Senin, 28 Februari 2011

Designing custom leather door pull for MX5 NA


Getting into MX5 and trying to close the door leaves you with a strange feeling, something is ... not really right. I guess if you are taller than average there is more than average chance to feel it hitting your leg.

First thing is to remove the door pull, second - to put some stripe there. I believe everybody has done this so far:).

Well, for track dedicated car a "stripe" mod could do, but I wanted to daily drive it and trip across Europe and ... started this project.

The requirements list (Die Anforderungsliste;)):
  • Material - thick and genuine leather to match rest interior, all black with exact cut.
  • Ensuring functionality - the original door pull holds the door trim to the door.
  • Offset from door trim (easy pull catch,  no trim scratches)
  • Tight fit
  • Wear-resistant
  • Universal for both sides
  • Better feel than original
  • Better look than original

The door package was simulated in 3D program. The design options converged with the technical solutions and after the obligatory comparison matrix for all the options, a design was nominated to continue.


Water proof and not stretchable leather was found for the purpose (convertible gets wet). It is 5mm black leather.
First draft was with laser engraving:
One first draft:

The actual design implements embeded "Roadster" writing to the leather. Elegant design element, presented in a decent way, that will match every interior.
The holes for the screws are secured with special rust resistant eyelets. 
The screw heads (original ones should be reused) are hidden with supplied black head caps.





This is very succesful end product, that expands the drivers leg room enorm, but also perfectly integrates in to the car leather interior and gives decent and fresh touch to it.

The door pulls can be also purchased, contact me at  automotiveconvepts.eu (at) gmail.com.

Minggu, 13 Februari 2011

Creating the Mazda MX5 "Roomster" edition


The write up "Creating the Mazda MX5 "Roomster" edition" can be found and is currently updated at this address:

Jumat, 11 Februari 2011

Designing fully functional rear towing hook for MX5/Miata MK1 NA.

The original NA MX5 towing bracket is ... well mine at least, already rusty. It is heavy and it is not alowing me to use any aftermarket rear spoiler, as it is not adjustable. As I do racing with the MX5, nice to have option is to comply with the FIA requirements for tow hooks.

On the other side, the original towing bracket is quite well engineered and dimensioned piece of mild steel. It is designed to withstand very high loads. And it is the guiding light in terms of strenght, dimensioning the new one.
Defining towing strenght, even for a small and light car like the MX5 is impossible. Towing it on a tarmac road doesn't require much strenght, but pulling the car from mud could be even impossible.
I desided to dimension my tow hook to withstand the strenght of a standard 1500kg rope. The rope has to tear before the hook breakes or bends, basicaly asuring the towing hook is reusable.
Broken hook can be a deadly weapon, as the rope accumulates very high energy, that accelerates the hook, when torn.

Lets collect the requirements so far:
  1. Strenght: it has to at withstand more than 15000N (1500kg) pull.
  2. Weight: lighter than original
  3. Rust-resistant
  4. Adjustable in the height

This below are animatated GIFs you can see on clicking on them.
1. I-shaped 4mm steel. Almost afordable stress levels for highest position.
2. As we want adjustable bracket, we test this also in the lowest position. This is already too much stress for the thin steel.
3. Next is to stiffen the steel design, by bending a wall and screwing the hook one more time at the back. Stress levels are affordable. The stress levels even in the lowest position are acceptable.
Downside on this design is the weight which is 522 grams. Still it is a good option, offering 3 point connection.
4. Next step is to change material - we took strongest airspace 2024 T3 (approx. 1,4 stronger than 6061-T6) duraluminum instead of steel. The calculation is with 10mm thickness and in already lowest position.
With a weight of only 300 grams, fully adjustable and covering the requirements this is another option to concentrate on.

The 10mm billet 2024-T3 duraluminium ready for real life test: