A rep from Exocet had one on display at the Petit Le Mans vendor village. He wasn't able to give rides that weekend, but said that he would if I stopped by their shop in Roswell, just north of Atlanta.
A rep from Exocet had one on display at the Petit Le Mans vendor village. He wasn't able to give rides that weekend, but said that he would if I stopped by their shop in Roswell, just north of Atlanta.
Adrian_Thompson wrote: 3. Cockpit sides parallel to the ground not sloping as per the original Lotus and Caterham. The only car that seems to carry this off is the all fiberglass Westfield’s.
I could never get past this aesthetic fault.
Alright, I'm not the social media guy, but I am Exomotive's engineer, and I have to go rogue for a minute.
In regards to the style bar, we had the same questions you guys did. There are many "excuses" we could come up with: "it's just a style bar, the UK guys love it to the tune of 400+ sold in two years, other cars are more dangerous", etc. Excuses are worth nothing when a soccer-mom pulls out in front of you and you're rolling down a hill. I love that the US enthusiast market asks these questions; it's a matter of national pride at this point.
The M-Style bar was designed for Sunday cruises around your little town in the UK. Out of ~450 cars sold, there have been two violent M-Style Exocet accidents, and all four occupants walked away with just bruises. For many that would be enough, but, hey, the shuttle made it to orbit 24 times with faulty O-rings.
Disclaimer: the M-Style bar is not intended to be a rollbar! That said, we reverse-engineered and analysed the M-Style bar for rollover strength in the same manner you would test formula car roll hoops. These are not guarantees, these are just results from computer simulations: As-is, the M-Style bar should hold to about a 3G impact. This corresponds to rolling over on hard ground, or a slow rollover on pavement.
With the addition of two diagonal tubes, the M-Style bar will actually hold the car off the ground in an 8G+ rollover impact. The top bends will deform, but it will keep the seats off the ground, and that's about where the sport bars sold for the NA and NB Miata leave you. You won't be happy, but you won't be in an upside-down bathtub, either. The seats should hide the new heart shape if you're sensitive to that.
The little purple arrows on the right are where the chassis would most likely hit first in a violent rollover. The loads are 12K lbs down, 6K lbs back, and 8K lbs in. The red area will fold over but should remain ductile. The diagonals come down in the center and mount to significant structure. We can add those tubes as a very cheap extra, but it will require you to mount the rear bodywork a bit further back.
Just as a rule of thumb, if you don't have 2" of clearance under the broomstick test to your helmeted head, you should NOT run a harness. Harnesses hold you in position pretty well, and you don't want to be a structural member in a rollover. We don't recommend that customers weld a harness bar to the M-Style bar. The M-Style bar is designed to work with the Miata's seat belts. We recommend the MSA-spec bar or the full Race version if you're going to explore the car's performance.
To address concerns about the MSA-bar's gusset plates: well, they're thicker and bigger than you think. The shape and placement are not ideal, but FEA testing shows that they won't start permanently deforming until about 10K lbs of vertical load. They should hold up to about 18K lbs before stuff starts tearing. My Miata's Hard Dog would tear through well before that, and for a ~1500lb car, 18K lbs is a hell of a rollover. The area of the gusset plates make them legal in all the rulebooks I've checked.
Why are the bars bolt-in instead of weld-in? We can fit twice as many Exocets in a shipping container with a bolt-in bar, and shipping containers are EXPENSIVE. If we started production of the chassis in the US, every chassis would have an integrated roll structure. Unfortunately we need to sell a few more kits to justify the startup cost of that venture.
Addressing the cost of the kit, we are confused by the oft-repeated "it's cheaper to buy it in the UK and ship it to the US myself". MEV sells the LHD kit in the UK for £3540. That's close to $5700 before the costs of shipping and importation. We sell that kit with some nicer components for $6k, and we'll make bodywork in any RAL color you'd like. The time that we put into the company doesn't even work out to minimum wage; we are more evangelizers than businessmen.
Overall build cost should be in the ballpark of $10k. As a test, we built a 1.8 base Exocet and got it powdercoated and road legal for well under $8k. At the end of the build, you are left with a lot of Ebay-able Miata parts to recoup the cost. The most expensive builds are bouncing around $13-14k, but those are with a bunch of Flyin' Miata parts. (I kid, Keith, we love you guys)
-Warren
Thanks for the pertinent info!
I'm still curious about these. I need to check and see if anyone has built one somewhat close to me.
Cool stuff! I didn't realize that they could be had for that much. In black it looks alright and i bet it is a hoot to drive.
So is this available as a "piece meal" kit like in the old days. I like all the bits but the body and windows. It would make for a fun looking monster.
I appreciate your thorough response here. I didn't intend to imply you guys were getting rich, just that I think it would be hard in the US to get to the net build costs the UK guys post on the MEV forum - the value proposition there is better. I think I read that the first one built here (Ohio?) had like $20k into it, but with a good number of optional cosmetic items.
As far as the MSA mounting goes, you know as well as I that an FE model can be made to say whatever you want it to. Structurally it has little to do with the area or thickness of the plate, more so the fixation. The fillet weld will never be a smooth quarter-round as modeled, it most likely won't be full penetration, has a built-in crack, and isn't inspectable. They are difficult to impossible to accurately analyse for, particularly in impact with HAZ embrittlement, which is why best design practice is to avoid them. The SCCA or NASA rules for mounting plates are intended for supporting punch loads when attached to a unibody / monocoque structure (the blue mustang situation). I'm sure they never contemplated the plate being cantilevered by a fillet weld.
Anyways, as you mentioned its fixable with an integral roll bar out to the main chassis spars. On the street its probably better off without any bar near an unprotected head. And relatively few of them will likely be run on a racetrack.
The ohio guy made special case of saying he put all new parts on it, he didnt just swap over the used miata donor bits with thousands of miles in many cases.
In reply to wearymicrobe:
Yep, we don't quite advertise it everywhere, but you can get the kit sans-bodywork for $4k. That still includes everything else, like the pre-formed bulkheads, floor panels, fasteners, side panels, etc.
Edit: I don't want to get too salesguy on you, but we offer 0% financing through GE Capitol.
Here is a video of a customer's naked Exocet like you were describing. This one has a Ford V-8 (V-7 when I shot the video). http://www.youtube.com/watch?v=wsCJMcg3s88
oh and warrenv, around here we would probably rather talk to an engineer than a social media guy anyway :P
The option with the welded steel floor and cage is that a carry over from the UK m150 or whatever they were called or something you guys were doing specifically?
In reply to MattGent:
I like you; you're asking the right questions. The weld is simulated at half the actual weld radius, and my Sy and St critereon were 25 and 40ksi respectively. Annealed and perfect welds would be 54 and 64ksi. A perfect MIG weld allowed to air cool should get you 36/58ksi. Ultimately we're talking about 13" of double-sided welds supporting a moment arm of less than an inch on two sides. I'm pretty confident about that particular joint, although I certainly would rather weld the bars directly to a node if we could. Indeed, plate area has little affect on strength here, but it will pass according to Tech. The Race versions have welded-in floors that back that plate up a bit.
It's true, Miatas in the UK are unbelievably cheap. Many build threads on the MEV forums start with Miatas that cost a few hundred pounds. That said, those cars are quite torn up. In Georgia, we are spoiled with nearly rust-free cars. With a good enough donor, it is quite reasonable to simply clean up your Miata's mechanicals before mounting the chassis with a clean donor. There is no need to replace all the A-Arms, hubs, halfshafts, etc.
Mark's up in Ohio was special ordered from MEV before Exomotive simplified the process, and it required quite a bit of custom fabrication to get it LHD. He also started with a rusted out donor and ended up buying just about every component again brand new. The end result is amazing, but it is likely the most expensive Exocet ever made. There are a few more in Ohio now, they were built for about half of Mark's build cost.
As the cars sit, they weigh almost exactly 1000lbs less than my daily-driven NB. The open experience makes it seem even faster, and it handles exactly like a Miata. You could build a FMII Exocet with 260rwhp for under $15k and 100 hours. The everyman cost is why I like the project so much.
I was pretty impressed with the car in person. I sat in the aforementioned Petit Lemans vendor village one at Road Atlanta. I have always wanted a locost / seven but at 6'3" 210lbs I don't really fit. The Excocet had plenty of room for me.
I think it would make a great first kit car especially when you take into account that you don't need to spend thousands on body work like a FF Roadster. Also the light weight and readily available donors is desirable as well. If a Miata is always the answer, I would think a lighter more elemental miata would be better.
In reply to Jaynen:
The Race version is an MX150R shipped directly from the UK. For now.
pimpM3:
Thanks for coming to visit us, that was an awesome race. I'm the shortest guy at Exomotive, at 6'2". I have to move the seat up sometimes. There is oodles of room in these things, as the Miata's fuel tank is placed a bit further back on top of the rear subframe.
In reply to warrenv:
I think I like it sans body work. All it needs is some pointy teeth painted on the radiator and I would be good to go! I also appreciate the fact that alternative drivetrains are capable of being used. You guys are on my radar now.
warrenv, safe to assume this is DRAMATICALLY stiffer than even a well stiffened NA/NB chassis?
PS, my wife would not be happy if she knew I could finance it. 
Wow, thanks for coming in and giving such detailed info. I've long been a fan of the Exocet and have linked pics here on GRM many times, and I poersonaly find it more attractive than any 7 bar the original or Westfield. I'm not knocking the prouct or doubting it in any way, but could you comment on the numer of mounts for the MSA roll cage? You posted the one pic abouve, but I'm wondering about the other mounts. I've highlighted my Q's in the pic below.
While your answering questions - here's a few more:
-1000lbs less than an NB is pretty light, mine is around 2350. Can you provide a measured weight with some breakdown of what was included (wheels, seats, exhaust)?
-Have you set up an FE model for torsional stiffness? The exo-cars have the advantage of very high sills and no doors, but the damper mounting points fore and aft on the exocet are just folded steel plate. The rollbar fixation probably isn't much help here either.
Has anyone boxed in the front strut plate, forming a shear web to the vertical portion?
The rears are already boxed in, but are kinda hanging off the side of the chassis. At least the rollbar can help here.
Some of the Cobra kit fabricators have shown a substantial increase in torsional stiffness with addition of only a few simple tubes.
I came pretty close to pulling the trigger on one this year, but some medical expenses equivalent to a few finished Exocets got in the way.
z31maniac wrote: warrenv, safe to assume this is DRAMATICALLY stiffer than even a well stiffened NA/NB chassis? PS, my wife would not be happy if she knew I could finance it.
That's not necessarily a good assumption - my Locost chassis is flexier than my Miata. Of course, it's not necessarily a good assumption to say the Exocet would be worse either. Those high sills can only help.
It would be cool to see an actual measurement. Restrain the back of the frame, bolt a beam to the front and see how many ft/lbs are required to twist it X degrees by hanging weights off it. If you use the subframe mounting points for the restraints, you could do the same thing to a Miata tub.
Adrian_Thompson wrote: Wow, thanks for coming in and giving such detailed info. I've long been a fan of the Exocet and have linked pics here on GRM many times, and I poersonaly find it more attractive than any 7 bar the original or Westfield. I'm not knocking the prouct or doubting it in any way, but could you comment on the numer of mounts for the MSA roll cage? You posted the one pic abouve, but I'm wondering about the other mounts. I've highlighted my Q's in the pic below.
Is that image the M150R spec one with the cage and welded floors?
A slight sidetrack, but from a track/impact perspective, what do you guys think of the Atom/Exocet layout where the primary logerons are elevated somewhat, and your hips are barely protected?
I would be interested in the torsion numbers as well.
Anybody else think the double hump bars look like the Golden Arches? Single hoop=SECKS, Double=Faiil IMHO
Adrian:
You nailed the cage points in your drawing. The front "dashboard" tube does have bolted points. The potential points in orange were not included on the old race versions, but I think the current race versions have them (not 100% sure, we haven't brought a Race over in a couple months). If they don't, they really should, as tubes are close enough to weld a gusset plate in there.
z31maniac:
A reasonable comparison is the book Locost chassis. The chassis weighs a little less than a Locost, and according to my FE models (for both Locost and Exocet), the stiffness is dramatically better due to the higher sides and using the subframes as stressed members. Reducing the mass of the car (Miata->Exocet) helps the perceived stiffness a lot, as there is a lot less force involved when you chuck it in a corner. The Brits haven't measured their chassis stiffness, and we have yet to figure out how to fixture it in order to measure the actual deflection. My old FSAE team used a very simple method involving a laser on each end of the chassis, a long arm, a front pivot, and a wall. It's much easier when you have a 1000lb+ table and the chassis is only 2ft wide. It's on our very long to-do list.
Torsional stiffness ultimately affects the car's steady state balance, transient response, and ability to handle bumps. From my butt-dyno, the effective stiffness is currently right around an NB1. From that same butt-dyno and a lot of time to look at a a chassis, I am pretty confident in saying it is stiffer than the Atom2, mainly due to wall thicknesses, the number of loadpaths in bending, and how the Atom2 resolves the frame behind the passenger compartment.
MattGent:
First off, the pictures you've got are of Kevin's prototype LHD car. The production chassis are a bit different in a lot of places and have a bit more gusseting and different mounts.
My NB is a porker. It's an NB2 with chassis stiffening, 6MT, Torsen, 16" wheels, big brakes, HardS bracing, ABS, and a Hard Dog Ace DD. The average Exocet build weight is about 1450. If you use the stock Miata seats and exhaust, expect around 1500. The Corbeau Forza seats fit quite nicely and are pretty light. The only downside is that you sit as high as the stock NA seats. If you tossed the sliders and mounted them directly to the chassis, you could save about 2.5" and maybe 15 lbs. Yes, I do have an FE model for torsional stiffness. We don't want to release actual numbers, as it invites meaningless comparisons of absolute stiffness values. Ft-Lbs/degree tells you very little without considering the mass distribution, overall weight, unsprung vs sprung mass, bending stiffness, etc. The bottom line is that it drives exactly like an NB, just 900-1000lbs less. That weight difference brings throttle modulation into the Miata game, which is awesome.
The point of chassis stiffness is to keep the inboard suspension points from moving around too much relative to each other, not the shock mounts. It may seem intuitive that the car is "hanging" from the damper mounting points, but that's not really the case due to motion ratios and the effects of forces in motion. That said, it does make a difference, and thankfully the damper mounting points are more rigid than they look from a distance. There are welded-in stiffening "flanges" on every side of the tophat mount plate, and the forces involved are all in line to be resolved with that vertical plate. The bolted in tophat mount provides a bit of stiffness as well. The rear rollbar does help the back end a bit, and you can also see that the rear and front boxed end areas lead right into the rear subframe mounts and don't put that tube in torsion for more than an inch or so. We have identified and FE tested some improvements we can make to stiffness, but again, we need to sell a few more chassis before we can justify the cost of setting up more than a composites shop and an office.
The Honorable Keith:
You obviously get it, the Miata is a much heavier car, and comparing raw stiffness numbers doesn't tell you much. The high sills do help, and the front and rear subframes are both tied into the floor to increase the moment couple. Measuring the stiffness is on our list, we just don't have an anchor point that can hold a Miata frame. We would have to measure the Exocet with the Miata subframes installed, as they are stressed members. Also, keep in mind that your method would result in displacements from combined torsion and bending. Pure torsion would require a pivot point in the front, preferably located at front/rear static roll centers' line of action. The simple combined loading would be a valid way to test the FE models validity if we set up an identical virtual experiment.
kreb:
Logerons? I'm curious, is that a typo or a French term for mainstay or beam? I don't know many French engineering terms, but that would be cool (it means stay or linger for those confused). Anyways, the Exocet has a big tube on the outside of the seat, and you actually have a little bit of protection from side impacts. Sure, you'll get bruised from the tube itself, but intrusion is less scary (except for your flopping legs, that's kinda bad for any exocar). I don't know if you've been in an Atom, but you basically are sitting in a very thin carbon tub that hangs down from the main chassis tubes. That's a big reason why it's 100 lbs lighter than our car, but it's genuinely terrifying to think about. Carbon does not do impact well at all, and the Brammo-built Atoms have tubs so thin that you're not even supposed to step on the floors. I'm not here to knock the Atom, as they are incredible amazing cars, but that is the one thing that bugs me the most about them. I haven't been in a TMI Atom, but I think Brammo still makes the tubs.
jmc14:
Unfortunately, raw ft-lbs/degree numbers are just a tiny part of how the chassis performs. Comparing these numbers among different cars is almost meaningless, and for that reason most manufacturers of sports cars do not publish those numbers and instead speak in relative terms against cars of the same platform. This is why you see "20% stiffer than the previous model" in advertisements rather than "our Z4 is 40% stiffer than a Miata". Talking raw stiffness gets us in trouble: Australia now has minimum raw stiffness targets for kit cars with no consideration for mass distribution, impact loadpaths, or even vehicle weight. This killed the kit car market in Australia (yes the Atom is a kit car, and no, it doesn't pass their crazy test). The only kit car that has passed their test is the MEV Rocket, and even that required a bit of additional stiffening. The only close comparison would be a Miata, and according to our simulations, it's right around an NB in perceived stiffness.
Thanks for the response. I agree that the ft-lbs/degree number is only part of the picture. But, I think that it is an important one. I have built a number of performance kit cars and have used the lever/weight technic to test the frames. A friend has a commercial garage with tie downs embedded in the floor. I use these to lash the frame down while supported on 3 jack stands. The car in my Avatar had the best numbers that I had tested and it is by far the best handling car that I have ever driven. It uses C5 Corvette cradles.
I also have a scratch built Cobra tribute and am on a Cobra Forum. There are a lot of guys from Australia that have built or are building Cobra kit cars there. They must be passing the test? I also thought that the RCR cars, such as the Superlite have passed. At least that's what the owner, Fran Hall told me.
Just so you know, I am not being critical of the Exocet. I am just trying to learn all that I can about frame design. I love sports cars that are different and I appreciate the vision and effort that went into developing the Exocet and bringing it to market. I wish you the best with it.
In reply to jmc14:
You might have given me an idea about using the mount points of a two-post lift. That car looks pretty awesome, how did you do the bodywork?
Sorry, I should have specified exo-cars. The FF Mk4 Roadster will pass the Australian test, but that frame is ~320lbs!
There are a lot of people here apologizing for criticism of the car. Nonsense. Grassroots guys and engineers are our smartest and most demanding customers. Your suggestions, concerns, and needs help us triage our future updates and improvements.
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