Early style frame:
Based on location photo.
Alien robot gun designs:
#1 and #7 on the right were chosen.
I didn't make these, they were made by some of the many talented people I work with, but never meet.
Gun light options:
Upper left lighting painted for fire to be added by compositor.
Painted 2D battle damage onto 3D model:
To save time, one robot was modeled in 3D, then 2D damage was painted to create variety.
On left, added bullet holes, smoke damage, broken door, rubble. On right, created all damage.
work done @ The Mill