The articulated tank chassis by EXTREME3DPRINT is available for purchase here: https://cults3d.com/en/3d-model/gadget/pipbot-1-print-in-place-robot

Inspired by the models from FAB365: http://www.fab365.net/

My design process is covered in this video: 

I normally would link to my source CAD for remixing convenience, however the tank chassis is a paid model so I cannot. Two STEP files are provided instead.

Print instructions

As far as print in place goes this model is not very challenging (especially compared to the tank chassis it sits on). I used PETG on the Bambu Lab P1P. The steepest overhangs are only 45 degrees and clearances are set to 0.3mm. The most challenging part is probably the the adhesion of the turrent base to the bed, which has the chance to be knocked loose during printing.

Assembly

Fold into shape, and then use 2 x 12mm M3 bolts to attach the body to the chassis. I drilled the chassis bore with a 2.5mm drill bit to help the M3 bolts cut their own thread.