Sbeckman7's Project: BR1

[sbeckman7]

Sounds good. In other news, just bought a set of S38B36 ITB's for the race engine because I couldn't pass on the price. The collection of performance parts is starting already...

[sbeckman7]

Finished drilling the holes for the front subframe mounts today. I decided to give it a little extra strength and use the counter-sync already built into the rear two holes on the subframe itself, so I should have a pretty decent connection. The second picture shows how they fit on the frame itself. Once I get these last two front pieces welded up, the front and rear axles will finally be connected.

[Tammer in Philly]

You're running long bolts all the way through the box section? Are you putting a cylindrical spacer in there for the bolt to run through?

-tammer

[mooseheadm5]

Definitely you do not want the bolt to crush the tubing. Good job using the dowel to position the subframe. That is the proper way to go.
Go ahead and reinforce the steering box mount as described in the sticky at the top of the tech talk forum.
Looking good so far.

[sbeckman7]

Yes to the spacing cylinder, will look into the steering box reinforcement, and thanks for the encouragement!

[sbeckman7]

Just got back from Daniels shop after a couple of hours of finishing up the last two parts of the beams. It took a while to set the beams parallel and at the right angle but it was definitely worth it. I think there was about 1/16" error for the total width which ended up being 98 3/4" so not bad for no jig. I'll post pictures as soon as I get them test fitted on Monday.

[sbeckman7]

Today was a good day! Test fitted the finished beams for the first time and sat back and admired my work (a lot of Daniel's work, that is). I took a bunch of pictures, sat in it, and checked my projected visibility and it was really fun to be sitting in something that is now starting to resemble my plans. All in all, it's going to work out. The only issue I found is that my angles were slightly off for the midsections of the beams, leaving me with about 3/8 of an inch off from one of the bolt holes. I'll show it in the pictures, but my plans are to grind out the hole for it to fit, re-center both of the beams over the front subframe (both will be bowed out towards the front of the car about 3/16") and then weld the screw in place, filling in the rest of the hole and preventing it from moving in the beam itself. This is basically how the subframes were attached originally, with the subframes attached to the body via "pins" with a nut on one end. Here's what I've got:

A random picture of the m30 head thrown in. Still cant believe I lucked out with the condition of the internals on that thing... Wondering if I should modify it or buy a b35 and start with that?


Front view with the radiator resting on the original engine mounting points, where it will probably end up. The super beefy strut brace makes it handle sooooooo much better! And keeps the wheels supported.


Another shot of the front


Rear view. I moved the diff out of the way so I could get around it easier.


Still very excited about the wheels. Will eventually be running 215's in the front and 235's in the rear, ten larger all around.


More good news. After some more adjusting with the engine location and seating position, I realized that a complex shift mechanism won't be necessary. Placing the shifter in its original location (more or less) gives me the perfect reach and throw, so I will make a bracket attaching it directly to the transmission instead of a transmission tunnel. More direct
Short shifter coming later.


How I fit: nice and cozy. Just what I wanted.


More or less my view. I can see myself using coilovers in the future to further lower the strut towers (take about 3-4 inches off of the height in the picture due to load) so as to improve the line of sight and smooth out the front curves of the body.


Sitting in the car, this is the front most hole on the front subframe. It's a clear shot for the bolt. Somehow that worked..



The less fortunate side. Could be worse, just more work to do.

[sbeckman7]

At this point I'm wondering if I should start with the floor or move on to the strut towers. Is there any right or wrong order?

[mooseheadm5]

Strut towers. Make it mobile first so you can move it around and get it to a lift.

[sbeckman7]

Sounds like a plan. Any ideas to center the towers with the chassis? I think I'll get camber plates to correct any possible error, but I mean do I just eyeball it with a tape measure or is there a more accurate way?

P.S. Since I mounted the engine juuust behind the front axle, I'm able to use an x-brace without having to worry about interference issues.

[mooseheadm5]

You don't need camber plates. You can just make the mounts slotted for adjustment. As far as positioning, you will want to find a center point and measure from there. Unfortunately, you will have an issue setting the caster as well as the camber. I would suggest that you make the top mounts for the struts but don't make them permanent yet. At this point consider whether you want to use stock upper mounts or move to custom coilover upper perches (I suggest custom.) You would want to make an upper mount and then a plate to bolt it to. You would then want to temporarily tack the support structure to the frame and get the front end aligned. Once that is done, you can make a stronger, more permanent support structure for the upper mounts. The rears are no problem since the struts do not locate the arms.

[sbeckman7]

Thats a good idea. I guess I'll start with the rears while I save some money for coil-overs, then worry about it once I buy some. As for the frame itself, I came up with a weight/money saving way to make the car. The sketches of my design show the curves that I want the car to have, but I realized that the frame itself does not need to be in that shape (in fact I guess it shouldn't in case I get into an accident and have frame damage). I'm going to make the strut towers triangulated and incorporate them into the mid section, but the front and rear overhangs will be purely aesthetic.

[mooseheadm5]

PM incoming.

[sbeckman7]

PM incoming.

I'll count the minutes

[Tammer in Philly]

Decent pics of a tube frame "BMW" in this thread:
http://forums.bimmerforums.com/forum/sh ... ?t=1564561

Might be useful from a planning perspective. You want to triangulate every load-bearing point, preferably in multiple planes. You have the opportunity to make a very light, very rigid frame to which you can bolt your suspension.

-tammer

[tsmall07]

The sketches of my design show the curves that I want the car to have, but I realized that the frame itself does not need to be in that shape

You've said a few times that it won't have a body, but your sketches show a body. Which is it? Make it functional and then worry about form. It will look good if it is designed to function well.

[mooseheadm5]

If you choose to go with a body, may I suggest a stressed aluminum skin?

[sbeckman7]

Decent pics of a tube frame "BMW" in this thread:
http://forums.bimmerforums.com/forum/sh ... ?t=1564561

Might be useful from a planning perspective. You want to triangulate every load-bearing point, preferably in multiple planes. You have the opportunity to make a very light, very rigid frame to which you can bolt your suspension.

-tammer

Thanks for that link, very good to see how people are doing it. Since I'm retaining the struts I plan on using their pickup points as points of triangulation.

As for the body, let me make myself clear. The car will not leave high school with a body, however at some point I do intend on creating one for it. I was going to use fiberglass due to cost reasons (not that it's cheap), although the idea of a stressed aluminum body sounds very intruiging. I'm guessing it's to add rigidity? I'll try to post a sketch of what I plan on making the rest of the frame look like, but I'll try to describe it as well. Picture triangulation above and around the front strut pickup points, with support beams going from each strut tower to the opposite side of the main frames. Additional triangulation will follow in the mid section, although to a lesser degree. The rear suspension mounts will stem off of the rollbar, which is mounted just in front of the rear subframe mounting points. Reading this, I realize it's near impossible to get an idea of what I mean, so I'll make a sketch soon.

[sbeckman7]

Here we go:

Front view to show cross-sectional braces


Side view. Black lines show structural metal, red is aesthetic.


Top view. Same coloring scheme. Showing floor reinforcements as well as suspension supports. I still need to figure out where to mount the support for the differential.


Opinions appreciated.

[mooseheadm5]

Add a support across the tops of the rear shocks. Drop a couple of tubes down to the rear diff mount, and consider using the rear cover from an E36 that uses two mounting ears (might require some modifications to fit.)

[sbeckman7]

Ok, thanks as always. Wasn't sure if I needed it so I guess I'll throw a little more in between the rears. Other than that, it seems sound? It cut my project time roughly in half... Can't believe I didn't think to do it like this earlier.

[tsmall07]

It might just be me, but it looks like your "X" for the strut tower bracing is right in the middle of your engine.

[Tammer in Philly]

Top view. Same coloring scheme. Showing floor reinforcements as well as suspension supports. I still need to figure out where to mount the support for the differential.


Opinions appreciated.

Triangles. A couple of straight-across tubes for the floor is okay, but you'll do better by framing out your trans tunnel then doing node-to-node diagonal bracing any place where you won't interfere with the driveline.

-tammer

[sbeckman7]

Top view. Same coloring scheme. Showing floor reinforcements as well as suspension supports. I still need to figure out where to mount the support for the differential.


Opinions appreciated.

Triangles. A couple of straight-across tubes for the floor is okay, but you'll do better by framing out your trans tunnel then doing node-to-node diagonal bracing any place where you won't interfere with the driveline.

-tammer

Tammer, I'm not quite sure what you mean by the node to node bit. Could you expand?

[sbeckman7]

It might just be me, but it looks like your "X" for the strut tower bracing is right in the middle of your engine.

Don't worry it's just you. The engine will be mounted entirely behind the front axle

[Tammer in Philly]

A tube frame is should follow the same design principles of a proper roll cage, as it's basically the entire structure of a car. Unlike a unibody car, you've got no structure coming from sheet metal. So your tube structure has to be rigid and capable of handling all the loads that will be put on it: longitudinally, laterally, and torsionally.

So, your primary issues are tubes that can bend or twist. The way you prevent those motions is by supporting the tubes with bracing tubes. You want your bracing to resist twisting, so forming open squares or trapezoids is bad (the end tubes can twist relative to each other by bending the linking tubes). Systems of linked triangles are much stronger because there are no two tubes that can bend together; you're defining rigid planes by three linked points. Look at a bicycle frame.

A node is where you have multiple tubes coming into one point. A proper node is much stronger than having all of those tubes terminating at different points along the bar they are supporting. This is a good example of a node: http://picasaweb.google.com/tammerfarid ... 6291407554. The tubes radiating from that base plate are in two planes, vertical (up toward the main roll cage hoop behind the front seats) and horizontal (diagonal bars going across to the other vertical plane and main hoop). They support a third plane, the main hoop itself. There are no open squares anywhere in this cage except the door frame (supported by an X to minimize twisting of the door opening) and the roof (supported by small gussets tying the sides of the square together). Another example, you can see a small tube gusset here to strengthen the door opening. http://picasaweb.google.com/tammerfarid ... 1169314578

So, for your build, I'd be looking at those lateral bars and the single large X defining the floor and mid-body of the frame, and thinking of how to stop that structure from flexing. Weak points:
Two diagonal bars come back from front of main frame rails and terminate in the middle of a long horizontal bars. That is an unsupported node; there can still be bending at the middle of that horizontal tube. Can you extend those two diagonals back to the next horizontal tube back? They'll meet where the big "X" crosses the second tube. How high is that relative to your trans and driveshaft? Obviously that will limit what you can do, but you can put in a frame of tube around the transmission (you'll need a firewall there anyway), then tie that into the other tubes. Actually, I might ditch the 2nd and 4th horizontal bars, but add a big diamond around the X (from the node I pointed out before to the middle bar at the side rails, to the rear horizontal square tube's center--unless that's your subframe; I can't tell.

-tammer

[sbeckman7]

Wow, thanks for that detailed response. I'll follow your advice and find ways to further strengthen the middle of the car. I was planning on bolting the transmission directly to one of the pipes going across the floor, however I'll plan around a new transmission tunnel design. I'll try to get pictures soon.

[mooseheadm5]

Definitely use a tunnel. A tunnel provides a good backbone support.

[sbeckman7]

I'll try to connect the Center tunnel, firewall, and floor, hopefully to the struts as well. Like the caterham frame pictured, only my front mounting points will end at the front struts.

[mooseheadm5]

Definitely follow the lead on how they did that and why (since the exact design isn't applicable to the way your suspension is built.)