State Machine Lesson

What is a State Machine?

Definitions

  • Technical Definition: An abstract model to outline sequential logic.
  • Conceptual Definition: Think of it as a "map of choices" that are dependent on previous choices.

Core Concepts

  • State: Essentially represents a condition or a set of conditions.
  • Transition: If the condition or state changes, it results in a transition to the next state.

Examples of State Machines

1. Simple Example: Traffic Lights

In this example, the colors are the states.

stateDiagram-v2
 direction LR
 %% States
 Green
 Yellow
 Red

 %% Transitions
 Green --> Yellow : 60 Seconds
 Yellow --> Red : 60 Seconds
 Red --> Green : 60 Seconds

 %% Styling
 style Green fill:#90EE90
 style Yellow fill:#FFFF00
 style Red fill:#FF6B6B

The Logic Flow:

  • After 60 seconds: đŸŸĸ Green transitions to 🟡 Yellow.
  • After an additional 60 seconds: 🟡 Yellow goes to 🔴 Red.
  • After 60 more seconds: 🔴 Red goes to đŸŸĸ Green.

Constraints:

  • đŸŸĸ Green cannot directly transition to 🔴 Red.
  • 🔴 Red cannot directly transition to 🟡 Yellow.

2. Complex Example: Super Mario

In this example, Mario's forms are the states and the items are the conditions for transitioning.

stateDiagram-v2
 direction LR

 %% States
 state "🔴 Mario" as M
 state "🔴➡ī¸đŸ”ĩ Super Mario" as SM
 state "🔴➡ī¸đŸ”Ĩ Fire Mario" as FM
 state "🔴➡ī¸đŸĒļ Cape Mario" as CM

 %% Transitions based on Items (Conditions)
 M --> SM : 🍄 Mushroom
 SM --> FM : đŸ”Ĩ Fire Flower
 SM --> CM : đŸĒļ Feather

 %% Cross Transitions
 FM --> CM : đŸĒļ Feather
 CM --> FM : đŸ”Ĩ Fire Flower

 %% Styling
 style M fill:#FF6B6B,color:#fff
 style SM fill:#4A90E2,color:#fff
 style FM fill:#FFB347,color:#000
 style CM fill:#90EE90,color:#000

The Logic Flow:

  • One state can transition to several other states depending on the conditions.
  • Normal Mario has three different states he can transition to depending on the item he collects.
  • The other states can transition to one another depending on the item.
  • The diagram maps all the transitions Mario can make.

Why Use a State Machine?

  • Reliable: It is reliable and intelligent.
  • Automated Thinking: The code does the thinking for you.
  • Abstraction: Allows you to approach programming from a high-level/abstract perspective.
  • Structure: Think of code as step-by-step logic.

Case Study: 2024 Offbot State Machine

This diagram shows a real-world application used by Team 3255.

2024 Offbot State Machine Diagram

Key Mechanics:

  • Target States: Can be set at any time (via buttons), but the robot remains in the actual state until that state's preconditions are met.
  • Flow Example:
  • Intaking: Transitions to "Store Transfer" when sensor feedback confirms it is finished.
  • Store Transfer: Can branch into various "Prep" states (Speaker, Shuffle, Amp) based on inputs.
  • Shooting: Triggered when the "Same Shoot BTN" is pressed.
  • Climb: Triggered by the driver hitting "up on Climbers".

Implementation Guide

How to Implement a State Machine

Important

States are the goal that the robot is trying to achieve

  1. List States: Before programming, list the states.
  2. Identify Motors: Identify all motors/counts
  3. Categorize Motors: Decide what type of motor it is. Does it go in Motion or Rotors?
  4. Connect the motors: Identify which motors are involved in each state.
  5. Create Issues for Clustered Motors/States: Split the motors/states by Rotors and Motion to avoid merge conflicts.
  6. Assign and Implement Issues to Create Protobot Skeleton
  7. Assign Buttons: Assign buttons to trigger state transitions.
  8. Identify Conditions: Identify transition conditions, including inputs.
  9. Create Diagram: Create a diagram of the states and transitions to show how the completion of one command leads to the next.