meta_hardware

meta_hardware package is a ros2_control compatible hardware interface that implements management of DJI and MI motors.

List of hardware interfaces

Motor Vendor	Interface Name
DJI	MetaRobotDjiMotorNetwork
MI	MetaRobotMiMotorNetwork
BRITER	MetaRobotBrtEncoderNetwork

Supported motors

Motor vendor	Motor Model	Protocol
DJI	GM6020	CAN
	M3508	CAN
	M2006	CAN
MI	CyberGear	CAN
BRITER	BRT38	CAN

URDF configuration

To activate a motor network (a series of motors on a can network belonging to a single vendor), you simply need to create a ros2_control tag with motor information in your robot URDF.

Motor network params

can_network_name

The CAN interface name of the CAN network, usually can0 or can1.

Common motor params

motor_model

The model name of the motor.

mechanical_reduction offset

The mechanical reduction rate of the motor and the offset of the motor zero position with respect to joint zero position.

\[ \theta_{\text{joint}} = \frac{\theta_{\text{motor}}}{\text{mechanical reduction}} + \text{offset} \]

DJI motor params

motor_id

The DJI motor ID, can be adjusted by DIP switches on the motor, as described in DJI documentation.

MI motor params

motor_id

The MI motor ID, adjustable via MI motor debugging software.

control_mode

The operating mode of the motor. Can be dynamic, position, or velocity.

• Dynamic control mode is a flexible control mode that allows three inputs: pos_dst, vel_dst, and t_ff, the actual torque is computed by th following formula:

  \[ \tau = K_{\text{p}} \cdot (\theta_{\text{dst}} - \theta) + K_{\text{d}} \cdot (\omega_{\text{dst}} - \omega) + \tau_{\text{ff}} \]

  MetaRobotMiMotorNetwork accepts partial inputs to reduce user’s complexity:

  • If only position interface is present, pos_dst = position, vel_dst = 0, t_ff = 0.

  • If only velocity interface is present, pos_dst = 0, vel_dst = velocity, t_ff = 0.

  • If only effort interface is present, pos_dst = 0, vel_dst = 0, t_ff = effort.

  • If both position and effort interfaces are present, pos_dst = position, vel_dst = 0, t_ff = effort.

  • If both velocity and effort interfaces are present, pos_dst = 0, vel_dst = velocity, t_ff = effort.

  • If all interfaces are present, pos_dst = position, vel_dst = velocity, t_ff = effort.

  • The combination of position and velocity interfaces is not considered valid, as this generally doesn’t generate a stable system.

• Position control mode is an internal dual-loop PI controller that controls the motor’s position.

• Velocity control mode is an internal PI controller that controls the motor’s velocity.

Please refer to MI motor’s documentation for more information on control modes.

Kp Kd

Parameters used in dynamic control mode. Refer to MI motor’s documentation for more information.

spd_kp spd_ki

Parameters used in velocity and position control mode. Refer to MI motor’s documentation for more information.

loc_kp

Parameter used in position control mode. Refer to MI motor’s documentation for more information.

limit_spd

Maximum speed limit of the motor in position mode.

limit_cur

Maximum current limit of the motor in velocity mode.

Example URDF configuration

A robot with a DJI GM6020 and MI CyberGear (in dynamic control mode with a target position) can be configured as follows.

<ros2_control name="motor_control_dji" type="system">
    <hardware>
        <plugin>meta_hardware/MetaRobotDjiMotorNetwork</plugin>
        <param name="can_network_name">can0</param>
    </hardware>
    <joint name="motor1_joint">
        <command_interface name="effort" />
        <state_interface name="position" />
        <state_interface name="velocity" />
        <state_interface name="effort" />
        <param name="motor_model">GM6020</param>
        <param name="motor_id">1</param>
        <param name="mechanical_reduction">1.0</param>
        <param name="offset">0.0</param>
    </joint>
</ros2_control>

<ros2_control name="motor_control_mi" type="system">
    <hardware>
        <plugin>meta_hardware/MetaRobotMiMotorNetwork</plugin>
        <param name="can_network_name">can0</param>
    </hardware>
    <joint name="motor2_joint">
        <command_interface name="position" />
        <state_interface name="position" />
        <state_interface name="velocity" />
        <state_interface name="effort" />
        <param name="motor_model">CyberGear</param>
        <param name="motor_id">1</param>
        <param name="mechanical_reduction">1.0</param>
        <param name="offset">0.0</param>
        <param name="control_mode">dynamic</param>
        <param name="Kp">30.0</param>
        <param name="Kd">1.0</param>
    </joint>
</ros2_control>