why such a fuss when he has access to carpet
He likes the carpet??

Okay, I know... that wasn't very nice... While I was writing a note on the forum, yesterday, my younger cat was upstairs pooping on the bed. Granted, the washing machine was going and he is scared of it...and the Litter Robot shares the laundry room so Nuba went upstairs and did his thing on the bed. Tonight, same thing happened but no excuses this time... No washing machine going...
I forgot one essential, yesterday, when cleaning up after Nuba -- to spray the area he had used with a spray that neutralizes the odor so he won't be tempted to use the spot, again. Thus, I sprayed, tonight. Nuba will also be confined to the laundry room (in fact, he's there right now) until he is using the LR unfailingly and then, when he is out, again, I will be keeping a close watch on him during the times when he usually poops to assure that he is still using the Robot. A week is the maximum that he is confined. Often this cat is out sooner... within a few days. I also did a good clean job on the LR and put in some fresh litter in case Nub was getting a little fussy about LR cleanliness.
I hate this routine but it usually works. So, did you use a spray that will neutralize the odor in the area that he eliminated on?? And, did you give him lots of praise for using the L.R. ... maybe even a few treats? He may need some more time with the L.R. before he really gets that this is the ONLY place in the house that is actually the litter box!
Hang in there...
Kitties: Zen & Ariel. Litter Box: Litter Robot. Remembering Nuba, Ceba, and Yang Su Ling.