Markus Kossman

Building the next big thing: the development of 42009 Mobile Crane MK II

januari 01

Building the next big thing: the development of 42009 Mobile Crane MK

Imagine you’ve got in front of you the 42009 Mobile Crane MK II, un-built and still in its huge box. With 2600 elements, its the biggest ever LEGO® Technic model, and with 127 gears and multiple power functions, it’s also the most advanced. Quite a building challenge; we think you’ll agree.

How did these thousands of elements end up in the box in front of you, and why, as you embark on the exciting task of putting them all together, do they turn into a functional, authentic version of a mobile crane and not, say, a hovercraft? What sorts of building challenges are involved here? To answer this (in our biggest, most advanced blog ever!), we’re going to look at the various stages of the LEGO® Technic development and design process, from initial brainstorming through modelling and development to the finished item.

What are we going to make this time?

Long before the new 42009 Mobile Crane was even a twinkle in the collective eye of the LEGO® Technic design team, a bunch of them would have met up for a day of intensive brainstorming. Even though the category would probably have been decided at this point, very little would have been known about the upcoming model.

The idea of a brainstorm is, of course, ideas – and here almost anything goes (including one time an idea for a flying doll’s house!). The internet, magazines, TV shows, in fact anything that may inspire, is brought into use as literally hundreds of ideas – some more sensible than others – are pasted onto walls and across whiteboards.

Once the ideas are up (and after a well earned lunch!), it’s then time to sort out what might work and what definitely will not. The team splits into two or three groups, dividing the ideas between them. Questions asked run all the way from ‘What might be cool to build?’ to the less exciting, but still valid, ‘What will work in the market?’

As you can imagine, a lot of stuff doesn’t make it out alive from this stage (you’ll note that we’re still waiting on that flying doll’s house, for one … ). Some ideas will be good enough, but just don’t fit the category selected. These ideas are not scrapped, but are added to the LEGO® Technic idea bank, to be revisited another day.

The winning idea from the brainstorm (the one that answered the most questions correctly!) is then sketched, concept modelled and tested. In the specific case of the 42009, the design and development team, led by Senior Designer Markus Kossmann, decided that they wanted to go with a bigger, better version of the very popular 8421 XXL Mobile Crane from 2005. Updates worked on (and mentioned by Markus in a blog back in April) included:

  • Axles, from 4 to 5 featuring 4 axle steering
  • Gearing changes, featuring multi-function gearbox
  • More realistic supports, with extending outriggers and stabilisers (motorised)
  • Replacing lifting boom pneumatics with a linear actuator (motorised)
  • Power Functions
  • NEW, 2-stage boom extension
  • Use of more modern elements

Hands on modelling

For the 42009, generating ideas for the new functions, designing the first prototype elements and building a first rough sketch model took around two weeks. The first sketch model gives a good indication of size and proportion, how functions work and the location of any critical areas (weak points, stability issues and so on). To make the 42009 design process easier, construction was split into three modules:

  • Chassis, with steering, piston engine and outriggers
  • Crane housing, with motor, gearbox and battery box as counterweight
  • Boom, with two stage extension

Testing, testing, testing

Once the model – or models – have been built, the next phase is all about testing, rebuilding and testing again. The 42009 modules not only had to function in their own right, they also needed to work together while effectively drawing power from a single motor, via a multi-function gearbox (phew!). On top of this, anything a design team comes up with also has to be something you guys can have fun piecing together. It’s no good having fabulous functionality if building  a model requires a degree in advanced engineering! – so build flow (how much time and work required to build a section/entire model) also needs to be considered (double phew!).

Chassis challenges

The 42009 has the longest chassis of any LEGO® Technic model. The design had to be very strong and stable to support the crane and house steering, engine, outriggers, gearbox, etc., while not bending or breaking when picked up! Thus the chassis is built up in three layers – axles, outrigger functions, and gearbox – locked together within a sturdy frame.

Ensuring smooth steering was relatively straightforward, requiring changing the length of the steering arms on the wheel bearings to generate different turning angles. Synchronising the outriggers was a much tougher challenge, and involved the development of a new, pretty cool 8-tooth gearwheel, which can slide on cross axles and linear actuators.

Crane Housing demands

The Power Functions motor, all gear switching and the boom base are all located here. The major challenges faced here were gear selection and power management – both of which had to be seen in the context of build strength and, not least, build ability!

A single Power Functions motor drives all the crane functions. Some functions need a lot power; some need less, so to make everything work, only one function can be selected at a time. Getting the gearbox layout right was difficult. Motor power not only had to be split across individual functions (outriggers, boom function, etc.), but the gearbox also had to be easy for you guys to use and workable with one switch. After considering a five-function option, split between the housing and the chassis, a four-function solution was developed to fit with the overall modular design.

Boom or bust!

With the new boom, friction was the biggest problem faced by the design team.  As with any LEGO® Technic model, the idea was everything as realistic as possible (using (newly) available rounded 11x3 panel elements). However, the new look created a new problem – anything more than a minimal load force bent the beams in the boom to such an extent that the boom stopped working properly. The solution was to redesign the 11x3 rounded panel, adding extra Technic holes, to create a more solid structure. Copying the old boom design gave a lot of friction problems – and strengthening the boom didn't help. So the team came up with a new wheel bearing construction, with enough space around the elements to allow the boom to bend under heavy loads. Not only did this solve the friction issue, but power consumption was reduced by a third!

Getting the balance right

Think again about the building challenge that we started with above – finding the 10-15 hours needed to piece together all of the 2600 elements that make up the 42009. For the design team it takes on average about 8 months to create a finished LEGO® Technic model. The 42009, our most complex and advanced model ever, took a whole year to design and develop – as you can see, getting the balance right between authenticity (gearing, steering, motorisation, etc.) and model functionality (including all important build ability!) can sometimes be pretty tricky!

Hopefully, knowing a little more about all the work that goes into our models before you even get your hands on them will only add to your enjoyment of LEGO® Technic, not least the next time you’re facing a building challenge of your own … ;-)