Robobot MQTT-client

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MQTT-client in Python

This skeleton is intended as the mission controller app.

mqtt-client.py

This is the primary file in the mission control skeleton.

It is intended to run on the Raspberry Pi, using the command:

cd ~/svn/robobot/mqtt_python
python3 mqtt-client.py

All the interfaces have a network interface except the GPIO (General Purpose Input Output). This allows the app to run anywhere with network access to the robot.

Command line parameters

The app has defined a few command line parameters, among these help:

python3 mqtt-client.py --help
% Starting
usage: mqtt-client.py [-h] [-w] [-g] [-l] [-s] [-n]
Robobot app 2024
options:
 -h, --help    show this help message and exit
 -w, --white   Calibrate white tape level
 -g, --gyro    Calibrate gyro
 -l, --level   Calibrate horizontal
 -s, --silent  Print less to console
 -n, --now     Start drive now (do not wait for start button)

The command line options include some sensor calibration. The distance sensor calibration is missing (but needed).

Main loop

The

MQTT service

This module handles the MQTT communication.

Robot

This module decodes some of the robot's basic data, e.g., battery voltage.

All the data interfaces have an update counter that estimates the interval between updates. This is intended as a debug measure to detect potential slow network situations.

Pose

The robot pose has data related to the robot's movement.

The data is provided by requesting configuration data directly from Teensy and listening to the data streams configured by the teensy_interface.

The streamed data is

• Wheel velocity (message topic robobot/drive/T0/vel) in m/s.
• Motor velocity (message topic robobot/drive/T0/mvel) before the gear. The unit is radians/sec. This stream is probably not needed.
• The robot pose (message topic robobot/drive/T0/pose) is the x,y position and the robot heading as calculated in the Teensy.

Distance

The IR distances are received from Teensy and should be in meters, but this requires some calibration.

The distance sensor can give unreliable values if the infrared beam is not reflected within about 1m. This is why the sensor's default position points slightly down towards the floor.

Line

The line sensor has 8 reflection channels. This module receives a data stream with normalized values (assuming the sensor is calibrated).

Calibration on a white line is needed and can be done with a command line option.

There is a tape line position estimator in this module. It is based on an average calculation and is probably not good to follow a line edge in junctions.

See a data example in the next section.

Camera

The camera module captures images from the camera server stream.

The server sets the resolution and framerate.

A small example of using openCV to manipulate image frames is included.

The annotations in the image are the line sensor data with a white tape line to the left.

GPIO

Eight of the Raspberry Pi pins are available as general-purpose input-output. Two are dedicated as start and stop buttons.

The GPIO board has drivers capable of driving a high current (pull a relay or similar).

A button is available on all lines to give a signal to an input line and to simulate an output line.

See the circuit diagram for the IO board here Robobot circuits.

Log

A simple logging module is provided. The intention is to make a file with essential data that can be used for Matlab plotting.

The first lines are intended to describe the data columns. They are preceded by a "%" that will be seen as a comment by Matlab.

Remarks, like state change, can be added, and will be saved in the file with the "%" and a timestamp.

The default log looks like (logfile.txt):

% logfile for Python side
% 1 time (sec)
% 2 Mission state
% 3,4,5 (x,y,h) (m,m,rad)
% 6 Camera frame count
% 7 Line sensor line position
% 8,9 trip A (distance and heading change)
% 10,11 trip B (distance and heading change)
1737224641.0107589 0 0.000 0.000 0.000 2 -1.22 0.000 0.0000.0000 0.0000
1737224641.036046 0 0.000 0.000 0.000 2 -1.27 0.000 0.0000.0000 0.0000
1737224641.0549598 20 0.000 0.000 0.000 2 -1.25 0.000 0.0000.0000 0.0000
% 1737224641.05497 % State change from 0 to 20
1737224641.061122 20 0.000 0.000 0.000 2 -1.25 0.000 0.0000.0000 0.0000
1737224641.0862672 20 0.000 0.000 0.000 2 -1.22 0.000 0.0000.0000 0.0000
1737224641.1113825 20 0.000 0.000 0.000 2 -1.26 0.000 0.0000.0000 0.0000
1737224641.1366208 20 0.000 0.000 0.000 2 -1.21 0.000 0.0000.0000 0.0000
1737224641.201906 20 0.000 0.000 0.000 2 -1.20 0.000 0.0000.0000 0.0000
1737224641.2038832 20 0.000 0.000 0.000 2 -1.22 0.000 0.0000.0000 0.0000

The robot is not moving, but the state and line sensor estimates are visible.