InspirationMobile cranes are ubiquitous on construction sites nowadays, and somehow seem to be ideal targets for modelling with Technic Lego. Perhaps it has something to do with their apparent technical unseemliness; as a child, before I had a more formal grasp of mechanical engineering principles, I could never figure out why they didn't fall over! Nowadays, even with a better understanding of such things, it is still a challenge to create a Lego mobile crane that works well and more to the point, looks good. Sometime around 1980 I purchased Lego Set 855 in a sale with some Christmas money, and I thought it was great at the time, despite having several limitations. The outriggers were more cosmetic than functional, collapsing under very little strain, and I preferred the truck type crane to the single cabin type represented by this set. There was a model of this type based on the 855 set outlined in the "ideas" section in the instructions of some other models, but it too suffered from a large degree of flakiness. Nonetheless, the workings of the boom and superstructure were superb, and were part of the inspiration for the boom on this new model. A more recent Technic Lego set, number 8460, provided the main motivation for this model. Unfortunately I didn't get this set when it was available, so I thought it may be possible to recreate it with my existing Lego pieces and the instructions on Brickshelf. However, I soon grew bored of that idea and thought it would be great to build a crane based around the 8460, but with many of the functions motorised... then I thought it would be better to motorise all the functions; then even better to redesign and lengthen the exterior using the more streamlined parts in from my 8448 Supercar. In the end, I based the design of the outriggers and boom around that of the 8460 with a quite a bit of modification, particularly on the internal workings, and the rest ended up as my own design. As a guide, particularly with regard to proportions and style, I used the Liebherr LTM 1060. This particular crane was useful as it was around the right size for my intended model, and had a modern and streamlined look that I felt could be captured well with the pieces from the 8448 Supercar. Observant readers will note that the LTM 1060 has 4 axles whereas my model only has 3, the reason for this being that I only had six wheels of the type I wanted to use. Having one less axle also provided more room in the chassis, making it easier to fit several of the crane functions, a reason which was of course secondary in consideration to the lack of wheels... |
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BoomMost mobile cranes have a telescopic boom consisting of four or more segments which can be extended to amazing heights. Occasionally a lattice boom, normally stored alongside the main section of telescopic boom, is fixed to the end of the telescoping section to provide extra height. This can be a simple extension or a "luffing" boom which can be moved up and down independently of the main boom, providing increased horizontal range. Due to the size constraints of Lego, it is only really possible to have a boom with one telescoping section on a model of this scale, the problem being that the width of the boom must increase by two studs for each section. Still, it is the principle of the thing that really counts, and a working two section boom is better than none. While the boom is based around the design of the 8460, several modifications have been made. First of all, the length was increased by 50%; while in theory this was a simple modification, in practice some reinforcing had to be done to make the boom viable at this length, as it had begun to sag and twist too much. In addition to this, instead of operating the telescoping section manually, a micromotor attached to the base of the boom was used, with a small 9V battery box concealed as a counterweight to the rear of the superstructure. As mentioned in the superstructure section, the whole boom was raised and lowered by a rack and pinion system powered by an old style 9V motor. This arrangement worked exceptionally well, as the boom could be raised and lowered from its extremities, even at full extent with a significant load. The hook was raised and lowered by another old 9V motor mounted parallel to the boom one, as also mentioned in the superstructure section. From the photos, it can be seen that the whole arrangement was very effective, being capable of lifting a large 9V battery box, containing 6 AA batteries, at full extension and significant radius. The superstructure would also rotate perfectly well with this load, although the creaks emitted were sometimes a little disturbing... The main limitation was the strength of the boom itself - the bend in the boom in the photos was actually there and is not a trick of the camera. This was partly due to limitations of the design borrowed from the 8460, but more on that later... |
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ConclusionsI was pleased with this model - in common with the LS160 it had that thing that made people want to play with it, which I think is really what it is all about The strength of the crane was amazing, although in some cases this caused difficulties. For example, occasionally a two block situation would occur when the hook reached the tip of the boom and the operator failed to stop the motor, resulting in the thread snapping. In real cranes this is an incredibly bad thing to happen, and can cause the boom to rise or buckle. To prevent this, "anti two block" mechanisms are used to automatically shut down the hook controls upon an impending two block situation. Perhaps something of this type could be implemented with the Mindstorms sensors or even a simple switch and built into a future crane model..? The red colour of the crane sometimes caused confusion, leading to the mistaken identity of a fire engine! The reason I used red as opposed to the more common yellow is that I only had the more modern Lego parts in red - all my yellow stuff dated back to 1980 or earlier - and indeed one does occasionally come across a red mobile crane such as those available from Sparrow Crane Hire. Through the miracles of modern image processing technology I have included a picture of what the crane would look like were it yellow. I was still not happy with the boom when those photos were taken and made some subsequent alterations making it far less susceptible to bending and twisting, taking it much further away from the design in the 8460. It also looked better, in my humble opinion. A metal hook like the 8460 would also have been nice, but now I am nit-picking. With the completion of the LS160, I think I reached my personal zenith with respect to skid steer loaders, and it is unlikely I will ever make one again. However, I do feel that I have another mobile crane in me yet. Perhaps more yellow? Or perhaps with three telescoping boom sections? Or drive and steer and suspension to all wheels? Crab and coordinated steering? Pneumatic outriggers? Only time will tell! |
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References
Credits
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