Our build and extension of the Stanford Pupper Robot. Codename: C.E.R.B.A.R.I.S.
Introduction | Team | Hardware | Software Overview | Software Setup | Computer Vision | Collision Avoidance | Web Interface | Odometry | Behavioral Control |
The Pupper robot operates by using a PS4 controller to send commands to the robot via bluetooth.To do this it utilizes the following 4 repositories from Stanford Robotics Club:
This package is central to how the robot communicates between asynhronously running parallel processes. This package functions through the use of Sockets and functions by setting up Server (UDPComms.Publisher) and Client (UDPComms.Subscriber) sockets on a local ethernet port facilitating one-way communication. Both the Publisher and Subscriber must be created before a message is sent or read, and if either end of the communication path is closed then both must be re-created.
To use UDPComms, the local ethernet, eth0, must be set to static IP 10.0.0.255.
Example usage of UDPComms:
from UDPComms import Publisher, Subscriber, timeout
pub = Publisher(1234)
sub = Subscriber(1234)
msg = {'name': 'John', 'height': 172}
pub.send(msg)
msg2 = {'name': 'Mary', 'height': 160}
pub.send(msg)
try:
recevied = sub.get()
except timeout:
received = None
The above code would result in received being {'name': 'Mary', 'height': 160} since that was the last message sent. The Publisher adds messages to a first-in-last-out stack and the Subscriber pops the top message from the stack. Calling sub.get() again would return John’s information. UDPComms sends messages by first converting them to bytes, so any object that can be reliably converted into bytes can be sent via UDPComms.
This library handles connection and communcation with a PS4 controller via bluetooth. This is handled through the Joystick object which when instantiated will wait for a PS4 controller to connect. The PS4 controller can be paired by holding the share and power buttons at the same time until you see a double-blinking white light.
Example:
from PS4Joystick import Joystick
joystick = Joystick()
joystick.led_color(red=0, blue=0, green=255)
values = joystick.get_input()
The get_input() command will return a dictionary representing the current state of the controller.
Keys:
This repository houses the joystick.py script which run a loops that periodically queries the PS4 joystick and reformats the command to send to the Pupper robot command loop via UDPComms channel 8830. This can be run directly as python script or via a UNIX background service.
This project contains the code that actually controls to robot’s movement,
chooses it’s gait and behavior and sends PWM signals to the servos. This is all
carried out by the execution of the run_robot.py script. This script
initalizes and maintains 4 important objects:
State object which keeps track of the Pupper’s behavioral_state (REST,
TROT, HOP, FINSIHHOP, or DEACTIVATED), orientation, velocity, foot locations
and joint anglesJoystickInterface which reads command input from UDP channel 8830 which
should be coming form the PupperCommand joystick.py script.Conrtoller which uses the current state and command input to compute the
next joint angles for the robot and update the State object.HardwareInterface which gets the joint angles from the state object and
sets the servos to those angles.This process can be run directly as a python script or run as a background unix service. See Software Setup to see how to setup and run this.
In order to take programatic control of the Pupper robot we replaced the function of the PupperCommand joytick.py script with our own pupperpy.CommandInterface.Control object.
If pupperpy is installed with sudo pip3 then all necessary processes for robot operation can be run with sudo python3 /path/to/PupperPy/pupperpy/run_cerbaris.py
Unlike the joystick script, our controller is an object that is instantiated and is then run.
When created the Control object creates:
pupperpy.ControllerState.ControllerState object which keeps track of the
current commands to be sent to the robot and acted uponpupper_vision.py scriptpupperpy.object_detection.ObjectSensors object to monitor the state of
the IR object sensorspupperpy.position.PositionTracker object which maintains a pointer to the
ControllerState object and setups comunication with the IMU so that it can
use current command state and IMU information to update a Kalman filter and
track robot position, velocity, acceleration and heading._step() function every 1/20 secPS4Joystick.Joystick object so that the PS4 controller can be used to
activate and emergency stop the robotOn every iteration of the loop the _step() function checks the joystick for
activation (L1) or emergency stop (L2) commands, otherwise it uses
update_behavior() to check sensor data and update movement commands and then
sends those to both the run_robot script and to the web interface.
Additionally, this interface simplfies the creation of new behaviors through the use of simplified movement commands:
control.move_forward() # moves forward at max safe velocity
control.move_backward() # moves backward at max safe velocity
control.move_stop() # stops forward and backward movement
control.turn_left() # turns left
control.turn_right() # turns right
control.turn_stop() # stops turning
control.activate() # Activates robot, initializes motor positions
control.start_walk() # switches robot gait from REST to TROT
control.stop_walk() # switches robot gait from TROT to REST
One can simply extend the control object and override the update_behavior
function in order to implement new behavior.
The existing behavior is very simple.