The Ostrich Eggbot kit should have come with a more flexible hinge, and the engraver kit comes with a stiffer hinge. You can get additional stiffness by stacking hinges.
The pen arm height is *very* adjustable, perhaps in some ways that you haven’t thought of. There are two positions to mount the servo motor assembly, as described in Step 33 of the assembly instructions. If you are nearly bottomed out in position, you should definitely be using the lower pair of holes.
The servo adjustment points that I was referring to are the software settings that you use to adjust the servo motor positions.
The correct position of the pen motor in the Ostrich Eggbot chassis depends on the shape of object that you are engraving. For an object with (roughly) spherical geometry, it should be at the top position, and for increasingly elongated objects, it should be lowered.
