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

Interface Definition

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

LowLevelMotionController — Low-Level Motion Controller

Item	Description
Class Name	LowLevelMotionController
Overview	Low-level joint motion controller providing precise joint control
Main Functions	Joint state subscription, joint command publishing, control period setting
Use Cases	Precise motion control, custom gait, research and development

initialize

Item	Description
Method Name	initialize
Declaration	bool initialize()
Overview	Initialize the controller and establish low-level connections.
Return Value	true for success, false for failure.
Note	Must be called before first use.

shutdown

Item	Description
Method Name	shutdown
Declaration	void shutdown()
Overview	Shut down the controller and release low-level resources.
Note	Used together with initialize.

set_period_ms

Item	Description
Method Name	set_period_ms
Declaration	void set_period_ms(int period_ms)
Overview	Set the control period in milliseconds.
Parameter	period_ms: Period in milliseconds.
Note	Non-blocking interface. The controller uses this period to set the frequency of joint command sending.

subscribe_leg_state

Item	Description
Method Name	subscribe_leg_state
Declaration	void subscribe_leg_state(callback)
Overview	Subscribe to leg joint state data.
Parameter	callback: Callback function to handle received leg joint state data. Function signature: callback(data : LegState) -> None
Note	Non-blocking interface.

publish_leg_command

Item	Description
Method Name	publish_leg_command
Declaration	Status publish_leg_command(LegJointCommand command)
Overview	Publish leg joint control commands.
Parameter	command: Leg joint control command containing target angles/velocities, etc.
Return Value	Status::OK for success, others for failure.
Note	Non-blocking interface.

enable_send_msg

Item	Description
Method Name	enable_send_msg
Declaration	Status enable_send_msg(bool enable)
Overview	LCM channel switch.
Parameter	enable: LCM channel switch information.
Return Value	Status::OK for success, others for failure.
Note	When using high-level motion control, turn off the LCM channel; when using low-level motion control, turn on the LCM channel.

Data Structure Definitions

LegJointCommandArray — Leg Joint Command Array

Item	Description
Type	Python binding of std::array<magic::dog::SingleLegJointCommand, magic::dog::kLegJointNum>
Overview	Fixed-size array of leg joint commands, containing control commands for all leg joints
Main Methods	Supports index access, iteration, and length query. Length is fixed to the number of leg joints.
Use Cases	Leg motion control, joint coordination control, gait planning

LegJointStateArray — Leg Joint State Array

Item	Description
Type	Python binding of std::array<magic::dog::SingleLegJointState, magic::dog::kLegJointNum>
Overview	Fixed-size array of leg joint states, containing real-time state information for all leg joints
Main Methods	Supports index access, iteration, and length query. Length is fixed to the number of leg joints.
Use Cases	Joint state monitoring, motion feedback, safety detection

SingleLegJointCommand — Single Leg Joint Command Structure

Field Name	Type	Description
q_des	float	Desired joint angle
dq_des	float	Desired joint angular velocity
tau_des	float	Desired joint torque
kp	float	Position gain
kd	float	Velocity gain

LegJointCommand — Leg Joint Command Structure

Field Name	Type	Description
timestamp	int	Timestamp
cmd	LegJointCommandArray	List of joint commands

SingleLegJointState — Single Leg Joint State Structure

Field Name	Type	Description
q	float	Joint angle
dq	float	Joint angular velocity
tau_est	float	Estimated joint torque

LegState — Leg State Structure

Field Name	Type	Description
timestamp	int	Timestamp
state	LegJointStateArray	List of joint states

URDF Reference

Robot URDF

Introduction to Low-Level Motion Control Robot States

The robot's low-level motion mainly refers to the three-loop joint control, enabling developers to further develop the robot's motion capabilities. The basic control state switching mechanism: