mini-cheetah-motor-driver-socketcan 0.4

A Python Driver for MIT Mini-Cheetah Actuator which uses SocketCAN for communication.

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

Issue Fixed: When having 2 motors on the CAN bus with either PCAN CAN-USB or ESD CAN-USB/2, sometimes the motors experience an initial short kick/impulse at when they are enabled again after being disabled. This was fixed.

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