Provides low-level motion control services for the robot system. Through LowLevelMotionController, you can use topic-based communication to send joint commands and receive joint states.

Interface Definition

LowLevelMotionController is a motion controller for low-level development, supporting direct control and state subscription of leg and other moving parts.

LowLevelMotionController

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

~LowLevelMotionController

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

Initialize

Item	Description
Function Name	Initialize
Declaration	virtual bool Initialize() override;
Overview	Initializes the controller and establishes low-level connections.
Return Value	true means success, false means failure.
Note	Must be initialized on first call.

Shutdown

Item	Description
Function Name	Shutdown
Declaration	virtual void Shutdown() override;
Overview	Shuts down the controller and releases low-level resources.
Note	Used together with Initialize.

SetPeriodMs

Item	Description
Function Name	SetPeriodMs
Declaration	void SetPeriodMs(uint64_t period_ms);
Overview	Set control period time (milliseconds).
Parameter	period_ms: Period time in milliseconds.
Note	Non-blocking interface. The controller uses this period parameter internally to set the frequency of joint command sending.

SubscribeLegState

Item	Description
Function Name	SubscribeLegState
Declaration	void SubscribeLegState(LegJointStateCallback callback);
Overview	Subscribe to leg joint state data.
Parameter	callback: Callback function to handle received leg joint state data.
Note	Non-blocking interface.

PublishLegCommand

Item	Description
Function Name	PublishLegCommand
Declaration	Status PublishLegCommand(const LegJointCommand& command);
Overview	Publish leg joint control command.
Parameter	command: Leg joint control command containing target position/velocity and other control information.
Return Value	Status::OK means success, others mean failure.
Note	Non-blocking interface.

EnableSendMsg

Item	Description
Function Name	EnableSendMsg
Declaration	void EnableSendMsg(bool enable);
Overview	LCM channel switch
Parameter	enable: LCM channel switch information
Note	When using high-level motion control, turn off the LCM channel; when using low-level motion control, turn on the LCM channel.

Type Definitions

SingleLegJointCommand — Control command for a single leg joint

Field Name	Type	Description
q_des	float	Desired joint position
dq_des	float	Desired joint velocity
tau_des	float	Desired feedforward torque
kp	float	P gain, must be positive
kd	float	D gain, must be positive

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LegJointCommand — Control command for the entire leg

Field Name	Type	Description
timestamp	int64_t	Timestamp (unit: nanoseconds)
cmd	std::array<SingleLegJointCommand, kLegJointNum>	Array of control commands

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SingleLegJointState — State of a single leg joint

Field Name	Type	Description
q	float	Actual joint position
dq	float	Actual joint velocity
tau_est	float	Estimated torque

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LegState — State information for the entire leg

Field Name	Type	Description
timestamp	int64_t	Timestamp (unit: nanoseconds)
state	std::array<SingleLegJointState, kLegJointNum>	All leg joint states

URDF Reference

Robot URDF

Introduction to Low Level Motion Control Robot States

The robot's low-level motion mainly provides three-loop joint control for developers to enable secondary development of robot motion capabilities. The basic control state switching mechanism: