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Yo, anybody home?

Thanks for the approval, Jack... Judging from your screen name, I'm sure you can relate...

Meanwhile, the continuing saga of:

Bubba the Bracket Builder
Here lately, the only thing that I seem to get accomplished revolves around brackets. I've built imaginary brackets out of cardboard. I've built brackets out of steel, and hired other people to build brackets for me. I've bent brackets, and hammered brackets. I've used grinders and cutoff wheels on brackets. I've sanded and painted brackets. I've bought heim joints to attach to brackets, and threaded spuds to put into tubes to attach to heim joints to attach to brackets. I've drilled holes in brackets to attach them to tubes. I've drilled holes in brackets to attach them to bushings [and then tossed them out and drilled other holes in other brackets so they'd actually fit the bushings...

But then Sunday, it kinda came together a little bit, and made it all seem worthwhile. We measured and checked and measured and then checked again and then welded some of the new brackets (I did tell y'all I'd been makin' brackets, didn't I?) onto the shear plates in the rear of the frame. Then I took some of the big C-brackets (Eeeek! More brackets!!!) and put them on the T-bird upright and attached some 'fake' control arms to 'em and put them on the brackets (there's that word again!!!) on the frame. Guess what? She articulates like a doll-baby!!! I might be in love... Had to get James to take a picture of me playin' with it!!! Looky-

*Side Note* After seeing this pic, I decided to A) Go on a diet, B) Get a haircut, and C) Trim that moustache!!!

As you can probably tell, I'm a little bit excited about the rear suspension comin' together so good. We gotta cut those tubes in the control arms to the proper lengths, weld it all up, and then build the other side (Shoot, I thought it wuz gonna be somethin' hard to do...) and then we'll be somebody!!!

See y'all next time-
Bubba the Bracket Builder

a) yeaaaaah right
b)only on top
c)most definitely, it gets in the way of eating!!

What's it like when you torque down those brackets at the wishbone they way they should be? It would probably hold itself up then. I'm asking because it looks like they are adjustable at the outboard end and I wonder how much load it takes to twist the bushings when the suspension moves. If the brackets are welded onto the arms they would have a wider base to twist those bushings. I know having both ends adjustable is easier, but I don't have a feel for how hard it is to twist those bushings, so wondering if that loads up the threaded/bolt part on the bracket (bending loads on threads are bad).

I guess that is a normal method for the Miata uprights. When folks use rod ends on the outboard end of the wishbones they just bolt them on in single shear, including the coilover. Here's a picture of an old Lotus that shows that. Just because I like these pictures, I guess. I'm not sure how you would fill in the big holes in the Miata piece, but you could work something out.

Looking at it that way makes me wonder as well.

With a 3 point mounting as you have it, how do you stop the upright from rotating on itself? Because its on the heims, it'll twist, right?

Wouldn't be the first time I missed something!

KS

Yo, Horizen & Botbasher!
Lemme see, I know it's actually Marcus... Bot, are you Ken? I fergit... Anyway....

The pic is kind of misleading, in that it doesn't show the cross bracing that's going to go between the two lower "arms" that you see in the pic, and my text doesn't say that we're gonna do that. There will be at least two cross bars, one straight across, one diagonal, and some gussets. It's not gonna stay two un-connected arms as shown. It'll be more like Maxlessca's lower control arms, or the ones Factory Five uses on their Cobra. Not an "A" arm, more like an "X" arm or a "Z" arm.

Also, at this point, should I be totally embarrassed that I almost screwed things up, or delighted that y'all caught and corrected me? I'm kinda leaning toward embarrassed... Oh wait, I know:

Here at Slotus HQ, after looking at the pic again, and talking with James (the chief assembly officer of SWEET), we have made an executive decision, based entirely on our engineering (egineering?) genius, that we should weld the outer brackets to the arms and not use the bolts. This would spread the loading surface across the bracket more and eliminate the side loading on those bolts when torque is applied to the rear axles. (Did that sound convincing?)

Yeah, screwed up is the word. Thanks for catching that. Geeze... Well, told ya, I ain't no engineer.... Proved it again...

But thanks, many times over, to both of you for the constructive comments. 'Preciate ya both.

Sincerely,
JD Kemp

Hell Man... don't be embarrassed. Won't be the first time one of us has left a bit off or out of the design. That's why the title states.. Learning how to build...! And Yes.. it's Ken!

OK, maybe there is something still left out of your description I'm not seeing, but I expected you to tie the lower arms together. It was more the top arm I was referring to. Even with the lower arm boxed and welded together, won't the single point upper mount allow the bottom to twist? Welding and boxing it will limit it, but that's a lot of stress to the bottom of that upright!

Look at the pic that horizenjob showed. The upper and lower pivots are a single point outboard, but they are tied forward to the frame to resist rotation and maintain orientation.

Like on mine, I only have a single upper point at the upright, but the inboard side is a two point mount. It resists twisting on it's own coupled with a boxed lower, it cannot rotate. Hopefully!

I might have you barking up a tree erroneously due to my limited knowledge of the type of car your building and I apologize if that is the case. It just struck me as odd based on the type of upright your using and other cars that I have looked at while designing mine. I hope I'm just missing it and we're not kicking you back to square one repeatedly!

Cheers!

KS

Yo, Ken-
Thanks for the kind words. I'm actuallly glad to know somebody's reading this stuff I post, and I'm not just massaging my own li'l ego, alllll alone... I'm also relieved every time I open the Board index and see that my log hasn't been moved to "In Theory..." with the other wild-haired ideas!

My standard disclaimer applies, "I ain't no engineer!" (And Marcus had to teach me how to spell engineer!) However, in the rear suspension, like the front suspension, I didn't design much. The front I mostly stole ideas from the circle track folks. For the IRS, however, I moved up in the world and stole the idea from Factory Five, in the IRS they use in their Cobras. The uprights are from a mid-nineties T-bird/Cougar. The three point uprights are Ford's design, and the mounting for the control arms are stolen directly from this photo:

James and I had discussed using a trailing arm to limit "unintended wheel base changes" (Jamey said people would think we were cheatin'!!!) but we were gonna hook the TA to the lower control arm. Honestly, I was concerned about fore-and-aft movement of the upright because of compression of the bushings. Hadn't occurred to me that it might be due to rotation of the uprights. Perhaps you're onto something there... I'll report back to ya on it, let me do a little research and some general head-scratching... Would look kinda cool with some trailing arms up top, like the Lotus in the pic, wouldn't it????

And about that Lotus- All that lovely chrome and magnesium, and what appears to be a Cosworth DFV, and they got some cheap-ass plastic catch bottle tie-wrapped on the thing??? Geeze, even here at Team Slotus we's classier than that!!!


Peace, Love & Pushrods-

JDK

That's funny, my race car has the same catch can, even on the same side of the transaxle. Never knew it was the Lotus setup though. THe original plastic container is long gone and I use a pair of quart oil containers now. It's nice to have something see thru actually, so that you can tell how much is in it.

I don't know what to say about Ken's point. The brakes will certainly try to wind up those arms. You can see the factory five has pretty beefy arms. The stock Miata and Ford arms are probably pretty stiff too. The bottom tubes won't twist much after you connect them with an X or some such.

Looking at the pic you patterned off... I wonder if this point here isn't used for some kind of anti-rotation?

It could just be a sway bar mount of course! Do you have any pics of a complete FFF rear? Maybe installed in a car?

KS

I looked at a bunch of sites and this was the only pic of a FFR IRS I could find.. it appears no one like the $1200 option and goes for the Live Rear!



There is nothing here except for the tab (I wonder what it is for?!?), so it would appear that they overcome the torque by shear size and rigidity. As you mentioned earlier, I think that it would squirm around on the bushings, but I cannot prove they do it any other way!

Hope this helps the SWEET design team!

KS

Yo!
There's lotsa pics of these set-ups, just not in FFR Cobras. The Cobra guys like their 8.8 or 9 inch stick axles, apparently. (Hmmmmm...) The street rodder community uses them, as do some of the tricked-out-truck folks. In looking back at the pics from there they seem to: A) Use the entire subframe, including the wide, stamped steel upper control arms, or B) Use a trick set of control arms, which also tend to be wide/thick and mounted on a wide bushing at either end. Sample of the latter-

Also note the pic shows a sway bar mounted to the LCA. I had always assumed (famous word) that the bracket (Eeeek, brackets!!!) you pointed out on the UCA was for a sway bar. Maybe not... Hmmmmm, some more.....

I'm working in Jacksonville this week, and can't get to the shop (Slotus World HQ) until Sunday. After I look at the chassis again then, I can maybe give more intelligent answers. (Maybe) Right now I'm wondering about turning the upper into an A-arm, or putting in a radius arm forward to the frame/cage off of the upper mounting point. Something similar to the Lotus, or the strut-style lowers Ford used to use. Either way, I'll be in touch in a few days... Try to remain calm, everybody, keep your seatbacks in the upright position...


JDK

It looks like that would be the easiest for you to do, there is space on the frame and all you'll need to do is make another bracket and weld another piece of tube onto the upper arm you already have.

Progress looks good JD.

I'll second that motion regarding making the upper link an arm. As a bonus, it will end up much stiffer and more structurally efficient for essentially no weight penalty versus just having a triangulated lower arm trying to resist the twisting motion from the upright.

what i notice on the FFR is the bushings used at the outer ends instead of rod ends. could rod ends allowing more twist be a problem "as compared to the use of bushings"? is so a trailing link might be just the ticket on the upper arm but it is another adjustment point (".. will adjust it wrong" as one of our members quotes). i've always used bushings on my stuff so i can't directly answer from experience but i can tell you that changing to ali bushings on the lower trailing link seemed to cause floors ( brackets ) ripping out and using (even) hard bushings was enough to prevent it.

whoops i just took another look at your pic and you do use bushings on the outside. .. nevermind

This may be a case where the motion of the suspension required compliance in the bushings. Rod ends might have worked fine in this case. Unless the pivots where in a line, like you could put an axle thru them, the trailing bushing might have had to have some give to allow the movement...