state-management-services.md

Overview

This week, we built an enum, all_states.py to represent the varying states of the robot, and two ROS services: StateChange manages state changes, as well as any associated publishes, and StateQuery reports the current state of the robot. Both services are hosted in the state.py node.

While the robot's states aren't too complicated yet, our goal was to create a modular architecture to make it easy to add new states as the robot's functionality expands.

StateQuery

StateQuery is a service that takes no arguments, and returns the state of the robot as the string value of the appropriate enum.

all_states.py

all_states.py serves two purposes: It defines a series of enums for the various states of the robot, and it defines methods to act as the service clients. In any node that needs to request a state change or get the current state of the robot, add from all_states import * to gain access to the enums (type State) and the two methods.

• get_state acts as a client method for the StateQuery service, taking no parameters and returning the string value of the robot's state.

• change_state acts as a client method for the StateChange service, taking up to three parameters and returning a boolean value of whether or not the state change was legal:

  • new_state: The string value of the desired new state

  • to_say: A message to be said by talk.py upon the state change

  • pose_to_pub: A Pose to be published, if the new state is either NAVIGATING or LOCALIZING

state.py

state.py contains the code needed to keep track of the robot's current state and facilitate state changes. It includes the is_legal method, which contains a dict mapping every state to an array of the states that could legally follow it.

If an illegal state change is requested, the current state of the robot is set to States.ILLEGAL_STATE_CHANGE.

Ari Carr and Ben Albert 11/14/2018