8.7 Dual Arm Joints

8.7.1 Status Acquisition Interfaces

1. Get Dual Arm Joint Information

• Description: Get status information of dual arm joints, including current position, speed, current, and temperature of the joints. Applicable to all series of Walker Tienkung.

• Control Method: topic

• Topic Name: /arm/status

• Data Definition Location: bodyctrl_msgs::msg::MotorStatusMsg.msg

• Data Format:

  std_msgs/Header header
  MotorStatus[] status
  
  MotorStatus definition:
  uint16 name    # MotorName
  float32 pos    # rad
  float32 speed  # rad
  float32 current # A
  float32 temperature
  uint32 error

  Error field value definitions:

  error = 33072,	Device offline
  error = 33073,	Joint position out of limit
  error = 1,	Joint motor overheating
  error = 2,	Overcurrent
  error = 3,	Undervoltage
  error = 4,	Joint mos overheating
  error = 5,	Stalling
  error = 6,	Overvoltage
  error = 7,	Phase loss
  error = 8,	Encoder error

8.7.2 Control Interfaces

1. Position Mode

• Description: Position control interface for joints, requiring desired position, desired speed, and maximum current. Applicable to all series of Walker Tienkung.

• Control Method: topic

• Topic Name: /arm/cmd_pos

• Data Definition Location: bodyctrl_msgs::msg::CmdSetMotorPosition.msg

• Data Format:

  std_msgs/Header header
  SetMotorPosition[] cmds
  
  # SetMotorPosition.msg 
  uint16 name  # MotorName
  float32 pos  # rad
  float32 spd  # rad/s
  float32 cur  # Current

• Example Commands:

  ros2 topic pub /arm/cmd_pos bodyctrl_msgs/msg/CmdSetMotorPosition "{cmds: [{name: 12, pos: 0.3, spd: 0.2, cur: 8.0 }]}"
  ros2 topic pub /arm/cmd_pos bodyctrl_msgs/msg/CmdSetMotorPosition "{cmds: [{name: 22, pos: -0.3, spd: 0.2, cur: 8.0 }]}"

2. Force-Position Hybrid Mode

• Description: Force-position hybrid control interface for joints, requiring desired position, desired speed, feedforward torque, kp, and kd coefficients. Applicable to all series of Walker Tienkung.

• Control Method: topic

• Topic Name: /arm/cmd_ctrl

• Data Definition Location: bodyctrl_msgs::msg::CmdMotorCtrl.msg

• Data Format:

  std_msgs/Header header
  MotorCtrl[] cmds
  
  # MotorCtrl.msg
  uint16 name
  float32 kp
  float32 kd
  float32 pos
  float32 spd
  float32 tor

• Example Commands:

  ros2 topic pub /arm/cmd_ctrl bodyctrl_msgs/msg/CmdMotorCtrl "{cmds: [{name: 13, kp: 30.0, kd: 10.0, pos: 0.2, spd: 0.0, tor: 0.0}]}"
  ros2 topic pub /arm/cmd_ctrl bodyctrl_msgs/msg/CmdMotorCtrl "{cmds: [{name: 23, kp: 30.0, kd: 10.0, pos: 0.2, spd: 0.0, tor: 0.0}]}"

3. Speed Mode

• Description: Speed control interface for joints, requiring desired speed and maximum current. Applicable to all series of Walker Tienkung. Note that once this message is published, the motor will continue to rotate at this speed until a message with spd=0.0 is received on this topic, so use with caution.

• Control Method: topic

• Topic Name: /arm/cmd_vel

• Data Definition Location: bodyctrl_msgs::msg::CmdSetMotorSpeed.msg

• Data Format:

  std_msgs/Header header
  SetMotorSpeed[] cmds
  
  #SetMotorSpeed.msg
  uint16 name # MotorName 
  float32 spd # rad/s
  float32 cur # A

4. Arm Joint Homing

• Description: Homing interface for dual arm joints. When this interface is called, it will set the current position of the specified motor on the arm as the zero position. When pressing D on the remote control to home, the motor will move to the current position. Generally, it needs to be used with a homing tool. Please use with caution when there is no homing tool. Applicable to all series of Walker Tienkung.
• Control Method: topic
• Topic Name: /arm/cmd_set_zero
• Data Definition Location: std_msgs::msg::String
• Data Format:

  Send the joint id in string form to achieve homing
  Dual arm joint ids:     
      Left arm: 11---17,   
      Right arm: 21---27；