Rear Shock Turrets For Volvos

Sofa King Wrote:
-------------------------------------------------------
> hudson Wrote:
> --------------------------------------------------

>
> From Timm's earlier pictures (and from preliminary
> measurements made by John and I on my car), the
> top of the turret is going to be just below and in
> front of the bottom edge of the rear window.
>

Me Timm? or typo... Who else has two M's? What pics?

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Welcome to the cult of JVL drink the koolaid or be banned.

Hey Kevin,

You're good with the pix there, guy. It helps a lot. When all is said and done, the last drawing that Andrew posted is what we will be doing on the Opel, except that:
- the forward connection of the tube over the tower will be up a ways on the backstay
- the tubes over the tower will take all the the strut load, which should 99% vertical like I believe will be in the Volvo case (There will actually be no new tower in the Opel; we will cut off the tops of the original shock towers, which are too weak to carry the strut load, and pass the struts up through these.)
- these tubes over the strut tops will be one continuous, bent piece of tubing on each side (like mini- main hoops), from some point on the backstays, to plates on the floor behind over a similar box reinforcement.
- there will be bracing across the tunnel between the backstays and between these strut support tubes that will also integrate the mounting of the fuel cell 'box in a box'.

The main hoop and backstay plates (on the floor) are in the car and I estimate that the angle will be a bit under 40 degrees from vertical; I'll see if I can get a measurement.

In looking at the photos supplied by John and the pix of the Volvo towers, the pix show a much closer intergation of relatively short strut towers into the floor and inner fender area. The Volvo towers really stick way up and would not appear to support the fore-aft forces on the cage without risk of pushing/crumpling these tall towers over; once they startto give at all, the main hoop would then put a bending force on the bottom welds of the main hoop (and some to the lower ends of the A-pillar hoops), which is not desired. The added lower bracing from the tower tops to the lower end of the main hoop helps, but still, if the towers give at all, then all the fore-aft force goes into the bottom ends of the main hoop, and that is not what is desired; the backstays should carry this force.

Hey Andrew, I am not following why 45 degrees is the most efficient, but I am probably not totally thinking things through.

Regards,
Mark B.

starion887 Wrote:
-------------------------------------------------------
> Hey Kevin,
>
> You're good with the pix there, guy. It helps a
> lot. When all is said and done, the last drawing
> that Andrew posted is what we will be doing on the
> Opel, except that:
> - the forward connection of the tube over the
> tower will be up a ways on the backstay
> - the tubes over the tower will take all the the
> strut load, which should 99% vertical like I
> believe will be in the Volvo case (There will
> actually be no new tower in the Opel; we will cut
> off the tops of the original shock towers, which
> are too weak to carry the strut load, and pass the
> struts up through these.)
> - these tubes over the strut tops will be one
> continuous, bent piece of tubing on each side
> (like mini- main hoops), from some point on the
> backstays, to plates on the floor behind over a
> similar box reinforcement.
> - there will be bracing across the tunnel between
> the backstays and between these strut support
> tubes that will also integrate the mounting of the
> fuel cell 'box in a box'.
>
> The main hoop and backstay plates (on the floor)
> are in the car and I estimate that the angle will
> be a bit under 40 degrees from vertical; I'll see
> if I can get a measurement.
>
> In looking at the photos supplied by John and the
> pix of the Volvo towers, the pix show a much
> closer intergation of relatively short strut
> towers into the floor and inner fender area. The
> Volvo towers really stick way up and would not
> appear to support the fore-aft forces on the cage
> without risk of pushing/crumpling these tall
> towers over; once they startto give at all, the
> main hoop would then put a bending force on the
> bottom welds of the main hoop (and some to the
> lower ends of the A-pillar hoops), which is not
> desired. The added lower bracing from the tower
> tops to the lower end of the main hoop helps, but
> still, if the towers give at all, then all the
> fore-aft force goes into the bottom ends of the
> main hoop, and that is not what is desired; the
> backstays should carry this force.
>
> Hey Andrew, I am not following why 45 degrees is
> the most efficient, but I am probably not totally
> thinking things through.
>
> Regards,
> Mark B.

Hi Mark

All of the bracing being tossed about is structurally redundant. The Volvo frame is an open c-channel that is barely 0.120" thick and ends unsupported 6 inches behind where we cut in the towers on the orange car in the pictures. We spliced thru the frame-rail and welded on face to the cross-member in the location we picked.

As you stated the only loads that exist back there are inline with the shock aka: pin-pin two force member and if you want to get really technical a small concentrates moment from bearing friction. I didn't make the turrets out of truck driveshaft or thick pipe because they were intended to be supported by the cage backstays. I still can't find in the rules where it says I have to go to the floor. The FIA rules has this:

The backstays must be attached near the roofline and near the top
outer bends of the main rollbar, on both sides of the car, possibly
by means of removable connections.
They must form an angle of at least 30° with the vertical, must run
rearwards and be straight and as close as possible to the interior
side panels of the bodyshell.

The NASA rules seem to be a paraphrased version of the FIA regs. and they also say as close to the sides of the car as possible but there is no definition of that. We seem to be arguing over the perceived buckling strength of a structure that I can't find a rule formally regulating. Please point me to the proper rule if I'm missing something.

Tim

Tim Taylor Wrote:
-------------------------------------------------------
>
> Hi Mark
>
> All of the bracing being tossed about is
> structurally redundant. The Volvo frame is an
> open c-channel that is barely 0.120" thick and
> ends unsupported 6 inches behind where we cut in
> the towers on the orange car in the pictures. We
> spliced thru the frame-rail and welded on face to
> the cross-member in the location we picked.
>
> As you stated the only loads that exist back there
> are inline with the shock aka: pin-pin two force
> member and if you want to get really technical a
> small concentrates moment from bearing friction.
> I didn't make the turrets out of truck driveshaft
> or thick pipe because they were intended to be
> supported by the cage backstays. I still can't
> find in the rules where it says I have to go to
> the floor. The FIA rules has this:
>
> The backstays must be attached near the roofline
> and near the top
> outer bends of the main rollbar, on both sides of
> the car, possibly
> by means of removable connections.
> They must form an angle of at least 30° with the
> vertical, must run
> rearwards and be straight and as close as possible
> to the interior
> side panels of the bodyshell.
>
> The NASA rules seem to be a paraphrased version of
> the FIA regs. and they also say as close to the
> sides of the car as possible but there is no
> definition of that. We seem to be arguing over
> the perceived buckling strength of a structure
> that I can't find a rule formally regulating.
> Please point me to the proper rule if I'm missing
> something.
>
> Tim
>
>
>
Hey Tim,

I'm not suggesting all this from a rules perspective; sorry if I gave that impression but that was never the intent. You are correct that this is not identified in any rules. I'm also not making suggestions from the prespective of how to support the suspension loads on the new strut towers.

I'm writing from a perspective of 'where do the loads from the cage go in a wreck, and how do they get transmitted into whatever they attach to'. The backstays are there primarily to take to fore-aft loads on the cage (particular on the upper part) and spread them. If the backstays go to the top of strut towers that have a large height-to-base ratio, those towers will tend to bend and give. Once they give just a little bit (like a fraction of an inch), all the fore-aft load imposed on the cage end up on the main hoop welds to the floor (and to some degree to the welds at the base of the A-Pillar hoops). This is not where you want the fore-aft loads to go.

Short strut towers which have tops that are within a few inches of the rest of the car, and that have a very short height-to-base ratio, are not going to give and yeild like this. The tall towers will, IMO, and put some of the cage loads in the wrong places.

Backstays are part of the cage for safety; the fact that they get used for bracing the rear suspension mounts is good, but came after the fact and after some smart folks saw they could kill 2 birds with one stone. But the latter (suspension support) should not take priority over the former (cage integrity).

BTW if the walls of the C-channels (box channels once spot welded under the floor) are .102 thick, that's pretty thick! But, then again, it is a Volvo.....

Regards,
Mark B.

I was looking again at the pictures of the blue 240 earlier in this thread.
Here's a shot that shows a side view of the rear triangle. Notice that it is a full triangle, and not just a backstay.


The rear triangles actually attach to the rear bulkhead, just below the package shelf, and well into the corners of the existing structure. The towers are tied into the cage with a crossbar that runs from corner to corner.



This looks quite reasonable to me, although my main hoop is not so far back.


ps, sorry Timm, I meant Tim.

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Monika Hawkinson
Seattle, WA



Edited 1 time(s). Last edit at 04/21/2008 05:42PM by Sofa King.

Generally, the further from 45deg a structural member is to the load (regardless of direction of load), the more load it will take. This requires it to be heavier (stronger). It of course doesn't mean that part of the load magically disappears, it just means that member doesn't see as much of it.

You can run some analysis if you want.

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Andrew M
Onterrible
30ish

hoche Wrote:
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> Sweet. I gotta come up and take another look at
> the car. It's looking like it's coming along
> nicely.

Hey Michel,

You're going to log book the the car so do you want to come by the shop and give a definitive yes or no on this? The driver side turret is most likely going in some evening this week with the cage following shortly thereafter.

Tim

Sofa King Wrote:
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> This looks quite reasonable to me, although my
> main hoop is not so far back.

That cage is the bees knees. Notice the angles? I think that's why they A had the main hoop so far back and B why they didn't go all the way to the *top of the* tower.

I'm pretty terrible at expressing myself

I also agree with Mark and making sure the cage isn't likely to do anything strange if it is actually used. You don't want any funny loads due to design or crushing of "shell" where it's attached.

It doesn't appear that the back stay triangle is attached to the frame section in the back.. although it might be. But that cage is well braced and they have that extra bar on the 45 deg into the main hoop (probably because the bars up top are so long from moving the main hoop so far back).

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Andrew M
Onterrible
30ish



Edited 1 time(s). Last edit at 04/21/2008 06:29PM by hudson.

Yeah, I see that both diagonal members of the triangle are near 45, I just don't get why you are all hung up on this particular number. I think you have a particular loading scenario in mind where 45 degrees is the right answer, but you are not letting us in on the details. And then you say something like "regardless of direction". Dude. C'mon on.

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Monika Hawkinson
Seattle, WA

I too am thoroughly befuddled by the insistence that 45degrees is some sort of magic number and that it is necessary/desirable to move the main hoop back to get an equilateral triangle in the backstays. Having the main hoop back in the blue car makes the span across the doors even longer decreasing the extra stiffness you can get out of the x-brace. Aside from that what loading are we considering? The old rules (before Lurch wrecked it ) were loading on the roof simultaneously 1.5G laterally, 5.5G fore/aft, and 7.5G vertical. Let's see a free body diagram...

Sofa King Wrote:
-------------------------------------------------------
> Yeah, I see that both diagonal members of the
> triangle are near 45, I just don't get why you are
> all hung up on this particular number. I think you
> have a particular loading scenario in mind where
> 45 degrees is the right answer, but you are not
> letting us in on the details. And then you say
> something like "regardless of direction". Dude.
> C'mon on.

It's just that 45deg is desirable. Whenever I design anything I use a 45 degree angle unless some constraint means I can't.

To explain the regardless of direction comment. If the load is vertical and acting up, either a 45 degree angle from the vertical up or down are two of the best angles in limiting the amount of force that member will take. The less force a member takes, the less it will transmit into whatever it's attached to.

"Bad" angles in a system can make forces larger than what they initially were, "good" ones reduce them.

What started me down this long path was that I didn't like the angles in your doodle and was also concerned about, like Mark has said, the tower crushing and thus putting funky load situations into your cage in the event of a roll over.

I saw that you were doing this design primarily to reinforce the towers. And was trying to suggest there are other ways to reinforce them (that could be lighter).

Does that make sense? I'm terrible at expressing myself.

It's more than possible that what you've proposed works perfectly fine in the real world.

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Andrew M
Onterrible
30ish



Edited 1 time(s). Last edit at 04/21/2008 07:09PM by hudson.

Oh, ok Kevin, I was like "WTF? whats he talking about...."

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Welcome to the cult of JVL drink the koolaid or be banned.

Oooohh, I want to play MS paint too. Here is a fairly realistic rendering of where the current turret install will make the cage land.

Tim Taylor Wrote:
-------------------------------------------------------
> Oooohh, I want to play MS paint too. Here is a
> fairly realistic rendering of where the current
> turret install will make the cage land.

Yeah that looks a lot better.

I understand that your truck just got stolen. But this is a DIRECT quote from what I said earlier, "I'm not saying it's a stupid idea. I'm saying from the mspaint representation that the angles don't look right."

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Andrew M
Onterrible
30ish



Edited 1 time(s). Last edit at 04/21/2008 10:04PM by hudson.

Andrew, I'm really not trying to pick a fight with anyone over this, honest. All of the previous drawings had the towers twice as tall as what I'm using so I did another drawing. If I get some time tonight I'll do a real free body diagram of the back of the cage too (since John V. asked so nicely)

Tim