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 Post subject: Re: Exo Hot Rod
PostPosted: August 26, 2016, 9:14 am 
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Location: Waterloo, WI
Omaha Vette Graveyard wrote:

I suppose I could make the 'hood tubes', as I call them, removable pieces, but it's simpler, cheaper, lighter, and more rigid to have them welded in, so I'm going to try it this way first. The solution just ticks all the right boxes for me. If I find myself wishing for better engine access through the top, I'll just cut them out and fab up some plates for bolt-in rods (If I do that I'll use aluminum to make up for some of the extra weight).

Another thing is that part of my approach with this build is to take every advantage I can of the Corvette setup. I see two of those advantages being the ability to eliminate the driveshaft tunnel and the ability to triangulate over the engine bay.


-Graveyard.


Makes sense. Certainly can't argue with simpler, cheaper, lighter and more rigid! :cheers:

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 Post subject: Re: Exo Hot Rod
PostPosted: August 26, 2016, 3:37 pm 
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Posts: 397
Here’s a start on the framing layout. It’s sort of schematic now and we can fill in details later. I sketched up the spools also. I like them. They are a good way to tie several tubes into a hard point.
Keep the info coming but don’t stop building!


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OmahaVet4.jpg
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 Post subject: Re: Exo Hot Rod
PostPosted: August 29, 2016, 9:33 pm 
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Location: Omaha, Nebraska
Bobber,

The plans look correct, except that there is no tube across the rear of the front subframe. The engine sits in that spot.

I have some new measurements for you:

The front hoop is made of 1.75" round tubing with .120" wall thickness. It is welded to the side tubes of the front subframe, as close to the front spools as possible, so the width at the bottom is exactly the same as the side tubes of the subframe.

It is 20" in height (above the frontmost subframe mounting pad), and the bends are each 85 degrees on a 7" radius. The radius is measured from the middle of the tube.

The front hoop leans back 2.5 degrees from vertical.

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I did manage to get a few other pieces fitted in the last few days, though I've been pretty busy. The support tubes that go from the top to the sides have been upgraded to 1.75". I determined that this would be worth the weight penalty since these are the pieces that will do most of the work in connecting the roof structure to the front of the car.

Attachment:
File comment: support tube upgrade
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I also fitted the little tubes that go directly under the new support tubes, and these are also 1.75" pieces, but I don't seem to have any pictures of those fitted just yet.

More pictures and stuff soon...

-Graveyard

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 Post subject: Re: Exo Hot Rod
PostPosted: August 30, 2016, 12:19 am 
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Here's an update. Make sure I got the height of the hoop right. I took the dimension to top of tube.


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 Post subject: Re: Exo Hot Rod
PostPosted: August 30, 2016, 9:15 pm 
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Bobber,

The measurements and drawings look to be exactly correct. Awesome.

Here are measurements for the rear hoop:

It's exactly like the front hoop, pushed up against the rear spools, 85 degree bends on a 7" radius, etc.

However, it's 21.5" tall, measured in the same way as the front, and it leans back 15 degrees.

Attachment:
File comment: rear hoop
IMG_2479.jpg
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----

I've now installed the link tubes and what I call the dash tube. The link tubes sit under the roof support tubes, creating, with the dash tube and links to the bottom, a very 'hard' interface for the birdcage structure I'm planning between the dash, cowl, and front bulkhead. Lots of tetrahedral structures here. (Birdcage here is a reference to Maserati, not sprint cars.)

Here are some pictures of the planned birdcage, still without the complementary floor and side tubes. I'm open to feedback on this, and on everything actually, but I'd like to know if anyone sees any opportunities here that are better than what I've found.

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File comment: birdcage
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More soon.

-Graveyard

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 Post subject: Re: Exo Hot Rod
PostPosted: August 31, 2016, 12:19 am 
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Build is looking good. Here's some more with the rear hoop. Always ready for more.


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 Post subject: Re: Exo Hot Rod
PostPosted: August 31, 2016, 11:26 am 
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I'm starting the layout of the upper framing.


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 Post subject: Re: Exo Hot Rod
PostPosted: August 31, 2016, 4:29 pm 
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I added some more upper framing. The stuff in red I guessed where it goes.


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OmahaVet 10.jpg
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 Post subject: Re: Exo Hot Rod
PostPosted: August 31, 2016, 9:36 pm 
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Location: Omaha, Nebraska
Looks good, Bobber.

Here are some numbers for the outside floor tubes:

The middle section is nearly parallel with the centerline of the car, being 26" from centerline at the front bend line (the bend line is the indexing line right where the bend begins), and 26.4" from centerline at the rear bend line.

A line drawn from the front bend line on one side to the front bend line on the other is 19" from the center of the spool at the rear of the front subframe.

A line drawn across the rear bend lines is 21" in front of the center of the front spool of the rear subframe.

The bends are again on a 7" radius, as are all of my bends.

The tubes, from a side view, follow a direct line between the spools which they connect, and they are welded to the spools as low as they can go.

You can see in this picture the papers on the tubes, which were used to draw, and then redraw, the bend lines, and how I used them to locate the floor tubes. I've found bend lines and indexing lines to be invaluable for getting symmetry when fitting bent tubes.

Attachment:
File comment: First connection between subframes.
IMG_2451.jpg
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As soon as you've got these outside floor tubes, I have measurements for the main roll hoop. The rest of the car after that should be pretty easy I think, as most of the tubes are just connecting stuff, or have simple bends. You could almost guess most of it and get pretty close.

---

I did a bunch of welding this morning. First I welded some practice pieces for about 40 minutes to warm up, which was very help full to the quality of what I did today. I really should do this every time I need to weld, as it probably saves me time in grinding and re-welding. I know all of the things I need to know to make very nice welds, but without practice they just don't turn out as they should.

I'll post pictures when there's something new to see.

-Graveyard

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 Post subject: Re: Exo Hot Rod
PostPosted: September 1, 2016, 3:47 pm 
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Here's the lower frame rails. Let me know if I got them right.
I'm going to start setting up the analysis model pretty soon. What grade of steel are you using?

The chassis is coming along fast. This should be a stiff structure.


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OmahaVet 12.jpg
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 Post subject: Re: Exo Hot Rod
PostPosted: September 2, 2016, 6:19 pm 
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Location: Omaha, Nebraska
Bobber,

I'm using almost exclusively 1020 ERW.

The floor tubes you already have look perfect. They are .120 wall tube though.

The main hoop is also 1.75" with .120 wall. Let me give you some specific dimensions:

It leans back 10 degrees.

The top is 37 inches from the floor bars to which it is welded. (This is measured on the 10 degree incline, so they are not 37 vertical inches.)

The top bends are 66 degrees.

The middle bends are 32 degrees.

The widest point is 57.25", and that comes 16" from the bottom (again measured on the 10 degree incline).

The roll hoop is welded onto the outer floor tubes that you already have, and it is centered on the rear bend lines that you already have.

The bend lines on the top of the hoop are 29.25" apart, so they are 14.625" from the centerline.

The bend lines for the lower bends aren't visible anymore, unfortunately.

Hopefully, that info is sufficient. Let me know if not. I think this is one of the last bits that is a bit complicated to measure and dictate. I'm focusing on the bent parts first here, as the straight tubes will be pretty simple. I'll try to measure up the inside floor tubes and the top outside front tubes this evening.

Thanks for all your interest in this.

-Graveyard.

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 Post subject: Re: Exo Hot Rod
PostPosted: September 3, 2016, 7:56 pm 
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Here's some more. I took the hoop measurement as outside to outside. Also the hoop height is from the centerline of main tube. This is working out well for me. No questions yet.


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OmahaVet 016.jpg
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 Post subject: Re: Exo Hot Rod
PostPosted: September 4, 2016, 12:07 am 
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Location: Omaha, Nebraska
Bobber,

It looks good. The height of the roll hoop was, however, measured from the top of the base tubes. Same with the widest point, so both are .875" too short.

I didn't have time or energy to measure anything else today. If I'm still awake in an hour I'll go out and get some numbers. I want to get the inner base tubes and front outer top tubes for you next.

---

I was able to spend most of the day working on the chassis today, and I feel like I should have more to show for it, but I did get some important work done.

First, I figured out how I'm going to complete the front tube structure, and how I'm going to get it to interface with the suspension mounts. This is complicated, as the C5 upper control arms have a strange way of connecting to the chassis and I'm trying to allow for a lot of adjustability. I'm especially interested in perhaps trying less anti-dive. I'm not going to mess with the simulations and math on it yet, and even if I did I have no way of knowing if my 'improved' geometry would drive better until I drive it. Hence, lots of adjustability.

For the shock mount up front, I have lots of vertical strength built into the chassis there already, but very little lateral support. I had to figure out a way to brace across the front of the engine so that lateral loads on the shock/coilover mount are directed to the mount on the opposite side and tied into lateral hard points.

I figured out solutions to both of these, but I'll save a thorough explanation for when I have some of it built. Here's a masking tape mock-up of the future tube setup. You can't see the bits going across the engine bay in this picture though. The piece of tape with the X is the shock mount tube.

Attachment:
File comment: Proposed suspension structure.
IMG_2638.jpg
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I also put in The little tube that fills in the X and connects the harness tubes. This was harder to fit than it should have been. I also welded the seam above it before I fitted it in, since it's a little tight.

Attachment:
File comment: Little tube in the middle of the roll-hoop bulkhead.
IMG_2636.jpg
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Since I finally had that tube fitted, I could add the pair of tubes that connect there. These are welded to the front spools of the rear subframe, and they should keep the right half of the floor from trying to move forward in relation to the left, at least in the back of the car. These are important, as the floor is not continuous. I'll do something similar in the front. They were slow to fit, because I took out the other diagonal tubes that are fitted inside the side trusses, fitted the new tubes, welded all of the seams that would be covered of hard to get at, and then re-fitted the old diagonals so that they were coped around the new tubes. They're sharing space on the spools, and I've usually found that it's easier to remove the already fitted tubes and add cutouts than it is to try to fit new tubes and get the cutouts right. I got excellent fitment and welds, but it took a lot of extra time.

Attachment:
File comment: New lateral diagonals.
IMG_2633.jpg
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Finally, I fitted one of the two smaller diagonals which are going to fill in the big triangle of the side truss. I was hoping to get both of them done, as this is pretty easy fitting, but I was pretty tired and these ones have to meet up just right and have the right angle. My pickiness here is not a matter of engineering but aesthetic. I think I got the new ones right, the ones behind have to sit at just the right angle so that they look 'obvious'. I also need them to be exactly the same side to side. Here's the tube I was able to fit:

Attachment:
File comment: Front support.
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Here's my proposed rear tube in tape. I think the angle looks right, let me know if you think otherwise.

Attachment:
File comment: right angle?
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Long day, hopefully I can be just as productive tomorrow.

-Graveyard

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 Post subject: Re: Exo Hot Rod
PostPosted: September 6, 2016, 1:24 am 
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More stuff done, but not as much as I'd like. I finished fitting the side tubes, and I think they look about right.

Attachment:
IMG_2641.jpg
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I also fitted the top links that match the top to the roll hoop main supports. The tubes on the top hit the roll hoop not at the corners, as with most cages, but in toward the middle. This is to help getting in and out of the car. The top will have an X brace linking all of this together.

Attachment:
File comment: Links
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Before tacking in the new bits I had to weld up some spots which would be more difficult to weld after.

Here's a (bad) picture of before they were tacked in.

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IMG_2643.jpg
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Progress seems slower when I'm fitting little things. It takes just as long to fit a little tube as it does to fit a big one, but the change is not as noticeable so it doesn't seem like I got all that much done. That's what I'm telling myself now anyway.

-Graveyard

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 Post subject: Re: Exo Hot Rod
PostPosted: September 6, 2016, 8:43 pm 
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A question about your roll cage bars not hitting the corners. I thought that was verboten even tho it makes more sense for a street car.

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