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Small Turntable 1

Tuesday, June 2nd, 2009

This post continues the Ideas section here on my blog. I want to point out that one of the main reasons I created this blog is to help me communicate these ideas and works-in-progress.

I’ve decided that I want to present my ideas (even the ones that don’t work out) and the stuff I’m currently developing. It takes a long time for me to finish a MOC and then present it on my website. While I’m building a typical MOC, I’ll go through many design iterations and mess around with many different ideas.

So, I’ll show them here. Maybe they’ll inspire some readers. Maybe some readers will help me out by leaving constructive comments. Anyway, here’s the next installment of my Ideas section:

Small Turntable 1

The classic Technic turntable is a fantastic part. It’s one of my favorite LEGO elements.

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However, it has its cons, especially when you attempt to build a large and heavy model with it. Specifically, there is a lot of friction generated within the turntable and it also pops apart when loaded by an overturning moment (think about a crane lifting a heavy load).

A better turntable design will use two things: 1) a thrust roller bearing, and 2) some means of “capturing” the top and bottom components so that they don’t separate under load.

The turntables I’ve built so far have been rather large, just because it takes a lot of space to incorporate the above two ideas into a functional assembly.

I’ve been wanting to build a turntable that is similar in size to the classic Technic turntable. Below is one, quick idea that incorporates rollers to provide a low friction bearing and a method of “capturing” the assembly so that it doesn’t pull apart under a high overturning moment.

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The double-stacked 40-toothed gears are captured by 8 rollers. The flat edge of the gears (on their sides) ride against the rollers.

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The “core” of the assembly is squeezed together with multiple threaded axles. The Technic threaded axle is a rare part and is no longer produced by LEGO. Note that this concept of a “core” made using threaded axles was used on my 4×4 telescopic crane. You can see that core design in this photo.

This assembly is not finished and is not functional. It’s basically just developed to a point where the major parts and geometry have been worked out.

What’s left to do is make a base that the “core” will attach to. It also needs a stronger centralizing support (the red 2×8 Technic plate) so it will rotate about a fixed center and also handle lateral loads applied to the turntable assembly.

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I’m not sure how this assembly will function. My gut feel is that the method of “capturing” the 40-toothed gears with rollers is a little flakey. They might slip off. They might grind too much under load and not rotate smoothly.

I’ve stopped development of this idea in favor of a new one (a different design for a compact turntable). I’ll present that one later.