I may soon be getting back into a Pathfinder campaign and had a notion for finally realizing a character concept I've had in the back of my head for a few decades, but which I never had the game mechanics to pull off: a tinker gnome piloting a clockwork armoured-knight mech which he builds and upgrades as the campaign progresses. The Synthesist, with an appropriate amount of backstory and aesthetic changes seems a good way to pull it off without needing to reinvent the wheel. Summoned creatures could similarly be adapted by describing them as various clockwork creatures the gnome deploys when needed
The only issue I have with the concept is the notion that the eidolon/mech and clockwork creatures appear and disappear regularly. Though it's a super convenient way of acquiring and discarding of the character's mechanical creations as needed, it's rather at odds with the idea that these are big clunky mechanisms that the character builds and maintains in his off hours. In battle, I'd imagine that the slaying of the eidolon would result in the gnome being knocked out of or being forcefully ejected from the non-functional knight-mech. Unfortunately the broken down mech-eidolon wouldn't stick around for the gnome to go about fixing it; it would immediately disappear. In fact, there seems to be no way for the gnome to step out of his eidolon-mech-suit without it immediately disappearing in a puff of smoke.
One notion I had was to imagine the eidolon as an animating spirit that, once it departs, leaves behind a big pile of broken and largely useless machinery; the actual knight-mech body. That seems easy enough, except that I wouldn't want the responsibility of carting around a big mound of scrap metal to become a burden for the party.
I'd like to hear possible solutions to this conundrum. Any ideas?