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Rate my build plan (c3 corvette)

23786 Views 80 Replies 10 Participants Last post by  MattsAwesomeStuff
5
Location: San francisco, CA

Budget: Like 15k for the donor car, and hopefully less than 20k for all the conversion parts and any labor costs.

Donor car: 1975 c3 corvette. They're cheap, easy to convert the bumpers back to the wonderful 68-72 chrome bumper design, and have some decent safety equipment upgrades over the early cars. A clean 1975 is like 15k, a clean 1970 is 25k or more, YIKES

also, maybe some race car flair to it, need big rear tires to hold all that torque eh?






Motor: Tesla model S P85 large rear drive unit OR Tesla model 3 performance rear drive unit. The entire tesla rear subframe and all the suspension components, fabricating mounts so it bolts onto the c3 ladder frame. This could be relatively easy or the hardest, most expensive part of the entire project. The motor 3 motor is more efficient when not under heavy load, and FAR FAR better cooling capacity BUT nobody supports their firmware yet and it isn't clear how many years it'll be until the T-1C supports it.




Battery: 34kw of chevy volt batteries. I'd like Gen2 but the Gen1s are half the price and only slightly lower capacity. Some in the engine bay with a battery enclosure to make it look like a V8 because yummy under hood candy, like ICON's derelict mercury EV did. the rest of the batteries go where the gas tank used to be, which may or may not hang lower and thus cause the full size spire tire sling to have to go away. Volt batteries have excellent high performance because of almost no voltage sag. They're also cheap, work very reliably, have a nice log-like form factor, and have built in excellent battery cooling. I'm hoping for 80+ miles of range




Cooling: unsure yet, but the water pump and electrically controller diverter valve out of a tesla. chevy volt batteries and the tesla motors have built in cooling systems so no need to screw around making chill plates.

Controller: EV Controls T-1C, pretty close to turn-key, i'd buy it from EV west specifically so i can lean on them for tech support and general info. This controller's already been used in a few tesla motor/chevy volt battery builds



Contactor: unsure

Power steering: I really want to keep hydraulic power steering, electric pump driven. It's wasteful but it feels so much better than electric power steering. EV West makes a belt fed pump but i'll probably re-use the one that came with the car.

A/C: MVP might omit this since i live in a SF and A/C is kinda unnecessary

Charger: Not sure how to get there, but i absolutely want to shoot for a 50kw charger which interfaces with CCS. With such a short range this feels like a heavy requirement for this to be driveable. There's some noises about CCS charging for DIY builds but this might be a wait and see, hopefully this becomes a mature thing soon (within a year). For 50kw, maybe just stack 5 of those 10kw tesla chargers...?

Safety: Haven't researched much but i would really like switchable fuses between every 72 volts or so, so at any given moment during assembly or maintenance, if i make an oopsie, i only get shocked with 72v before a fuse cuts it. Also, inertial fuses so in a crash, everything is isolated from everything else. Also, a first responder safety line, mimicking tesla's implementation with a BRIGHT RED WIRE right under the hood with a really obvious label on it.



Timeline: purchase the c3 within a few months, spend about a year maintaining it, adding quality of life upgrades, more deeply researching the platform, more deeply researching the feasibility of my componentry and fabrication. HOPEFULLY buy most of the drivetrain bits in advance and make sure the entire thing works on a bench, THEN start converting in fall of 2020 and be done some point before fall of 2021


So, what am i missing, what bad assumptions or assessments am i making, etc
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also, new battery possibility.
for about the same nominal voltage and the same capacity (36kw) i can build this smart EV battery box, which will take up much less space and weigh more like 600lbs instead of 900lbs
https://youtu.be/hp4eyaZzwts?t=154

only problem is, that many smart ev modules is liks $7800, phew
also, revisiting the idea of getting an aftermarket tube chassis, after talking with an expert fabricator about my subrame swap idea. he didn't want to give a quote or estimate but claimed it wouldn't be that difficult, just pretty time consuming to plan out since you can't exactly trial and error this, only got one frame. His wordage was along the lines of "if the client doesn't have 20 to 30 grand to sink into this, they probably shouldn't try".
and even after putting that subframe in, the amount of chassis flex this setup could introduce is pretty high, with the C3's frame being famously flexy and noodly, this would be bad.

enter: tube chassis

http://www.sriiimotorsports.com/196382corvette.html

the advantages being
i get a proper modern rear IRS setup, tons of chassis rigidity i'd otherwise have to weld into a stock c3 frame
extremely good ride/handling balance on par with a modern corvette
you even get more engine bay space for batteries since the front suspension geometry is less bulky.
Importantly, all that rigidity makes the motor mounting itself FAAAR easier, i'd only need some thin steel bits to bolt into the motor casing's mount points.

if you look at the model 3's subframe



the actual parts which hold the motor into the subframe, they're just thin little bits, that's all. That'd be incredibly trivial to model in cad and weld to a good tube chassis, and again because of the massive stiffness in said tube chassis i almost don't have to think about where those mounts go in terms of stressing it. so, that negates basically all the motor mounting hardship

But as previously observed, these things are crazy expensive. A stage two c6 style setup (with shocks/brakes/suspension) is $21,000 :eek::eek:

on the other hand...
There's some forum scuttlebutt which claims a 5 or 6 point roll bar can offer immense improvements in stability for not that much investment, on top of adding frame gussets here and there
Since most of the cost is just planning and engineering, i'd be happy to do a ton of that in cad on my own over some months, modeling stresses and such, and then have a "solved problem" to give to the expert welders who just weld it in. This fabricator fellow even offered to give occasional pointers
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2
I used Solidworks for all the CAD files.


I was (am) going to replace the Pb-acid with Leaf modules and rework the car for racing.

But I needed to get the car to the track and I didn't want an ICE truck... so I decided to convert a tow vehicle.


I chose a 1962 Mack Model B-46.
A lot of photos on Flickr: https://www.flickr.com/photos/emack/albums

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That is one cool truck. Got a thread for that conversion...?
... Importantly, all that rigidity makes the motor mounting itself FAAAR easier, i'd only need some thin steel bits to bolt into the motor casing's mount points.

if you look at the model 3's subframe
...
the actual parts which hold the motor into the subframe, they're just thin little bits, that's all. That'd be incredibly trivial to model in cad and weld to a good tube chassis, and again because of the massive stiffness in said tube chassis i almost don't have to think about where those mounts go in terms of stressing it. so, that negates basically all the motor mounting hardship
Yes, the drive unit mounts are relatively thin stamped plates, but they are strong in the vertical direction. Vertical is the important direction because the weight of the drive unit and reaction to axle torque are all vertical forces (although there is horizontal force in proportion to the drive unit mass and acceleration). These are not trivial forces, so mount design and placement of the mounts on the frame are important.

These mounts are easier than mounts for the subframe or direct mounts for suspension components, which take high forces in all directions.

There's some forum scuttlebutt which claims a 5 or 6 point roll bar can offer immense improvements in stability for not that much investment, on top of adding frame gussets here and there...
That makes sense. The flexibility of the stock frame results from the whole frame being in nearly one plane; the cage makes it into a big and much more sound box. Even in a unibody adding a cage can make a noticeable difference in flex and handling.
I used Solidworks for all the CAD files.
are those cad files available to share? like on grabcad or something?



I was (am) going to replace the Pb-acid with Leaf modules and rework the car for racing.
good, although, might want to make some chill plates, those leaf batteries don't last too long without em

However did you need to do some stuff to counter the c3's floppiness? or did you leave that alone and its fine?
if your build is upwards of 600 ft lbs of torque with no bad effects on frame flex, i'm far less worried
When you are talking chassis design you can use CAD

Or you can get old school and make yourself a decent build table and just make the chassis to go between the mounting points of the subframes (easy) or suspension (bit more difficult

Cut the steel to fit and if you are not sure of your welding tack it together and get the expert to finish the welds
When you are talking chassis design you can use CAD

Or you can get old school and make yourself a decent build table and just make the chassis to go between the mounting points of the subframes (easy) or suspension (bit more difficult

Cut the steel to fit and if you are not sure of your welding tack it together and get the expert to finish the welds
i'm thinking of cadding up some square-ish mount adapters, i'm not sure how best to describe their shape and can't find any examples online, so i threw something together in tinkercad.
imagine this shape but made of four thick pieces of steel intersecting and welding together into the boxy shape
of course, the danger with this approach is cadding something that won't actually fit in the real world due to reasons.

If i could, i'd rent one of those 3d scanner things, take all the rear suspension off a c3, put the entire rear assembly from an S under the suspended c3 and line everything up then do a detailed 3d scan of the gap between the two pieces and use THAT to cad up a beefy interface mount

cost effective hand held 3d scanner rentals when :(

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I was thinking the same shit for fabbing up motor mounts for my awkward Mini subframe...
i'm thinking of cadding up some square-ish mount adapters...
imagine this shape but made of four thick pieces of steel intersecting and welding together into the boxy shape
The subframe mounts are so close to the frame members that this simple approach looks like it would be suitable. But why does the mount box extend to the structure of the subframe, instead of ending level with the face of the block in the middle of the mount? Or have I misinterpreted the image?
also, new battery possibility.
for about the same nominal voltage and the same capacity (36kw) i can build this smart EV battery box, which will take up much less space and weigh more like 600lbs instead of 900lbs
https://youtu.be/hp4eyaZzwts?t=154

only problem is, that many smart ev modules is liks $7800, phew
Since those are Tesla modules for the Smart (each generation of Smart ForTwo ED seems to use a different battery supplier), these would presumably have the same performance (per weight or volume) as the more common Tesla Model S/X modules; both are filled with Panasonic 18650 cells.

I understand that the point of this selection to get a module with fewer cells in parallel (22p15s versus 74p6s), so the target pack voltage is reached with a lower total pack mass and bulk. It would take only 6 of the smaller Smart modules (totalling only 252 pounds of modules) to get 90s, but that wouldn't handle enough power, so modules need to be paralleled to be adequate and the result is a 504 pound (plus structure and housing) 44p90s pack, as in the video. You end up with lots of modules, and only 200 amp output capacity.
I just posted some CAD models (Solidworks) of the frame on Grabcad.
I just posted some CAD models (Solidworks) of the frame on Grabcad.
https://grabcad.com/library/c3-corvette-frame-1

nice, thank you
did you super dupe validate all the measurements, or is this more of a rough model to get an idea
Just FYI: https://www.diyelectriccar.com/forums/showthread.php?p=1047545

You two should watch each other's threads. You're solving the same problems on the same vehicle.
Hi,

I was wondering if I could be part of your build. I'm also in the San Francisco area. I tried private messaging you. Let me know.
There's some weird rule about not being able to send or receive PMs until you have a certain number of posts, I think.
Hi,

I was wondering if I could be part of your build. I'm also in the San Francisco area. I tried private messaging you. Let me know.
got your pm and your email, replied to said email
some days i feel like that always sunny conspiracy meme but, with c3 corvette suspension geometry

ok so, hold up, listen
what if
listen guys
what if i took the detroitspeed decalink rear kit.....

https://youtube.com/watch?v=-_QvhXUyqSc

https://www.detroitspeed.com/detroi...remote-shocks-30-spline-axles-600hp-041741-dr

https://www.facebook.com/detroitspe...803914911813/2117803784911826/?type=3&theater

https://www.chevyhardcore.com/news/...orvettes-handling-with-detroit-speed-part-ii/

...and threw in some thick cut steel motor mount fingers on the frame/decalink to fit the model 3's diff opening where the decalink half shafts go? Since the decalink kit completely removes the diff as a suspension member, no more weird forces on the model 3 motor.

also the model 3 motor is already in the configuration i need (ass-first) so it'll fit in the gap where the diff was. Might need to cut some of the body but that's whatever at this point.

cheaper than the $17500 for a replacement frame, will perform about as well, and simplifies motor mounting decently, no more subframe mount design
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Finally purchased a car, a 1971 in black.
Fully restored, and heavily modified by the previous owner with all kinds of upgrades.
I'll make a new thread for it though
current status: sitting in garage, looking at $1800 to register it due to use tax
also needs new tires, i got three but trying to find a very lightly used 235/45/18 pilot sprt 4s is proving difficult (new ones are $238 a piece, yikes)
it also needs some engine work to be daily driveable, probably just minor adjustments to the distributor etc.

also held up by costs and garage space, I'm getting 16k later in the summer, and 5k whenever i sell my miata, and at that point i'll start buying parts (yay)

but man, i could really use a two car garage to have work bench space and work space!
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