Supercar 2015

This is a rather simple supercar model but the development of it was anything but simple: many compromises, setting new goals a few times and a complete start over characterized the building. Scale: 1:10.


Features:
  • Independent double wishbone suspension with horizontal shock absorbers.
  • Hand of god and cockpit steering
  • Rear wheel drive
  • V8 fake engine
  • 3+R gearbox
  • Adjustable rear wing/spoiler. The operating mechanism is placed between the seats
  • Scissor doors
  • Everything opens. The doors are locked by a simple mechanism and the bonnet is suspended by shocks.

Design process and challenges

Original goals
The original goal of the build was to build a manual supercar model with a sequential gearbox, realistic suspension and steering geometry that worked reliably and only used legal techniques and current, easily available parts. For a manual car with fake engine, the scale of the model depends heavily on the fake engine size, and also I didn't want a too large mode that was hard to lift and handle. This meant that I gave up the advanced suspension geometry soon because of the limited space and because at this scale, the small realistic angles are extinguished by the backlash of the LEGO parts and hubs (though many legendary builders would argue with that view...).

The gearbox
For the sequential gearbox, the plan was to have a gear stick in the middle console of the cockpit like in some race cars and to use the new 3L driving rings because they only have three stages instead of five.
About ten prototypes were made for the gearbox but none of them worked perfectly.
One of the main issues was the force required to engage and disengage the new driving rings (the 42056 Porsche with its thinned 3L connectors wasn't in existence that time yet). Since switching gears means engaging one ring and disengaging the other at the same time, the force became so big that the selector mechanism with the stick deformed while switching, resulting in much bigger stroke needed to properly switch a gear.
Another issue was the transformation from the sequential rotation of selector to the driving ring switching mechanism. This was implemented with a crankshaft. Because of the nature of cranks, the linear motion gets over the midpoint more quickly than the end points. This meant the two driving rings was engaged at the same time for a short period during switching. Placing the 24-tooth torque limiting gear could solve this problem.
A solution for these issues would have been to use the old driving rings with smooth 2L axle joiners, but that was on the border of illegal techniques.

The gearbox placement was also a great challenge. Since the gear selector mechanism was located between the seats, the gearbox itself had to be placed somewhere else. One obvious place would have been at or behind the rear axle (just like in real mid-engine cars), but gearboxes built from LEGO parts are usually large. And since the sequential gearbox needed a very stiff structure, the gearbox section quickly became too huge for the scale: it would have meant an disproportional overhang behind the rear wheels. Placing between the rear axle and the engine would mean the engine had to be placed between the seats. This would have ruined the proportions of the car.

The solution was a completely flat gearbox that's placed under the fake engine. That meant the engine was placed higher (an acceptable compromise).



The final solution with the flat gearbox still had the reliability issue, meaning the only one unique selling point feature didn't work as flawlessly as one would expect from a toy.

New goals had to be set.


New goals
The goal was to create a simple supercar that focused on the looks, realistic proportions, realistic engine placement, simple but reliable functions, and was sturdy enough to endure a child's play. 100% legal techniques, ease of building, using recent and easily obtainable parts were also requirements.

The design process started with the chassis which had to be low as possible. This first sketch was used to figure out the overall proportions of the car.


By figuring out the proportions, the chassis was designed in a relatively short time period.


The chassis became very low as planned. For designing the body, I created many sketches, sometimes by copying the screen of LDD. I wanted to make the model look more of the classical style than the modern supercars with the gunhole-like side windows and bulky shapes.

Design goals for the body
I always start with big plans about wacky panel angles and such but usually these desires are overwritten by my principles in building: sturdiness, everything should be defined (for example there shouldn't be panels fixed with only one pin), model made for playing should be obvious to use and handle so the model should be possible to grab and lift at every places that implies to be strong grabbing points (so parts need to endure pulling to a reasonable extent).
I made a few sketches during the development, they were really helpful to find the right proportions. Some sketches were made after the main lines of the face were defined. The three vertically placed round lamps concept was born quite early.



Designing the front hood was the biggest challenge of the body, because the front had to be as low as possible to look good and the wheels were not allowed to touch the hood even when pushed and steered (it's important to note that I wasn't that strict with the wheel arches, since they were made from flexible axles and even when they rubbed the wheels, they didn't deform other parts of the body or cause noticeable rolling resistance).

Instructions
The final challenge was to make proper building instructions for the model. This included minor redesigns to ensure that the model was easily buildable. There were quite some issues with my computer, so Blakbird helped me to finish the instructions. Due to the heavy use of floating subassemblies, there are some parts list per page errors. You can find the instructions on Rebrickable.com or you can download it directly from here.