I must say I'm really, really having loads of fun making this model. Not sure why but this has been a real pleasure to construct. Maybe it because it's so different from the others.
I was going to go with some hard carving of the original wooden discs I bought for the wheel to get a solid, integral whole but after carving two triangles I found it too tediously hard. I slipped a fine saw into the hole and cut out the circular ring "tires" instead, and used square pieces to make the spokes. You can see these processes in the photos from complete disc to circular ring and the final wheel.
Painted? I'm not sure many of these catapults were actually painted. Unlike European siege engines, wars in China were not quite, 1. frequent enough, 2. based on nationalist/factional pride, to warrant much attention to painting or even naming catapults simply because catapults were usually only built just for a particular battle or siege and except for really large mobile catapults, seldom have I read that they were stored for later use unlike say, the records from the Tower of London for storage of Springalds and other arms. Chinese armies are a lot more like modern armies today in their treatment of arms and soldiers too. Arms were probably massed produced based on standard designs, so unlike European records of huge singular and personalised catapults belonging to various strongmen and their castles getting names like Warwulf etc, the Chinese seldom if ever put personal names on their catapults. If anything, naming would follow official names or be just pet names given by the soldiers themselves, kinda like the artillery pieces of modern armies.
That's what I tried suggesting earlier but was ignored. 
