Reminder: Readings are your responsibility. You will be expected to come to class prepared, having read the material, and ready to participate in the discussion
Logistics
Homework submission details
- If you submit an assignment, code, a video or whatever
- We may very well grade it
- If you want to submit a revision before the cutoff
- You need to tell us because we don’t get a notification
- Your assignment will be considered late and so cannot get an “exceeds”
Team Standups
| Project | Team |
|---|
| Tom and Jerry: The Cheese Napping | Vedanshi Shah and Parthiv Ganguly |
| Red Object Picker | "Sonny George and Alex Danilkovas |
| Starship Bot Clone | "Artem Lavrov, Zach Hovatter, Ephraim Zimmerman |
| Precision Agriculture Robot | Ming-Shih Wang and Jiahao Li |
| Dungeons and Robot | "Yutian (Tim) Fan |
| Smart Cleaning Bot with Voice Control | Zhenxu Chen Pang Liu |
| Rights of Robot | Haochen Lin and Zixin Jiang |
| Autonomous Taxi Sim | Chao An |
| Hide and Seek | Jungju Lee Daphne Pissios abd Chloe Wahl-Dassule |
| Micro Mouse | Sam Herman |
| Bot Follower/Mapper | Eric Hurchey |
| Counter Strike Bot | Zared Cohen Harry Yu and TsunOn Kwok |
| Gesture Control Bot | Leo Gao and Jeffrey Wang |
| Micro Mouse | Ben Zhang |
Introduction to Behavior Trees
- Some similarity to FSM, however…
- BTs are specifically trees, with one root and leaves
- BTs have different
kinds of nodes with very different semantics
- The
leaves represent the actual control actions
- All the other nodes are part of the control logic
py_trees
- This example uses this library: py_trees
- As we are using ROS1, you need to use py_trees 0.7 of this library
- Latest version is not compatible with the current version of ROS
Behavior Tree Execution
- “Tick” oriented control flow
- A tree is “ticked”, which “ticks” the top node
- Each node type has specific semantics about what happens on a tick
- Nodes can return one of: SUCCESS, FAILURE, RUNNING
Node Types
- These control flow
- Sequence - perform each child node in turn as long as they return SUCCESS
- Selector - perform the first child node that returns SUCCESS
- … several mode
- Behavior nodes actually DO somerthing
Behavior Tree Returns
Behavior Nodes - Example
- Behavior nodes are the leaf nodes.
- They execute code which actually “do something” to outside of the tree
- They could cause an action or read a sensor or anything else.
- Simple example:
blink light once would:
- On Update: Tell the hardware to turn the light on and off; Return SUCCESS (because it always works.)
- Simple example:
turn light on with a parameter: n seconds, would:
- On Init: set initial time <- current time; turn the light on
- On Update: if current time > initial time + n: turn off the light; return SUCCESS; else return RUNNING
Behavior Nodes
- Life Cycle of a behavior node
- Setup (optional): one time initiatlization of state when first instantiated
- Initialize (optional): called each time that the node is entered anew (i.e. when its not RUNNING)
- Update (required): called each time the node is ticked
- Terminate (optional): called whenever the node goes to not RUNNING
Composites
- The non-leaf nodes are all known as composites
- Generally the leftmost leaf is
ticked first
- Depending on Composite type and returned status of that node, different next nodes may be ticked
- Core (traditional) set of Composites are: Sequence, Selector, Parallel
- But depending on the library, there may be other variations (which are all extensions of this set.
Sequence
- Most common
- Tick from left to right
- Each SUCCESS result leads to the next node
- Any non-SUCCESS ends the sequence and returns that same status up the chain
Selector
- Also very useful, kind of the reverse
- Tick from left to right as long as the child returns FAILURE
- The first non-failure makes the whole Composit3e return
Parallel
- Returns FAILURE if any child returns FAILURE
- Otherwise keeps ticking all the children
- Depending on policy it will return when one or all the children have returned SUCCESS
Thank you. Questions?
(random Image from picsum.photos)