heinzboehmer's 2002 Topaz 6MT Coupe

[bigjae46]

Not sure what exact part is the issue but GSR Motorsports makes a sturdy aluminum part that holds the lower fender liner in place.

https://gsrmotorsports.net/products/spec-e46-coupe-splash-shield-brackets

[heinzboehmer]

Wait what am I doing. I just need to print the entire tab laying down...

[heinzboehmer]

Drove the car a good amount today and broke a couple things.

First up, the zip tie that holds the right side brake duct upright broke and allowed it to pivot down. Was scraping nicely on the wheel when turning:




Will need to print another one and reattach it with higher quality zip ties, that Bryson recommended.

I also snapped the top piece of my phone holder:



Of course it landed inside the dash, so retrieving it was fun:




This is a tricky piece to print since it needs to be strong along multiple orthogonal axes. I considered experimenting with printing it at an angle, but instead decided to try this approach:



Blue piece will be printed upright (as seen in the screenshot) and yellow will be printed laying down. Yellow is designed to press fit into blue and should help to keep it from breaking again in the same way it did today.

[heinzboehmer]

Alright, signed up for the 14 day SimSolid trial. Integrates very nicely with Onshape, but it's $675 per month once the trial ends, so I've got a deadline for finishing this project now!

[heinzboehmer]

For the load case, you can just calculate the bucking load for the beam. All you need is diameter, length, wall thickness and material. Since it’s notched, it will fail below this number because it has an initiation point. That way you can use a real number and get a real safety factor.

Added to TODO list!

I would leave the ribs for bonding area, and leave the extended surface to stiffen up the windshield sheet to avoid peeling adhesive as much as possible. That’s the place that makes the most sense to go overkill to me. You could also tab and slot the machined part and sheet then just weld it up. That would allow you to ignore bonding area internal to the part.

You bring up an excellent point that I did not consider yesterday. We ran the analysis assuming the top surface of the aluminum piece was fixed in place, not bonded. I'll mess around to see if I can produce something useful that takes into account the adhesive area.

Also, ran some super quick tests in CAD just to get an idea of the theoretical min weight of the assembly. Baseline is the overkill design, which weighs 579 g total.

First up, extended surface fully removed, but everything else the same. This saves 111 g (19%):



Next up, extended piece removed, ribs removed and wall thickness decreased to 2mm. This saves 235 g (41%):



This means that a realistic minimum weight I can get this assembly to is 400-450 g, which raises an interesting question: do I really care about saving max ~200 g? The weight is being added to a terrible spot in the chassis, but the potential tradeoff of saving the 200 g is ending up with a subpar piece that will fail and essentially require a chassis replacement. It might make more sense to focus my attention on saving weight in other pieces (CF cabin air filter housing and firewall plug for instance).

I still want to run the FEA on everything (because new toy to play around with), but I'm not sure I'll actually end up making any changes to the design.