I have an electric walkie stacker (outrigger style) which I have been using for about 4 years. Mostly smooth concrete with seams and a couple of areas that are 'bumpy'. One is has one of those yellow bumpy sidewalk patches, a seam in a doorway between indoors and out, and some areas that are ever so slightly lower than others. Going through the doorway has always been problematic, requiring speed - stopping halfway through the door has sometimes meant getting stuck.. Over time, this problem has become so severe that I can no longer go between indoors and out. One bit of advice I got was to replace the poly wheels with rubber ones. I called a service tech to talk about doing this and he said that would not help and might make things worse. HIs claim was that the machine I have is not appropriate for 'uneven surfaces'. Since it has gotten progressively more difficult, and the salesman who sold it to me visited the site beforehand, I'm not sure sure this makes sense. The outrigger straddle legs have two exposed wheels near the end. On both sides, the 'innermost' of these spins freely, whereas the one in front makes contact with the floor. I am not sure if this is intentional or may be part of the problem. Besides alterations of fixes to the machine itself, I would consider some sort of temporary mat/flooring that I can use just during the short periods when I need to go in and out. But not knowing what the problem is, I am hesitant to invest much. I do have a small piece of sheet metal and a stiff rubber backed carpet mat. Each of these seemed to help at first, but now neight works at all. The wheels just move them. The tech also suggested battery issues, but I see no reason to suspect this is correct. It is always fully charged before I attempt to go through the doorway. Any ideas would be very welcome. I am in a small town so repair people with any knowledge of an unusual device like this are nonexistent. Thanks!