Automatic Litterbox Central

I have 4 cats and 1 LR (Old style). Lately one of my cats has been going poop on the step or carpet in front of the liter Robot. I tried different litters and cleaning the waste out more often with no success. I finally got tired of cleaning my carpet I put a normal box down with litter. Now all the cats are using both boxes. So my problem is that i can afford to buy another LR right now. The litter boxes are in my closet so I can't get a Cat Genie (even if I could afford one) and I am getting tired of scooping.

They seem to be using them both about evenly.

How do I get them to just use one box? Or does anyone else have any ideas for a 2nd box that is not $$$ until I can afford another Robot?

Also I am worried that the cats won't use the 2nd robot but go back to going on the floor but I guess with the 18 month warrenty I could just return it if they do.

The scoop free is not too pricey but I have heard the cartidges are $$.

Anyone else have this problem? What did you do?

Tiffany in OK.