Well my main (Joshua Nightshade) makes tiny robotic avatars so I know a bit about this.
First off, it's a really creative robot! Unfortunately though I think you're going to run into some trouble trying to convert it into an avatar. The obvious problem is that for the most part the basic human shape is going to stick out of the torso area. People who make non-human avatars usually get around this by using scripted invisiprims but I personally really hate those. They are hacky and in my opinion tend to look gross. Here's a good overview on their problem and why there should be a better solution.
http://jira.secondlife.com/browse/VWR-812Anyway, getting around that, the second problem is that the avatar is not going to move appropriately. On your robot the "legs" are like tank-treads, and the normal SL avatar walks using regular legs, so you would find the treads flopping around as you walked.
My personal way of getting around both of those (and how I make my own avatars) is to use an animation/pose and a script to force the avatar body into a different position. It's more complicated to build but looks better as far as I'm concerned without using invisiprims.
If this were my avatar I would personally make the arms their own attachments, the head one, and the torso/treads one attachment as well. Head would attach to skull, arms would attach to arms, and the torso would attach to the spine or pelvis.
If you poke me in-world I'll even make an animation for you to counteract the walking problem, but my suggestion is that you get poser or the free qAvimator and play around with it yourself if you want to go that route.
http://www.qavimator.org/If you have any questions feel free to look up my main (Joshua Nightshade) and ask me, I don't tend to check these forums too often.
