Marine Pedestal Crane

Marine Pedestal Crane

This is a model of a typical heavy duty pedestal crane used in the offshore construction and transportation industry. It is not modeled after any specific crane, but incorporates typical characteristics of such cranes.

Details of the Model:
Completion Date: July 2002
Maximum Lift: 48.0 lb (21.8 kg)
Scale: 1:30 (approximate)
Power: 12V battery
Controls: 4-channel R/C prototype from HiTechnic
Total Lifting Lines: 2 (main hoist and whip hoist)
Total Height: 6.5 feet; 2.0 meters
Boom Length: 5.5 feet; 1.7 meters
Total Motors: 14
Thrust Roller Bearing: 29 Wheel Hubs (30.4 x 14 VR)

The only modified parts used were the sheaves (pulleys). The cross-axle holes were bored out so that they spun independently of the axle. The non-Lego parts used were the battery, string, counterweight ballast (scrap steel), and the R/C controls from HiTechnic.

Extra Photos:

1 2 3 4 5 6 7


Base Development


Bottom of Base


Close-up


Roller Detail


Superstructure


Turntable Drive


A-frame front


Counterweight box


Winch motors


U-joint detail


U-joint detail


Boom


Boom


Chosen Design


Base Complete


Roller Ring


Roller Detail


Bottom of Supers.


Turntable Drive


A-frame Back


Counterweight box


Winch assy.


U-joint detail


Top of Boom


Boom


Boom

CONSTRUCTION DETAILS

I began by constructing the turntable in early June 2002. I knew the turntable would be the most difficult part of the model, and I figured that if I could make a large, functioning turntable with a thrust roller bearing, then I would be able to build a large crane around the turntable. My goal was to make a large, complex model to take to Brickfest in July of that year.

I struck upon the idea of making the model modular. It was going to be fairly large, and I needed it to be portable and packable. So I figured that it would help by making it in large, interconnecting chunks (modules).

1. Base

I started the base first since it contained the lower half of the turntable, and I was keen to design and build the complex turntable first. After a little trial-and-error, I arrived at an arrangement of radial and circumferential beams that worked. It had 12 sides, and was about the right diameter I wanted.

The strength of the base comes from the plates oriented radially (the black plates on the inside) and circumferentially (the gray plates on the outside- the shell). The plates are stiffened, or "backed", by Technic beams. This model makes use of plates in a structural way, and is very different from how I've used them before.

2. Rollers

The idea of a thrust roller bearing is to provide low-friction vertical support to a large rotating structure. I used 29 white 30.4 x 14 VR wheel hubs to create a ring of rollers for the turntable bearing. The wheel hubs, or rollers, were backed by a sandwich of small plates and 1x2 Technic beams.

The design of the base provided a rough circle for the turntable, and the circumferential beams (on their sides) provided a flat surface for the rollers. They also created a lip or flange that restrained and roughly centralized the roller assembly.

After I figured out the geometry and constructed the base and roller assembly, the rest was easy :-) Not really, but it was a steady downhill slope from that point to construct the rest of the crane.

3. Superstructure

The upper rotating frame (superstructure) was the heart of the machine. The large Technic turntable "keyed" into the base and provided a fixed gear to drive against when slewing (rotating) the crane. The motors driving the turntable were placed inside the superstructure and allowed it to rotate 360 continuously (i.e. no wires pass through to the base, it is static).

The superstructre was the basic framework that connected the upper works of the crane to the turntable. The superstructure had parallel I-shaped beams running the length of the crane (from the boom hinges to the counterweight box).

I used a newly developed design involving plates and Technic beams. The plates formed the web of the beam (the vertical part) and the beams formed the flanges of the beam (the top and bottom flat surfaces). The result of this design is basically a composite (or built-up) beam that functions as one, large and strong member.

On the underside of these beams was a mirror-image of the turntable base. This "disk" completed the top half of the turntable and thrust roller bearing.

Another important feature of the frame was its "hook" shape in the rear (under the counterweight). The main frame had extensions that extended downwards and then back towards the crane center. These extensions would contact, or "grab", the lower lip of the turntable in the event the crane tipped over.

The thrust roller bearing provided vertical support only, and that vertical support was limited to compression. Once you lifted the crane's superstructure upwards, the turntable would come right apart. This would never have happened (unless you turned the whole thing over and held it upside-down), but with enough load on the crane hook, the superstructure would tip over. During tipping, the frame extensions in the rear would make contact with the lower turntable lip and prevent it from tipping over and falling off the base.

4. A-Frame

The A-frame of the crane sits on top of the superstructure frame. The very top of the A-frame is a connection point for the cables that hold the crane's main boom up.

The A-frame is in two pieces: 1) the actual A-shaped piece in front, and 2) a pair of "back legs" that tie into the superstructure frame behind the counterweight.

5. Counterweight

The large, red box in the rear of the crane was housing for the ballast used. Initially, I used water in large plastic sacks stuffed into the box. However, the water did not provide enough weight. I eventually used scrap steel to make a heavier counterweight.

The counterweight also housed the HiTechnic 4-channel R/C receiver prototype and battery. I used a 12V battery from my cordless drill to power all 14 motors.

6. Winches

Three winches were used in this model. The main hoist and also the boom luffing were powered each by a 4-motor winch. The whip hoist (the smaller hook at the tip of the crane) was powered by a smaller winch using two motors.

The power philosophy of this model was different from what I've used before. Instead of using a single motor with a large gear reduction for each function, I used multiple motors with less gear reduction. The difference is (considering that you have equal amounts of output power) the multiple motor approach will operate much faster.

An essential function of every crane (real or model) is the ability to brake the winches. If a winch is under load (e.g. during a lift) and the power is turned off, then the load will backwards-drive the winch. Therefore the winch needs some sort of brake to prevent it from turning.

I added spring-loaded stops to the main hoist and boom luffing winches. When not in use, I quickly snapped these stops in place to prevent the winches from turning.

7. Boom

The boom is a large truss structure. I had built trusses before, but not as complex like this. There are a few transitions in the boom shape as you travel from hinge to tip. These transitions were possible by making what is basically a U-joint that was in-line with the main truss members (chords). There are 3D renderings of this special joint in the photos to the left.

The boom was complex in design, but ended up being relatively straight-forward in construction. With some trial-and-error, I figured out all the diagonals and cross bracing required.

The boom did not break down easily into sub-parts and presented difficulty in transporting. I just had to break it down and then re-build it at Brickfest that year. I labeled each member carefully and took notes to use in re-assembly later.


45 lb lift


48 lb lift


48 lb lift


witness


45 lb lift


48 lb lift


50 lb attempt

PERFORMANCE

After Brickfest 2002, I decided to test the crane to its maximum load :-) On August 3, the crane picked up 48.0 pounds (21.8 kg) off the floor. Just for fun, the load radius of this lift was:
4.0" (10.2 cm) from load center to heal pins of boom
9.5" (24.1 cm) from load center to center of crane (i.e. center of rotation)

James Simpson witnessed this lift at my house. I also attempted a 50 pound lift, but the base started to buckle and I stopped the lift. I did not want to destroy the crane just yet.

VIDEOS

Boom moving (0.9 MB)

Lifting light loads (0.6 MB)

Lifting 20 lbs (2.1 MB)

Slewing (rotating) (0.6 MB)

Close-up of rollers in action (0.8 MB)


Packing


Trunk 2


Set up (2)


JC smiles


BF Award


Trunk 1


Set up (1)


BF Display


R996 lift


TexLUG (3)

EVENTS

Packing up this beast to fly to Brickfest in Washington D.C. was the final feat. I had two wooden trunks that were just inside the allowable dimensions by the airlines (at the time). I really did not want to exceed the allowable baggage size and weights and incur the extra expense of having oversized/weight baggage (nor did I want to mail anything ahead of me - mainly because I was still building the crane right up to the day before :-)

I managed to not only fit the crane into these two trunks, but also my R996 model AND a small foldable, rolling cart too :-) Of course the packing process took many hours, and I tried many different arrangements of the model parts before getting it all to fit. That was a late and stressful night, particularly because Brickfest was the next day!

Talk about geekiness - I even sketched out a packing map so that I knew where everything fit. (So where did I put all of my clothes and toiletries?.... yep, in my carry-on :-)

I hypothesized that the trunks would see little damage because the baggage handlers would NOT be able toss them (weighing nearly 50 pounds each) very far. I was wrong. Whatever happened to those trunks is beyond me, but they did get whacked around pretty good.

One of the trunks was almost split open. Perhaps the elephant that was being used to sort baggage got tired and sat on it.

The stuff inside took a beating too. Fortunately, I had taken a print-out of all my photos (just quick snap-shots that I made of both models) and used that as a guide for repairs and re-assembly.

The gray base of the crane sustained the most damage. Frank Filz, who had met me at the airport, sat down with me in my hotel room and helped repair it. It was a mess. I had to remove nearly all the gray plates, rebuild the insides, and then replace the plates. I had many extra parts left over after the repair, so I knew the job wasn't perfect, but it worked. Thanks, Frank!

I was very relieved and happy once I got both models up and functioning at Brickfest. I set up right next to Jennifer Clark (the Technic Goddess).

I had a lot of fun displaying the crane. Using HiTechnic's prototype 4-channel R/C unit, I was able to control it easily, from any point in the room. In fact, I would sit back in a corner, wait for a crowd to gather, and then swing the crane around quickly. It really surprized people!

-----------------------------------

I also took the crane to the fall 2002 state-wide TexLUG meeting. It seemed to be a big hit with the crowd. I let the little ones "drive" the monster, but I closely supervised.

Photo credits (used with permission):
(1) Photo by Joe Meno
(2) Photo by Calum Tsang
(3) Photo by Laura Hayden

THE REAL THING

The model is based on real offshore pedestal cranes, but not one specific crane. It incorporates typical features that are characteristic of such cranes.

The images to the left show one particular example of a real offshore crane, similar to the model. The crane is aboard Technip's pipelay vessel, CSO Deep Blue. The crane is mounted near the stern of the vessel, on the port side.

Thomas J. Avery 2002