Using UltraBorg and two Ultrasonic sensors to drive Diablo's two motors

Please help! my code is not working
See my code below:-

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

# Import the libraries we need
import UltraBorg
import time
import Diablo

# Settings
distanceMin = 100.0             # Minimum distance in mm, corresponds to servo at -100%
distanceMax = 300.0             # Maximum distance in mm, corresponds to servo at +100%

# Start the UltraBorg
UB = UltraBorg.UltraBorg()      # Create a new UltraBorg object
UB.Init()                       # Set the board up (checks the board is connected)

# Calculate our divisor
distanceDiv = (distanceMax - distanceMin) / 2.0


# Motor sequence script

# Setup the Diablo
DIABLO = Diablo.Diablo()            # Create a new Diablo object
DIABLO.Init()                       # Set the board up (checks the board is connected)
DIABLO.ResetEpo()                   # Reset the stop switch (EPO) state
                                    # if you do not have a switch across the two pin header then fit the jumper

# Power settings
voltageIn = 7.4        # Total battery voltage to the Diablo
voltageOut = 7.2        # Maximum motor voltage
 
# Setup the power limits
if voltageOut > voltageIn:
    maxPower = 1.0
else:
    maxPower = voltageOut / float(voltageIn)

# Loop over the sequence until the user presses CTRL+C
print 'Press CTRL+C to finish'
try:
    # Initial settings
    servo1 = 0.0
    servo4 = 0.0
    while True:
        # Read all two ultrasonic values, we use the raw values so we respond quickly
        usm1 = UB.GetRawDistance1()
        usm4 = UB.GetRawDistance4()
        # Convert to the nearest millimeter
        usm1 = int(usm1)
        usm4 = int(usm4)
        # Generate the servo positions based on the distance readings
        if usm1 != 0:
            servo1 = ((usm1 - distanceMin) / distanceDiv) - 1.0
            if servo1 > 1.0:
                servo1 = 1.0
            elif servo1 < -1.0:
                servo1 = -1.0
        if usm4 != 0:
            servo4 = ((usm4 - distanceMin) / distanceDiv) - 1.0
            if servo4 > 1.0:
                servo4 = 1.0
            elif servo4 < -1.0:
               servo4 = -1.0
        # Display our readings
        print '%4d mm -> %.1f %%' % (usm1, servo1 * 100.0)
        print '%4d mm -> %.1f %%' % (usm4, servo4 * 100.0)
        print
        # Set our new servo positions
        DIABLO.SetMotor1(maxPower * servo1)
        DIABLO.SetMotor2(maxPower * servo4)
      
        # Wait between readings
        time.sleep(.1)
except KeyboardInterrupt:
    # User has pressed CTRL+C
    print 'Done'