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Post by nickmpower on Jul 31, 2016 20:50:59 GMT
I'm very interested in an Exocet. I am thinking of building one, and documenting the build then using the car as a promotion vehicle for my automotive related business. Being in California I plan on driving it on the street a lot, but will also be taking it to the track. I know I want more protection than the sport version, but the race version might be a little much for several reasons. First I will need to modify it regardless because the top diagonal bar will interfere or be very close to my helmet. Second, for a vehicle that will see so much street time it would be nice to have easier entry/exit. And third, if I could also get it to look better that would be great as well. At first I was thinking of trying to create a bolt on front section of the cage, but it seems hard to design it in such a way that would it would be strong and still look half decent. Then I thought of possibly something like this, where there is a front hoop that is braced to the back hoop towards the center. This would provide much easier entry/exit. Although the top corners of the front hoop would be weaker than the race version, overall the car would still be a hell of a lot safer than the sport version. And a thicker wall tube could be used for the front hoop to help increase the strength.  Here is a concept. Note that I'm new to photo editing and just did this as a mockup. I originally just quick changed the color of the frame from yellow to gray (ignoring the details) to see what it looked like, then came back later and messed with the cage design.  Instead of just the two bars between the hoops, some additional bracing could be added. But because of my height I would have to keep the bracing a little more towards the inside so it isn't close to my head. But someone that was shorter could do the full x design. I think I'd probably end up with a combination of the top two designs.   Instead of running the cage to the floor (it's the weakest point), I would run it to the top chassis rail, then have another tube braced between the top and bottom rail, made in gray in the top picture below. Note that I would add an additional brace between the front hoop and top chassis rail, like the race version has.  I would also like to point out that there isn't as much room as the above diagrams show. I'm less than the 6'3 that these diagrams specify, and when I sat in Colin's car my helmet was above the bottom edge of the cage. With the seat rails removed I think it would be about even maybe still higher.  Has anyone else attempted anything different than "stock"? |
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Post by kiwicanfly on Jul 31, 2016 22:18:57 GMT
I did a similar thing to my Rocket. First thing though is that if you are adding a cage for any reason then you might as well have it motorsport aproved which limits your options. However not meeting motorsport regs limits your future use even more. Whilst you don't need a cage for track days you might decide to go further and enter competitions. If the cage is not approved you may be limited in the competitions you enter and you also may not be able to take passengers. Finally even if you don't want to compete the lack of an approved cage may limit your resale options. Of course everything depends on your local regulations but it would be well worth investigating them. Your front connection point would not require a vertical member as the triangulation of the other two tubes gives the strength. You are right about connecting to tubes rather than the floor. In my case I wanted a removable cage, I didn't want to run a cage on the road and I like the styling of the Rocket M hoop however that design won't allow competition use in NZ. The full solution uses taper bosses and sleeves. The cage is split into two sections - main roll bar and front cage with top bars. I can actually run it as a roll bar only or a full cage. My design was computer analysed and is actually way stronger than minimum. Installation takes less than 20 minutes although I need help for a couple of minutes to physically lift it on/ff to avoid scratching the paintwork. When I first installed it getting in and out was tricky, especially the 7 second exit rule, as I was going in though the side. However I now drop in from the top and it is as easy as. I have more trouble getting into saloon car with cages as they often have side intrusion bars. Regarding height, if your helmet is too close to, or above, the cage top then again you won't get approval, there are rules on clearance. Thus you might have a design that is strong enough but is too low for you personally. mevowners.proboards.com/post/60245/threadmevowners.proboards.com/post/82736 |
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Post by nickmpower on Jul 31, 2016 23:07:43 GMT
Hmm I never thought about having a cage completely separate from the roll bar. But your design does give me the idea that I could just have bars that bolt between the two hoops to install for track days. When it comes to clearance though I think I'd be screwed. how this bar bolts to the rear hoop could just be done on both the front and rear hoops of my design, in addition to the bars I'd have towards the middle.  here is a sligntly better rendering I made of my idea, picture is small intentionally haha  |
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Post by kiwicanfly on Jul 31, 2016 23:40:45 GMT
If I had been happy with the shape of an MSA roll ball for road use I could have built just the front part although to be honest I probably would have not bothered adding the cage. But that would have been short sighted as I would not have been able to carry passengers in competitions (not track days). The final comment that made me go for a cage over just a bar though came from our scrutineer who told me that he "would not be picking up my head if I went through a wire fence"  If you installed a permanent front hoop you would never get the top cross bars in using the bush and pin method, you would need a plate to bolt to and that will be well ugly! You could have the front hoop bolt in and bars bolt in front and back though. The top bars also have to be towards the outside rather than central as per your design. My suggestion is you find a local expert on these things and also find your governing body regulations to see what applies. However you are doing the right thing by considering this early, nothing worse than having to weld through a new paint job or being told your pride and joy does not pass scrutineering! |
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Post by phocup on Jul 31, 2016 23:50:30 GMT
Hey NickM. Funny timing. I just checked out Colin's car yesterday to decide finally if I want the race or sport chassis. Like you, there's aspects of both chassis that I prefer, just depending on the occasion / mood of the day / lunar cycle / ect. I actually talked to Kevin @ Exomotive about custom ordering a 'bolt in cage' section but unfortunately that's not possible. It is however possible to order the race chassis with the 'cage portion' unwelded so your local shop can do whatever customization is required. The cost for this is the same as the completely welded chassis. After talking to Kevin, I went to talk to Tony @ TC Design ( www.facebook.com/tcdesignfabrication/ ) who builds a lot of cages for race Porsches. Tony quoted me around $2500 for a custom cage if I got the sport chassis. He figured after the $700 extra cost on race chassis to get the Exomotived designed cage pipes, then his labor to customize those 7 joints to be bolt on, its even money vs starting from scratch with his personalized cage. Hope that helps! |
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Post by nickmpower on Jul 31, 2016 23:56:17 GMT
Yeah I know the side bars need to be to the outside for most racing groups etc. My Idea to have them be bolt in with a permanent front and rear hoop would be to just use spacers welded inside the hoops tubing. It would only be as strong as the bolts in the perpendicular load direction, but parallel is the load direction they're intended for anyways. something like this inside the hoops:  |
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Post by nickmpower on Aug 1, 2016 0:08:10 GMT
Hey NickM. Funny timing. I just checked out Colin's car yesterday to decide finally if I want the race or sport chassis. Like you, there's aspects of both chassis that I prefer, just depending on the occasion / mood of the day / lunar cycle / ect. I actually talked to Kevin @ Exomotive about custom ordering a 'bolt in cage' section but unfortunately that's not possible. It is however possible to order the race chassis with the 'cage portion' unwelded so your local shop can do whatever customization is required. The cost for this is the same as the completely welded chassis. After talking to Kevin, I went to talk to Tony @ TC Design ( www.facebook.com/tcdesignfabrication/ ) who builds a lot of cages for race Porsches. Tony quoted me around $2500 for a custom cage if I got the sport chassis. He figured after the $700 extra cost on race chassis to get the Exomotived designed cage pipes, then his labor to customize those 7 joints to be bolt on, its even money vs starting from scratch with his personalized cage. Hope that helps! Wow that's more money that I was hoping. I guess having to be bolt in does complicate things. I think I'm pretty happy with the weld in design I came up with. Still much safer than sport, easier egress, and I personally think it looks better. |
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Post by kiwicanfly on Aug 1, 2016 0:27:39 GMT
Yeah I know the side bars need to be to the outside for most racing groups etc. My Idea to have them be bolt in with a permanent front and rear hoop would be to just use spacers welded inside the hoops tubing. It would only be as strong as the bolts in the perpendicular load direction, but parallel is the load direction they're intended for anyways. something like this inside the hoops: I reread your post after posting mine and realised I had missed the bit where you intended making the side bars an addition to centre bars. I don't think you can rely on the strength of the bolt though, my design uses a male taper boss inside a female taper boss, the bolt simply secures this pair together. If I had wanted to use face to face attachment I would have needed a number of bolts (I think 4xm8 mininimum) and a large support plate. |
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Post by kiwicanfly on Aug 1, 2016 0:36:48 GMT
The cost figures seem on par for what it would have cost me to have a cage designed and made.
Lukily I was able to do all the design work myself, I had to pay for the analysis though. I having the tube bent on a CNC bender, I cut and prepared all the joints and then paid a welder for his time. I reckon it cost me about US$500 plus certification fees. BUT I saved a lot by doing the design work and the prep work myself and the other costs were "cash".
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Post by dietcoke on Aug 1, 2016 1:26:49 GMT
The top diagonal bar is required to pass NASA and SCCA tech. That's why it exists as such.
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Post by nickmpower on Aug 1, 2016 1:34:16 GMT
The top diagonal bar is required to pass NASA and SCCA tech. That's why it exists as such. Are you sure? I looked through here (cage stuff starts on page 43) and didn't see it anywhere, even in the cage diagram. Maybe you're thinking of the main hoop diagonal? nasa-assets.s3.amazonaws.com/document/document/282/2016.7.pdf |
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Post by Trenon on Aug 1, 2016 4:52:17 GMT
Sounds like you are in the same boat i was in. Here is what I did, half cosmetic, half for protection. I will be adding 2 additional braces on the side of the windshield that should stop the corners from folding in should something clip the side of the windshield.   |
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Post by nickmpower on Aug 1, 2016 22:26:29 GMT
Yes that is pretty similar!
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Post by kiwicanfly on Aug 1, 2016 23:25:17 GMT
Just had a cunning plan  As discussed earlier top side bar would be required for competition use but adding them neatly could pose a problem. Well when in place it would be Ok but when removed it could result in ugly fixing points exposed. A sngle bolt won't cut it but using a taper boss and bush at each end will be impossible to assemble. So..... imagine a taper boss in each end of the top tubes with the large end of the taper inside the tube, carry this taper profile through to a female boss welded into the hoops. Now have a male taper plug inside the top tube that can be pulled into position to lock everything together. Hopefully this picture illustrates the idea. The green colour is the cross tube, the red a boss inside the hoop, hoop is blue. Pin is grey and shown in closed and open positions.  Same used each end of the cross tube. Whether it would be certifiable I don't know but might be worth a poke and it would be significantly stronger than a bolt alone. |
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Post by dietcoke on Aug 2, 2016 0:49:20 GMT
Page 110 and 113 of the scca GCR. NASA doesnt require the diagonal, thats why I said both. Maybe the wording was off.
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