Hancha Rear Lower Control Arm
 

Hi everyone,

Now that we've finalized our toe link, we've been able to make progress with our rear lower control arm. After seven design revisions, we finally found one we were satisfied with. This is a rendering of what the final product should look like

http://i1304.photobucket.com/albums/...ps2faddaf3.jpg

It will be made from a trade secret aluminum alloy different than our toe link, but very similar in all mechanical properties. This is simply because this material is readily available in plate, whereas the toe link comes in rods. It has the strength of 2024, while having the corrosion resistance of 6061. The linkage adjuster and rod end are made of 7075 to keep all threaded contacts aluminum to prevent galvanic corrosion. Our control arm will be anodized clear for that extra bit of protection. We expect the entire assembly to weigh around 3.2 lbs.

We designed our control arm to be strong, light, stiff, while having the widest usable range of adjustment since every user will use it at different ride height. Due to the suspension layout we had to make a sacrifice somewhere, and we gave up a little bit in aesthetic (it looks odd, we know) and overall stiffness for a wider range of adjustment. It might not be the strongest, stiffest, or lightest, but we feel this is the best possible combination between the three.

The FEA was more difficult for the control arm than the toe link. This is because the damper dissipates some of the force through heat. We don't have access to a more complex solver like ANSYS, and even if we did, we wouldn't be able to accurately model all the forces going on, truth be told. However, FEA is just a modelling technique, and using some SWAG (scientific wild ass guess :confused0068:) I used fixed hinge connections as boundary conditions where necessary. I did not account for reduction in corner weight from load transfer, but I did account for an increase in corner weight from load transfer. This simplified model is less accurate than real life, but because the loading conditions are more severe, it's an extra safety factor built into the study. Therefore, if it passed our FEA studies, we know it will pass with flying colors in the real world. We analyzed all foreseeable conditions.

The control arm in 4G bump

http://i1304.photobucket.com/albums/...ps868a4bbf.png

The control arm in 2G braking

http://i1304.photobucket.com/albums/...psdf3600bd.png

A worst-case scenario of 2G cornering, 2G braking, 2G bump.

http://i1304.photobucket.com/albums/...ps220d0f90.png

This is the failure mode. The linkage adjuster would break in this case. However, if your car is simulataneously doing 2G braking and cornering, please teach me because you've built a hell of a car. If you are concerned about strength or durability, we can upgrade you to a 3/4" linkage and rod end for an additional cost. This will also increase weight about .2 lbs. Or we could swap to chromoly and use a stainless steel threaded insert in the body if you're worried about galvanic corrosion.

Our manufacturer sent a picture today of our prototype.

http://i1304.photobucket.com/albums/...ps4787da9f.jpg

This is just a simplified, 6061 piece we had machined to spot check and to be able to translate distance to degrees at various ride heights so we know if we need to make a revision for the adjustment range. This does not reflect the final part. We expect to have the design production-ready next week, along with pricing.

Now, is this the right control arm for you? It depends on what you're looking for. I don't know if we have the strongest, stiffest, or lightest control arm on the market, but we feel we have the right combination of all three.

Do you drive your car hard at track days?
We use a special aluminum alloy that is 20-25% stronger than 6061 while maintaining the same level of corrosion resistance.

Do you daily your car through snow and salt?
We use an anodized 7075 linkage adjuster and rod end with our anodized body which means no pesky rust and no galvanic corrosion.

Do you want something strong, but light?
We expect our control arms to weigh about 3.2 lbs +/- .1 lb each.

Do you want better suspension articulation?
Our control arm is stiffer than OEM and replaces the rubber bushing with a spherical bearing for better suspension articulation and load transfer.

Do you want a wide range of adjustment?
As the design stands, it can go from 430-470 mm safely, from mount to mount. OEM is 450 mm as a reference.

So stay tuned. We will finalize pricing within a week and can package it in with our toe link group buy for a better discount for those buying both.

As always, thanks for your interest in Hancha.

Looks good. Which country are these being manufactured in?

ALL our products are made in the US. Right now we're using an ISO 9001 certified manufacturer in Indiana, but we're discussing with a few other manufacturers to hopefully get some of the machining cost down.

That linkage adjuster (black part between the red rod end and main arm) is going to be machined 7075? The one that gets all colourful under the 4g bump?

If so, cut thread aluminum, a part that will be constantly loaded and unloaded and fatigue don't really mix well.

Correct. However, 4G is a very extreme load. I don't expect most to do be doing that at a regular basis. I did do a fatigue analysis of the control arm under more realistic loading conditions (1.5G cornering, 1.5G braking, 2G bump) and here is the result:

http://i1304.photobucket.com/albums/...psd9aced5f.png

It will take around 13 million fully loaded and reversed life cycles. However, as I've said, if it is something that is going to bother you, we can swap to zinc plated chromoly for both the linkage and rod end. If you will be driving through snow and salt, I recommend an optional stainless steel threaded insert.

you guys are cool...I'm gonna have to check out your stuff...

I would probably make that little threaded adjuster out of a strong stainless just for security's sake. I'm not a huge fan of locking aluminum threads by clamping down with a secondary nut.

I understand your concerns. We had thought about making our own adjuster as well, but it would add about another 150 dollars in price to the part. Plus we'd recommend adding a threaded insert which costs more money. If you are willing to pay close to $1000 for control arms, I can make it happen, using the same aircraft grade stainless as our toe link stud. However, we thought it to be unreasonable since there is a pre-existing, off-the-shelf part, that will work. So, in an effort to get some of the cost down, we chose the aluminum threaded adjuster.

For those where money is not a concern and for maximum strength, lightness, and durability, we can even make you custom control arms from 6Al-4V Titanium, but that would be around $4000. We explored all options. This is our seventh design, and the one we we thought was the best overall package.

If you are not comfortable with the aluminum linkage and rod end, you can choose the chromoly linkage adjuster and rod end (for no additional cost, but a little heavier). A stainless insert into the control arm will be additional though.

Is that a premade part with good anodizing on the threads? That puts my mind at ease a bit. :)

Yup, they are made by QA1. The only reason I don't like to continually advertise the fact is because we're paying to use their product, they're not paying us for free marketing lol. I'm also not taking for granted that because they are made by QA1 that I don't have to do the research myself.

Earl

thats great, seems like its gonna be easy to adjust the rear camber.

Titanium has no place in control arms. Terrible stiffness to weight and notch sensitivity.

For an adjuster I was thinking of taking a big NF stainless or G8 alloy bolt, and drilling and tapping it for a LH rod-end. You get rolled threads, a narrower surface for the wrench and assuming you buy quality bolts, excellent material.

Specific stiffness really depends on the grade. Certain alphas that have a specific stiffness of nearly 28 10^6 m^2/s^2 while having the same tensile strength as 6Al-4V. Normalized 4130 is around 26 for reference. But I wasn't planning on it, it's a hypothetical. ;)

You have a good idea, and I had a similar one around the 4th iteration. But in order to do that, we'd have to make the control arm longer, adding weight (about a lb each arm) and machining time; the adjustment range is also reduced. Drilling and threading a bolt adds cost, and if I were to buy off-the-shelf, I would use NAS, which isn't cheap either. In the end, I didn't feel the pros would outweigh the cons.

If we collectively can come up with a better idea, I have no problem adopting it. I am not married to the design, I just want to put out the best possible product, no matter where it comes from. :w00t:

I only pay attention to Grades 2, 5 and 9 and their 'E' is ~ half of steel give or take.

As for the design, with the FEA that you're doing, the colours represent stress? So the more to red the more stressed? Could you basically just subtract material where it's blue and add it where it starts to become yellow? Same for fatigue? Get it do it stays a universal colour at whatever loading you decide for your safety factor?