Python Motor Driver for Mini Cheetah-type Actuators from T-Motor/CubeMars

This driver was developed at the Underactuated Lab in Robotics Innovation Center at DFKI GmbH, Bremen.

It assumes the use of a CAN to USB adapter (such as PEAK System's PCAN-USB or ESD's CAN-USB/2) connected to a linux (tested on Ubuntu) computer. The SocketCAN interface is used, thus allowing the use of Python Socket library.

Initial tests show communication (send-reply) frequencies of ~800Hz using PCAN-USB and ~1500Hz using ESD CAN-USB/2 with a single motor connected.

Dependencies:

• bitstring

Install via:

pip3 install bitstring

Documentation

• Useful videos:
  • From T-Motor
  • From Skyentific
• Motor Datasheets
• Ben Katz Documentation

Pre-requisites:

• Setting up the CAN interface:

  • Run this command and make sure that can0 (or any other can interface depending on the system)shows up as an interface after connecting the USB cable to your laptop: ip link show

  • Configure the can0 interface to have a 1 Mbaud communication frequency: sudo ip link set can0 type can bitrate 1000000

  • To bring up the can0 interface, run: sudo ip link set up can0

• To change motor parameters such as CAN ID or to calibrate the encoder, a serial connection is used. The serial terminal used on linux for this purpose is screen. Example usage:

sudo apt-get install screen
screen /dev/ttyUSB0 921600

Usage:

Import: from motor_driver.canmotorlib import CanMotorController if installed via pip. Otherwise, adjust import statement based on system's PYTHONPATH (e.g. when cloned from GitHub).

Example Motor Initialization: motor = CanMotorController(can_socket='can0', motor_id=0x01, motor_type='AK80_6_V2', socket_timeout=0.5)

Available Functions:

• enable_motor()
• disable_motor()
• set_zero_position()
• send_deg_command(position_in_degrees, velocity_in_degrees, Kp, Kd, tau_ff):
• send_rad_command(position_in_radians, velocity_in_radians, Kp, Kd, tau_ff):
• change_motor_constants(P_MIN_NEW, P_MAX_NEW, V_MIN_NEW, V_MAX_NEW, KP_MIN_NEW, KP_MAX_NEW, KD_MIN_NEW, KD_MAX_NEW, T_MIN_NEW, T_MAX_NEW)

All motor communication functions return current position, velocity, torque in SI units except for send_deg_command. change_motor_constants does not return anything.

Supported Motor Configurations:

• AK80-6 (From Cubemars, Firmware versions V1, V1.1, and V2): motor_type='AK80_6_V1', motor_type='AK80_6_V1p1' and motor_type='AK80_6_V2'
• AK80-9 (From Cubemars, Firmware version V1.1 and V2): motor_type='AK80_9_V1p1' and motor_type='AK80_9_V2'
• AK70-10 (From Cubemars, Firmware version V1.1): motor_type='AK70_10_V1p1'
• AK10-9 (From Cubemars, Firmware version V1.1): motor_type='AK10_9_V1p1'. TODO: The temperature and error codes are received but not yet decoded for the new firmware for this motor.

# Working parameters for AK80-6 V1.0 firmware
AK80_6_V1_PARAMS = {
                "P_MIN" : -95.5,
                "P_MAX" : 95.5,
                "V_MIN" : -45.0,
                "V_MAX" : 45.0,
                "KP_MIN" : 0.0,
                "KP_MAX" : 500,
                "KD_MIN" : 0.0,
                "KD_MAX" : 5.0,
                "T_MIN" : -18.0,
                "T_MAX" : 18.0,
                "AXIS_DIRECTION" : -1
                }

# Working parameters for AK80-6 V1.1 firmware
AK80_6_V1p1_PARAMS = {
                "P_MIN" : -12.5,
                "P_MAX" : 12.5,
                "V_MIN" : -22.5,
                "V_MAX" : 22.5,
                "KP_MIN" : 0.0,
                "KP_MAX" : 500,
                "KD_MIN" : 0.0,
                "KD_MAX" : 5.0,
                "T_MIN" : -12.0,
                "T_MAX" : 12.0,
                "AXIS_DIRECTION" : -1
                }

# Working parameters for AK80-6 V2.0 firmware
AK80_6_V2_PARAMS = {
                "P_MIN" : -12.5,
                "P_MAX" : 12.5,
                "V_MIN" : -38.2,
                "V_MAX" : 38.2,
                "KP_MIN" : 0.0,
                "KP_MAX" : 500.0,
                "KD_MIN" : 0.0,
                "KD_MAX" : 5.0,
                "T_MIN" : -12.0,
                "T_MAX" : 12.0,
                "AXIS_DIRECTION" : 1
                }

# Working parameters for AK80-9 V1.1 firmware
AK80_9_V1p1_PARAMS = {
                "P_MIN" : -12.5,
                "P_MAX" : 12.5,
                "V_MIN" : -22.5,
                "V_MAX" : 22.5,
                "KP_MIN" : 0.0,
                "KP_MAX" : 500,
                "KD_MIN" : 0.0,
                "KD_MAX" : 5.0,
                "T_MIN" : -18.0,
                "T_MAX" : 18.0,
                "AXIS_DIRECTION" : 1
                }

# Working parameters for AK80-9 V2.0 firmware
AK80_9_V2_PARAMS = {
                    "P_MIN" : -12.5,
                    "P_MAX" : 12.5,
                    "V_MIN" : -25.64,
                    "V_MAX" : 25.64,
                    "KP_MIN" : 0.0,
                    "KP_MAX" : 500.0,
                    "KD_MIN" : 0.0,
                    "KD_MAX" : 5.0,
                    "T_MIN" : -18.0,
                    "T_MAX" : 18.0,
                    "AXIS_DIRECTION" : 1
                    }

// Working parameters for AK70-10 V1.1 firmware
AK70_10_V1p1_params = {
                      "P_MIN" :  -12.5,
                      "P_MAX" :  12.5,
                      "V_MIN" :  -50,
                      "V_MAX" :  50,
                      "KP_MIN" :  0,
                      "KP_MAX" :  500,
                      "KD_MIN" :  0,
                      "KD_MAX" :  5,
                      "T_MIN" :  -24.0,
                      "T_MAX" :  24.0,
                      "AXIS_DIRECTION" :  1
                    }

# Working parameters for AK10-9 V1.1 firmware
AK10_9_V1p1_PARAMS = {
                "P_MIN" : -12.5,
                "P_MAX" : 12.5,
                "V_MIN" : -50.0,
                "V_MAX" : 50.0,
                "KP_MIN" : 0.0,
                "KP_MAX" : 500,
                "KD_MIN" : 0.0,
                "KD_MAX" : 5.0,
                "T_MIN" : -65.0,
                "T_MAX" : 65.0,
                "AXIS_DIRECTION" : -1
                }

To add a new constants configuration use the change_motor_constants function or create an issue with the constants and motor information on the GitHub page to be added to the driver.

Known Issues

Currently, the driver does not support multiple CAN busses i.e. multiple CAN2USB devices. The fix for this is in the works...

As this is experimental software, there might be other unknown issues.