I've been designing an alternative head for Bittle since April. It can be mounted on the existing head servo and equipped with an ultrasonic distance sensor.
Edit: The files are online at https://www.printables.com/model/993292-servo-rotatable-cat-head-with-slot-for-distance-se
@Rongzhong Li I just found out through another thread that there is a custom Petoi RGB distance sensor for the NyBoard. Don't you sell these anywhere? https://docs.petoi.com/extensible-modules/ultrasonic-sensor