I knew even early on in planning out the 3D aspect of Steinton, that rigging him wasn't going to be easy and the main reason: He has wheels to move about instead of legs, and even though I had thought of several methods in my head to get it to work I knew that there were probably going to be issues with building a rig around his unique body type. I started with the upper half as this was the most straight forward, with standard anatomy with certain adjustments such as the addition of a jaw bone so i can animate his mouth to open and close (Though considering how i modeled the jaw part of his mesh as one solid shape i may need to tweak teh envelope weights to make it look more flexible... or his jaw will end up falling through his skull).
I looked at adding various parts for some of teh trickier aspects of Steinton's mesh: I made the computer rig a spine bone, with the extra arm coming off it. The wheels I had the idea of making custom bones for using meshes that fit the shape of the wheels more..... as expected this didn't work at all, as the bones are all linked to teh spine, and so their pivot isn't individually local, but connected to the root point.
Applied the Cat Rig to Steinton even though his wheels still weren't sorted to see how he moved without legs: actually looked better than I expected, I assumed without feet platforms with which to judge his movements on, he'd just flop about but it based it off his pelvis movement and so his upper half had natural movement regardless. I had to still tweak a lot of the values though on individual parts of his bones, as without making it more subtle Steinton rocked far too much and his upper half looked too unstable to remain on his wheels, especially his back half that is quite top heavy anyway, and so I made it rock, but in a less dramatic way to keep him looking like he is trundling as opposed to being on the verge of a barrel roll.
I decided on making the wheels separate meshes to the rest of Steinton's body: This is so I could adjust their individual pivots (which you cant do for each element when its part of a single mesh), and rotate them all at the same time, as an animation that ran along at the same time as the walk cycle, the theory being that it would run alongside it acting all at the same time, looking seamless. This fell down however when I changed the walk cycle to walk in a line: on the spot it worked perfectly, but as soon as he moved forward Steinton would leave his wheels behind.... still rotating, but not following the rest of his rigged mesh.
After numerous tutorials and research, I found a method that would make the wheels follow the rest of the rig and mesh as one fluid movement. I basically had to manipulate the hierarchy setup so the separate wheels were attached to the rest as children, and so even though they were on their own animations and not attached directly, they moved along when the walk cycle was activated. Not only this, but as well as rotating on their own, they also rocked along with the rig, which was great in giving Steinton that uneven and unique movement to his animation.