D R A G L I N E   crawler crane (2014)


Building instructions (PDF)
(472 pages)
Example instructions (PDF)
Parts Inventory:
(2.208 parts)

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Remote Controlled: Power Functions

Dragline crawler cranes are rarely seen in daily life in The Netherlands and I can only recall one seeing in operation when I was a child. However, I always liked this kind of cranes for the clever mechanism of the lower rope to load or empty the bucket in combination with chains connected to the bucket.

The challenge was to have the crane full Power Functions enabled. In total the crane hides 5 M-motors, 2 L-motors, 2-XL motors, 4 IR-receivers and 2 battery boxes! Together these motors make sure the crane can crawl, swing, raise/lower the boom, wind/unwind the 2 drum winches with ropes, and operate a 'free fall' system whereof the drum winches are temporary released from their motors. The latter was the main requirement for this model to act as a real dragline; eg. being able to swing the bucket to the outer side followed by a drop down on the sand. Although this model is able to simulate this mechanism... it takes severe practise with the remote controls to do so.

It took some redesigns to swing the superstructure smoothly without crunching gears; the limitation is the turntable being 'too small' for this kind of models. I resolved this by powering the turntable with a double gear system, synchronized in transmission and driven by 2 M-motors together. On my wish list is a 'bigger' turntable being developed by LEGO®. Maybe in the future, who knows?!

Surprisingly the whole development of the crane in LEGO® took less than 6 months, although I guess I did spend more than 150 hrs on it.

Btw: the Dragline Crawler Crane fits nicely on my Truck 8x4 with lowloader MOC.



The dimensions of Dragline crawler crane:
* Length for transport, only A-frame + boom foot: 65 cm
* Height superstructure: 18 cm
* Width undercarriage: 21 cm
* Length boom (3 sections): 92 cm
* Height with raised boom (3 sections): 98 cm
* Boom angle range: -10 till 80 degrees
* Weight: 2,7 kg (including 2 battery boxes)

* Lifting capability:
   - 250 gram (save range for full PF operations)
   - max 500 gram (heavy stress on PF operations) 

* Total number of parts: 2.208

Photo-shoot (The Netherlands):
* Reconstruction high-way A1, near Weesp
























Liebherr HS 875 HD in BAM colors
The dragline is based on the original Liebherr HS 875 HD hydraulic crawler crane that includes 2 main winches. The crane comes with a boom that can be extended with multiple sections. The crane equipment is modular designed to operate as a crane, dragline or clamshell.
The working range of the main boom is between 15 - 82 degrees wit a maximum length of 50 meters. The total weight of the crane is approx. 93 ton.

The color scheme I used is taken from the famous Dutch Construction Company, 'Royal BAM Group' which history goes all the way back to 1869 when it was started as a family company. Today, Royal BAM Group is a successful European construction group and active in the sectors construction and mechanical and electrical services, civil engineering, property and public private partnerships.


Sometimes an abbreviation is only known for itself; by doing research for this model I learned that BAM refers to 'Bataafsche Aanneming Maatschappij'.




Most of the time was spend to build a sturdy superstructure and to find locations for the many PF devices. Multiple 5x7 and 7x11 'open center frames' are used to deal with the forces that are applied by the boom and the weight of the PF devices. Both drum winches are powered by a PF XL-motor, whereof the drive train between the XL-motor and the drum winches passes a clutch-gear box. This clutch provides the 'free fall system' by decoupling the drum winch drive train from the XL-motor. Although this systems works fine, it is very sensitive for distortion of the superstructure and 'free run' of all axles and gears.

Directly under the gear-box at both sides a M-motor is located. These 2 M-motor are connected to a single output of a PF IR-receiver, as such they run synchronized and drive a single drive train with 2 worm gears that provides the swing of the superstructure. To provide a reliable swing without 'gear crunching' the turn-table is driven by 2 single 16 tooth gears, connected to the 2 worm gears. One can see the drive train with 2 worm wheels in the picture between the 2 drum winches.












The rear drum winch is powered by a single M-motor, located 'upside down' between the 2 XL-motors. Its function is to raise/lower the green 'A-frame' via a double rope system.

Under the rear drum winch a PF rechargeable battery box is mounted. The choice for the rechargeable battery box a logical one: its weight and size are less compared to the 'normal' PF battery box (as used in the undercarriage). As well, the 3 PF IR-receivers can be found here. There was still enough space left under the XL-motors to deal with all the wires of the several PF devices!

From a cosmetic point of view the 3 PF IR-receivers can be hidden behind the black 3x11 curved panel.












Technical inside (cut-away render):



Boom & A-frame
The main boom exists of multiple sections. A boom foot connected to the superstructure, an extension section and a boom head. The length of the main boom is approximately 110 studs or 7x beam 15L.
According to the scale of this model, the boom length represents 22 meter.

An green A-frame is mounted on top of the boom foot. By larger cranes, the A-frame provides momentum being able to lift the main boom.

The boom head consists of a main pulley on the top, and a smaller pulley somewhat under the top.

Remark: the original Liebherr HS 875 HD has an allowed maximum 30 meter boom by dragline operations. Unfortunately I had to compromise the boom length for this model; I tried a longer boom but that ended up in too much stress on key LEGO® parts and easily tipping of the whole crane itself.
















I used the dragline buckets of the ESCO Corporation (developer and manufacturer of highly engineered wear parts) as an example. That is why the bucket has a red color touch.

Providing the bucket's free movement, both the front and rear drag chains can pivot without touching the bucket. For the rear chain this is achieved by the beam spreader bar that is 1 stud wider than the bucket itself. The front chains are linked to a 3L bar that is mounted on the outside of the bucket. LEGO® bionicle chain links appeared to be the most realistic chains for the bucket.

The 8 red teeth (bionicle) can be quickly replaced if one is broken by just snapping of the axle of the bucket, just as in the original one.

It took a while to figure out the best position to fit the front drag chains to the drag line; it appeared to be 47 cm measured from anchor bracket (red 2L axle). In this way the bucket is able to drop vertically.

Both lines can be easily disconnected from the bucket.


Crawlers & Undercarriage
The undercarriage was a relative easy exercise. The 'new' LEGO® track system was used to develop the crawlers. Each crawler is driven by a PF L-motor. A standard PF battery box is located beyond the L-motors. The PF IR-receiver is mounted as much as possible to the outside.

When I designed and developed the crawler crane, I was afraid that the PF IR-receiver's ' line-of-sight' was distorted by the superstructure above it, resulting in loss of RC functions for crawling.
I was however surprised how it turned out, even outdoor; It works just as I intended too!

Remark: at the left side of this picture one can see both M-motors in the inner side of the superstructure, used to control the 'free fall' system.





Double rope lifting
The rope of the 'drag line' drum winch can easily be rerouted to the boom head section that has a second smaller pulley available; in this case double rope lifting is possible.

All the ropes (4 in total) of the crawler crane are the ones found in the LEGO® 42009 Mobile Crane MKII.