[EricH]

Originally Posted by bs7280

What would the limits be then

It depends on the printer and the settings and the material.

For any 3D printed part, there is a size limit--can't build any bigger than the machine's build envelope, unless you're doing something where two parts mate into one.

Different materials print differently, and different temperatures can make a material act differently. For example, we once took a lot of warping out of medium PLA parts by cutting the print head temperature by about 30 C. (For that matter... if you plan to use a color on the robot, test it first. Some colors on the printer WILL act differently--we always had a problem with white PLA cracking, for example, not so much with any other color.)

Support structure can be a limiting factor, but I don't know much about that, so I'll pass on commenting.

The printers I'm used to--RepRap types--are sensitive to a level surface, condition of the heated bed covering tape, temperature of the print head and heated bed, tension of belts, height of the print head above the platform... In short, they HAVE to be dialed in. We'd check how dialed in we were every time we moved one from one location to another (though having it on a cart removed that for a while) and adjust if necessary. That's how sensitive they could be. We also did not have the ability to use support structure, so parts had to be printed in a certain orientation--actually, still an issue.

There's also the issue of precision--3D printers are only as accurate as their print heads' extruder tips in both travel and thickness of material--we'd always figure at least .003" oversize to allow for the tip running thick. Otherwise, holes would need to be drilled out.