I run an after-school technology education program and want to expose kids to real-life engineering by means of having them build commercially available Technic kits which we then deconstruct and analyze.
I am looking at 42042 Crawler Crane's second model as a good example of how to build a strong vertical structure, plus it serves as a good example of how a weight & counterweight works.
I would have loved to use 9398 4x4 Crawler as it showcases differentials, steering principles, a servo motor as well as suspension, but unfortunately that model is no longer for sale (I'm not willing to pay the ~$300 some sellers ask on Amazon.com), so I think I'm settling for the smaller, non-motorized 42029 Customized Pick-up Truck.
I assume both models will give me plenty of gearing examples.
I am looking for your advice: What other engineering principles does Technic LEGO showcase, and which (ideally current) model(s) would you suggest I use to illustrate these?