In 2018 the Bugatti Chiron came out in LEGO Technic. It’s quite a complex model, but very dense and seems inefficient and consequently negatively impacts some of its functions. Time for a redesign thus where the starting point was to keep the same modular build with almost identical interconnection points, and keep the overall looks in tact as much as possible. The objective was to reduce primarily parts and subsequently weight, while trying to improve the structural integrity without jeopardizing buildability.
Degrees of Freedom
When it comes to creating mechanisms, one has to consider the motion. Mechanisms are then usually defined in degrees of freedom and their connection points. These connection points are usually fixed in a rigid construction that has to cope with all the forces and loads from the different mechanisms. This means that in contrast with mechanisms structures should have no degree of freedom and be completely rigid. Often a casing is preferred to be in one single piece, but with LEGO bricks this can not be achieved. Here a structure consists of many parts, all of which have to be fixated (have no degree of freedom). Considering this each part in a brick built structure has one or more of the following functions:
- Bridging a gap (connecting 2 pieces or sections)
- Keeping in position (no force is applied but gravity)
- Locking in place (can cope with specific loads)
Ideally a piece fulfills more than one function.
When trying to improve a design, my method is to analyze the current model in detail first and then to ask for each section/ part what the purpose is or why it is needed. “What is this part doing here?”, “Is this part really essential?!”, “Can it be done in a different way?”, ” Can several parts be replaced by one?” are just a few common questions I ask myself.
Case 1: Rear Axle
The most peculiar aspect during the build of the rear axle was the crossbar that connects the left and right suspension arms. My suspicion is that this bar was added very late in the development process, when the structure of the suspension appeared to have too much flex. There are several reasons for this conclusion:
- The crossbar looks crammed in place with a lot of small parts to establish the connection and the odd position of the bar itself (half module offset in height).
- Due to interference with the engine module which has to be inserted from the top now, instead of from the front which seemed to be the plan initially. This assumption is made on the odd 5M axle in step 196 and 198, which could have been part of the engine module if this was inserted from the front. The 13M beam in step 173 was probably initially part of the rear axle module, likely after step 63.
- The fact that the whole gearbox is also inserted from the front.
- The crossbar reduces the flex problem only a little and can be considered a poor solution from a mechanical point of view.
So there were 2 objectives to deal with:
- A more rigid solution for the suspension arms that reduces flex
- Allowance to insert the engine module from the front.
Meanwhile the new solution preferably had to reduce parts but keep the same position of the hardpoints (the connection points of moving elements)
The image above shows the original design together with the redesign. This new solution allows for the engine module to slide in from the front and at the same time increases rigidity by triangulating the structure of the suspension arms. Another major benefit is that the diagonal beams are doubled up as seen in the image below, reducing the internal stress significantly, while adding further rigidity.
In the redesign the suspension arm module now takes care of all the load by itself due to the integration of the angled beams, whereas the original design is heavily depending on the additional crossbar (which is another indicator that this crossbar was added late in the design process).
The redesigned rear axle is perhaps slightly heavier, but this is a small price to pay considering the extra strength, the reduction in parts and an easier assembly process overall.
The plan for next time is to look at the redesigned gearbox presented at Eurobricks (which was copied pretty much 1 to 1, because of its near optimized design) and its beneficial implications on some other parts of the rear section.