Yup, you're looking for the Field Repair Bot 74A. The schematic is in Blackrock Depths, right before the Archmage boss; you need 300 Engineering skill to pick it up.
Here's the bot: http://wow.allakhazam.com/item.html?witem=18232
Here are the ingrediants: http://wow.allakhazam.com/db/spell.html?wspell=22704
Since it takes 12 Thorium Bars and a Fused Wiring, it isn't really useful to keep using a lot in an instance. The bot dies after 10 minutes.