crane project

angled view

close up

quarter view

back view

Henry & me

main block

side view
(w/ 2 boom sect.)

boomed out
(w/ 1 boom sect.)

at TexLUG show

up close

up close

short boom

aux. block

The Crane Project
(a model to test several different ideas)

This project was mainly a test of a few different ideas. I intended to reuse some of the sub-assemblies on a real crane MOC, but in the end, I decided to scrap the whole thing. This was because the turntable design was too flexible (more about that below in the turntable section). Redesigning the turntable would mean that the rest of the crane would need to be redesigned extensively. So, might as well start from scratch, right?

Main Points:
Built June-August 2008
Total height (w/ 2 boom sections): approx. 6.5 feet
Fully remotely controlled using prototype from HiTechnic
4 motorized features: two winches, slewing, and boom luffing
Made of 100% LEGO pieces, and no glue was used

flange pattern

the core & frame

all sans core


bot. of turntable ring

bot. of superstructure


the core

base w/ flange

base w/ ring

inner piece

1. Turntable

The turntable was a new design that used an idea of mine from several years back. The main feature was a solid "core" and a superstructure that centralized itself around this core.

The non-rotating core (more like a shaft) was fixed to the lower base structure. The superstructure rotated around this core (shaft) and was driven by gears that engaged the large turntable elements built into the core.

The core extended upwards through the superstructure and was capped at the top. The cap extended outwards and captured the superstructure; it prevented it from sliding upwards and off the base. The cap contained a counter roller bearing so that it rolled smoothly. The cap fit snugly in place, so the counter rollers were always engaged.

The whole assembly rotated smoothly and seemed to work very well. It was driven by two geared 9V motors and seemed to have plenty of power to drive the assembly.

The problem was that it was very flexible. When the crane lifted a load, the superstructure wanted to rotate forwards about an axis perpendicular to the axis of the turntable. The cap, as mentioned, was there to prevent the superstructure from disconnecting and sliding up and off the core. But due to the high amount of flexibililty and give in this assembly, the turntable opened up significantly (see the photo titled "flex" to the left).

As a result of this flexibility, when the turntable was rotated while a load was being lifted (or there was no load - the counterweight was heavy enough to flex the turntable significantly) the roller bearings popped out and fell out of the assembly.

Extensive operation of the turntable would have resulted in it basically tearing itself apart.

It was a good idea, but it just didn't work well enough in this case.

solid section

angled connection

top view of superstructure

front of superstructure

weight holder/bracket

truss section

close up


back of superstructure

control and battery box

2. Base and Superstructure

The X-shaped base and rotating superstructure both used large built-up members of plate and Technic beams. I've used this concept before in many other projects. It usually works well.

The design of the base was to experiment with angled connections between built-up members of plate and Technic beams. I wanted to take the concept a step more, and go beyond simple 90 connections between members. The base worked pretty well, although it was surprisingly flexible.

All of the basic members of the base and superstructure interlocked at joints and were pinned together with either friction pegs or axles. The whole crane could be broken down into basic members if needed.

I wanted a modular design because this works very well for large models like this. Being able to take it apart in sections makes modifications/fixes and also storage much easier.

The turntable centralizer and drive, winches, and control/battery box were all separate modules that fit within the main frame of the superstructure.

Control/Battery Box

Power came from eight rechargeable AA batteries (9.6 volt total). A prototype 4-channel radio controlled receiver (from HiTechnic; made in 2002) was used to control the winches and turntable drive.

winch package

control and winches

winch package
3. Winch Design

The winch packages were made as small as possible and were self contained. They fit within the frame of the superstructure and could be easily removed if needed.

Each winch used 4 motors (the old 9V geared motors) and had a mechanical brake. The brake was necessary because even small loads on the winch lines would spin the winch drums and let line out. The drums were always connected to the motors, but back-driving the motors doesn't take much load.

This problem could be solved by using a worm gear to drive the winch drums. But using a worm gear has two problems: 1) the gear reduction makes the winch drum spin much slower (1:40 ratio vs. 1:5), and 2) LEGO worm gears operate with a lot of friction (loss in efficiency and also wear on gears).

Both of the large winches fitted in the superstructure operated the main boom (one for the lifting line and one for boom luffing).

There was a third, smaller winch package fitted into the lowest section of the boom (see the info below about the boom). This winch operated the jib lifting line.

bottom and top sections

section break

middle sections

joint b/w sect.

close up of joint

top (fixed jib)

top section only

mid sect top and side

4. Boom Design

The boom was rather large and heavy and was made of four distinct modules. There was a base module (connects at hinges to the superstructure), two middle modules (simple truss sections to increase boom length), and a top module.

The top boom module was complex. The main chords of the truss angled down and in (complex angle) slightly. This double batter resulted in a complex arrangement of diagonals and connection points.

The head piece was a large block that became much larger and heavier, as I built it, than I had intended. A short fixed jib was built onto the top of this piece.

The two middle sections were identical except for color. I had intended to build one or two more middle sections, but I never got around to it.

The base boom module contained a small winch powered by two geared 9V motors. This winch was the lifting line for the jib.

in progress

first test

in progress

first test

Early Photos / The Build

This set just captures the build of this project and some testing. I started with the turntable first since it was the most complex feature of the crane.

I was impressed with the performance of the turntable at first. But later, when I used the crane to lift heavy weight, the shortcomings in the design became apparent.

double ring

centralizing ring

test base

double ring on base

centralizer on base

The Next Phase

I had intended to move into a future phase that possibly re-used some of the sub-assemblies. However, I decided to scrap the whole project because of the issue with the turntable.

Every function of the crane, except the turntable, worked well.

I begin building a revised version of the turntable (pics to the left). This design would have incorporated a larger core and, in basic, general terms, used a larger structure to retain the superstructure on the turntable (the result being lesser concentrated loads on the turntable and less flexing).

I messed around with this a lot but eventually scrapped it. I may revisit it someday if I need to build a turntable about this size.

This "crane project" is done, essentially. I do have a new project (as of early 2011) planned. It will most likely be a crane :-) But then I haven't firmly made up my mind yet.

Thomas J. Avery 2011