Drive fault above 18 volts

Dear Piborg,

I have a problem with my script that is use. normally when i have my output voltage to the motors set to 18v everything works fine. But when i set it to 20v or higher i get the fault failed sending motor drive level.
Do you know how this is possible? This is the script im using.

#!/usr/bin/env python

###
#
# diabloJoystick.py: A script for controlling motors with the Diablo using a joystick.
#
# 04-07-2019
# Thieu Verstijnen
###

# Load library functions we want
from __future__ import print_function
from diablo import *
from time import sleep
from os import environ
from sys import exit, stdout, stderr
import pygame
import RPi.GPIO as GPIO

GPIO.setwarnings(False)
GPIO.setmode(GPIO.BOARD)
GPIO.setup(8, GPIO.OUT, initial=GPIO.LOW)

# Power settings
voltageIn = 24.0              # Total battery voltage to the Diablo
voltageOut = 18.0             # Maximum motor voltage
 
# Setup the power limits
if voltageOut > voltageIn:
    maxPower = 1.0
else:
    maxPower = voltageOut / float(voltageIn)

# Re-direct our output to standard error, we need to ignore standard out to hide some nasty print statements from pygame
stdout = stderr

# Setup the left Diablo
DIABLO1 = Diablo()
DIABLO1.i2cAddress = 38
DIABLO1.Init()
if not DIABLO1.foundChip:
    boards = ScanForDiablo()
    if len(boards) == 0:
        print('No Diablo found, check you are attached :)')
    else:
        print('No Diablo at address %02X, but we did find boards:' % (DIABLO1.i2cAddress))
        for board in boards:
            print('    %02X (%d)' % (board, board))
        print('If you need to change the I2C address change the set-up line so it is correct, e.g.')
        print('DIABLO1.i2cAddress = 0x%02X' % (boards[0]))
    exit()
#DIABLO1.SetEpoIgnore(True)                 # Uncomment to disable EPO latch, needed if you do not have a switch / jumper
DIABLO1.ResetEpo()
 
# Setup the right Diablo
DIABLO2 = Diablo()
DIABLO2.i2cAddress = 55
DIABLO2.Init()
if not DIABLO2.foundChip:
    boards = ScanForDiablo()
    if len(boards) == 0:
        print('No Diablo found, check you are attached :)')
    else:
        print('No Diablo at address %02X, but we did find boards:' % (DIABLO2.i2cAddress))
        for board in boards:
            print('    %02X (%d)' % (board, board))
        print('If you need to change the I2C address change the set-up line so it is correct, e.g.')
        print('DIABLO2.i2cAddress = 0x%02X' % (boards[0]))
    exit()
#DIABLO2.SetEpoIgnore(True)                 # Uncomment to disable EPO latch, needed if you do not have a switch / jumper
DIABLO2.ResetEpo()


# Settings for the joystick
axisUpDown = 1                          # Joystick axis to read for up / down position
axisUpDownInverted = False              # Set this to True if up and down appear to be swapped
axisLeftRight = 2                       # Joystick axis to read for left / right position
axisLeftRightInverted = False           # Set this to True if left and right appear to be swapped
buttonResetEpo = 16                     # Joystick button number to perform an EPO reset (Start)
buttonSlow = 8                          # Joystick button number for driving fast whilst held (L2)
slowFactor = 1.0                        # Speed to slow to when the drive fast button is not held, e.g. 0.5 would be half speed
buttonFastTurn = 9                      # Joystick button number for turning fast (R2)
buttoncross = 14                        # Button cross for lights on                
buttoncircle = 13                       # Button circle for lights off
buttonsquare = 15                       # Button square for claxon on
buttontriangle = 12                     # Button triangle for claxon off
interval = 0.00                         # Time between updates in seconds, smaller responds faster but uses more processor time

# Setup pygame and wait for the joystick to become available
environ["SDL_VIDEODRIVER"] = "dummy" # Removes the need to have a GUI window
pygame.init()
print ('Waiting for joystick... (press CTRL+C to abort)')
while True:
    try:
        try:
            pygame.joystick.init()
            # Attempt to setup the joystick
            if pygame.joystick.get_count() < 1:
                pygame.joystick.quit()
            else:
                # We have a joystick, attempt to initialise it!
                joystick = pygame.joystick.Joystick(0)
                break
        except pygame.error:
            # Failed to connect to the joystick
            pygame.joystick.quit()
            time.sleep(0.1)
    except KeyboardInterrupt:
        # CTRL+C exit, give up
        print ('\nUser aborted')
print ('Joystick found')
joystick.init()

try:
    print('Motors are ready to drive.')
    print('Press CTRL+C to quit')
    driveLeft = 0.0
    driveRight = 0.0
    running = True
    hadEvent = False
    upDown = 0.0
    leftRight = 0.0
    # Loop indefinitely
    while running:
        # Get the latest events from the system
        hadEvent = False
        events = pygame.event.get()
        # Handle each event individually
        for event in events:
            if event.type == pygame.QUIT:
                # User exit
                running = False
            elif event.type == pygame.JOYBUTTONDOWN:
                # A button on the joystick just got pushed down
                hadEvent = True
                if event.button == buttoncross:
                    GPIO.output(8, GPIO.HIGH)
                if event.button == buttoncircle:
                    GPIO.output(8, GPIO.LOW)
            elif event.type == pygame.JOYAXISMOTION:
                # A joystick has been moved
                hadEvent = True
            if hadEvent:
                # Read axis positions (-1 to +1)
                if axisUpDownInverted:
                    upDown = -joystick.get_axis(axisUpDown)
                else:
                    upDown = joystick.get_axis(axisUpDown)
                if axisLeftRightInverted:
                    leftRight = -joystick.get_axis(axisLeftRight)
                else:
                    leftRight = joystick.get_axis(axisLeftRight)
                # Apply steering speeds
                if not joystick.get_button(buttonFastTurn):
                    leftRight *= 0.5
                # Determine the drive power levels
                driveLeft = -upDown
                driveRight = -upDown
                if leftRight < -0.05:
                    # Turning left
                    driveLeft *= 1.0 + (2.0 * leftRight)
                elif leftRight > 0.05:
                    # Turning right
                    driveRight *= 1.0 - (2.0 * leftRight)
                # Check for button presses
                if joystick.get_button(buttonResetEpo):
                    DIABLO.ResetEpo()
                if not joystick.get_button(buttonSlow):
                    driveLeft *= slowFactor
                    driveRight *= slowFactor
                # Set the motors to the new speeds
                # Set the motors to the new speeds
                    DIABLO1.SetMotors(driveLeft * maxPower)
                    DIABLO2.SetMotors(driveRight * maxPower)
        # Wait for the interval period
        sleep(interval)
    # Disable all drives
    DIABLO1.MotorsOff()
    DIABLO2.MotorsOff()
except KeyboardInterrupt:
    # CTRL+C exit, disable all drives
    DIABLO1.ResetEpo()
    DIABLO2.ResetEpo()
    print('Terminated')
print()
GPIO.cleanup()

Greetings Thieu