Quite relevant discussion here. I am not a Kangaroo expert, and I have been mainly dealing with engineering FEM tools (Abaqus, Ansys, Robot Structural Analysis for example). I recently came a cross Kangroo, and tried to develop it for initial stage design analysis for origami structures.
In the beginning, I must say that I was also confused by the terms such as ‘strength’ of the Hinge component and ‘stiffness’ in the SpringFromMesh component, because I immediately assumed that the terms were used in the same way as in solid mechanics or other commercial FEA tools. Later, I found out that Kangaroo uses dynamic relaxation method, which is as mentioned before, the main purpose of development is form-finding. Thus the terms were mainly used for the designers to provide arbitrary (and relative) values for creating geometrical forms, which can be verified again in FEA tools with material definitions and other constraints before the designs can be actually constructed.
Even if the values are arbitrary, it can be said that kangaroo was developed based on selected (not yet complete) laws of physics (it may be still abstract, but again it has been accepted as sufficient for many designers to serve as ‘form-finding’ tool). It would be true if one says that Kangaroo is not structural analysis tool, but it was never described so.
One point I would like to make here is that Kangaroo has still good potential to be developed for structural analysis tool if those initially confusing terms are properly addressed. For example, I recently examined the nodal displacements given by Kangaroo with a commercial FEM tool, and when the spring ‘stiffness’ value was defined based on EA/L (as Piker also mentioned initially), where the bar areas were calculated according to Filipov (2017) (also with Hrennikoff (1943), though it was for specific possion’s ratio only), the nodal displacements of both quadrangle and triangle elements under tension load were comparable to that of FE model. For lateral load, the discrepancy was larger, but I believe this can be also improved using further discretised bar elements with appropriate additional definition of bending stiffness between the bars; which I am currently working on.
Like Ivelin (and also me), many engineers may feel confused with the terms when they first use Kangaroo, however, it doesn’t take long to realise that the tool was not meant for structural analysis (it took me less than a day at least); yet in my humble opinion, its description as a physics engine will still be widely accepted also by engineers as long as it is clearly stated that it is developed for form-finding.
Sorry for long text. Just sharing my thoughts. Good evening to all. =)