Category Archives: fea

BRZ/FR-S/GT86 Rear Trailing Arm

This is our rear trailing arm concept

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It utilizes the same aluminum alloy as our lower control arm, with a 7075-T6 linkage adjuster, and an e-brake cable bracket.  Because the arm is a only a tension/compression member, it is not highly stressed so we tried to maximize stiffness and adjustability with our design.  We used 3G’s as the loading condition

The arm

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The fork

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The current assembly weighs would be just under 2 lbs, but we may end up changing the fork to a stainless steel one if we feel the aluminum fork is too costly to manufacture.  We feel this is an acceptable compromise because the linkage adjuster can be sacrificed when galvanic corrosion occurs because they are readily available available and are roughly $20 each.

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.

New Workstation

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Thanks to the Student Innovation Fund our workstation has finally arrived.  It’s a Dell Precision T7600 workstation with an Intel Dual Four Core Xeon processor, 64GB of DDR3 RAM, and a 1TB hard drive.  This includes a commercially licensed version of Creo Parametric 2.0 and will be setup with a virtual machine and remote desktop access so we can install OpenFoam and CADNexus so we can run CFD iterations 24/7.