I started with kpi’s file off of Thingiverse
I cut off the gun platform and reworked it with FDM printing in mind. I put it on a pivot on the gun base, so it can traverse, and reworked the gun itself with a new barrel, which can elevate and depress as well.
I created new wheels and mounts, and added detail to the gun base – bolts/gun stabilizer pads, etc.
As it is a re-work of k.p.i.’s file, this derivative file is a free download, in accordance with his license.