the last post before PI Wars 2017

It’s only 7 days before I compete in the 3rd Pi Wars, things still left to do? lots! “Max” my robot has been an adventure in learning! So why is my team has the terrible pun “two wheels or not two wheels” for a name? After the winning Pi Wars with monster of a robot “Revenge” last time round in the greater than A4 class to my great shock! At the time of filling in the application for this Pi Wars, I was playing with the idea of a balance robot, just was not sure this would work for Pi Wars, in the end, I decided that to be able to be able take part in all the challenges that a balance robot would not be practical. I based the Design of Max on ‘Tiny’ the robot I designed for the two articles, I wrote for the MagPi. Links to the copies of both issues are below.

Issue 51

Issue 52

Max is a 4-wheel direct drive rover type robot with monster truck wheels, with a voice prompts interface to select the running mode or option. I chose this type of rover because of it flexibility.

In my last post, I told you about the Python inputs library for interfacing with a games control, this time, I will expand on that post, so you can control your own robot, what ever type of motor driver, you are using.

If you have not already install the inputs python library using the instructions in my last blog post,

Python library ‘inputs’

Notes: one of the pros and cons using the inputs library is that it waits for the next event before moving on to the next step of your program, this is great for manual mode for a robot, but a pain in the rear chassis, if you wish to just use your controller as the stop/start buttons for the autonomous challenges, to work arounds you will need a hardware button connected to the GPIO pins or use another method for controller input.
The code, converts the input from the joysticks to a value between -1 and 1

Below is my code for control a robot with the inputs python library, the code will output a value between -1 to 1 for setting the speed and direction for each motor, you may need to adjust, the maths for your robot.

You can download all of my code for this year’s PiWars from Github, link below

Code listing

#!/usr/bin/env python
# coding: Latin-1

# Load library functions we want

from inputs import get_gamepad

# Power settings
voltageIn = 12.4                        # Total battery voltage
voltageOut = voltageIn*0.95              # Maximum motor voltage, limited it to 95% to allow the RPi to get uninterrupted power

# Setup the power limits
if voltageOut > voltageIn:
    maxPower = 1.0
    maxPower = voltageOut / float(voltageIn)

power_left = 0.0
power_right = 0.0
x_axis = 0.0
y_axis = 0.0

def mixer(inYaw, inThrottle,):
    left = inThrottle + inYaw
    right = inThrottle - inYaw
    scaleLeft = abs(left / 125.0)
    scaleRight = abs(right / 125.0)
    scaleMax = max(scaleLeft, scaleRight)
    scaleMax = max(1, scaleMax)
    out_left = int(constrain(left / scaleMax, -125, 125))
    out_right = int(constrain(right / scaleMax, -125, 125))
    results = [out_right, out_left]
    return results

def constrain(val, min_val, max_val):
    return min(max_val, max(min_val, val))

# main loop

exit_flag = True

    print 'Press CTRL+C to quit'

    loopCount = 0

    # Loop indefinitely
    while exit_flag:
        events = get_gamepad()
        #print events
        #print loopCount
        #loopCount = loopCount + 1

        for event in events:

            # print(event.ev_type, event.code, event.state)

# manual mode

            if event.code == "ABS_Y":
                if event.state > 130:
                elif event.state < 125:
                y_axis = event.state
                if y_axis > 130:
                    y_axis = -(y_axis - 130)
                elif y_axis < 125:
                    y_axis = ((-y_axis) + 125)
                    y_axis = 0.0
                print("Y: " + str(-y_axis))
            if event.code == "ABS_Z":
                if event.state > 130:
                elif event.state < 125:
                x_axis = event.state
                if x_axis > 130:
                    x_axis = (x_axis - 130)
                elif x_axis < 125:
                    x_axis = -((-x_axis) + 125)
                    x_axis = 0.0
                print("X: " + str(x_axis))

            if event.code == "BTN_TL":
                if event.state == True:
            if event.code == "BTN_TR":
                if event.state == True:
            if event.code == "BTN_Z":
                if event.state == True:
                    print("Top right")
            if event.code == "BTN_WEST":
                if event.state == True:
                    print("Top left")
            if event.code == "BTN_TL2":
                if event.state == True:

                    x_axis = 0
                    y_axis = 0

            mixer_results = mixer(x_axis, y_axis)
            print (mixer_results)
            power_left = mixer_results[0] / 125.0
            power_right = mixer_results[1] / 125.0
            print("left: " + str(power_left) + " right: " + str(power_right))

            set the motor speeds for your driver board here

            Set Motor 1 ((-power_right * maxPower))
            Set Motor 2 (power_left * maxPower)


            print("#### Manual ####")

except KeyboardInterrupt:

    # CTRL+C exit, disable all drives