Gents,
With regards to the placement of the harness bar, in FSAE the shoulder harness must be no greater than 20 degrees from the horizontal. I recall getting out of the 2010 car after a full day of driving doing suspension tuning with bruised shoulders and a sore neck from the harness with the belts at the horizontal . (I guess I'm a softie.)
I do agree that spinal compression may be an issue with 9" wide hoosiers and 4 piston wilwoods on a 1300 lb car whilst standing on the brakes.
It's not too big of a deal to relocate the harness bar upwards. I'd rather not have back problems going into old age.
From SCCA GCR:
"The shoulder harness shall be mounted behind the driver and
supported above a line drawn downward from the shoulder point
at an angle of 20 degrees with the horizontal. "
In terms of progress today, I cut the uprights, and I will be placing a 1/2" grade 8 bolt in double shear through a 0.85"x1.3" cross section. (With the 1.3" cross section in compression.)
Attachment:
cut uprights.jpg
Attachment:
upright cross section.jpg
it took me longer than expected to make these cuts today, as I continually stopped to check, and recheck the evenness of the rectangular cross section. I blended the cut into the I-beam shape of the upright making a smooth transition to the bearing.
Attachment:
smoothed transition.jpg
Therefore stress risers from geometric discontinuities will be kept to a minimum.
Also, I polished the cast iron flashing, and removed a few of the unnecessary bosses for ABS sensor, etc. I took great care ensuring I take as LITTLE MATERIAL away from the upright in sections which will experience heavy loads. I'm pretty certain this cross section will be more than sufficient to handle the loads induced by the AFCO tubes. Also, consider that the LCA pickup point is 0.68"x0.25", and the tie rod (soon to be toe link) pickup point is 0.77"x0.25" at the thinnest cross section.
Also, I did some suspension planning today and looked into using GSXR1000 shocks/springs and ran the math myself, and unfortunately Kurt is correct with regards to his analysis. In order to have a decent wheel rate (100 lb/in to 200lb/in), I will need an installation ratio of 0.3. (WR= SR*IR^2)
I love the fact that I can get GSXR1000 shocks for 20 to 30 bucks on ebay, but with 1.5" of travel, I will need a spring of 1000lb/in, (which will require shock revalving), to have 5" of total travel. (1" droop, 3" compression, 1" bumpstop). Also, with a spring rate this high, at full bump, the loads applied to the inboard damper support would have to support 1500lbf. (Which would necessitate additional bracing and weight support the load.)
I REALLY want to use GSXR1000 shocks, mainly due to the lightweight, and VERY low cost, but that math simply does not work out.
Say for instance, I have a direct actuation shock with the outboard point mounted on the control arm, and inboard point on the chassis. With the inboard shock point 7" above the LCA pickup point, and the outboard shock pickup point 8" away from the inboard LCA pickup, this gives an Installation Ratio of 0.86. This arrangement results in a 41.1 degree shock angle (measured from the horizontal). If we move the A-Arm up 1" in bump, and using the Law of Cosines, I can solve for the reduced shock length. Taking the before and after lengths gives me shock displacement, with which I can use to solve for the installation ratio.
I suppose this may be a blessing in disguise, as I really need to keep this build CHEAP, which means I'll probably use the integra springs/dampers. (But with 450lb/in spring, this results in wheel rate of 351 lb/in--way too high for my liking.)
So my hands are starting to develop vibration fatigue from the angle grinder and miter saw. (I'm wearing Mechanix gloves underneath heavy leather welding gloves. And I may need to somehow add some vibration isolation between my hands and grinder. Any thoughts?
Also, as I don't want to inhale TONS of metal dust, does anyone have any recommendations of a good respirator which does not suffocate me in the process?
I guess it's a good thing that it's back the office tomorrow, and I can go to work and rest my back which is starting to kill me.