Although some very valid anti-weld points have been brought up, out team has had 3 out of our 5 total robot frames (2008 included) with no trouble from welds cracking, or even the aluminum being weakened from the heat, I think we actualy bent our frame last year from so many hard impacts with both the arena, other robots and various shop components (students included
) and it still has full structural integrity with no strees points showing in metal or welds. I guess one of the main factors would be that they have either been welded with a TIG by students/mentors with more than proficent welding skills or it was sent out to be welded professionally.