Help with Pi Pan/Tilt Face tracker

yes, I have the same. The problem is the probe for board revision not being adequate for the Pi 3.

I would simply comment out line 36 and uncomment line 35 in Adafruit_I2C.py, so that the init method reads:

def __init__(self, address, busnum=-1, debug=False):
    self.address = address
    # By default, the correct I2C bus is auto-detected using /proc/cpuinfo
    # Alternatively, you can hard-code the bus version below:
    # self.bus = smbus.SMBus(0); # Force I2C0 (early 256MB Pi's)
    self.bus = smbus.SMBus(1); # Force I2C1 (512MB Pi's)
    # self.bus = smbus.SMBus(busnum if busnum >= 0 else Adafruit_I2C.getPiI2CBusNumber())
    self.debug = debug