The KR01 is using Hall Effect encoders on the motor shafts (closed-loop) in order to measure and set the velocity of the motors. This allows the robot to drive in a straight line despite the fact that the port motors are rotating the opposite of the starboard motors, and DC motors generally are more efficient (and faster) in one direction than the other. So to answer your question, no, the PMW3901 is only used to determine motion in front of its sensor lens, and is unfortunately is using a sensor designed really for flying drones, so I'm not using it on this robot at all. Upon request from myself and several others I believe Pimoroni are going to release a new Optical Flow Sensor based on the PixArt PAA5100JE-Q Optical Tracking Chip, which is tuned for sensing floors and close-range surfaces with a range of 15-33mm (whereas the PWM3901 has a range of about 90mm to infinity). I'm looking into using it for a mechanum-wheeled robot, where Hall Effect encoders on the motor shafts would be rather useless or at least extremely difficult to use since the wheels are slipping all the time.

I've reposted the actual python code used at: github.com/ifurusato/ros/blob/master/lib/video.py The format is set on camera.start_recording() as "mjpeg".