Turntable for Crane Project, Phase 1

Written by TJ on May 28th, 2009

For the first phase of my recent crane project, I designed a new turntable. The concept of this turntable is based on having a thrust roller bearing and also having the whole assembly centered about a solid core.

I first developed a 12-segment ring for the round bearing.

base of turntable
click for larger

This ring is based on “perfect” spacing, i.e. every other segment pins into normally-spaced holes. This basically means that the “round” ring is affixed firmly to a square frame and can be easily integrated with the framework of the crane.

geometry of turntable ring
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The next step was to create a set of rollers. The ring of rollers shown below is actually a new concept, one that I didn’t actually use in Phase 1. This new one is the same roller ring as the original, except that the holders for the rollers are on the outside of the ring instead of the inside.

with roller ring
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My new idea for this turntable was to have the whole thing centered about a solid core made of stacked Technic turntables. The core would extend upwards through the superstructure and contain a “cap” with counter-rollers to keep the whole assembly pinned together.

core of turntable
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One of the primary loads on the turntable is weight (vertical, downward load), but it also has to resist an overturning moment. For example, when a crane picks up a load, the whole thing wants to tip over. Therefore the turntable has to hold the superstructure down against the base, so to speak.

partial assembly
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The photos above were taken after I broke the crane apart into its main components. Here is a photo of the crane when it was assembled:

click for larger

Here is a diagram showing the cross section of the turntable. Note the different sections and bearings (rollers).

cross section diagram of turntable
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One component I haven’t shown in the photos is the assembly that actually centralizes against the Technic turntables in the core. It is a fairly straightforward design that uses two sets of four 24-toothed pinion gears (spaced at 12, 3, 6, and 9 o’clock). Two of these gears are powered so that the turntable can be rotated by a motor.

Phase 1 of this project proved that this turntable functioned well but couldn’t handle much load. The rest of the crane was robust, much like my marine pedestal crane.

When lifting, the overturning moment on the turntable pried it apart greatly. I pushed it until I felt uncomfortable, but I didn’t break anything. The solid core in the middle is just not strong or stiff enough to keep the superstructure flat against the base. The other downside was that it kept throwing rollers. The 2×2 round bricks would frequently pop off due to the flexing of the whole assembly.

So, in Phase 2 of this crane project, I’m going to try to redesign it.

2 Comments so far ↓

  1. Feb

    Have you seen the custom aluminum turntable at inanimatereason.com, youtube, and bricklink.com with stainless steel thrush bearing rated for dynaminc thrust load of 5000lbs?

  2. Feb

    No I have not, but thanks! His BL store appears to be down, and his blog does not have any info on the turntables.

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