Lotus E21 construction report part 27

Wheel design, wheel nuts and a real premiere: the first time I designed a working rear light.

The wheel nuts are a pretty simple. Indeed, I was not able to include the female features for picking up the wheel gun adapter. However, one wheel nut consists out of fife elements. Basically it is only two cylinders and a conical frustum. The wheel hubs are fixed to the rims on order not to lose them during a pit stop (this system was introduced in 2012 I think).
The wheel design was a lit le bit tricky. I needed three approaches to get them done:

1. The first approach (with white paper – because I was not able to find structural cardboard in the correct colour) was designed as medium size wheels. Page 44 of the 2013 FIA Formula One regulations:

12.4 Wheel dimensions:
12.4.1 Complete wheel width must lie between 305mm and 355mm when fitted to the front of the car and between 365mm and 380mm when fitted to the rear.
12.4.2 Complete wheel diameter must not exceed 660mm when fitted with dry-weather tyres or 670mm when fitted with wet weather tyres.

My wheels were designed with 33mm at the front and 37mm at the rear. I made a dimension check with the finished rim cylinder (without spokes). There, I detected, that the rear axle was about 4mm and the front about 3mm too wide (max. 180mm). So this design was dumped in a very early stage.

2. For the second approach, I found a cardboard, which has almost the correct colour. However, the rims are covered with a thin paper in the correct colour. In this approach, I designed the wheels to the minimum allowed distance. This time I made it to the complete rim with spokes, followed by another regulation test. To my astonishment, the car was to wide by 9mm at the rear and 7mm at the front.
The reason for this was, that the spokes collided with the brake calipers, so I had to redesign the whole cross section of the rims. One of the largest design faults I’ve ever done…

3. For the final approach, I redesigned the whole cross section with highest care and to the minimum dimensions permitted. This approach finally works and the car should be just within the regulations by less than half a mil.

At the moment I am waiting for the OZ logo which my dad is reworking it graphically (the logo is bent around the rim radius and I do not have a powerful photo tool to do this). Most of the tires are also finished and only waiting till the rim is lacquered.

And finally, a premiere: For the very first time, I designed a working rear light. It was a bit of a challenge to find appropriate electronic components. The geometrical boundary conditions are 9.5mm x 11.5mm in cross section (inner dimensions of the rear crash structure). Finally, I found a 6V micro cell battery (for an LED, a minimum voltage of 3V is required) with 10mm in diameter and 16.3mm in length. A sliding switch with 20mm x 14mm x 8.5mm was too large. Even if I removed the unnecessary material, the switch is too large. So my electronics consists only from the battery with a cardboard pick up structure, two LEDs incorporated in the light housing and wiring. It is just enough space to get it fit into the rear crash structure.