I just finished rebuilding a motorized LEGO Technic excavator, the third in a trio of large Technic sets I bought about ten years ago. I then stopped buying Technic sets until the recently released LEGO Technic Perserverance rover kicked off this nostalgia tour. I had forgotten why I stopped, but now that I've been reminded, I thought it would be worth writing down: LEGO Technic is great fun and lets me try out certain ideas almost instantly, but LEGO creations are mechanically constrained within a range due to parts availability. It takes a great deal of effort to go beyond this range, when it is possible at all.

The well-defined regular spacing of LEGO pieces is key to its easy modularity, but it also places a hard floor on how small we can build with official LEGO pieces. There are fractions: halves, thirds, quarters, but nothing in between. If I want to build something that interacts with a non-LEGO piece, matching the exact size is impossible. Example: if I wanted to build a coin-operated LEGO machine, I couldn't build a coin slot exactly the size of a real coin. There exist unofficial 3D-printed parts to circumvent such size restriction. But if I'm using 3D printing, I'm more inclined to just do the entire thing with 3D printing and ignore LEGO.

Likewise, the selection of available LEGO pieces imposes a practical upper limit on what we can build. LEGO beams have a maximum length and anything larger requires joining multiple beams. And everywhere there is a joint, there is a small tolerance that could move. It'll never be as strong or rigid as a single longer or thicker piece. My 3D-printed Sawppy rover can incorporate aluminum extrusion beams for structural strength, but such options are not available for pure LEGO creations. The Crane Truck chassis is very long by LEGO creation standards and is composed of many joined beams. Yet despite its sturdy construction, every time I pick up the crane truck I can hear and feel the crinkling sound of LEGO pieces flexing and moving, and the chassis sagging under its own weight.

To be fair, this is actually representative of challenges building real life machinery as well. Everything bends and twists under load, including real truck chassis. When I revisited the Technic site, I see the largest production set right now is 42146, modeling a Liebherr LR 13000 mobile crane. At that scale, those Technic beams are sure to wobble and flex. But beam flex happens on the real thing and must be accounted for in planning and operating real world cranes. So, I guess it's realistic. But is it fun?

Beyond size limits on the big and small ends, there's also the problem of building up intricate mechanisms via multiple LEGO pieces. Again, every joint introduces another point of movement and flexibility, which compounds into a floppy structure that might not even be able to hold itself up together in the face of gravity. Such was the case for the LEGO Technic Mars rover suspension. It was also true for all three of my large Technic sets, each of which featured an articulating arm and they all flop about when moved.

Every engineer learns to work within the constraints of a problem, and some people relish overcoming these mechanical challenges of building with LEGO. I thought I might become one of these people, but my frustrations went beyond the mechanical. LEGO also had ambition to incorporate electronics into the Technic line, and the 2010s were in the middle of the rise and fall of LEGO Mindstorm.