I got this achievement today.
Sure, itīs a bit late, but who knows.
I found a really easy way to destroy these two orange robots. I tried it several times and it worked always the same. So it has nothing to do with luck or anything like this.
I made a video. Maybe it will help someone who stuck on this two robots. The scene is two times. One on normal size and a second try a bit bigger. But you see it is always the same procedure.