Next step in getting the car rolling is to mount the steering rack. These parts were not laser cut but were cut with angle grinders and my bandsaw, because they’re, um, a design improvement. Yeah, a design improvement, that’ll work. It took me months to find a blade for my bandsaw, because Thailand. Anyway, now it’s useful for these kinds of tasks.
Once again we have something that looks simple, but took a great deal of thinking to arrive at. As Steve Jobs said, “Simple can be harder than complex: You have to work hard to get your thinking clean to make it simple.” I used to do almost exactly what Steve Jobs did; in fact, he once called my boss to persuade him to cancel the design we were working on, because Jobs was going to do it better (he didn’t). So I understand precisely what Jobs meant about simplicity. That might help explain why this was my fifth complete design for this subassembly. One downside of mechanical design: when you’ve sweated out an elegant design, anybody can take a casual glance at it and say “OBviously”. To which I reply, “OK, there’s probably an even better design out there somewhere. Let’s see you find it.”
Also attached are a few of the finite element analysis (FEA) tests that I performed to verify and improve this design.
So I was ready to build the suspension attachment points and decided I’d better do a finite -element analysis. It turns out they needed a lot of tweaking, and in a shin-bone’s-connected-to-the-thigh-bone kind of way, I ended up redesigning just about every suspension part all the way to the lug nuts. Part of this came when the quote on building the upper suspension attachment clevises came in way higher than expected, so I redesigned them so they could be laser-cut, hopefully much cheaper than CNC machining. Don’t have the new quote yet.
Also, I received the huge shipment of parts, supplies, and tools that I’ve been aggregating in LA for almost the past two years, and some idiot in purchasing (me) managed to order the wrong brake calipers. Everything was right except for the mounts, which are the lug style instead of the radial style. At least now I really know the tradeoffs between the two approaches. The upright for lug mount brake calipers is only about 35 grams heavier than the one for radials, and the calipers are $80 cheaper each. Over $1000/pound for that weight savings… Actually, that’s not quite fair as I don’t know the relative weights of the two caliper styles.
Anyway, we have lots of pictures of FEA meshes and results:
FEA mesh for lower suspension clevis, attachment point for all four lower control arms
Finite-element analysis results for lower suspension clevis
FEA plot for front upper suspension attachment bracket that will be welded to the chassis.
FEA plot for one half of the laser-cut upper front suspension attachment clevis
FEA plot of one half of the upper rear suspension attachment bracket
Detail of the FEA mesh for buckling analysis of left front lower A-Arm
FEA buckling plot for left front lower A-Arm under braking load
Detail of the FEA mesh for static analysis of left front lower A-Arm
FEA plot of left front lower control arm under 1600 pounds braking force
FEA plot for left front lower control arm under 1600 pound right-hand cornering load
FEA plot of left front lower control arm under 1280-pound left-hand cornering load
FEA mesh for front axle static cornering analysis
FEA plot of front axle under cornering load
FEA mesh for front axle static braking analysis
FEA plot of front axle under braking load
FEA mesh for front/rear steering arm
FEA plot for front/rear steering arm under maximum cornering load
FEA mesh for front upper control arm attachment bracket, to be welded to chassis
FEA plot of front upper suspension attachment bracket
FEA mesh for left front suspension upright static braking analysis
FEA plot of left front suspension upright under braking load
FEA mesh for left front suspension upright static cornering analysis
FEA plot of left front suspension upright under maximum cornering load
FEA mesh detail of left front suspension upright for snap-ring analysis
FEA plot of left front suspension upright snap ring slot under cornering load