guppy_state

Node, service, and message for managing the guppy state machine over ROS.

States

The following states are expected by the change_state service,

• STARTUP
• HOLDING
• NAV
• TASK
• TELEOP
• DISABLED
• FAULT

They are represented by 8-bit unsigned integers and published to the /state topic. When reading this state, use the constants provided by the state message for comparison as mentioned below.

Service Definition

Use the change_state service like this tutorial to format a request according to the definition:

guppy_msgs/State state
---
bool success

This can be imported from ../guppy_msgs/srv/ChangeState.srv as guppy_msgs::srv::ChangeState::Request in C++ or from guppy_msgs.srv import ChangeState in Python.

Constants

Defined in the state message from are the following constants.

uint8 STARTUP   = 0
uint8 HOLDING   = 1
uint8 NAV       = 2
uint8 TASK      = 3
uint8 TELEOP    = 4
uint8 DISABLED  = 5
uint8 FAULT     = 6

Use these to create a State message and ChangeState request to ensure you set the correct state. They are defined in ../guppy_msgs/msg/State.msg and are included. The startup state, for example, is represented by guppy_msgs::msg::State::STARTUP in C++ or State.STARTUP in Python.

Transitioning

Transitioning between states is handled by the state manager according to the graph below. Importantly, the STARTUP state is not reachable from any other state and once the FAULT state is hit there is no way to transition to another state. The service will return a true if transitioning to the state was successful and false otherwise.

Using /cmd_vel

The /cmd_vel topic is published to by the state manager by forwarding the twist messages of from the subtopic of the active state, ie. guppy_teleop now published to the /cmd_vel/teleop topic and, provided guppy is in the TELEOP state, the state manager will forward these messages to /cmd_vel.

Change State Example

After creating a node,

rclcpp::Client<guppy_msgs::srv::ChangeState>::SharedPtr client = node->create_client<guppy_msgs::srv::ChangeState>("change_state");

Then format a request using the State message from ../guppy_msgs/msg/State.msg.

auto message = guppy_msgs::msg::State();
message.state = guppy_msgs::msg::State::NAV;

auto request = std::make_shared<guppy_msgs::srv::ChangeState::Request>();
request->new_state = message;

auto result = client->async_send_request(request);

if (rclcpp::spin_until_future_complete(node, result) == rclcpp::FutureReturnCode::SUCCESS) {
    // SUCCESS
} else {
    // FAIL
}

Refer to this ROS2 tutorial for more information.