Provides robot system low-level motion control service. Through the LowLevelMotionController, you can control robot joints and obtain status via topic communication.

Interface Definition

LowLevelMotionController is a motion controller for low-level development, supporting direct control and state subscription of motion components such as arms, legs, head, waist, hands, etc., as well as body IMU data acquisition.

LowLevelMotionController

Item	Content
Class Name	LowLevelMotionController
Constructor	controller = LowLevelMotionController()
Function Overview	Constructor, initializes low-level controller object.
Notes	Constructs internal resources.

initialize

Item	Content
Function Name	initialize
Function Declaration	bool initialize()
Function Overview	Initialize controller, establish low-level connection.
Return Value	True indicates success, False indicates failure.
Notes	Must be initialized on first call.

shutdown

Item	Content
Function Name	shutdown
Function Declaration	void shutdown()
Function Overview	Shutdown controller, release low-level resources.
Notes	Used in conjunction with initialize.

set_period_ms

Item	Content
Function Name	set_period_ms
Function Declaration	void set_period_ms(int period_ms)
Function Overview	Set control period time (milliseconds).
Parameter Description	period_ms: Period time, unit is milliseconds.
Notes	Non-blocking interface, period parameter used internally by controller, controls joint command sending frequency.

subscribe_arm_state

Item	Content
Function Name	subscribe_arm_state
Function Declaration	void subscribe_arm_state(callback)
Function Overview	Subscribe to arm joint state data
Parameter Description	callback: Data processing function, signature is callback(data: JointState) -> None
Notes	Non-blocking interface.

publish_arm_command

Item	Content
Function Name	publish_arm_command
Function Declaration	Status publish_arm_command(JointCommand command)
Function Overview	Publish arm control commands
Parameter Description	command: Target position/velocity, etc.
Return Value	Status object, Status.code == ErrorCode.OK indicates success.
Notes	Non-blocking interface.

subscribe_leg_state

Item	Content
Function Name	subscribe_leg_state
Function Declaration	void subscribe_leg_state(callback)
Function Overview	Subscribe to leg joint state data
Parameter Description	callback: Data processing function, signature is callback(data: JointState) -> None
Notes	Non-blocking interface.

publish_leg_command

Item	Content
Function Name	publish_leg_command
Function Declaration	Status publish_leg_command(JointCommand command)
Function Overview	Publish leg control commands
Parameter Description	command: Target position/velocity, etc.
Return Value	Status object, Status.code == ErrorCode.OK indicates success.
Notes	Non-blocking interface, called when publishing or subscribing.

subscribe_head_state

Item	Content
Function Name	subscribe_head_state
Function Declaration	void subscribe_head_state(callback)
Function Overview	Subscribe to head joint state data
Parameter Description	callback: Data processing function, signature is callback(data: JointState) -> None
Notes	Non-blocking interface.

publish_head_command

Item	Content
Function Name	publish_head_command
Function Declaration	Status publish_head_command(JointCommand command)
Function Overview	Publish head control commands
Parameter Description	command: Target position/velocity, etc.
Return Value	Status object, Status.code == ErrorCode.OK indicates success.
Notes	Non-blocking interface.

subscribe_waist_state

Item	Content
Function Name	subscribe_waist_state
Function Declaration	void subscribe_waist_state(callback)
Function Overview	Subscribe to waist joint state data
Parameter Description	callback: Data processing function, signature is callback(data: JointState) -> None
Notes	Non-blocking interface.

publish_waist_command

Item	Content
Function Name	publish_waist_command
Function Declaration	Status publish_waist_command(JointCommand command)
Function Overview	Publish waist control commands
Parameter Description	command: Target position/velocity, etc.
Return Value	Status object, Status.code == ErrorCode.OK indicates success.
Notes	Non-blocking interface.

subscribe_hand_state

Item	Content
Function Name	subscribe_hand_state
Function Declaration	void subscribe_hand_state(callback)
Function Overview	Subscribe to hand state data
Parameter Description	callback: Data processing function, signature is callback(data: HandState) -> None
Notes	Non-blocking interface.

publish_hand_command

Item	Content
Function Name	publish_hand_command
Function Declaration	Status publish_hand_command(HandCommand command)
Function Overview	Publish hand control commands
Parameter Description	command: Hand joint target positions, etc.
Return Value	Status object, Status.code == ErrorCode.OK indicates success.
Notes	Non-blocking interface.

subscribe_body_imu

Item	Content
Function Name	subscribe_body_imu
Function Declaration	void subscribe_body_imu(callback)
Function Overview	Subscribe to body IMU data
Parameter Description	callback: IMU data processing function, signature is callback(data: Imu) -> None
Notes	Non-blocking interface.

Type Definitions

SingleHandJointCommand — Single Hand Joint Control Command

Field Name	Type	Description
operation_mode	int16_t	Control mode (such as position, torque, impedance, etc.), default value is 0
pos	list[float]	Desired position array (7 degrees of freedom)

HandCommand — Complete Hand Control Command

Field Name	Type	Description
timestamp	int64_t	Timestamp (unit: nanoseconds)
cmd	list[SingleHandJointCommand]	Control command array, left hand and right hand in order

SingleHandJointState — Single Hand Joint State

Field Name	Type	Description
status_word	int16_t	Status
pos	list[float]	Actual position (unit depends on controller definition)
toq	list[float]	Actual torque (unit: Nm)
cur	list[float]	Actual current (unit: A)
error_code	int16_t	Error code (0 indicates normal)

HandState — Complete Hand Status Information

Field Name	Type	Description
timestamp	int64_t	Timestamp (unit: nanoseconds)
state	list[SingleHandJointState]	All hand joint states (total two), left hand and right hand in order

SingleJointCommand — Single Joint Control Command

Field Name	Type	Description
operation_mode	int16_t	Operation mode (such as position control, velocity control, torque control, etc.), default value is 200
pos	float	Target position (unit: rad or m, depends on joint type)
vel	float	Target velocity (unit: rad/s or m/s)
toq	float	Target torque (unit: Nm)
kp	float	Position loop control gain (proportional term)
kd	float	Velocity loop control gain (derivative term)

JointCommand — Joint Control Command

Field Name	Type	Description
timestamp	int64_t	Timestamp (unit: nanoseconds)
joints	list[SingleJointCommand]	Joint control command array

SingleJointState — Single Joint Status

Field Name	Type	Description
status_word	int16_t	Current joint status (custom state machine encoding)
posH	float	Actual position (high encoder reading, may be redundant encoder)
posL	float	Actual position (low encoder reading)
vel	float	Current velocity (unit: rad/s or m/s)
toq	float	Current torque (unit: Nm)
current	float	Current current (unit: A)
err_code	int16_t	Error code (such as encoder exception, motor overcurrent, etc.)

JointState — Joint State

Field Name	Type	Description
timestamp	int64_t	Timestamp (unit: nanoseconds)
joints	list[SingleJointState]	Joint state array

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Joint Motor Order

Head Joints

Index	Joint Name
0	joint_hy

Upper Arm Joints

Index	Joint Name
0	joint_la1
1	joint_la2
2	joint_la3
3	joint_la4
4	joint_la5
5	joint_la6
6	joint_ra7
7	joint_ra1
8	joint_ra2
9	joint_ra3
10	joint_ra4
11	joint_ra5
12	joint_ra6
13	joint_ra7

Waist Joints

Index	Joint Name
0	joint_wy

Leg Joints

Index	Joint Name
0	left hip roll
1	left hip yaw
2	left hip pitch
3	left knee pitch
4	left ankle pitch
5	left ankle roll
6	right hip roll
7	right hip yaw
8	right hip pitch
9	right knee pitch
10	right ankle pitch
11	right ankle roll

URDF Reference

Robot URDF

Low-Level Motion Control Robot State Introduction

Robot low-level motion mainly develops three-loop control of joints for developers to perform secondary development of robot motion capabilities. Basic control state switching mechanism: