This is a fun little game, although I will say assembly of complex tanks can get frustrating, especially as the rotator and combiner won't give hints as to how they'll do their changes.
Unit pathfinding is... quite bad, especially in groups. If you were to continue on this project, I would focus there.
There is a ctd bug - if you set the belt to a height above 0, close away the belt tool, it'll crash when you select it again and try to draw a belt.