http://scifiwire.com/2009/06/how-the-giant-robot-fx-in.php
Visual-effects supervisor Scott Farrar was in charge of turning Industrial Light & Magic's computers up to 11 to create the new characters and told reporters that the sequel features 40 new characters. That and the increased resolution of the characters for new IMAX footage nearly exhausted ILM's render farms: After one hard night of rendering computer-generated footage, some of the hardware actually exploded.
"We did, we lost some machinery that night," Farrar said in a press conference on last week in Beverly Hills, Calif. "Little puffs of smoke, just like in the movie."