparam_result = groupBulkRead.addParam(DXL2_ID, ADDR_MX_MOVING, LEN_MX_MOVING)
if dxl_addparam_result != True:
    print("[ID:%03d] groupBulkRead addparam failed" % DXL2_ID)
    quit()

while 1:
    print("Press any key to continue! (or press ESC to quit!)")
    if getch() == chr(0x1b):
        break

    # Write Dynamixel#1 goal position
    dxl_comm_result, dxl_error = packetHandler.write4ByteTxRx(portHandler, DXL1_ID, ADDR_MX_GOAL_POSITION, dxl_goal_position[index])
    if dxl_comm_result != COMM_SUCCESS:
        print("%s" % packetHandler.getTxRxResult(dxl_comm_result))
    elif dxl_error != 0:
        print("%s" % packetHandler.getRxPacketError(dxl_error))

    # Write Dynamixel#2 goal position
    dxl_comm_result, dxl_error = packetHandler.write4ByteTxRx(portHandler, DXL2_ID, ADDR_MX_GOAL_POSITION, dxl_goal_position[index])
    if dxl_comm_result != COMM_SUCCESS:
        print("%s" % packetHandler.getTxRxResult(dxl_comm_result))
    elif dxl_error != 0:
        print("%s" % packetHandler.getRxPacketError(dxl_error))

    while 1:
        # Bulkread present position and moving status
        dxl_comm_result = groupBulkRead.txRxPacket()
        if dxl_comm_result != COMM_SUCCESS:
            print("%s" % packetHandler.getTxRxResult(dxl_comm_result))

        # Check if groupbulkread data of Dynamixel#1 is available
        dxl_getdata_result = groupBulkRead.isAvailable(DXL1_ID, ADDR_MX_PRESENT_POSITION, LEN_MX_PRESENT_POSITION)
        if dxl_getdata_result != True:
            print("[ID:%03d] groupBulkRead getdata failed" % DXL1_ID)
            quit()

        # Check if groupbulkread data of Dynamixel#2 is available
        dxl_getdata_result = groupBulkRead.isAvailable(DXL2_ID, ADDR_MX_MOVING, LEN_MX_MOVING)
        if dxl_getdata_result != True:
            print("[ID:%03d] groupBulkRead getdata failed" % DXL2_ID)
            quit()

        # Get Dynamixel#1 present position value
        dxl1_present_position = groupBulkRead.getData(DXL1_ID, ADDR_MX_PRESENT_POSITION, LEN_MX_PRESENT_POSITION)

        # Get Dynamixel#2 moving value
        dxl2_moving_value = groupBulkRead.getData(DXL2_ID, ADDR_MX_MOVING, LEN_MX_MOVING)

        print("[ID:%03d] Present Position : %d \t [ID:%03d] Is Moving: %d" % (DXL1_ID, dxl1_present_position, DXL2_ID, dxl2_moving_value))

        if not (abs(dxl_goal_position[index] - dxl1_present_position) > DXL_MOVING_STATUS_THRESHOLD):
            break

    # Change goal position
    if index == 0:
        index = 1
    else:
        index = 0

# Clear bulkread parameter storage
groupBulkRead.clearParam()

# Disable Dynamixel#1 Torque
dxl_comm_result, dxl_error = packetHandler.write1ByteTxRx(portHandler, DXL1_ID, ADDR_MX_TORQUE_ENABLE, TORQUE_DISABLE)
if dxl_comm_result != COMM_SUCCESS:
    print("%s" % packetHandler.getTxRxResult(dxl_comm_result))
elif dxl_error != 0:
    print("%s" % packetHandler.getRxPacketError(dxl_error))

# Disable Dynamixel#2 Torque
dxl_comm_result, dxl_error = packetHandler.write1ByteTxRx(portHandler, DXL2_ID, ADDR_MX_TORQUE_ENABLE, TORQUE_DISABLE)
if dxl_comm_result != COMM_SUCCESS:
    print("%s" % packetHandler.getTxRxResult(dxl_comm_result))
elif dxl_error != 0:
    print("%s" % packetHandler.getRxPacketError(dxl_error))

# Close port
portHandler.closePort()

Details

import os

if os.name == 'nt':
    import msvcrt
    def getch():
        return msvcrt.getch().decode()
else:
    import sys, tty, termios
    fd = sys.stdin.fileno()
    old_settings = termios.tcgetattr(fd)
    def getch():
        try:
            tty.setraw(sys.stdin.fileno())
            ch = sys.stdin.read(1)
        finally:
            termios.tcsetattr(fd, termios.TCSADRAIN, old_settings)
        return ch

from dynamixel_sdk import *                    # Uses Dynamixel SDK library

getch() gets the input which is for example code control.

os.sys.path.append() sets paths of function reference.

# Control table address
ADDR_MX_TORQUE_ENABLE       = 24                            # Control table address is different in Dynamixel model
ADDR_MX_GOAL_POSITION       = 30
ADDR_MX_PRESENT_POSITION    = 36
ADDR_MX_MOVING              = 46

# Data Byte Length
LEN_MX_GOAL_POSITION        = 2
LEN_MX_PRESENT_POSITION     = 2
LEN_MX_MOVING               = 1

Dynamixel series have their own control tables: Addresses and Byte Length in each items. To control one of the items, its address (and length if necessary) is required. Find your requirements in http://emanual.robotis.com/.

# Protocol version
PROTOCOL_VERSION            = 1.0                             # See which protocol version is used in the Dynamixel

Dynamixel uses either or both protocols: Protocol 1.0 and Protocol 2.0. Choose one of the Protocol which is appropriate in the Dynamixel.

# Default setting
DXL1_ID                     = 1                             # Dynamixel ID: 1
DXL2_ID                     = 2                             # Dynamixel ID: 2
BAUDRATE                    = 57600
DEVICENAME                  = "/dev/ttyUSB0".encode('utf-8')        # Check which port is being used on your controller
                                                            # ex) Windows: "COM1"   Linux: "/dev/ttyUSB0"

TORQUE_ENABLE               = 1                             # Value for enabling the torque
TORQUE_DISABLE              = 0                             # Value for disabling the torque
DXL_MINIMUM_POSITION_VALUE  = 100                           # Dynamixel will rotate between this value
DXL_MAXIMUM_POSITION_VALUE  = 4000                          # and this value (note that the Dynamixel would not move when the position value is out of movable range. Check e-manual about the range of the Dynamixel you use.)
DXL_MOVING_STATUS_THRESHOLD = 10                            # Dynamixel moving status threshold

Here we set some variables to let you freely change them and use them to run the example code.

As the document previously said in previous chapter, customize Dynamixel control table items, such as DXL_ID number, communication BAUDRATE, and the DEVICENAME, on your own terms of needs. In particular, BAUDRATE and DEVICENAME have systematical dependencies on your controller, so make clear what kind of communication method you will use.

The example uses two Dynamixels DXL1_ID, DXL2_ID connected with the port DEVICENAME.

Dynamixel basically needs the TORQUE_ENABLE to be rotating or give you its internal information. On the other hand, it doesn’t need torque enabled if you get your goal, so finally do TORQUE_DISABLE to prepare to the next sequence.

Since the Dynamixel has its own rotation range, it may shows malfunction if your request on your dynamixel is out of range. For example, Dynamixel MX-28 and Dynamixel PRO 54-200 has its rotatable range as 0 ~ 4028 and -250950 ~ 250950, each.

DXL_MOVING_STATUS_THRESHOLD acts as a criteria for verifying its rotation stopped.

# Initialize PortHandler instance
# Set the port path
# Get methods and members of PortHandlerLinux or PortHandlerWindows
portHandler = PortHandler(DEVICENAME)

portHandler() function sets port path as DEVICENAME and get PortHandler instance, and prepares an appropriate functions for port control in controller OS automatically. portHandler would be used in many functions in the body of the code to specify the port for use.

# Initialize PacketHandler instance
# Set the protocol version
# Get methods and members of Protocol1PacketHandler or Protocol2PacketHandler
packetHandler = PacketHandler(PROTOCOL_VERSION)

packetHandler() function initializes parameters used for packet construction and packet storing.

# Initialize GroupBulkRead instace for Present Position
groupBulkRead = GroupBulkRead(portHandler, packetHandler)

groupBulkRead() function initializes grouped parameters used for packet construction and packet storing. The utility functions of bulk read deals simultaneously with more than one Dynamixel through port, building packets by the function which uses PROTOCOL_VERSION.

# Open port
if dynamixel.openPort(port_num):
    print("Succeeded to open the port!")
else:
    print("Failed to open the port!")
    print("Press any key to terminate...")
    msvcrt.getch()
    quit()

First, controller opens port to do serial communication with the Dynamixel. If it fails to open the port, the example will be terminated.

# Set port baudrate
if dynamixel.setBaudRate(port_num, BAUDRATE):
    print("Succeeded to change the baudrate!")
else:
    print("Failed to change the baudrate!")
    print("Press any key to terminate...")
    msvcrt.getch()
    quit()

Secondly, the controller sets the communication BAUDRATE at port opened previously.

# Enable Dynamixel#1 Torque
dxl_comm_result, dxl_error = packetHandler.write1ByteTxRx(portHandler, DXL1_ID, ADDR_MX_TORQUE_ENABLE, TORQUE_ENABLE)
if dxl_comm_result != COMM_SUCCESS:
    print("%s" % packetHandler.getTxRxResult(dxl_comm_result))
elif dxl_error != 0:
    print("%s" % packetHandler.getRxPacketError(dxl_error))
else:
    print("Dynamixel#%d has been successfully connected" % DXL1_ID)

# Enable Dynamixel#1 Torque
dxl_comm_result, dxl_error = packetHandler.write1ByteTxRx(portHandler, DXL2_ID, ADDR_MX_TORQUE_ENABLE, TORQUE_ENABLE)
if dxl_comm_result != COMM_SUCCESS:
    print("%s" % packetHandler.getTxRxResult(dxl_comm_result))
elif dxl_error != 0:
    print("%s" % packetHandler.getRxPacketError(dxl_error))
else:
    print("Dynamixel#%d has been successfully connected" % DXL2_ID)

As mentioned in the document, above code enables each Dynamixel`s torque to set their status as being ready to move.

write1ByteTxRx() function orders to the #DXL1_ID and #DXL2_ID Dynamixels in PROTOCOL_VERSION communication protocol through port, writing 1 byte of TORQUE_ENABLE value to ADDR_MX_TORQUE_ENABLE address. The function checks Tx/Rx result and receives Hardware error. getTxRxResult() function and getRxPacketError() function get results on the console window if any communication error or Hardware error has been occurred.

# Add parameter storage for Dynamixel#1 present position
dxl_addparam_result = groupBulkRead.addParam(DXL1_ID, ADDR_MX_PRESENT_POSITION, LEN_MX_PRESENT_POSITION)
if dxl_addparam_result != True:
    print("[ID:%03d] groupBulkRead addparam failed" % DXL1_ID)
    quit()

# Add parameter storage for Dynamixel#2 moving value
dxl_addparam_result = groupBulkRead.addParam(DXL2_ID, ADDR_MX_MOVING, LEN_MX_MOVING)
if dxl_addparam_result != True:
    print("[ID:%03d] groupBulkRead addparam failed" % DXL2_ID)
    quit()

addParam() function stores the Dynamixel ID and address ADDR_MX_MOVING, byte length LEN_MX_MOVING of required data to the bulkread target Dynamixel list.

while 1:
    print("Press any key to continue! (or press ESC to quit!)")
    if getch() == chr(0x1b):
        break

    # Write Dynamixel#1 goal position
    dxl_comm_result, dxl_error = packetHandler.write4ByteTxRx(portHandler, DXL1_ID, ADDR_MX_GOAL_POSITION, dxl_goal_position[index])
    if dxl_comm_result != COMM_SUCCESS:
        print("%s" % packetHandler.getTxRxResult(dxl_comm_result))
    elif dxl_error != 0:
        print("%s" % packetHandler.getRxPacketError(dxl_error))

    # Write Dynamixel#2 goal position
    dxl_comm_result, dxl_error = packetHandler.write4ByteTxRx(portHandler, DXL2_ID, ADDR_MX_GOAL_POSITION, dxl_goal_position[index])
    if dxl_comm_result != COMM_SUCCESS:
        print("%s" % packetHandler.getTxRxResult(dxl_comm_result))
    elif dxl_error != 0:
        print("%s" % packetHandler.getRxPacketError(dxl_error))

    while 1:
        # Bulkread present position and moving status
        dxl_comm_result = groupBulkRead.txRxPacket()
        if dxl_comm_result != COMM_SUCCESS:
            print("%s" % packetHandler.getTxRxResult(dxl_comm_result))

        # Check if groupbulkread data of Dynamixel#1 is available
        dxl_getdata_result = groupBulkRead.isAvailable(DXL1_ID, ADDR_MX_PRESENT_POSITION, LEN_MX_PRESENT_POSITION)
        if dxl_getdata_result != True:
            print("[ID:%03d] groupBulkRead getdata failed" % DXL1_ID)
            quit()

        # Check if groupbulkread data of Dynamixel#2 is available
        dxl_getdata_result = groupBulkRead.isAvailable(DXL2_ID, ADDR_MX_MOVING, LEN_MX_MOVING)
        if dxl_getdata_result != True:
            print("[ID:%03d] groupBulkRead getdata failed" % DXL2_ID)
            quit()

        # Get Dynamixel#1 present position value
        dxl1_present_position = groupBulkRead.getData(DXL1_ID, ADDR_MX_PRESENT_POSITION, LEN_MX_PRESENT_POSITION)

        # Get Dynamixel#2 moving value
        dxl2_moving_value = groupBulkRead.getData(DXL2_ID, ADDR_MX_MOVING, LEN_MX_MOVING)

        print("[ID:%03d] Present Position : %d \t [ID:%03d] Is Moving: %d" % (DXL1_ID, dxl1_present_position, DXL2_ID, dxl2_moving_value))

        if not (abs(dxl_goal_position[index] - dxl1_present_position) > DXL_MOVING_STATUS_THRESHOLD):
            break

    # Change goal position
    if index == 0:
        index = 1
    else:
        index = 0

During while loop, the controller writes and reads each Dynamixel position or moving status through packet transmission/reception(Tx/Rx).

To continue their rotation, press any key except ESC.

write2ByteTxRx() function orders to the #DXL1_ID and #DXL2_ID Dynamixels in PROTOCOL_VERSION communication protocol through port, writing 2 byte of dxl_goal_position[index] value to ADDR_MX_GOAL_POSITION address. The function checks Tx/Rx result and receives Hardware error. getTxRxResult() function and getRxPacketError() function get results on the console window if any communication error or Hardware error has been occurred.

txRxPacket() function orders to the Dynamixel #DXL1_ID and #DXL2_ID at the same time through port, making it possible to require data bytes from different address. (In this example, LEN_MX_PRESENT_POSITION bytes of the values to the address ADDR_MX_PRESENT_POSITION and LEN_MX_MOVING bytes of the values to the address ADDR_MX_MOVING, each.) The function checks Tx/Rx result. getTxRxResult() function gets result on the console window if any communication error has been occurred.

isAvailable() function checks if available data is in the groupbulkread data storage. The function returns false if no data is available in the storage.

getData() function pop the data received by txRxPacket() function out. In the example, it stores LEN_MX_PRESENT_POSITION byte data got from ADDR_MX_PRESENT_POSITION address of DXL1_ID Dynamixel and LEN_MX_MOVING byte data got from ADDR_MX_MOVING address of DXL2_ID Dynamixel, each.

clearParam() function clears the Dynamixel list of groupbulkread.

Reading their present position will be ended when absolute value of (dxl_goal_position[index] - dxl1_present_position) becomes smaller then DXL_MOVING_STATUS_THRESHOLD.

At last, it changes their direction to the counter-wise and waits for extra key input.

# Disable Dynamixel#1 Torque
dxl_comm_result, dxl_error = packetHandler.write1ByteTxRx(portHandler, DXL1_ID, ADDR_MX_TORQUE_ENABLE, TORQUE_DISABLE)
if dxl_comm_result != COMM_SUCCESS:
    print("%s" % packetHandler.getTxRxResult(dxl_comm_result))
elif dxl_error != 0:
    print("%s" % packetHandler.getRxPacketError(dxl_error))

# Disable Dynamixel#2 Torque
dxl_comm_result, dxl_error = packetHandler.write1ByteTxRx(portHandler, DXL2_ID, ADDR_MX_TORQUE_ENABLE, TORQUE_DISABLE)
if dxl_comm_result != COMM_SUCCESS:
    print("%s" % packetHandler.getTxRxResult(dxl_comm_result))
elif dxl_error != 0:
    print("%s" % packetHandler.getRxPacketError(dxl_error))

The controller frees the Dynamixels to be idle.

write1ByteTxRx() function orders to the #DXL1_ID and #DXL2_ID Dynamixels in PROTOCOL_VERSION communication protocol through port, writing 1 byte of TORQUE_DISABLE value to ADDR_MX_TORQUE_ENABLE address. The function checks Tx/Rx result and receives Hardware error. getTxRxResult() function and getRxPacketError() function get results on the console window if any communication error or Hardware error has been occurred.

# Close port
portHandler.closePort()

Finally, port becomes disposed.