Ok, Highlander, this one was all about patience! Almost kicked those R-bots off the level a few times.
Patience, patience, grasshopper. Just keep still and keep watch. No matter how much you want to fling a bot… Don't do it!
I say, go ahead and clobber some R bots to get it out of your system! Then start over and try to really solve the level. The basic hint is to Spoiler try to get as many R bots as far down the level as you can.