The ultrasonic module consists of 7 HC-SR04 distance sensors and a 3-D printed enclosure. The module will be mounted on the front of the robot base, a second one can be mounted on the backside if necessary. So far I finished the 3-D drawing of the enclosure.
7 HC-SR04 mounted:
I also designed an extension shield for the two Arduino MEGA's to have better access to the remaining I/O and analog pins:
Populated extension shields for the two Arduino MEGA's, MARB has on board: