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post #21 of 41 (permalink) Old 02-13-2014, 04:43 AM
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Originally Posted by pwildfire View Post
Actually, this is what I am assuming the difference probably is. The problem is that according to both of the posted regulations, the 3K load is for the shoulder belts explicitly, and there is a separate load for the lap belt.
It seems like a lot of this may be based on SCCA roll cage specs, which do specify a 1.5" harness bar, but I would like to see what loading was in their design, as it doesn't jive with the 3K requirements. It is easy to believe that they are using something similar to what you just said, but that would not be very good communication between them and SFI if the belts are designed 10x stronger than what they are attached to.
Actually you may be on to something there. It could well be, and should be, the case that the belts are required to a higher FoS than the steel bars. The belts are a consumable made of materials with a high rate of degradation in UV and are also subject to fraying and wear along with strength loss just due to the wrapping and buckle arrangements. Having difference FoS is no different than in the crane industry where the cables use 5:1 FoS on BS versus 1.25 x YS on steel, now in crash situations things ar euseagly not designed to an allowable working stress but rather to some ultimate point just below total collapse. Their even mild steel will typically not fail below 100 ksi.

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Last edited by Julian73; 02-13-2014 at 04:48 AM.
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post #22 of 41 (permalink) Old 02-13-2014, 07:11 AM Thread Starter
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You need an automotive engineer... can I suggest you ask simply sports cars to supply you their harness bar along with the certification of compliance. That way you know it was designed by an automotive engineer and conforms to the required standard.

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The cost of the bar will be less than the cost of engineering a custom one
Actually, I am an automotive engineer, although admittedly my expertise is in performance development and not structural design. Still, I think you will find that an engineering degree is not a magical free pass nor does it certify that everything one does is correct.
The reason for this project initially had nothing to do with strength of the bar, I am building my own because with my seating position I can use a bar that clears the speaker pods and requires minimal modification to the interior trim. And because I like to design and build my own parts. The issue with strength came after I started the design and realized that the strength requirements I could find for the belts and mounting far exceeded the static strength of all the available designs.

Where on SSC or any other supplier's advertising do you see anything that shows any official certification of conformance to government (or other documented) safety standards? All the SSC one states is that it deforms similarly to the OEM one. I don't think the OEM bar is DOT approved.

Once again I think the difference is likely that the dynamic loading that these are designed to involves energy absorption during deformation, which is not possible, or at least very hard, to calculate. What I am not understanding is what, if any, published standard they are evaluated to, and how that differs from the ones that I was able to find that seem to indicate static loading.

The cost of designing, for me, is zero. I am just not comfortable building it without knowing what the proper assumptions are for loading.

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post #23 of 41 (permalink) Old 02-13-2014, 07:50 AM Thread Starter
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One more thing to add to this mess:
I just realized that usually UN vehicle standards make more sense than US ones, so I looked up the EN standard (ECE R014r5) for seat belt anchorages, and not surprisingly, shoulder belt anchorages are required to test to 13500N, which is 3035lb, so same requirement.
One thing the UN specification does specify that is not in the US one is that the structure must only hold the load for 0.2 seconds, and that deformation of the structure is acceptable. This indicates that my assumption that static loading is inadequate may be the answer. There is a limit to this though, as total deformation must not pass a plane inclined 10* forward from the hip point of the seat.

I have to admit I don't know how to calculate total plastic deformation for a case like this, and am hesitant to let an FEA model do it for me. To me, this means that comparing calculated stress to yield strength is not applicable in this case, but I would assume that if calculated stress exceeds UTS, then the structure will fail completely. Since UTS for most tubing is still less than 100ksi, I am still having to conclude that the use of 1.5x.125 wall or similar low alloy tubing probably does not meet these standards.

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post #24 of 41 (permalink) Old 02-13-2014, 05:56 PM
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Originally Posted by pwildfire View Post
Actually, I am an automotive engineer, although admittedly my expertise is in performance development and not structural design.
Cool
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Still, I think you will find that an engineering degree is not a magical free pass nor does it certify that everything one does is correct.
Agree (I have one) - which is why I won't give a calculated answer
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The reason for this project initially had nothing to do with strength of the bar, I am building my own because with my seating position I can use a bar that clears the speaker pods and requires minimal modification to the interior trim. And because I like to design and build my own parts.
All good - I understand those drivers.

The SSC bar does minimise modification to interior trim and leaves the speakers alone BTW.
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Where on SSC or any other supplier's advertising do you see anything that shows any official certification of conformance to government (or other documented) safety standards? All the SSC one states is that it deforms similarly to the OEM one. I don't think the OEM bar is DOT approved.

Once again I think the difference is likely that the dynamic loading that these are designed to involves energy absorption during deformation, which is not possible, or at least very hard, to calculate. What I am not understanding is what, if any, published standard they are evaluated to, and how that differs from the ones that I was able to find that seem to indicate static loading.

The cost of designing, for me, is zero. I am just not comfortable building it without knowing what the proper assumptions are for loading.
Can I suggest you give SSC a call and discuss it - ask to speak with Lee. They are the leading Lotus race workshop in Australia and they develop and test their own designs extensively and they support a number of racing teams (particularly in endurance events). They are easy to talk to and I suspect you'd get the definitive answer you need much faster than from this forum.
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post #25 of 41 (permalink) Old 02-16-2014, 06:48 AM
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I suggest racing motorcycles. They are cheaper, faster, and do not need harness bar calculations.
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post #26 of 41 (permalink) Old 03-11-2014, 12:35 PM Thread Starter
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Finally got some time to work on this...

Design is done, materials will be here today or tomorrow, harnesses will be here in a couple days. Should have it all built and installed in a week or so if I get some time in the garage.

I wasn't able to make it super strong without making it too bulky, but as drawn it meets the 3000LB load requirement and according to CAD it will weigh about 10lbs. I will be making it in 4130 which I had wanted to avoid, but mild steel would have been another couple pounds and I decided it was not worth the weight to save $25 and some time pre- and post- heating the welds.

Didn't quite meet my goals on lack of trimming, but it will clear the speaker pods.
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post #27 of 41 (permalink) Old 03-25-2014, 09:26 AM
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3000 lbs for 10 seconds

Using half the weight of the 200 lbs driver at 30g's deceleration as the 3000 lb example; the vehicle would need a starting velocity of 6,600 mph to achieve a constant 30 g deceleration over 10 seconds. So unless this Lotus is being shot into space and subsequently crashing at 660 mph/s, it will never see 3000 lbs over 10 seconds.

100 mph into a tire wall with a 1/4 second deceleration to zero is 18 g's.

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post #28 of 41 (permalink) Old 04-01-2014, 07:59 AM Thread Starter
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Done, installed in the car. Ran it at the track this weekend, worked great. Almost got to test it too due to a failed brake line, but luckily was able to avoid the wall. I will take some more pics next time I am in the garage. I still need to take it back out and paint it and put the rear trim panel back in.
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post #29 of 41 (permalink) Old 04-01-2014, 08:19 AM
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Looks nice but will it be too high? Belts will be above parallel to the ground, which harness manufacturers really don't like.

With the new Blackwatch Harness bar, we provide a lower mount and an anti-rotation bar. You could try a re-design with that or perhaps buy one of the ones we have on offer.... :P


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post #30 of 41 (permalink) Old 04-01-2014, 09:18 AM Thread Starter
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Looks nice but will it be too high? Belts will be above parallel to the ground, which harness manufacturers really don't like.

With the new Blackwatch Harness bar, we provide a lower mount and an anti-rotation bar. You could try a re-design with that or perhaps buy one of the ones we have on offer.... :P
No, belts run down at about 5* from my shoulders. I do wish I had made it a little lower to accommodate shorter passengers. I will post a pic with the real seats in there and you can see it easier. With this design no anti-rotation bar is needed as it mounts to both holes in the roll structure.

I see how it looks that way from that picture, it is at a funny angle.

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post #31 of 41 (permalink) Old 06-01-2014, 10:32 PM
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Quote:
Originally Posted by fzust View Post
Looks nice but will it be too high? Belts will be above parallel to the ground, which harness manufacturers really don't like.

With the new Blackwatch Harness bar, we provide a lower mount and an anti-rotation bar. You could try a re-design with that or perhaps buy one of the ones we have on offer.... :P
The way sponsors on this site pedal their wares reminds me of the annoying Afghan street hawkers. Do you also shake hands and not let go until they buy something? He just went through all this trouble and discussion to build his own, and he built it. Get your hand out of his pants.

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post #32 of 41 (permalink) Old 06-02-2014, 11:08 PM
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Done, installed in the car. Ran it at the track this weekend, worked great. Almost got to test it too due to a failed brake line, but luckily was able to avoid the wall. I will take some more pics next time I am in the garage. I still need to take it back out and paint it and put the rear trim panel back in.
I have followed this thread with interest. Had I known you were planning to install harnesses for use with stock Elise seats I would have spoken up sooner.

Per Schroth, Sabelt, Sparco and doubtless many other manufacturers, this type of seat is not to be used with racing harnesses. Here is an image from the Schroth installation instructions:

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The Elise-type seat is the one at far right, with the big red X marked through it. This is not safe. I urge you to shop for some proper seats.

EDIT: as noted in a couple of posts below, the OP will be using a different seat. But please be aware that the photo he posted is not a valid application.

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Last edited by luxige; 06-03-2014 at 09:46 AM.
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post #33 of 41 (permalink) Old 06-03-2014, 02:10 AM
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No, belts run down at about 5* from my shoulders. I do wish I had made it a little lower to accommodate shorter passengers. I will post a pic with the real seats in there and you can see it easier. With this design no anti-rotation bar is needed as it mounts to both holes in the roll structure.

I see how it looks that way from that picture, it is at a funny angle.
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...
Had I known you were planning to install harnesses for use with stock Elise seats I would have spoken up sooner.
...
But do you know what seats he is actually using??
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post #34 of 41 (permalink) Old 06-03-2014, 05:40 AM
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But do you know what seats he is actually using??
That's exactly what I was thinking the other day. I was going to ask about it, but then I read what he posted, and that he had other seats.

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post #35 of 41 (permalink) Old 06-03-2014, 09:38 AM Thread Starter
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I am using Corbeau FX1 Pro seats.

I am long overdue to post some more pictures of the finished installation, but have not had the time to get them off my phone. I will try to post them soon.

I did originally intend to run the stock seats with grommets, however as it turns out I am much too tall for the belts to be properly routed that way. I already had the FX1s from a different project, so I trimmed them a little bit and installed them instead.

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post #36 of 41 (permalink) Old 06-03-2014, 09:42 AM
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But do you know what seats he is actually using??
Of course not, as he hadn't posted it. I now see that there is a brief mention of "the real seats" but that's not much of a description of this installation.

I understand that PW didn't start the thread to document a harness bar/seat installation, rather to ask some questions of his own. My concern was that someone new to safety mods would take this picture, posted by someone evidently very well-versed in the analysis of this technology, as an example of an expert and safe installation. Which, as pictured, it certainly is not. So I'm still glad I posted a warning.

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post #37 of 41 (permalink) Old 06-03-2014, 01:12 PM Thread Starter
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I realize these are terrible quality pics, but this is what I had on my phone. I will change them for better ones someday, but for right now, you can see how I trimmed the seats and made rails, and how the bar fits with the seats and belts. You can also see that it allows retention of the OEM speaker locations without modification, which was one of my goals.

As mentioned before, the belts are only barely below horizontal (about 5*) from the seat to the bar, and there is barely enough room for the 3-bar adjuster. If I were going to build another of these, I would modify the design a little to put the bar about 1/2" lower and about 3/4" farther back. I am happy with the fit and safety as-is, though, so I will likely not build another.
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post #38 of 41 (permalink) Old 06-03-2014, 08:50 PM
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I wouldn't worry about the shoulder strap angle - anything from 0 to 20 degrees down is good to go.

Two questions:
- How do you like the seats?
- Those appear to be 4 point ASM harnesses, correct? If so, the passenger side installation is wrong. The shoulder belt with energy converter (as indicated by the yellow tag) must be the inboard belt.

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post #39 of 41 (permalink) Old 06-03-2014, 09:19 PM
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Of course not, as he hadn't posted it. I now see that there is a brief mention of "the real seats" but that's not much of a description of this installation.

I understand that PW didn't start the thread to document a harness bar/seat installation, rather to ask some questions of his own. My concern was that someone new to safety mods would take this picture, posted by someone evidently very well-versed in the analysis of this technology, as an example of an expert and safe installation. Which, as pictured, it certainly is not. So I'm still glad I posted a warning.
Good point
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post #40 of 41 (permalink) Old 06-03-2014, 09:22 PM
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- Those appear to be 4 point ASM harnesses, correct? If so, the passenger side installation is wrong. The shoulder belt with energy converter (as indicated by the yellow tag) must be the inboard belt.
Yup. Like so.



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