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 Post subject: Exo Hot Rod
PostPosted: July 3, 2016, 1:37 am 
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Greetings Locost Forum Members,

Long-time lurker, first-time poster here. Hopefully my build will interest some. Comments are welcome.

This is the build log for my current project, a hot-rod inspired exo car based on a C5 corvette 'roller skate'. Often called a rolling chassis by those who sell such things, the roller skate came with the full drivetrain, suspension, wheels, brakes, fuel system, computers and wiring, steering column, pedals and hydraulics, and lots of other stuff from a 2000 M6 Corvette. 55k on the clock. Not as cheap as a Miata roller skate, but I like a V8.

Attachment:
File comment: Hot rod, right?
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Hopefully my reason for calling it 'hot-rod inspired' will be obvious from the photos. The tube chassis was to incorporate a full cage, and I knew it had the potential to look entirely un-aesthetic. So I drew before building it and found a basic shape I liked. The high cowl is not great for visibility, and I don't need it for the engine, but it looks so much better than anything else I could draw. I used graph paper and drew it to scale to sort out the aesthetics, and built from the drawing. The steel is not a perfect replication of the drawing, but it's close to within a half an inch or so.

The engine is an LS1, which makes 350ish hp/tq when it's in the Corvette, in this car it will make about 400 initially, with different exhaust and intake, and maybe I'll bump it up to 500 or so with heads and a cam someday if that seems like the thing to do. No forced induction is planned.

The Transmission is a T56, and the diff is Getrag. Drivetrain should be good for 500 crank horsepower without any changes. Might need a stronger clutch at that level though.

The suspension is all aluminum, including the subframes, and I may or may not use the transverse springs initially, but the finished version (such a thing?) will employ coilovers.

I intend to use stock brake parts except for the pedal assembly and master cylinders. Same for the clutch. I've not yet picked out a pedal assembly, trying to decide between Wilwood and Tilton.

I have two sets of C5 thin spoke wheels, so although they are staggered from the factory (17x 8.5 front, 18x9.5 rear), I'll be able to run the car square. They are light for stock wheels, forged. Also cheap.

I'm using a pair of Kirkey seats. Comfortable, even with no padding, and 12lbs each.

If and when I run an actual windshield, it will be split down the middle and Lexan. Duval style.

I'll run a 5 gallon plastic vertically oriented fuel cell mounted behind passenger's seat on the other side of the rear firewall, and will have space if not provisions to mount another behind the driver's side. The idea here is to be able to run a very small fuel load without sucking air. No foam. I'm leaving space in the back for a large, road-racing fuel cell, just in case, but I envision this as more of a short race vehicle. An autocross/trackday/occasional street driver.

The space/tube frame is being constructed from locally-sourced mild steel round tubing in various diameters and thicknesses. The really heavy stuff, for just a couple of spots, is 1.75x.134 wall; the lightest stuff I'll probably use is 3/4 diameter in 16 gauge. It's all ERW except for a few pieces of DOM I had lying around. Most of the tubing is 1.75" diameter with .120 wall. I would have preferred to use .095, but the 11 gauge is the only wall thickness available at my local supplier in that tubing diameter (it's only $1.50 a foot), plus it bends and welds very nicely. The smaller diameters of tubing have thinner walls: 1.5" x .104"; 1.25" x .078"; 1" x .065". All the welding is FCAW.

My weight target is under 1800 lbs wet in race trim. Should still be under 2000 in street trim. This goal is based on my calculation of the weight of the roller skate at about 1200 lbs. With a 400 pound allowance for my steel tubing, aluminum bulkheads, and bracketry, I'll have 200 pounds left to 'spend' on battery, fuel system and load, cooling system, seats, controls, wiring, gauges, and hardware. This is a heavy car by locost standards. It could be 200 lbs lighter if I valued things differently, but I decided at the beginning of this build that chassis stiffness/robustness, safety, and an overall shape I find aesthetically pleasing were to be more highly valued than minimal weight.

I'm shooting for a 50/50 weight distribution front to back. It should be possible, barely, with me in the car. I'd love to have a rearward weight bias of 5%, but with this drivetrain layout and wheelbase I don't think that's possible without ballast.

I do not plan to have a driveshaft tunnel, as there is a torque tube. I want to take advantage.

The full chassis will unbolt from the subframes--8 bolts--and lift off. So the engine will come out the bottom. I plan to take advantage of that, structurally. That advantage will be offset by the structural disadvantage of not having a continuous, flat floor. I'm still working on solutions there.

Finally, I know it's asking for trouble, but I plan to put the radiator in the back of the car. It's really the only complicated aspect of my plans. I have two reasons for this: first, I'd like more weight in the back of the car; second, I might be able to turn it into an aero advantage on this highly aero-disadvantaged vehicle. It will add weight and complexity, but I think I have a little wiggle room on this car when it comes to cooling. The openness of the front of the car, the position of the engine, and the aluminum block are big advantages in keeping temperatures down. If I can use aluminum tubing under the car to plumb the coolant to the back (fins?), I'll gain some extra cooling, allowing for a smaller radiator, and perhaps negating some of the weight penalty of the extra plumbing and coolant. It shouldn't be a problem getting air to the radiator in the back; hopefully I can scoop some from underneath. This is an exo car, after all.

Attachment:
File comment: This is how I aligned the front and rear subframes until they were solidly linked.
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Attachment:
File comment: Here you can see the steel 'spools' I fabricated as attachment points for the subframes. 1/8" plate one each end, 1" x .083" compression tubes in the middles.
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Attachment:
File comment: A side view of the cowl peak. It'll make sense when you see how it links to other tubes.
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 Post subject: Re: Exo Hot Rod
PostPosted: July 5, 2016, 9:27 pm 
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Location: Omaha, Nebraska
A few more pictures:

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File comment: Tape will become tubing
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File comment: Here you can see how the roof bars are angled back to the main hoop to make it easier to get in and out of the car.
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File comment: Here you can see where I need to make the mounts for the upper a-arms.
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File comment: Balsa model I made to learn what made things stiffer. It's incomplete in these pictures.
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 Post subject: Re: Exo Hot Rod
PostPosted: July 6, 2016, 8:12 am 
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Howdy Omaha-
Welcome to the forum/nut house!

Interesting build/concept ya got there, Pilgrim... Gonna keep an eye on this one.

Rear radiator has been done by some other folks. You're new here, so I can get away with talking about Mallocks, my favorite car. (Long time members are now rolling their eyes and saying "Here he goes AGAIN..." Ignore them.) In those single seater "Clubman" style cars, the plumbing ran down the passenger side of the frame, usually to the outside. Air was typically fed by a large NACA duct in the bodywork beside the cockpit.

In your design, you could feed air to a rear radiator with side scoops or a roof-top scoop like the McLaren F1 of yore. Or both!

Keep us posted, keep the pictures comin' and good luck!
:cheers:
JDK

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Quinn the Slotus:Ford 302 Powered, Mallock-Inspired, Tube Frame, Hillclimb Special
"Gonzo and friends: Last night must have been quite a night. Camelot moments, mechanical marvels, Rustoleum launches, flying squirrels, fru-fru tea cuppers, V8 envy, Ensure catch cans -- and it wasn't even a full moon." -- SeattleTom


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 Post subject: Re: Exo Hot Rod
PostPosted: July 7, 2016, 11:40 am 
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Thanks, JD.

I've see Mallocks, but I never knew about the rear radiator. I'll look again.

-Omaha

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 Post subject: Re: Exo Hot Rod
PostPosted: July 7, 2016, 2:56 pm 
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Tell me more about your steel spools you're using to attach the subframes. Have you seen it done that way before?

I'm faced with a similar problem on a project for my son in that the attachment points aren't in a single plane and therefore you can't just attach the frame directly. I was thinking a length of tubing with the crush tube inside because I thought I needed a little more support side to side, but if you've seen your system work before then that simplifies my planning.

Oh, good looking build. Can't wait to see how the cowl and windshield work out.

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 Post subject: Re: Exo Hot Rod
PostPosted: July 7, 2016, 7:47 pm 
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Hi Carguy,

The steel spools are 1.75" diameter tubing with .134 wall thickness. Each end is welded to 1/8" steel plate.

Then I drilled out a 1" diameter hole in each end plate, beveled the hole pretty significantly, and put a 1" diameter tube (.083 thickness) through the hole. The crush tube.

Then I welded the crush tube to the end plates, and used the grinder to bring the end of the crush tube level with the plate. The job of the bevel was to leave lots of room for weld once everything was ground flat.

So each end of each of the spools is totally flat, but there is in fact a crush tube welded in.

This is my solution and I've never seen it done before. However, the factory attachment at these points used 1" crush tubes through the frame rails so I copied that. Also, the entire contact area where the subframe met the factory frame rail is being met by the bottom of each spool. The size matches up very nicely.

I hope that clarifies. Let me know if you need more info or pictures.

Best,
Omaha

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 Post subject: Re: Exo Hot Rod
PostPosted: July 7, 2016, 10:06 pm 
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Omaha Vette Graveyard wrote:
I've see Mallocks, but I never knew about the rear radiator. I'll look again.
I should clarify, that's some Mallocks, not all. Look for the big NACA duct beside the cockpit, that's the usual tell-tale.
Attachment:
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The pointed nose gives it away here.
Attachment:
Simon Marsh and His Mallock.JPG
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The "snowplow" nose is another give-away...

See, ya shouldn't have started anything about Mallocks... I just can't help myself sometime... :mrgreen:

:cheers:
JDK

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Quinn the Slotus:Ford 302 Powered, Mallock-Inspired, Tube Frame, Hillclimb Special
"Gonzo and friends: Last night must have been quite a night. Camelot moments, mechanical marvels, Rustoleum launches, flying squirrels, fru-fru tea cuppers, V8 envy, Ensure catch cans -- and it wasn't even a full moon." -- SeattleTom


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 Post subject: Re: Exo Hot Rod
PostPosted: August 11, 2016, 11:49 pm 
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I already made this update once, but the site dropped it as soon as I submitted. Really frustrating. SO, this version will be short and I'll just put up the pictures. That's all anybody really needs anyway. Here we go:

Attachment:
File comment: Added tubes to the top of the engine compartment.
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File comment: These are about to become the insides of the floors. Two parallel bottom trusses. Later they will be linked with bridges. Stay tuned.
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Attachment:
File comment: Fitting. This was tricky.
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File comment: In place, with the help of jack stands and some bungee straps.
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File comment: Still needs final fitting. A little too close at 1/2 inch, I want about 3/4.
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File comment: same here
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Attachment:
File comment: Seat goes about here.
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 Post subject: Re: Exo Hot Rod
PostPosted: August 16, 2016, 10:02 pm 
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Just a quick update, without pictures, unfortunately. All I had time to do this evening was cut and bend tubes. I'm using 1.5" with .104 wall for this spot, though the top tube of the X on the driver's side will be .078 wall. Saves a little weight (only a pound, but it's something) where it's not a bent tube. I like using thicker walled stuff when it has to be bent, both because it helps make up for the weakness inherent in a bend and because the thicker stuff bends so smoothly and perfectly. Sometimes I think about the fact that when all is said and done this chassis will be about 40 pounds heavier than it could have been if the tubing thickness was more optimized, but this is cheaper, easier to weld, has more margin for error, and will be very slightly stiffer. Maybe someday I'll build something more optimized.

I'm working on the front bulkhead, and I've finally found a design I like. The little spot right at the front of the torque tube, where it bolts to the bellhousing, is very important, as it I'm using that location to create not only triangulation of the bulkhead between the engine and passenger compartments, interfacing with the cowl tube and floor structure, but I also need a kind of fore and aft bracing for the floor. I need to keep the left side from trying to slide forward in relationship to the right, or the other way around. Using the same node for both functions should get more chassis stiffness out of it.

I find those places where the tube chassis goes from a series of two-dimensional trusses arranged into a series of three-dimensional boxes to a fundamentally three-dimensional tetrahedral concept very interesting. The two concepts interact in interesting ways.

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 Post subject: Re: Exo Hot Rod
PostPosted: August 19, 2016, 12:41 am 
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Worked on the front bulkhead tonight. It's tough tube fitting, as the tube's I'm adding are bent 40 degrees and the tubes they're coming from and going to are also bent. I had to build a little jig to measure the first side.

Attachment:
File comment: Jig setup with the 'real' tube.
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File comment: curved side
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File comment: straight side
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Then I fitted the real tube for one side.

Attachment:
File comment: Fitted.
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I had enough time to measure angles for the other side, top and bottom, but not enough time to fit them. This is tricky.

Attachment:
File comment: Plumb line to mark the intersection point.
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Attachment:
File comment: Matched that intersection point with tape the same width as the tubing (1.5"). So, I need two 70 degree coping patterns.
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Hopefully I'll have time to finish this job tomorrow.

I generally listen to music while I work in the garage in the evenings. I turn on a CD and tell myself I just need to work until the album is over, though I usually work well past. Most of the first part of this chassis was built listening to Sophie Watillon's Marais, then it was Wolf's Morike Lieder (Dieskau, of course), but for the last few weeks it's been A Love Supreme. It's not my favorite Coltrane album, that would be Giant Steps, but I like it more than I did five years ago. It's probably about time for something new. The Waste Land is not music, per se, but I listen to it in much the same way. I'd love to use that again for a bit, but it's so short and I already know it well. It'll probably end up being Four Quartets. Lines therefrom ring in my head, but I can never finish them. "The wounded surgeon plies the steel that questions the distempered part..."

Time for bed. A love supreme, a love supreme, a love supreme...

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 Post subject: Re: Exo Hot Rod
PostPosted: August 19, 2016, 8:40 am 
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Very cool build! Thanks for sharing. Good build music tunes too. 8)

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 Post subject: Re: Exo Hot Rod
PostPosted: August 19, 2016, 1:18 pm 
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I'm a chassis engineering freak and I am interested in your chassis layout. I like the triangulation over the engine bay, a real soft spot in most cars.
I like to run structural analysis on different chassis (just did an Ar-i-el At-om - very flexible). Would you give me some chassis dimensions to play with? I usually just make a run for torsional stiffness. I usually make a cad file and can send you a copy, along with a printout of your chassis twisted more than you want to see (graphically only).


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 Post subject: Re: Exo Hot Rod
PostPosted: August 19, 2016, 11:28 pm 
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Bobber wrote:
I'm a chassis engineering freak and I am interested in your chassis layout. I like the triangulation over the engine bay, a real soft spot in most cars.
I like to run structural analysis on different chassis (just did an Ar-i-el At-om - very flexible). Would you give me some chassis dimensions to play with? I usually just make a run for torsional stiffness. I usually make a cad file and can send you a copy, along with a printout of your chassis twisted more than you want to see (graphically only).



Bobber,

Sure. Just tell me what dimensions you need.

-Graveyard

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 Post subject: Re: Exo Hot Rod
PostPosted: August 19, 2016, 11:52 pm 
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Got a few more things fitted today, and did some of the welding of seams that will be a little harder to reach once these tubes are in. My welding was pretty out of shape for the first few, as it's been a few months since I last did anything but tack welds. By the end I was pretty much in gear again, and even the un-pretty welds are solid. They're inside seams anyway. I do need a new light, because I have a hard time seeing where I'm going when I'm running a bead.

Attachment:
File comment: First side.
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Attachment:
File comment: Little curved tube added. This one was very difficult to get fitted properly.
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Attachment:
File comment: From the back side.
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Attachment:
File comment: 8 tubes at this node. I plan to have one more.
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I'm going to replace the support tubes that meet the bend where the A-pillars meet the roof. I think one of the weakest parts of this chassis will the tendency to lozenge horizontally in the passenger compartment space. The roof structure (which I must have anyway as part of the cage) should help this somewhat, but all of the rigidity it adds will be delivered through the A-pillars and the support tubes. Switching from a 1.25" support tube to a 1.75" will help me get the most out of the roof structure. The total weight cost is about 2 pounds. I guess it will make the cage just a little bit safer as well, though that's really not part of the consideration as it's quite a bit stronger than it needs to be already.

Attachment:
File comment: My last piece of .095 for this spot. I suppose it will go on the driver's side. The other side will be .120 wall.
IMG_2566.jpg
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Monteverdi Vespers of 1610 today. The antiphonal singing isn't really that when it comes out of a portable CD player, but I can imagine. Must have been incredible in St. Mark's.

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 Post subject: Re: Exo Hot Rod
PostPosted: August 20, 2016, 10:48 am 
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I was going to send you some info but first wanted to say I've seen USB Proctology scopes (seriously) used to inspect welds inside tubes. You can get them cheap (or just ask your doctor if you can bring your frame in).


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