5.1.6 Joint Control

The joint control interfaces provide precise control over each robot joint, supporting multiple control modes and joint groups.

Key Features

Control Modes

Position Control: Drive a joint to a specified target angle.
Velocity Control: Drive a joint at a specified angular velocity.
Torque Control: Command a joint to output a specified torque.

Supported Joints

Left Arm Joints: 7-DoF (3 shoulder joints, 1 elbow joint, 3 wrist joints).
Right Arm Joints: 7-DoF (3 shoulder joints, 1 elbow joint, 3 wrist joints).
Left Leg Joints: 6-DoF (3 hip joints, 1 knee joint, 2 ankle joints).
Right Leg Joints: 6-DoF (3 hip joints, 1 knee joint, 2 ankle joints).
Waist Joints: Yaw, pitch, and roll.
Head Joints: Pitch^N.Y.A., and yaw

Joint Control Topics

Joints are controlled by body part (arms, legs, waist, head), and closed-loop control can be implemented using status feedback.

Topic Name	Data Type	Description	QoS	Frequency
`/aima/hal/joint/*/command`	`JointCommandArray`	Joint control commands	-	Hz
`/aima/hal/joint/*/state`	`JointStateArray`	Joint state feedback	`TRANSIENT_LOCAL`	Hz

Here, * can be head (requires supported head hardware), arm, waist, or leg.

JointCommandArray ros2-msg @ hal/msg/JointCommandArray.msg

# Joint control command array
MessageHeader header             # Message header
JointCommand[] joints            # Joint command array

JointCommand ros2-msg @ hal/msg/JointCommand.msg

# Joint control command
string name                      # Joint name (optional)
float64 position                 # Position (rad)
float64 velocity                 # Velocity (rad/s)
float64 effort                   # Torque (N·m)
float64 stiffness                # Stiffness (N·m/rad)
float64 damping                  # Damping (N·m·s/rad)

The length and ordering of JointCommand[] are defined in the table below.

Joint group	Length	Contents	Notes
head	2	`head_yaw`, `head_pitch`	only yaw now, and pitch is unavailable
waist	3	`wrist_yaw`, `wrist_pitch`, `wrist_roll`
arm	7*2	`shoulder_pitch`, `shoulder_roll`, `shoulder_yaw`, `elbow`, `wrist_yaw`, `wrist_pitch`, `wrist_roll`	All left-side joints first, then all right-side joints
leg	6*2	`hip_pitch`, `hip_roll`, `hip_yaw`, `knee`, `ankle_pitch`, `ankle_roll`	All left-side joints first, then all right-side joints

JointStateArray ros2-msg @ hal/msg/JointStateArray.msg

# Joint state array
MessageHeader header             # Message header
JointState[] joints              # Joint state array

JointState ros2-msg @ hal/msg/JointState.msg

# Joint state information
string name                      # Joint name (currently unused)
float64 position                 # Position (rad)
float64 velocity                 # Velocity (rad/s)
float64 effort                   # Torque (N·m)
uint8 coil_temp                  # Coil temperature (°C)
uint8 motor_temp                 # Motor temperature (°C)
uint8 motor_vol                  # Motor voltage (V)

The length and ordering of JointState[] follow the JointCommand[] joint ordering described in Joint Order.

Joint State Query Service

Service Name	Data Type	Description
`/aimdk_5Fmsgs/srv/GetAllJointState`	`GetAllJointState`	Actively query joint states

GetAllJointState ros2-srv @ hal/srv/GetAllJointState.srv

# Get all joint states
# Service: /aimdk_5Fmsgs/srv/GetAllJointState

# Request
CommonRequest request            # Common request

# Response
CommonResponse response          # Common response
JointState[] head_joints         # Head joint states
JointState[] arm_joints          # Arm joint states
JointState[] waist_joints        # Waist joint states
JointState[] leg_joints          # Leg joint states

The length and ordering of JointState[] follow the JointCommand[] joint ordering description above.

Programming Examples

For detailed examples and code explanations, refer to:

C++ Example: Robot Joint Control Example
Python Example: Robot joint control example

Safety Notes

Warning

Joint Limits

All joints have motion range limits; exceeding them may cause mechanical damage.
It is recommended to check that joint angles are within their safe ranges before sending commands.
Be especially cautious about safety limits when using torque control.

Caution

As standard ROS DO NOT handle cross-host service (request-response) well, please refer to SDK examples to use open interfaces in a robust way (with protection mechanisms e.g. exception safety and retransmission)

Note

Best Practices

Use smooth trajectory planning to avoid sudden joint motions.
Implement joint state monitoring and anomaly detection.
Ensure the robot is in a safe state before issuing control commands.