Main hoop foot location

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drummingpariah
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Main hoop foot location

Post by drummingpariah »

Most of the cages I've seen mount the base of the main hoop directly into the floor, and I wanted to get some thoughts on a different (potentially better, in this application?) location. The partial cage that was in the car when I bought it isn't very close to the body, and would be really difficult to gusset, and doesn't have A pillar bars ... so starting from scratch is going to be easier than using this as a starting point.

Here's what I have now, and the main hoop is essentially just welded to some plates that are welded to the floor.
Image

I'd like to build some more substantial foot boxes that the main hoop tube goes through. I'm planning to cut a hole in the top plate, weld the main hoop tube to the plate welded to the floor, then box in the top plate. It seems like that would be substantially more rigid overall. This is the basic idea:
Image

Finally, I'd like to inset those boxes into the rocker base here, which is higher than the floor. I don't think this poses a safety/tech concern, but it does mean that the sill bar would have to be angled down toward the floor, then would have a bend to get it parallel with the floor.
Image

As for door X bars, two continuous pieces seems like the only way to go ... but is there a substantial downside to having two bends in each to make entry/exit a bit less cumbersome? I'm looking at something like this:
Image

I would still end up with 4 forms of side intrusion protection (those two, the sill bar, and the stock rocker/door reinforcement), so I don't think they're even necessary to pass tech ... but I like the idea of going above and beyond tech where I can. Also, is there a downside to a few verticals connecting the lower bar to the sill bar? That seems commonplace with NASCAR door bars, but rally cars always seem to omit verticals on X-style door bars.
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Re: Main hoop foot location

Post by jkale »

The best way to attach the main hoop to the chassis on the lower leg in my opinion is to notch the inner rocker, drop the vertical portion of the tube half way into it, plate under the main hoop(inside and outside the rocker). Weld. Then plate the inner rocker to the main hoop. This ensures maximum vertical welded length... A box around your main hoop after it is sitting on the floor is not going to do much for added strength..
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Re: Main hoop foot location

Post by drummingpariah »

If I understand you correctly, that would have the outside half of the main hoop leg inside the rocker, and the other half in the cabin? Would that require moving the sill bar above the rocker, or would you somehow run it inside the rocker? I think I would need to see a photo of it in-progress to be able to envision what you're recommending.

In my thinking, one side of the box would be the inner rocker, the other would be the cargo tray shelf (two of the most substantial sections behind the seats on the RX-7). The other two could just as easily be a single plate to make a triangle rather than a cube (if that matters).
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Re: Main hoop foot location

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My email is kalescustom@yahoo.com. Shoot me a quick email and I will send you a few pics of what I mean..
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Re: Main hoop foot location

Post by walterclark »

If the foot of the main hoop sits on that step you are pointing to, the sill bar can have a bend to get it to tie in as well as run along the sill. The sill bar can run along the top of the sill, so there shouldnt be much of a bend needed.

For side bars, you could simply add one straight bar that starts high on the main hoop and ends low (above the sill bar) on the A-pillar bar. If you want to go with a X bar then 2 V bars with good gussets is the preferred method. I have never seen what you show and cannot image that with 2 bends each and no gusset joining them where they are parallel that is a good design. Maybe someone else has some experience with something similar. For a more elaborate side bar, you might consider a NASCAR style, with 2 bars (plus the sill bar) that bend out into the door pocket and are joined with vertical stub between the 2 side bars and the lower side bar and sill bar. Especially in a narrow car, this can make fitting up a seat a lot easier, not to mention the extra side impact protection.
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Re: Main hoop foot location

Post by drummingpariah »

jkale wrote:My email is kalescustom@yahoo.com. Shoot me a quick email and I will send you a few pics of what I mean..
Will do, I'll try to get that out tonight.
walterclark wrote:If the foot of the main hoop sits on that step you are pointing to, the sill bar can have a bend to get it to tie in as well as run along the sill. The sill bar can run along the top of the sill, so there shouldnt be much of a bend needed.
That's great news, I'm happy to hear that it would be a decent solution.
walterclark wrote:For side bars, you could simply add one straight bar that starts high on the main hoop and ends low (above the sill bar) on the A-pillar bar. If you want to go with a X bar then 2 V bars with good gussets is the preferred method. I have never seen what you show and cannot image that with 2 bends each and no gusset joining them where they are parallel that is a good design. Maybe someone else has some experience with something similar. For a more elaborate side bar, you might consider a NASCAR style, with 2 bars (plus the sill bar) that bend out into the door pocket and are joined with vertical stub between the 2 side bars and the lower side bar and sill bar. Especially in a narrow car, this can make fitting up a seat a lot easier, not to mention the extra side impact protection.
Sorry, I wasn't implying that there wouldn't be gussets. The two would have taco gussets and vertical gussets that would run the whole length. I think the two bends in each run is my main question.

The problem with NASCAR style is that this is still going to be a street car, and I'm going to have to keep windows that roll up and down. I'd really prefer to keep some form of door cards in it. The plan for seat fitment is to massage the transmission tunnel in slightly, so I can actually get a seat that's centered to the steering wheel.
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Re: Main hoop foot location

Post by sachilles »

Assuming it's the RX7 we are talking about here, I'm pretty sure it has my old Corbeau seats in it. The base of those things towards the front, are about the widest thing on the market. It was one of the factors in replacing them for me, as I had the same issue with the edge of the seat fouling on the tunnel in the WRX. Very wide at the front.
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Re: Main hoop foot location

Post by Mopar 151w2 »

I think you are generally on the right track. If you were to plate over the top and down the side of the inner rocker, using ~ 11-14 ga, hammer-bent and perimeter welded - then holesaw into that, to form your socket. the holesaw breaking out to the inside could work to your advantage, as in Joey's suggestion. The slight gap where the vertical tube meets the socket provides for a good root pass, covered by a nice fillet,.
I like the double door bar idea you showed, and your idea of a vertical or 2 to the sill bar or rocker is excellent. Image ImageI think it's important to have some outward arch in these features, as shown here, to keep the bars from immediately bowing in on a small impact. there are a number of good ideas to be cribbed from this Distance Race Cars chassis - built in Maine, by NASCAR veteran wizard Stan Meserve. These are the elite of "Super Late Model" racing in the northeast. I particularly like the extra footbox protection. Also noteworthy is the use hereImage in this Howe "roadrace spec" cage, of "taco gussets" to gusset cage legs to main rails, and of an alternate reinforcement for the 'A" pillar, rather than the traditional "Flemke" post shown hereImage
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Re: Main hoop foot location

Post by drummingpariah »

Lots of awesome advice, thanks guys. I'm definitely under the gun to finalize this, so I'll have to settle for incorporating 'as much as I have time for' rather than 'all the things'. Here's roughly what I was thinking for seat mounts: I'm not in love withusing the sheet metal floors of any of my cars for structural purposes, especially after ~50 years of rust got to them. Getting the seats low isn't going to be much of an issue, as I still have plenty of head room in the Miata even with the seat vertical and 6" off the floor. The problem, as Seth indicated, is getting the seats in-line with the steering wheel, facing forward.

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Re: Main hoop foot location

Post by walterclark »

As I learned, one of the trickier things about FIA seats is the mounting holes from the seat brackets to the floor (or to purpose built supports) isnt a standard either side-side or front-back. The front to rear oriented mounting brackets I made up when I built the car and opted for Sparco Evo seats didnt fit the seat brackets for the Cobra Sebring Pro seat I bought to replace the drivers seat. In particular the rear of the Sebring was so much narrower than the Sparco (and narrower than the front of the Cobra) that I needed to weld additional plates to the inside of the existing 1/8" plate in order to move the rear mounting bolts inboard enough to fit the Cobra's seats brackets. In my new design I was able to pick a side-side distance between the mounting studs that accommodated either the front or rear of the Cobra bracket only because of the elipse or slotted shape of the holes in the FIA seat brackets...but is just barely. I am planning to make a pair of seat brackets similar to the FIA brackets, but with a longer base to allow for more front-rear positioning, and with this I plan to drill the line of holes in the bottom of each so they are parallel to each other and matching the studs I put in the car. A different FIA seat would probably require the studs be relocated or a new set of holes in my side brackets. Of course per the seat manufacturer, any bracket other than the ones sold by the manufacturer FOR the seat voids the FIA certification, however fabricating custom side brackets is a fairly common practice in the US and I have yet to see a car fail tech at a US rally or NEHA event for having custom brackets, or a seat failure in a crash because of using them.

So, in planning of the design of your seat attachment framework, keep this in mind.
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