Ok, this is actually right near the end of this level, just shortly before the final boss battle (if i have you placed right this time). Jump across into the middle and hover with flamethrower- this will turn the big gear to the other platform. When you get over there kill the bugs and do a running jump to hover across collecting the green orbs along this next gap.
Just so you know, i have been checking varius walkthroughs to find this- while I am playing through the game myself i haven't quite had time to get to this point.