After the introduction of Power Functions in 2007, the amount of motorized models has seen an exponential growth. Since then not only has the Technic line introduced at least 2 sets with motor every year, but also it seems like Power Function models are the new standard among fan creations, gaining even more popularity due to the various Trial Truck competitions. It has become quite a phenomenon, showing LEGO Technic trucks clearing a challenging obstacle course, something that would have been unimaginable several years ago. Those trucks have evolved very fast, with high focus on efficiency, meaning that structures have to be as light and strong as possible, whereas power trains as short and compact as possible with end reduction. On a positive note those competitions have drawn a lot of people into Technic and teaches many of the elementary principles of kinematics. There are however a few other things to consider.
The trend of today is that things have to be cool, not necessarily realistic. LEGO Technic seems to follow this trend. When launched it became well known in Germany under the slogan 'Technik wie in wirklichkeit' (Translated roughly as Mechanics like in reality). Today, 2 of the pillars are Authenticity and Functionality, but that doesn't necessarily mean authentic functions.One example could be the linear actuator, which in many cases is used for functions that are in reality hydraulic. Pneumatics would have been a more suitable alternative considering authentic functions.
But probably a better example is comparing the Technic 'Supercars' that LEGO has introduced over the years. In the past it has been all about the interaction between drivetrain and engine through a gearbox. Of course there are limitations with the system, so things had to be simplified and put in perspective, but the focus was on authentic functions and their educational value. Looking at the latest 'Supercar' 8070, I can't help but imagine a child that is playing with the gearstick in a real car and wonders why the doors are not opening. Not very realistic, but it's 'cool' especially when those functions are motorized with Power Functions.Why wasn't Power Functions used for motorizing the drive and steering function instead, especially considering that in this case there was not the problem of a complex drivetrain like with previous 'Supercars'? That would have been much cooler, right, looking at the popularity of the Trial Truck models?
Courtesy of Paul Ian Kmiec (Sariel)
Could it be that motorizing large, wheel based LEGO vehicles with Power Functions is actually beyond what is reasonably possible with the system? Looking at what kind of driven remote controlled Power Functions models LEGO has launched so far it is striking to realise that all of those have been track based. Another interesting thing to notice is that 3 of the recent Technic flagships with Power Functions, 8275, 8258 and 8043 all seem to have had some issues which led to revised parts and/or building instructions. It seems like motorizing big complex LEGO models is really challenging what the system is able to handle and made for.
So apparently official LEGO designers are already pushing the boundaries of what is safe, but this is in no comparison of how far beyond the limitations of the building system certain fan created models, and in particular Trial Trucks, are. Either broken or grinding gears, twisted or bent axles, and stalled motors are just a few common indicators that show that the system is not capable of handling well the high forces and torque applied. To get high clearance big wheels are often used, but from a torque and stress point of view it only demands more from the system. Maybe that explains why we haven't seen any official LEGO set with big wheels and driven by Power Functions?
In conclusion with LEGO you can build anything, but the system certainly has its limitations. How far (beyond) the boundaries are pushed is up to the individual on what is acceptable. With my background I try to keep things within reason. Due to the popularity of Trial Trucks, and the coolness of Power Functions, however, many people have higher expectations of models, pushing the system beyond limitations, shifting the focus from authentic functions to effective and cool functions.