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
Function Name	LowLevelMotionController
Function Declaration	LowLevelMotionController();
Function Overview	Constructor, initializes low-level controller object.
Notes	Constructs internal resources.

~LowLevelMotionController

Item	Content
Function Name	~LowLevelMotionController
Function Declaration	virtual ~LowLevelMotionController();
Function Overview	Destructor, releases resources.
Notes	Cleans up low-level resources.

Initialize

Item	Content
Function Name	Initialize
Function Declaration	virtual bool Initialize() override;
Function Overview	Initialize controller, establish low-level connections.
Return Value	true indicates success, false indicates failure.
Notes	Must be initialized on first call.

Shutdown

Item	Content
Function Name	Shutdown
Function Declaration	virtual void Shutdown() override;
Function Overview	Shutdown controller, release low-level resources.
Notes	Used in conjunction with Initialize.

SetPeriodMs

Item	Content
Function Name	SetPeriodMs
Function Declaration	void SetPeriodMs(uint64_t period_ms);
Function Overview	Set control cycle time (milliseconds).
Parameter Description	period_ms: Cycle time, unit is milliseconds.
Notes	Non-blocking interface, cycle parameter used internally by controller, controls joint command sending frequency.

SubscribeArmState

Item	Content
Function Name	SubscribeArmState
Function Declaration	void SubscribeArmState(ArmJointStateCallback callback);
Function Overview	Subscribe to arm joint state data
Parameter Description	callback: Data processing function
Notes	Non-blocking interface.

PublishArmCommand

Item	Content
Function Name	PublishArmCommand
Function Declaration	Status PublishArmCommand(const JointCommand& command);
Function Overview	Publish arm control commands
Parameter Description	command: Target position/velocity etc.
Return Value	true indicates success, false indicates failure.
Notes	Non-blocking interface.

SubscribeLegState

Item	Content
Function Name	SubscribeLegState
Function Declaration	void SubscribeLegState(LegJointStateCallback callback);
Function Overview	Subscribe to leg joint state data
Parameter Description	callback: Data processing function
Notes	Non-blocking interface.

PublishLegCommand

Item	Content
Function Name	PublishLegCommand
Function Declaration	Status PublishLegCommand(const JointCommand& command);
Function Overview	Publish leg control commands
Parameter Description	command: Target position/velocity etc.
Return Value	true indicates success, false indicates failure.
Notes	Non-blocking interface, called when publishing or subscribing.

SubscribeHeadState

Item	Content
Function Name	SubscribeHeadState
Function Declaration	void SubscribeHeadState(HeadJointStateCallback callback);
Function Overview	Subscribe to head joint state data
Parameter Description	callback: Data processing function
Notes	Non-blocking interface.

PublishHeadCommand

Item	Content
Function Name	PublishHeadCommand
Function Declaration	Status PublishHeadCommand(const JointCommand& command);
Function Overview	Publish head control commands
Parameter Description	command: Target position/velocity etc.
Return Value	true indicates success, false indicates failure.
Notes	Non-blocking interface.

SubscribeWaistState

Item	Content
Function Name	SubscribeWaistState
Function Declaration	void SubscribeWaistState(WaistJointStateCallback callback);
Function Overview	Subscribe to waist joint state data
Parameter Description	callback: Data processing function
Notes	Non-blocking interface.

PublishWaistCommand

Item	Content
Function Name	PublishWaistCommand
Function Declaration	Status PublishWaistCommand(const JointCommand& command);
Function Overview	Publish waist control commands
Parameter Description	command: Target position/velocity etc.
Return Value	true indicates success, false indicates failure.
Notes	Non-blocking interface.

SubscribeHandState

Item	Content
Function Name	SubscribeHandState
Function Declaration	void SubscribeHandState(HandStateCallback callback);
Function Overview	Subscribe to hand state data
Parameter Description	callback: Data processing function
Notes	Non-blocking interface.

PublishHandCommand

Item	Content
Function Name	PublishHandCommand
Function Declaration	Status PublishHandCommand(const HandCommand& command);
Function Overview	Publish hand control commands
Parameter Description	command: Hand joint target position etc.
Return Value	true indicates success, false indicates failure.
Notes	Non-blocking interface.

SubscribeBodyImu

Item	Content
Function Name	SubscribeBodyImu
Function Declaration	void SubscribeBodyImu(const BodyImuCallback& callback);
Function Overview	Subscribe to body IMU data
Parameter Description	callback: IMU data processing function
Notes	Non-blocking interface.

Type Definitions

SingleHandJointCommand — Single Hand Joint Control Command

Field Name	Type	Description
operation_mode	int16_t	Control word
pos	vector<float>	Desired position array (7 DOF, unit: rad)

---

HandCommand — Complete Hand Control Command

Field Name	Type	Description
timestamp	int64_t	Timestamp (unit: nanoseconds)
cmd	vector<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 word
pos	vector<float>	Current position (unit: rad)
toq	vector<float>	Current torque (unit: Nm)
cur	vector<float>	Current current (unit: A)
error_code	int16_t	Error code

---

HandState — Complete Hand State Information

Field Name	Type	Description
timestamp	int64_t	Timestamp (unit: nanoseconds)
state	vector<SingleHandJointState>	All hand joint states (left hand, right hand order)

---

SingleJointCommand — Single Joint Control Command

Field Name	Type	Description
operation_mode	int16_t	Control mode identifier: • 200=Ready state • 3=Mixed loop force control (position+torque) • 4=Series PID (position loop+velocity loop) • 5=ADRC position control (active disturbance rejection control)
pos	float	Target position (unit: rad)
vel	float	Velocity limit (unit: rad/s)
toq	float	Torque limit (unit: Nm)
kp	float	Position loop proportional gain
kd	float	Velocity loop derivative gain

• Left arm or right arm joints 1-5 operation_mode needs to switch from mode: 200 to mode: 4 (Series PID mode) for command sending;
• Waist joint 1 operation_mode needs to switch from mode: 200 to mode: 5 (ADRC position control mode) for command sending;
• Left leg or right leg joints 1-6 operation_mode needs to switch from mode: 200 to mode: 3 (Mixed loop force control mode) and ADRC position control mode (5) for command sending;

---

JointCommand — Joint Control Command

Lower limbs contain 12 joint items, upper limbs 10(14), head 1(2), waist 1:

Field Name	Type	Description
timestamp	int64_t	Timestamp (unit: nanoseconds)
joints	vector<SingleJointCommand>	Control commands for all joints

---

SingleJointState — Single Joint State Information

Field Name	Type	Description
status_word	int16_t	Current joint state (custom state machine encoding)
posH	float	Actual position (high-precision encoder reading)
posL	float	Actual position (low-precision encoder reading, for redundancy check)
vel	float	Current velocity (unit: rad/s or m/s, automatically switches based on joint type)
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., see error code reference table)

---

JointState — Joint State Data

Lower limbs contain 12 joint items, upper limbs 10(14), head 1(2), waist 1:

Field Name	Type	Description
timestamp	int64_t	Timestamp (unit: nanoseconds)
joints	vector<SingleJointState>	State data for all joints

---

Joint Motor Order

Head Joints

Index	Joint Name
0	joint_hy
1	joint_hp

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: