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Hi, the German Company Wilbert produces tower cranes with a unique feature: in order to optimize transport dimensions, the jib changes its height as well as its width along its length. To be able to travel the whole length of the jib, the traveller has two sets of wheels at different widths, which travel on different levels along the jib. Thus, Wilbert cranes can easily be identified due to the distinctive step in the middle of the jib, which can be seen for example here. Today I was wondering if this unique design can be built using Lego Technic. Here is the result of three attempts, rebuilt in LDD: This is a view of the boom with the traveller on it here the jib alone, shown from the tip and here from the other side this is the traveller. The ropes which move the traveller can be knotted to the center holes of the traveller. The end leading to the tip runs around the pulley at the tip and is then leaded back through the jib by several eyes (parts 32034 and 87082), which also act as distance holders and stiffeners for the bottom of the jib. The lifting rope runs around the pulleys in the traveller down to the hook block. It's end can be knotted at the grey eye at the tip below the pulley (part 6536). I haven't tried yet if the assembly works with ropes. But the traveller runs very smooth along the jib, and there is hardly any step at the transition between upper and lower level. Thus I think that motorizing this thing shouldn't be a problem. Also I'm quite satisfied with the bending stiffness of the jib, so I guess it could take quite some load. Interesting enough, the heights of both jib parts match really good. When taking the WT 650 as a prototype, the scale in height is 1:45,1 for both parts. This is altough the height is kind of predefined by the Lego-parts and the function of the jib. The width doesn't match as well, the Lego-jib is quite a bit too wide. There are two details I'm not really happy with: 1) the connection of the inclined 1x11 Liftarm to the tip of the large jib section. The LA is supported by a 3L pin only from one side, which is not good regarding bending forces. If there were 1x7 LAs with an axle hole at one end, this could be done with a 5L axle. Since such parts don't exist, a 6L axle could be used in combination with half-width bushings. 2) I'm not really confident about the connection of the traveller frame to the upper part only by the four 3x5 L-liftarms and the black pins. maybe it'd be better using 1x7 or 1x9 LAs to transmit the vertical forces. On the other hand, the traveller as it is now is quite compact and reduced to the absolute necessary. That's it for now. I don't know whether I'll proceed with this model or not. If anyone wants to improve or complete it, here's the LDD-file. cu, Robert