Due to the accuracy of the internal calculations required and limitations, in 3D modeling and CAD software you can adjust the world scale. If you are going to work with small objects (milimeters or centimeters), the world scale must be set in milimeters or centimeters . If the scale of the world differs greatly from the scale of your work, you will get drawing or calculation errors.

In phun, you can build extremely large objects almost without simulation errors (with more precission) but, if you build a tower with 20 cm. real scale bricks, simulation itself becomes unstable. If you build a 4 meters length car, small pieces like dampers (5/50 cm.) becomes unstable and polygon overlapping appears instantly when small forces are aplied to them.

In future releases, will be increased the accuracy? The solver will be improved to avoid polygon/object overlapping? Will be possible to build a real scale small scene without simulation errors? Hinges will be solid when large forces/weights are aplied to them? Why the weight of the objects affects to the strength of the springs linked to those objects?. Sometimes, increasing the weight, the strength of the spring is also increased :-O

Thanks!! And please, keep the project alive