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@lambertius I really appreciate the efforts you put into this platform, Dropped off my car today to have my ceiba coilovers and cat bypass installed today, when the car was up in the air I looked at the ball joints, my left rear control is done, lots of play. The replacement part from Maserati is $$$ crazy expensive I would much rather replace the rear control arms with something with interchangeable ball joints for future serviceability.

Not sure how close you are to having these arms produced but I am interested for whenever that is!
 

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Discussion Starter · #42 ·
@lambertius I really appreciate the efforts you put into this platform, Dropped off my car today to have my ceiba coilovers and cat bypass installed today, when the car was up in the air I looked at the ball joints, my left rear control is done, lots of play. The replacement part from Maserati is $$$ crazy expensive I would much rather replace the rear control arms with something with interchangeable ball joints for future serviceability.

Not sure how close you are to having these arms produced but I am interested for whenever that is!
Very close, just waiting on my ball joints and then I'll order the first batch for my car.
 

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Discussion Starter · #43 ·
So the first order is getting placed next week. COVID-19 willing, I should have them fitted to my car by late June.

I'll be setting up a business for liability and warranty because I've gotten so many messages regarding these. If you want a set let me know, if there is enough interest I might set up a pre-order option to prioritise where the parts go.
 

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So the first order is getting placed next week. COVID-19 willing, I should have them fitted to my car by late June.

I'll be setting up a business for liability and warranty because I've gotten so many messages regarding these. If you want a set let me know, if there is enough interest I might set up a pre-order option to prioritise where the parts go.
Take your car and run the 24hr Lemans after you install them and report back! ;)

On a serious note, I really hope this plays out well. Obsolete parts is the only thing I fret about owning mine.
 

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Discussion Starter · #45 ·
Take your car and run the 24hr Lemans after you install them and report back! ;)

On a serious note, I really hope this plays out well. Obsolete parts is the only thing I fret about owning mine.
That arms themselves will be fine - 6061-T6 is what brake rotor hats are made from. The only question is the longevity of the ball joints, which will probably still be low. The reason they get stuffed so quickly is that they're arranged the 'wrong' way and the forces on the joints pull the ball back and forth instead of side to side. That combined with the weight of the vehicle just means they don't have a good life expectancy. So even if I get 'factory life' out of the replacement ball joint they will only last up to 50 000km.

But here we get onto the good news, the ball joints will only be about $150 AUD each, so even if they only last 20 000km it just isn't a big deal anymore. It would take ~25 replacement ball joints to equal the cost of one replacement arm, and as it is the top one is NLA so I don't really have a choice.

If the ball joints just don't last, then I've got an arm designed to take a custom ball joint and I'll make my own ball joint!
 

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Can't wait to see how it all comes together, I'm sure I'll need a set soon.
 

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Discussion Starter · #53 ·
I haven't really provided any technical updates on this for a while, and I've gotten a few PMs from a user who had some (valid) technical questions about the robustness of the design.


i) the Design looks a mite "delicate" and "light" around where the ball joints thread-in. Now I'm not sure how the threaded BJ's are tightened-in, torque-in to their sockets (and is Loctite Red or Blue used)... but the thread-roots constitute crack propagation points... and these cannot be externally observed, checked-for. So I'd think the arms would need huskying-up in that area; and

ii) the ribs are pretty thin, and they transition to the adjacent portions of the arm in a fairly small-radiused manner. Would thicker ribs and more "blunt" features/transitions have merit?

I know these comments, at this point in time, are "late"... but I am just giving you my unbiased impressions as a.mechanical engineer.


I want everyone to know that if you spot anything that concerns you I'd much prefer to know I'm wrong than miss something, so please raise it! For anyone who wants to know my answer to those questions, it is below!

1) The threaded ball joints are a 1.5mm pitch, and are far far too fine to thread into aluminium. I'd be able to thread them in once and that is it, when you go to replace them the thread on the arm would be damaged. The thread in the photos is a 3mm pitch, so a very thick and coarse thread, where a steel insert will be used and the ball joint will be threaded into that. Red loctite will hold it in as it is intended to be permanently affixed, this is the same solution that Maserati used to secure the toe rods. This will effectively allow infinite replacement of the ball joints without affecting the thread on the aluminium. I did want deeper threads, but there is only so much space in the wheel well. However, there is roughly 6 times more material (in a stronger aluminium grade) in those threads than the original peened lip that held the ball joint in place. The below exploded diagram should show you the implementation.

Bicycle part Material property Font Magenta Auto part


Below is the lip that held the entire ball joint in previously:

Automotive lighting Eyelash Wood Automotive tire Gas


I haven't received the arms yet, but below is an image sent by the manufacturer of the threaded insert in the arm. The insert is 304 stainless steel and requires a C-Spanner to install.

Watch Communication Device Gadget Finger Clock


2) The arms are thicker in almost every dimension than the OEM arms and they weigh more. This is intentional because I'm expecting them to be rebuilt periodically instead of being disposed of. In CAD, the lower arm weighs 1875g compared to the OEM 1296g. Below is an overlay of the two models which should give a good perspective on how much more robust these arms are. Also, every curve is shallower. The ribs are taller making the arms stiffer in flexure and the FEA hasn't highlighted any critical concerns.

Product Bicycle part Font Automotive lighting Auto part


Automotive exterior Auto part Font Rectangle Toy


Automotive exterior Personal protective equipment Font Rectangle Bag


By going further out, the torsional stiffness increases. I can increase the radius further but from the FEA at some point I'm just adding further mass without return. The radius on the ribs appears to be adequate to prevent stress risers.

Below is the von mises set to the ssame scale. The arms can't be loaded in a vertical motion because of the double pivot (the ball joint and the bushings). This analysis is applying 4200N at the ball joint, an arbitrary value chosen to compare the two arms. You can see that in the design I've done that there is slightly more stress in the same scale exactly where you'd expect it to be in this load scenario. This is because this portion of my arm is a thinner material. However, the yield strength is much higher.

Font Plastic Electric blue Office supplies Kitchen utensil


Font Electric blue Plastic Fashion accessory Plastic arts


If you look at the FOS plot below, the different material grade shows an overall better but roughly equivalent performance. A FOS is a good way to visualise how close a component is to failure. With the load applied neither arm is close to failure, both requiring roughly 3.5 times the load applied in simulation to reach a failure case.

Bicycle part Electric blue Font Plastic Fashion accessory


Font Electric blue Plastic Slope Science


In my arms, I've made the material around the bushings and ball joints thicker because the factory arms are known to fail around the bushings through the casting seam. Even though these are billet and have no casting seam, I anticipate that they will go through multiple bushing changes, so safety first. This si where the majority of the extra mass in these arms has come from.
 

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Discussion Starter · #56 ·
Musical instrument String instrument String instrument String instrument accessory Musical instrument accessory


So the arms arrived today and I decided to bench assemble them with the ball joints.

Gotta say, I'm pretty pleased!

I'm going to make a couple of small changes for the next pair, nothing consequential. The big job coming up though is going to be getting these onto the car and making sure they're all as they should be!
 

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Discussion Starter · #59 ·
Test fit was done today on the upper arm, tomorrow is the lower. There are no clearance issues and everything is where it should be. The shims for setting everything in the correct place sucks. What a giant pain!

Motor vehicle Automotive tire Hood Vehicle Automotive design

Automotive lighting Hood Automotive design Motor vehicle Vehicle

Automotive tire Motor vehicle Automotive design Bumper Coil spring

Wheel Automotive tire Light Motor vehicle Tread


Automotive tire Motor vehicle Coil spring Automotive fuel system Red



Needing to lower the subframe is very annoying!

Hood Automotive tire Vehicle Motor vehicle Bumper


I'm making a few revisions, all superficial. A bit more material in a few places, and making the shape a bit smoother in others.

Over the next two weeks I'll be organising all the correct warranty and liability insurance and then these will be made available to purchase.

The final versions will be made in black.
 
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