Unitree B2 SDK

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Unitree B2 SDK is a development guide for the B2 quadruped robot, providing documentation on...
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### Control Robot Position with MoveToPos API in C++

Source: https://support.unitree.com/home/en/B2_developer/AI%20Motion%20Interface

This C++ example shows how to control the robot's position using the `MoveToPos` API. It subscribes to odometry data to determine the current position and orientation, calculates a target position one meter forward in the robot's base frame, and then commands the robot to move to that target. Dependencies include the Unitree SDK, Eigen for matrix operations, and C++ standard library components.

```cpp
/**
 * @file move_to_pos_test.cpp
 * @brief Use the api named MoveToPos to control the pos of robot
 * @date 2025-07-10
 */
#include <unitree/idl/go2/SportModeState_.hpp>
#include <unitree/robot/b2/sport/sport_client.hpp>
#include <Eigen/Dense>
#include <unitree/robot/channel/channel_subscriber.hpp>

//The topic of odom
#define TOPIC_ODOM_STATE "rt/lf/odommodestate"

using namespace std;
using namespace unitree::common;
using namespace unitree::robot;

//Forced close progress
void MySigintHandler(int sig)
{
  exit(0);
}


class MoveToPosTest{
public:
    MoveToPosTest(){
        sport_client_.SetTimeout(1.0f);
        sport_client_.Init();
    }
    ~MoveToPosTest(){}
    
    void Init(){
        
        odommodestate_subscriber_.reset(new ChannelSubscriber<unitree_go::msg::dds_::SportModeState_>(TOPIC_ODOM_STATE));
        odommodestate_subscriber_->InitChannel(std::bind(&MoveToPosTest::OdomModeStateMessageHandler, this, std::placeholders::_1), 1);
    }
    
    void OdomModeStateMessageHandler(const void *message){
        unitree_go::msg::dds_::SportModeState_ sport_mode_state = *(unitree_go::msg::dds_::SportModeState_*)message;
        
        Eigen::Matrix<float, 3, 1> cur_pose;
        
        yaw_ = sport_mode_state.imu_state().rpy()[2];

        cur_pose[0] = sport_mode_state.position()[0];
        cur_pose[1] = sport_mode_state.position()[1];
        cur_pose[2] = 0.0;

        if(this->have_odom_data_ == false){

            this->have_odom_data_ = true;

            Eigen::Matrix<float, 3, 1> target_in_base;

            //Move one meter along the robot's direction
            target_in_base << 1.0, 0.0, 0.0;

            Eigen::Matrix<float, 4, 1> qua;

            Eigen::Matrix<float, 3, 3> r;

            float c_yaw = cos(yaw_);
            float s_yaw = sin(yaw_);

            r << c_yaw,-s_yaw,0,
                 s_yaw,c_yaw,0,
                 0,0,1;

            target_pos_ = cur_pose + r * target_in_base;

            std::cout << "[Target Pos] is : " << target_pos_.transpose() << std::endl;
            std::cout << "[Target Yaw] is : " << yaw_ << std::endl;

        }
    }

    void run(){
            sport_client_.MoveToPos(target_pos_[0],target_pos_[1],yaw_);
    }


private:
    
    ChannelSubscriberPtr<unitree_go::msg::dds_::SportModeState_> odommodestate_subscriber_;
    
    bool have_odom_data_ = false;
    bool have_send_ = false;

    Eigen::Matrix<float, 3, 1> target_pos_;
    float yaw_;

    unitree::robot::b2::SportClient sport_client_;
};


int main(){

    signal(SIGINT, MySigintHandler);

    unitree::robot::ChannelFactory::Instance()->Init(0);

    MoveToPosTest move_to_pos_test_;

    move_to_pos_test_.Init();

    while(true){
        move_to_pos_test_.run();
    
        sleep(1.0);
    }

    return 0;
}
```

--------------------------------

### Control Robot Velocity with Move API in C++

Source: https://support.unitree.com/home/en/B2_developer/AI%20Motion%20Interface

This C++ example demonstrates how to control the robot's velocity using the `Move` API of the SportClient. It initializes the client, sets the robot to a balanced standing state, enables classic walk mode, and then applies a linear velocity. Dependencies include the Unitree SDK for B2 sport client andunistd.h for sleep functionality.

```cpp
/**
 * @file move_test.cpp
 * @brief Use the api named Move to control the vel of robot
 * @date 2025-07-10
 */
#include <unitree/robot/b2/sport/sport_client.hpp>
#include <unistd.h>

//Forced close progress
void MySigintHandler(int sig)
{
  exit(0);
}

int main()
{
  signal(SIGINT, MySigintHandler);
  
  //Init channel
  unitree::robot::ChannelFactory::Instance()->Init(0);

  //Create SportClient
  unitree::robot::b2::SportClient sport_client;

  //Set time-out period for request
  sport_client.SetTimeout(10.0f);
  
  //Init SportClient
  sport_client.Init();

  //Use api to balance stand  
  sport_client.BalanceStand();
  
  //Use api to ClassicWlak Mode
  sport_client.ClassicWalk(true);
  
  sleep(3);

  //Use api to move
  sport_client.Move(0.3, 0., 0.);
  
  sleep(3);

  //Stop move
  sport_client.StopMove();
  
  return 0;
}
```

--------------------------------

### PathPoint Structure Definition

Source: https://support.unitree.com/home/en/B2_developer/AI%20Motion%20Interface

Defines the structure of a PathPoint, which contains information about a specific point along a tracked path. This includes the time from the start, x and y coordinates, yaw angle, and corresponding velocities (vx, vy, vyaw).

```cpp
typedef struct
{
  float tFromStart; // Time at which the path point is located
  float x; //x position
  float y; //y position
  float yaw; // Yaw angle
  float vx; //x speed
  float vy; //y speed
  float vyaw; // Yaw speed
} PathPoint;

```

--------------------------------

### TrajectoryFollow

Source: https://support.unitree.com/home/en/B2_developer/AI%20Motion%20Interface

Commands the robot to follow a predefined motion trajectory. The trajectory consists of up to 30 PathPoint objects.

```APIDOC
## POST /api/walk/trajectory

### Description
Command the robot to follow a specified motion trajectory.

### Method
POST

### Endpoint
/api/walk/trajectory

### Parameters
#### Request Body
- **path** (array) - Required - An array of PathPoint objects defining the trajectory. Maximum 30 points.
  - **PathPoint** (object) - Represents a point in the trajectory.
    - **x** (float) - X-coordinate.
    - **y** (float) - Y-coordinate.
    - **yaw** (float) - Yaw angle.
    - **duration** (float) - Time duration to reach this point.

### Request Example
```json
{
  "path": [
    {
      "x": 1.0, "y": 0.0, "yaw": 0.0, "duration": 2.0
    },
    {
      "x": 2.0, "y": 1.0, "yaw": 0.5, "duration": 4.0
    }
  ]
}
```

### Response
#### Success Response (200)
- **status** (int32_t) - 0 if successful, otherwise an error code.

#### Response Example
```json
{
  "status": 0
}
```
```

--------------------------------

### ClassicWalk

Source: https://support.unitree.com/home/en/B2_developer/AI%20Motion%20Interface

Enables or disables the classic gait mode. High or low speed levels can be set.

```APIDOC
## POST /api/walk/classic

### Description
Enable or disable the classic gait mode.

### Method
POST

### Endpoint
/api/walk/classic

### Parameters
#### Request Body
- **flag** (boolean) - Required - Set to true to enable classic walk, false to disable.

### Request Example
```json
{
  "flag": true
}
```

### Response
#### Success Response (200)
- **status** (int32_t) - 0 if successful, otherwise an error code.

#### Response Example
```json
{
  "status": 0
}
```

### Remarks
High or low speed levels can be set separately.
```

--------------------------------

### FreeWalk

Source: https://support.unitree.com/home/en/B2_developer/AI%20Motion%20Interface

Activates the free gait mode for the robot. High or low speed levels can be set.

```APIDOC
## POST /api/walk/free

### Description
Activate the free gait mode.

### Method
POST

### Endpoint
/api/walk/free

### Parameters
None

### Request Example
```json
{
  "action": "start"
}
```

### Response
#### Success Response (200)
- **status** (int32_t) - 0 if successful, otherwise an error code.

#### Response Example
```json
{
  "status": 0
}
```

### Remarks
High or low speed levels can be set separately.
```

--------------------------------

### Ai Sport State Types

Source: https://support.unitree.com/home/en/B2_developer/AI%20Motion%20Interface

Details on the data structures and types used to represent the robot's sport state, IMU data, and path points.

```APIDOC
## Ai Sport State Types

### Description
Provides a detailed breakdown of the data structures and their fields used for reporting the robot's sport state and associated information.

### SportModeState_

- **stamp** (TimeSpec) - Timestamp of the state data.
- **errorCode** (uint32_t) - Error code indicating the status of the sport mode.
- **imuState** (IMU) - Structure containing IMU (Inertial Measurement Unit) data.
- **mode** (Uint8_t) - The current sports mode of the robot.
  - 0: idle, default stand
  - 1: balanceStand
  - 3: locomotion
  - 5: lieDown
  - 6: jointLock
  - 7: damping
  - 8: recoveryStand
  - 9: FreeWalk
  - 18: ClassicWalk
  - 19: FastWalk
  - 20: Euler
- **progress** (float) - Action execution status (0.0 for false, 1.0 for true).
- **footRaiseHeight** (float) - The height the foot is raised.
- **position** (std::array<float, 3>) - The 3D position of the robot (x, y, z).
- **bodyHeight** (float) - The height of the robot's body.
- **velocity** (std::array<float, 3>) - The 3D velocity of the robot (vx, vy, vz).
- **yawSpeed** (float) - The rotational speed around the yaw axis.
- **rangeObstacle** (std::array<float, 4>) - Distances to obstacles in different directions.
- **pathPoints** (std::array<PathPoint, 10>) - An array of path points the robot is currently tracking.

### IMU

- **quaternion** (std::array<float, 4>) - Orientation represented as a quaternion (w, x, y, z).
- **gyroscope** (std::array<float, 3>) - Angular velocity in radians per second (x, y, z).
- **accelerometer** (std::array<float, 3>) - Acceleration in m/s^2 (x, y, z).
- **rpy** (std::array<float, 3>) - Roll, Pitch, Yaw angles in radians.
- **temperature** (int8_t) - Temperature sensor reading.

### PathPoint

- **tFromStart** (float) - Time at which the path point is located from the start.
- **x** (float) - X coordinate of the path point.
- **y** (float) - Y coordinate of the path point.
- **yaw** (float) - Yaw angle at the path point.
- **vx** (float) - Velocity along the x-axis.
- **vy** (float) - Velocity along the y-axis.
- **vyaw** (float) - Yaw angular velocity.
```

--------------------------------

### C++: Control B2 Robot Motion with SportClient

Source: https://support.unitree.com/home/en/B2_developer/AI%20Motion%20Interface

Demonstrates how to use the SportClient class in the SDK to send motion commands to the B2 robot, such as balancing, standing, and crouching. It requires the SDK's sport_client library and handles signal interruption for graceful exit. The output is robot motion executed on the B2.

```cpp
/**
 * @file sport_client_test.cpp
 * @brief Use the class named SportClient to request sport mode
 * @date 2025-07-10
 */
#include <unitree/robot/b2/sport/sport_client.hpp>
#include <unistd.h>

//Forced close progress
void MySigintHandler(int sig)
{
  exit(0);
}

int main()
{
  signal(SIGINT, MySigintHandler);

  //Init channel
  unitree::robot::ChannelFactory::Instance()->Init(0);

  //Create SportClient
  unitree::robot::b2::SportClient sport_client;

  //Set time-out period for request
  sport_client.SetTimeout(10.0f);

  //Init SportClient
  sport_client.Init();

  //Use api to balance stand  
  sport_client.BalanceStand();

  sleep(3);

  //Use api to sit down
  sport_client.StandDown();

  sleep(3);

  return 0;
}
```

--------------------------------

### FastWalk

Source: https://support.unitree.com/home/en/B2_developer/AI%20Motion%20Interface

Enables or disables the running gait mode. High or low speed levels can be set.

```APIDOC
## POST /api/walk/fast

### Description
Enable or disable the running gait mode.

### Method
POST

### Endpoint
/api/walk/fast

### Parameters
#### Request Body
- **flag** (boolean) - Required - Set to true to enable fast walk, false to disable.

### Request Example
```json
{
  "flag": true
}
```

### Response
#### Success Response (200)
- **status** (int32_t) - 0 if successful, otherwise an error code.

#### Response Example
```json
{
  "status": 0
}
```

### Remarks
High or low speed levels can be set separately.
```

--------------------------------

### SUBSCRIBE /rt/sportmodestate

Source: https://support.unitree.com/home/en/B2_developer/AI%20Motion%20Interface

Subscribe to the 'rt/sportmodestate' topic to receive real-time motion data from the robot. This includes position, speed, attitude, and IMU status. The topic is published at a high frequency (500Hz).

```APIDOC
## SUBSCRIBE /rt/sportmodestate

### Description
Subscribes to the topic "rt/sportmodestate" to obtain the robot's motion states, including position, speed, and attitude.

### Method
SUBSCRIBE

### Endpoint
rt/sportmodestate

### Parameters
#### Topic Parameters
None

#### Query Parameters
None

#### Request Body
None

### Request Example
None

### Response
#### Success Response (200)
- **state** (unitree_go::msg::dds_::SportModeState_) - A structure containing the robot's current motion state.

#### Response Example
```json
{
  "stamp": {"sec": 1678886400, "nanosec": 123456789},
  "errorCode": 0,
  "imu_state": {
    "quaternion": [0.0, 0.0, 0.0, 1.0],
    "gyroscope": [0.0, 0.0, 0.0],
    "accelerometer": [0.0, 0.0, 9.81],
    "rpy": [0.0, 0.0, 0.0],
    "temperature": 25
  },
  "mode": 1, 
  "progress": 0.0,
  "footRaiseHeight": 0.0,
  "position": [0.0, 0.0, 0.0],
  "bodyHeight": 0.5,
  "velocity": [0.0, 0.0, 0.0],
  "yawSpeed": 0.0,
  "rangeObstacle": [1.0, 1.0, 1.0, 1.0],
  "pathPoints": [
    {
      "tFromStart": 0.0, "x": 0.0, "y": 0.0, "yaw": 0.0, "vx": 0.0, "vy": 0.0, "vyaw": 0.0
    }
  ]
}
```

### Error Handling
None specified for subscription.
```

--------------------------------

### Subscribe to Robot Sport Mode State (C++)

Source: https://support.unitree.com/home/en/B2_developer/AI%20Motion%20Interface

This C++ code snippet demonstrates how to subscribe to the 'rt/sportmodestate' topic to receive real-time motion state data from the robot. It includes a callback function to process incoming messages and print position and IMU quaternion data. Dependencies include the unitree/idl/go2/SportModeState_.hpp and unitree/robot/channel/channel_subscriber.hpp headers.

```cpp
#include <unitree/idl/go2/SportModeState_.hpp>
#include <unitree/robot/channel/channel_subscriber.hpp>

//high frequency (500Hz)
#define TOPIC_HIGHSTATE "rt/sportmodestate"

//low frequency (500Hz) 
//#define TOPIC_HIGHSTATE "rt/lf/sportmodestate"

using namespace unitree::robot;

//Callback function
void SportModeStateHandler(const void* message) 
{
  unitree_go::msg::dds_::SportModeState_ state = *(unitree_go::msg::dds_::SportModeState_*)message;
  
  
  std::cout<<"position: "
           <<state.position()[0]<<", "
           <<state.position()[1]<<", "
           <<state.position()[2]<<std::endl;
  
  std::cout<<": "
           <<state.imu_state().quaternion()[0]<<", "
           <<state.imu_state().quaternion()[1]<<", "
           <<state.imu_state().quaternion()[2]<<", "
           <<state.imu_state().quaternion()[3]<<std::endl;
}


int main()
{
  //Init
  unitree::robot::ChannelFactory::Instance()->Init(0);

  //Create a subscriber to get sport mode state
  ChannelSubscriber<unitree_go::msg::dds_::SportModeState_> sport_mode_state_sub_(TOPIC_HIGHSTATE);

  //Init channel
  sport_mode_state_sub_.InitChannel(SportModeStateHandler);
  
  while(1)
  {
    usleep(20000);
  }
  
  return 0;
}

```

--------------------------------

### VisionWalk

Source: https://support.unitree.com/home/en/B2_developer/AI%20Motion%20Interface

Enables or disables visual walk functionality. When enabled, the robot uses visual input for walking.

```APIDOC
## POST /api/walk/vision

### Description
Enable or disable visual walk mode.

### Method
POST

### Endpoint
/api/walk/vision

### Parameters
#### Request Body
- **flag** (boolean) - Required - Set to true to enable visual walk, false to disable.

### Request Example
```json
{
  "flag": true
}
```

### Response
#### Success Response (200)
- **status** (int32_t) - 0 if successful, otherwise an error code.

#### Response Example
```json
{
  "status": 0
}
```
```

--------------------------------

### Euler

Source: https://support.unitree.com/home/en/B2_developer/AI%20Motion%20Interface

Sets the robot's orientation using Euler angles (roll, pitch, yaw). It is recommended to call BalanceStand before calling Euler.

```APIDOC
## POST /api/pose/euler

### Description
Set the robot's orientation using Euler angles.

### Method
POST

### Endpoint
/api/pose/euler

### Parameters
#### Request Body
- **roll** (float) - Required - Roll angle in radians, range [-0.6~0.6].
- **pitch** (float) - Required - Pitch angle in radians, range [-0.6~0.6].
- **yaw** (float) - Required - Yaw angle in radians, range [-0.6~0.6].

### Request Example
```json
{
  "roll": 0.1,
  "pitch": -0.2,
  "yaw": 0.3
}
```

### Response
#### Success Response (200)
- **status** (int32_t) - 0 if successful, otherwise an error code.

#### Response Example
```json
{
  "status": 0
}
```

### Remarks
It is recommended to call BalanceStand before calling Euler.
```

--------------------------------

### MoveToPos

Source: https://support.unitree.com/home/en/B2_developer/AI%20Motion%20Interface

Commands the robot to move to a specified position (x, y) and yaw angle in the odometer coordinate system. The robot will continue stepping even if the current speed is 0 after initiating continuous walk.

```APIDOC
## POST /api/move/position

### Description
Move the robot to a specified position and yaw angle.

### Method
POST

### Endpoint
/api/move/position

### Parameters
#### Request Body
- **x** (float) - Required - The target X-coordinate.
- **y** (float) - Required - The target Y-coordinate.
- **yaw** (float) - Required - The target yaw angle.

### Request Example
```json
{
  "x": 1.0,
  "y": 0.5,
  "yaw": 0.1
}
```

### Response
#### Success Response (200)
- **status** (int32_t) - 0 if successful, otherwise an error code.

#### Response Example
```json
{
  "status": 0
}
```
```

--------------------------------

### Ai Sport State Data Structure Overview

Source: https://support.unitree.com/home/en/B2_developer/AI%20Motion%20Interface

This section outlines the various data fields available within the Ai sport state, including timestamps, error codes, IMU status, sport modes, action progress, and physical attributes like position and velocity. It details the methods for accessing these states and provides a reference for different sport modes.

```cpp
TimeSpec stamp(); 
uint32_t errorCode(); // Error
IMU imuState();// IMU status
Uint8_t mode();// Sports mode
/* Sports mode
0. idle, default stand
1. balanceStand
3. locomotion
5. lieDown
6. jointLock
7. damping
8. recoveryStand
9. FreeWalk
18.ClassicWalk
19.FastWalk
20.Euler

*/

float progress(); // Action execution status: 0. dance false; 1. dance true

float footRaiseHeight();// Leg lift height
std::array<float, 3> position();// 3D position
float bodyHeight();// Body height
std::array<float, 3> velocity();// Three-dimensional velocity
float yawSpeed();// Yaw speed
std::array<float,4> rangeObstacle();// Obstacle distance
std::array<PathPoint, 10> pathPoints();// The current tracked path point

```

--------------------------------

### HandStand

Source: https://support.unitree.com/home/en/B2_developer/AI%20Motion%20Interface

Activates or deactivates the handstand function. This is a dangerous function and requires a 3-meter radius clear of people and obstacles.

```APIDOC
## POST /api/action/handstand

### Description
Enable or disable the handstand function.

### Method
POST

### Endpoint
/api/action/handstand

### Parameters
#### Request Body
- **flag** (boolean) - Required - Set to true to enable handstand, false to disable.

### Request Example
```json
{
  "flag": true
}
```

### Response
#### Success Response (200)
- **status** (int32_t) - 0 if successful, otherwise an error code.

#### Response Example
```json
{
  "status": 0
}
```

### Remarks
Ensure a 3-meter radius is clear of people and obstacles before enabling. Unitree Technology is not responsible for damages caused by misoperation.
```

--------------------------------

### AutoRecoverySet

Source: https://support.unitree.com/home/en/B2_developer/AI%20Motion%20Interface

Enables or disables the automatic recovery function. When enabled, the robot attempts to recover its balance and defaults to free gait upon success. Ensure a 3-meter radius is clear during recovery.

```APIDOC
## POST /api/recovery/auto

### Description
Enable or disable the automatic recovery function.

### Method
POST

### Endpoint
/api/recovery/auto

### Parameters
#### Request Body
- **flag** (boolean) - Required - Set to true to enable automatic recovery, false to disable.

### Request Example
```json
{
  "flag": true
}
```

### Response
#### Success Response (200)
- **status** (int32_t) - 0 if successful, otherwise an error code.

#### Response Example
```json
{
  "status": 0
}
```

### Remarks
Ensure a 3-meter radius is clear of people and obstacles when the robot is recovering.
```

--------------------------------

### IMU Data Acquisition Methods

Source: https://support.unitree.com/home/en/B2_developer/AI%20Motion%20Interface

This snippet details the methods used to retrieve Inertial Measurement Unit (IMU) data, including orientation as a quaternion, angular velocity, acceleration, and Roll-Pitch-Yaw (RPY) angles. It also includes a method for obtaining the IMU temperature.

```cpp
std::array<float, 4> quaternion();    // Quaternion (w, x, y, z)
std::array<float, 3> gyroscope();    // Angular velocity (unit: rad/s)
std::array<float, 3> accelerometer();    // Acceleration m/(s2)
std::array<float, 3> rpy();    // Unit: rad
int8_Temperature ();// temperature

```

--------------------------------

### SwitchMoveMode

Source: https://support.unitree.com/home/en/B2_developer/AI%20Motion%20Interface

Switches the robot's movement response mode. Continuous response mode ensures the robot always responds to the latest command, while disabling it makes the robot stop after one second without new commands.

```APIDOC
## POST /api/move/mode/switch

### Description
Switch the robot's movement response mode between continuous and default.

### Method
POST

### Endpoint
/api/move/mode/switch

### Parameters
#### Request Body
- **flag** (boolean) - Required - Set to true to enable continuous response mode, false to disable.

### Request Example
```json
{
  "flag": true
}
```

### Response
#### Success Response (200)
- **status** (int32_t) - 0 if successful, otherwise an error code.

#### Response Example
```json
{
  "status": 0
}
```

### Remarks
Continuous response mode is disabled by default. Use with caution.
```
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