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RC Robot Project

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Assembling the Kit

Notice the red & black wires

Left Side Back = Red on top

Left Side Front = Black on top

Right Side Back = Black on top

Right Side Front = Red on top

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Something like this ...

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Front

Back

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The Raspberry Pi

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The L298N H-bridge (motor controller)

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Left

Right

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Connect the Raspberry Pi to the L298N

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Use the wires like this

  1. Connect GPIO17 on the rPi to IN1 on the L298N
  2. Connect GPIO27 on the rPi to IN2 on the L298N
  3. Connect GPIO23 on the rPi to IN3 on the L298N
  4. Connect GPIO24 on the rPi to IN4 on the L298N

​

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Ground the Raspberry Pi to the L298N

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Use the wires like this

  1. Connect any Ground on the rPi to the GND on the L298N

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Something like this ...

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Mount the battery packs

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A look inside

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Python Tutorial

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  • https://www.programiz.com/python-programming
    • At a minimum, complete the following sections
      • Introduction
      • Flow Control
    • ​

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What’s next?

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  • Gamepad code - On Laptop
  • Motor Controller (L298N) code - On Raspberry Pi

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Gamepad Code (on your laptop)

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  • Install python v3:
  • After python has been installed …
      • install pygame: pip3 install pygame
    • Install pynetworktables: pip3 install pynetworktables
  • Attach the gamepad to a usb port
  • Download the gamepad controller app
    • xbox360_windows.py
  • Run the app
    • python xbox360_windows.py

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Gamepad Code

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Gamepad Code

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  • In the following slides we will
    • Update the xbox360_windows.py to output to the networktable
    • Show the expected output in the OutlineViewer

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Outputting to the NetworkTable

  • Import the NetworkTableInstance in the code.

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  • Initialize the instance to get global default instance

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Outputting to the NetworkTable

  • Start the client which should be the laptop’s ip address

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Outputting to the NetworkTable

  • If the IP address is not known it can be found with “ipconfig” in the command prompt. The IP address is the IPv4 address.

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Outputting to the NetworkTable

  • Start a table named “drive” and create 3 entries (right, left, stop)

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Outputting to the NetworkTable

  • Inside the axis logic, make a condition that if the desired axis is used than set the entry to output joystick values.

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Here, the axis 1 is the left joystick up and down, while the axis 3 is the right joystick up and down.

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Outputting to the NetworkTable

  • Inside the button logic, make a condition if the desired button is pressed than set the third entry to be true.

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Variable “i” should be the button number while variable “button” will always be 1 when pressed.

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Networktable in OutlineViewer

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Motor Controller (L298N) code

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  • Copy the template at the following link to your laptop and open it in VSCode
  • Follow the comments in the template to create the code for the project

​

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Setup the Raspberry Pi

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Motor Controller (L298N) code

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  • Copy the tankDrive.py to your raspberry pi
  • Run the app
    • python3 tankDrive.py
  • ​

​

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Try Different Drive Mode

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  • Now that you have tank drive working, try to update the code for one of the following
    • Arcade
    • Split Arcade

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Add an Encoder

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Correcting Bad Pulses

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  • A capacitor was added to correct the “bad pulses”
    • 100nF (104) metallized polyester Capacitor was added
    • See the following for a detailed explanation:

https://androminarobot.blogspot.com/2016/07/en-este-tutorial-mostramos-como-usar-el.html

  • ​

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Encoder Wiring

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You don’t have to use the wire colors in the photos - use what you have

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Encoder Wiring

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Encoder - Python

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  • Copy the template at the following link to your laptop and open it in VSCode
  • This will be the beginning of our autonomous code
  • Follow the comments in the template to create the code for the project
  • Copy your auto.py to the raspberry pi
  • ​

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Encoder - Python

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  • How did we get 2.55 ticks per inch?

​

TPI = ticks per inch

TPR = ticks per revolution = 20 (# slots on our encoder wheel)

C = circumference = 2𝝿r

𝝿 = 3.14159

r = wheel radius = 1.25 (wheel diameter is 2.5 inches)

​

TPI = TPR/C

TPI = 20/(2*3.14159*1.25)

TPI = 20/7.853975

TPI = 2.55

​

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Encoder - Python

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  • Run the app
    • python3 auto.py
  • Run it a few times measuring that it is driving the distance that you expect
    • How accurate is it?
    • Repeat for different distances
  • Extra credit - try to change the code to read in the distance to travel on the command line

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Implementing PID

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  • TBD

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Add an Ultrasonic Range Finder

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  • We will use the HC-SR04

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HC-SR04

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  • To be used to stop the robot once it gets too close to an object
  • Can be done with either Java or Python
    • Tutorials for both to follow
  • We will use the breadboard and will have to add resistors to step down the voltage received on the echo as it can be over the capacity of the GPIO pins

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HC-SR04 Wiring

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HC-SR04 Wiring

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You don’t have to use the wire colors in the photos - use what you have

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HC-SR04 - Java

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  • <TBD>

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HC-SR04 - Python

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  • Copy the template at the following link to your laptop and open it in VSCode
  • Follow the comments in the template to create the code for the project
  • Copy your hc-sr04.py to the raspberry pi

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HC-SR04 - Python

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  • In order to use the python code you just created you will need to activate the piGPIO daemon
  • First, set it to start when the raspberry pi boots
    • Execute: sudo systemctl enable pigpiod
  • Start the daemon
    • Execute: sudo systemctl start pigpiod
  • Run the app in the background (“&” at the end)
    • python3 hc-sr04.py &
    • We run it in the background so that it runs all the time while also allowing us to run auto.py at the same time
    • Verify that you are seeing the distance value updating in the Outlineviewer

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HC-SR04 - Python

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  • Next, update auto.py to read the distance value from the networktables and do something with it
    • For example, stop if the robot is within a # of inches from an object

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Vision

  • The next several slides will walk you through getting the …
    • Tools & software setup on the raspberry pi
    • Tools & software setup on your laptop
    • Python code to work with the camera
    • Object detection

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Vision: Tools & software setup on rPi

  • TBD
  • USB vs PiCamera

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Vision: Tools & software setup on Laptop

  • TBD

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Vision: Python code to use camera

  • TBD

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Vision: Object Detection

  • TBD

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End