Meccano TAKRAF Level Luffing 35 Ton Electric Dockside Crane

Designed and built by Michael Adler

Cranes are an ever-popular subject for Meccano builders and seem to demonstrate like no other models the many features and advantages of the Meccano system.  While searching for a suitable subject, I came across this beautiful crane on a German dockside and was immediately struck by its graceful yet powerful appearance.  Its all-welded construction gave it a clean, uncluttered look, free of bracing and rivets, and one was struck by the very long flying jib and prominent driver’s cab on the end of a long walkway giving an unprecedented view of the work area.

Many examples of real beauty are found in industrial objects, and here, surely, was one of them.  Perhaps this could be captured in Meccano, also using sound engineering principles?  

Prototype Takraf 35 ton level luffing crane

Research revealed that TAKRAF stands for Tagerbergbau-Ausrustungen, Krane und Forderanlagen (Surface mining, Cranes and Conveying Equipment).  The company,  based in Leipsig, Germany, is one of the world’s leading manufacturers of heavy surface mining and transportation equipment. The company’s history goes back to 1725 when its first factory was opened near Dresden; it started crane production in 1906.  After German unification, Takraf became part of the MAN company is now called Tenova.   

The crane, which stands on the dockside at Saarlouis in the Saarland, was manufactured in 1988 and has a load capacity of 35 tons at 17 metres.  It is a double-luffing crane with two winch systems for a four-rope grab operation, but it can handle a variety of other loads – it can be fitted with a hook for general cargo, an electro-magnet for loading scrap and a spreader for lifting containers.

The Meccano TAKRAF crane stands on four floating bogeys, two of which have their own motors, and it picks up its power from a dockside cable lying next to the track.  The cable is rolled onto a self-reeling wheel mounted on the gantry and is paid out and taken in as the crane moves.   The roller bearing is the standard type with trapped balls; jib luffing is by rack and pinion.  The jib and flying jib are fully counterbalanced by an overhead counterweight linked to the jib.  There are four falls of wire from the end of the flying jib wound from four separate winch drums.  

Meccano Takraf crane

A number of photographs of the crane were found and from these a set of drawings were made with a scale of approximately 1:12.  Construction began with the bogies and one of the braced side frames of the gantry.  The scale of the construction quickly became apparent; the final height of the completed crane would be over seven feet.  Large models bring their own problems, with requirements for high strength and weight loads.  A very strong transverse gantry beam was required which had to be entirely free from sagging.  This was achieved using a long box construction and very strong internal bracing, further reinforced to prevent flexing from the column rising above its middle.  The gantry was then completed, together with its two powered floating bogies, and run on tracks for the first time.   6 volt Faulhaber-type motors with 60:1 output were used and drive all the wheels via a series of reduction gears.  This type of motor and reduction gear was used throughout the model.

Work then commenced on the machine house chassis and the roller bearing.   The original construction incorporated a section inside the column with the weight bearing at its lower end and a ring of side rollers above, but this was changed to a more conventional system of trapped balls within doubled tracks which proved more stable.   Flexing was encountered at the junction of the bearing and the chassis, which had to be strengthened with a series of vertically-laid narrow strips sandwiched between flat plates.  The completed structure was very strong indeed.  The slewing mechanism was completed, incorporating a 5.5” gear ring and 20 DP pinion.  The jib attachment at the front, the floor supports on each side and the mountings for the superframe were then constructed and reinforced.

 

The superframe was then built and attached, and the very large size of the model became quickly apparent.  Particular attention was paid to the upper end where a complex construction was needed to support the jib counterweight, the flying jib tie bar and the rope sheaves.

The luffing rack runs inside a floating frame which adjusts to any rack angle; rollers grip it above and below.  Power from the motor comes through reduction gearing and a worm drive to the final pinion; the mechanism is mounted half way up the superframe.

The jib is over 4 feet long and built to withstand strong compressive forces while receiving support from the counterweight.  It is surmounted by the long, distinctive flying jib controlled by a tie bar back to the top of the superframe.  The geometry of the flying jib and superframe was calculated to provide true level luffing; with the jib, flying jib and counterweight attached, almost full balance was achieved at the outset and the luffing mechanism ran smoothly and strongly.

The winch system was designed to operate a grab, as in the prototype, using two winches and four drums - two for suspension and the others to operate the open/close mechanism.   There are a number of options in doing this, including using two identical motors linked motors though a differential, or providing a means to shorten the open/close cables relative to the hoisting cable by running them through a roller system.  The differential system was chosen for this model and proved reliable and realistic in operation.    

 

Winch system

The winch house was completed in blue plates to match the prototype; they contrast with the structure of the rest of the crane built in zinc girders and strips.    The driver’s walkway was attached to the right side of the chassis in front and required very rigid internal bracing to prevent it from sagging.

Radio, as a means to control the crane, proved reliable and efficient, using five channels of a conventional model aircraft-type duel joystick transmitter and extension.  Each motor was controlled by its own electronic power supply plugged into the receiver, giving secure forward and reverse and speed control to each of the motors.  There was certainly something fascinating about watching the grab close on a load and then release it again, and seeing the crane slewing, luffing and travelling.  This is what the real crane driver must experience.  

Drivers cab and the grab

If one lives at a distance from an exhibition hall, it is a pretty formidable business to transport and erect the whole large system and then expect it to function correctly and reliably. The prototype Meccano TAKRAF was built in my study, and could not be moved out of the room, let alone exhibited in another country.  The model would only ever be shown if it were built in England.  Richard Payn kindly agreed to build it, and he carefully followed my documentation and photographs. He also suggested a number of features to improve the model like strengthening the roller bearing attachment to the chassis and redesigning the winch system.  His use of 1972 pristine dark blue girders and plates enhanced the crane’s appearance immensely and I am deeply grateful for his collaboration in this project.  

The Takraf crane with Michael and Richard at Skegness 2014

We will always be fascinated by cranes, and the TAKRAF has been a wonderful Meccano project extending over eighteen months, with many problems solved and challenges experienced and overcome.

Michael Adler 2016