Tag Archives: rear lower control arm

New Partnerships

We believe computer simulation is only one side of the coin, real world testing is the other.  We are just as careful of selecting our testers as we are in designing our product.  We choose people that will really push our products to the limit and put them in the conditions they were designed for.

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Robert Fuller, owner of Robispec, most well known for suspension setup, tuning and component development for Evos and STis, will aid us with development.  He actively competes in time attack and NASA time trials and has one of the fastest FR-Ses on the west coast.  He will be testing the full gamut of our suspension components customized to his specifications and providing us with feedback for further improvements.  To stay updated with Robi’s FR-S, please check his build thread here.

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For those without race cars and that want to see its road-worthiness, Edmunds.com will be testing our control arm on their long-term test car.  Their goal is to create a pure dual-purpose car that is just as comfortable and livable as OEM, but outperforms it at autocrosses and track days.  They are very selective of their modifications and will be making small changes at a time to see how each modification affects the vehicle.  To stay updated with their long-term test car, you can check out their website here.

LCA Test Fitting

I was able to test fit our simplified prototype (this does not reflect the final design) yesterday and spot check everything. While I wasn’t able to translate it to degrees (which depends on ride height anyways), you can shorten or elongate the arm about 20mm from stock.

Since we opted to use a linkage adjuster, adjustment was a breeze. With other thin adjustment bolts, you’re going to have to get creative to turn it when it’s in the subframe.

LCA Prototype

Our manufacturer sent us a picture of the prototype.

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Since we are only using it to spot check the range of adjustment, it is a highly simplified version, without all the bells and whistles.  It should reach us sometime over the weekend or early next week.  Once we have tested it, and make sure the adjustment we want is there, we will make any necessary corrections before we make the final model.  It should end up looking like this though

Control Arm ASMThe way the suspension was designed for the car means there needs to be a sacrifice in either usability, strength, stiffness, or price.  After seven design revisions, this is the one we finally settled on.  Since every user is different, we wanted to offer a wide range of camber adjustment, while keeping it strong and light. Although we sacrifice a little bit in stiffness by using a long adjustment link, we feel the benefits outweigh shortcomings.  However, side-by-side, still managed to design a stiffer unit than stock, which will improve driver feedback.

FEA was a bit more difficult for the control arm than the toe link.  This is because the damper dissipates some of the force and I don’t have ANSYS nor the skills to accurately model that.  To simplify the FEA and as an added Factor of Safety in design, I used fixed hinge connections where necessary for the boundary conditions.  This is a less accurate way to analyze the control arm, because the loads transferred into the model are more severe, so I knew if it could stand up to these conditions, it would be okay out in the real world.

We FEA’d the control arm for all foreseeable loading conditions, including a 4G bump

4GBump2G braking

2GBraking

Displacement

Braking Displacement

OEM

OEM Braking Displacement

And a combined 2G bump, 2G braking, 2G cornering.

Combined

Displacement

Combined Displacement

OEM

OEM Combined Displacement

As you can see, this is the limit and is a failure mode.  The adjustment link will break where it threads into the control arm.  It’s highly unlikely a FR-S/BRZ could achieve this condition, but we wanted to be absolutely sure the control arms will be ready for anything.  Also, remember, this on top of the extra safety factor built in from the boundary conditions.

If you compare, our control arm manages to be about 29% stiffer under combined loading, but an impressive 313% stiffer under braking!  Take this with a grain of salt as the boundary conditions are imperfect, but both parts were analyzed in the exact same way.

I even did a crash scenario, loading the arm in 10G compression

Crash

Displacement

Crash Displacement

Once we have finalized the production design, we will work on getting the price finalized.  We will then put up an initial group buy.  If we have enough buyers interested, we expect to take delivery before the end of April.

BRZ/FR-S/GT86 Rear Lower Control Arm Design

There are two major problems with the OEM rear lower control arm on the BRZ/FR-S/GT86:
1. It doesn’t offer any camber adjustment
2. It is very weak under longitudinal loading

OEM LCA

Originally, I was going to try a shim stack design for the rear lower control arm.  However, I was unsatisfied with the design because it would either be too heavy or too soft.  So, I went back to the drawing board and started from scratch.  This time I went with a threaded rod adjustment rather than shim stacks because the shims were adding too much mass.  This is the design:

LCA V4

With a threaded rod design, we were able to reduce the mass of the arm while increasing stiffness. Here you can see the stress plot side-by-side.  The OEM arm:

OEM Stress

Note how twisted the arm becomes where the arm tapers.  Under extreme loading, the arm is likely to break at the welds.  Our arm:

LCA V4 Stress

Our FEA results show that stress is reduced in the arm by 900%, and stiffness is increased by 1100% while maintaining the same mass.