Sometime after I bought my second LEGO Mindstorm NXT set, I conceded I had to give up on my idea of building a large enough LEGO collection to build whatever I can think up. I had thought it would be a matter of buying enough sets to have a sufficient base collection of important pieces. After all, how many of those can there be? The harsh answer: more than I can afford.

Exhibit A: This LEGO Technic turntable. It consisted of two pieces that snap into each other and can rotate. Geared teeth both inside and out allow building motorized mechanisms for one or the other (or both) pieces. This piece is critical for building any rotating mechanism that demands more strength than a single LEGO axle can support. It formed the base for a crane in both the Crane Truck and Unimog U400 sets, and also the pivoting point between the base and body of the Motorized Excavator.

I had forgotten I was obsessed by this piece. The aforementioned three Technic sets were all interesting in their own right, but seeing this turntable reminded me my long-term goal was building a LEGO Mindstorm NXT robotic arm. A robot manipulator with just 3 degrees of freedom isn't very interesting, and that's why I bought a second NXT set to give me six NXT motors and six degrees of freedom. Structurally, the end manipulator might be something an NXT motor can handle directly. But as I worked out the design from finger to wrist to elbow to shoulder joint, I realized I need something beefier than just a LEGO axle in an NXT motor. Enter the LEGO Technic turntable: I would need several of them for a 6DOF robot arm.

But these turntables are rare. Only one in each of the Technic sets I bought, and none of those sets were exactly cheap. Furthermore, as I built those three sets, I would encounter and learn about even more interesting pieces I would want to incorporate into my own LEGO Technic creations. This was exciting until I stepped back and did some math. I realized buying enough sets to get me enough special pieces (not just turntables) will cost thousands of dollars. Furthermore, as I collect parts towards a long-term plan, there's no guarantee LEGO wouldn't switch up something important partway through this process forcing a costly redesign. As much as I've enjoyed LEGO, given all of these issues, I decided to stop spending my disposable income this way.

Until, that is, the Mars Rover Perseverance set that kicked off this LEGO nostalgia tour. And putting it together, I was very amused to see a familiar face: the turntable rendered in white+gray instead of black+gray in earlier sets. It was used for the stressful job of main rover suspension joint to either side of rover body. The geared teeth inside and out were unused in this case, but the axles to transmit corner steering forces did pass through its center. I didn't know they were used in this set when I decided to buy it (just being a LEGO rover was enough) but the fact two turntables are used in this rover set meant I've accidentally stumbled into the most cost-effective way to acquire turntables years later. I had a good laugh at my own expense, but I'm not interested in reviving my old project idea of an NXT robot arm for multiple reasons. There's the fact I'm far fonder of 3D printing now, that LEGO had discontinued the Mindstorm line, and even if I want to build it independent of now-discontinued Mindstorms, LEGO had changed their motor connectors again.