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Liebherr LTM 1220 220 Ton Mobile Road Crane

By Greg Clarke

» Watch a video of this model in action in our Model Gallery.

The Prototype

The LTM 1220 is a 5-axle medium to heavy size road crane with a transport weight of 60 tons and length of 15.5 metres. Its carrier engine is a six-cylinder 503hp diesel and the crane engine is a 4-cylinder 245hp diesel. The crane fitted with its maximum of 74 tons of ballast can lift 220 tons at a radius of 6 metres but a far more useful lift is 36 tons at 18 metres using 50 metres of its extension capability.

All lift functions are monitored by its own on-board computer called LICCON. This system prevents dangerous lifts by locking out the crane if it's going to exceed its lift parameters like high winds/uneven stabilising etc.

Liebherr Mobile Crane Model

The Model

This is the second example of current Liebherr produced cranes I have built, the first being the 300 ton lattice boom crane I made in 2008. For this model I wanted to try several new build techniques and take it to the next level.

The model is roughly 1:17 scale with the carrier assembly 750mm long and the height of the boom fully extended at maximum elevation 1350mm. The model took about 150 hours to build over a one year period. It's made in 70's yellow, zinc and blue which in my opinion is definitely the best colour for modern day plant. The crane is based on three main sub-assemblies: the carrier; crane body and boom.

The carrier chassis is made from 4 x 24½" double angle girders with 2½" girders as cross-members. The wheels are the 2¾" diameter rubber type which give the right width but are a little undersize for scale. Rather than attempting to create drive I concentrated on suspension and steering. The suspension is independent for each wheel and is based on a parallelogram design using narrow 4-hole strips and 2" rods as link bars. The springs were the very nicely made 1½" compression spring units from Stewart Borrill. The cab features windscreen wipers, headlights and side mirrors and can be removed to get to the stabiliser motor.

The stabilisers are made from 5½" double angle strips running out on a 4½" x 2½" plate using ½" plastic rollers as guides. All the arms extend and retract together using a push/pull arrangement with cord. An M5 motor geared down turns the forward cord shaft and a PTO takes the drive to the rear. After slewing the crane body two panels at the rear can be lifted to show the drive mechanism. The turntable is made up using ball bearings sandwiched between 4" circular plates and 5½" circular strips. The drive for this is also located in the carrier assembly.

I tried to model as much as possible in Meccano but one area where I deviated was the luffing ram which lifts the boom. I had see several examples from other builders using various techniques with cord, pulleys and threaded rod but all these methods lacked the prototypes single large ram with a chrome rod taking all the strain.

Liebherr Mobile Crane Model

Taking the idea from Tony James JCB Loadall, I used a ¾" chrome towel rail for the piston rod but there the similarity ended. The pulley cord system Tony used clearly was not going to be man enough for this job so I built a mock-up and experimented with various screwed rod drives until I settled for M6 size. With a ¾" thrust bearing taking the vertical load the whole boom is elevated by rotating the rod which in turn drives a special M6 threaded coupling attached to the bottom of the chrome rail. A ¾" hydraulic dowty seal provides a very realistic cylinder seal and journal. An MO motor/gearbox linked to a 3:1 bevel gear provide the drive. Externally the crane body features a tilting cab, side ladders, folding safety handrails, removable dummy counterweights and exhaust muffler for both the carrier and crane engines.

The boom was originally going to be in three segments but the load proved to be too high for the luffing ram to lift so I settled for two. This is made up from 49-hole girders for the primary and 37-hole for the secondary which run very smoothly on a bearing of plastic collars. The hook is a double sheave design with the hook free to rotate and swivel like the prototype.

Thanks to Brian Maunder for feeding me a regular supply of parts and Stewart Borrill and Dave Taylor for some of the more unusual pieces. Can't wait to start the next one!

 

» This article appeared in the January 2009 issue of SELMEC News.

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