[brian_]

I now think I can make a 4 module pack and use it 4 places. this would give the possibility of 16 modules although i do not think I would want to go the full 16 route. It occurs to me that if each pack had the final voltage, then theoretically I could build with one pack, then add a second, third and even a fourth later? Is this a good approach?

You can do that, and some builders essentially do that with sets of battery modules from plug-in hybrids (such as the Chevrolet Volt and Chrysler Pacifica Hybrid), because each set only holds about 16 kWh. Each set (or "string") runs at the desired overall battery voltage, and the sets are connected in parallel. This is valid whether the sets are packaged as separate packs, or all in one box.

The issues with parallel packs are that each one needs a complete BMS, and they will never quite equally share current (either when discharging or when charging). These can be manageable, but they are why production EVs don't use parallel sets of modules.

Although people talk about starting with one set and adding more later, I haven't noticed anyone actually doing it... which doesn't mean that it wouldn't work.

This is assuming Tesla S batteries and a Tesla LDU.

But Tesla modules are not small; if you string 16 of them together you get the full 350 volts. There is a somewhat dicey modification to change a Model S module from 6S to 12S (with of course half as many cells in parallel), but for a set of four modules to have the 96S configuration required to give the full 350 volts, each one would need to be reconfigured to 24S, and there's no reasonable way to do that.

 

[remy_martian]

If it doesn't to some degree, then this is a fake pic:

You can see one of the two chassis torsion-reaction mounts behind the CV joint at the spring mounting point.

You'll also notice the engine is not falling over...it too is mounted on the same crossmember as the front spring.

 

[428RC]

If it doesn't to some degree, then this is a fake pic:
View attachment 126850

You can see one of the two chassis torsion-reaction mounts behind the CV joint at the spring mounting point.

You'll also notice the engine is not falling over...it too is mounted on the same crossmember as the front spring.

AHHH, I see that now. that makes more sense.

 

[428RC]

I already mentioned it. Adding a properly triangulated roll cage when the body gets put on will increase the torsional stiffness.

It also could put the "rockers" in tension to where you might do some tube removal and get four Tesla modules under the floor. Break out your FBD's to work that one out.

If you're just doing tire burnouts and not going animal in the twisties, it won't matter if you have a floppy-noodle chassis. Pulling the torque tube will make it worse, I think. All depends if you want a muscle car, or a sports car in more than appearance.

For roadholding, the chassis mount for the suspension is ideally supposed to be fixed in horizontally moving cartesian coordinates, not moving up and down. This is why unsprung weight is such a big deal.

The C5 was brilliant and revolutionary in this aspect. I mentioned how they did it with the closed tunnel, roof (that was a reason the FRC became the Z06), and shear plates. No doubt, your chassis' designers anticipated a roll cage for competition use. It may look ugly in a classic, so you ultimately decide if you want show or go.

For me, the C5 is go (Z06 was the first car to do 1g on the skidpad for under $100,000...it did it for half that) or why bother?

I've beaten this to death, so consider me done with commenting on your wet noodle 🤓

edit: I came up with 12 Tesla modules as the magic number for weight and fit under the C5 hood, with 2 displacing gas tank weight in the back. Availability of electronics components has me pushing and pulling everything - frustrating AF.

I am not 100% following you here, can you sketch something?

as far as how I will drive, its not an autocrosser or a drag car, just normal get into it on paved roads every once in a while type of driving

What if I cannot triangulate like a roof would, where would you strengthen the frame in that case. even a flat plate will not bend if it is strong enough right, if this was a 2 " thick steel plate then no torque in the auto world would flex that.

 

[428RC]

this is the 4 x 4 battery concept, with the LDU, driver and passenger it seems like this would be pretty good, keeping the weight as low as possible and trying to get 50/50 distribution, the 3 cross areas would help tie the frame sides together around the battery packs

 

[brian_]

AHHH, I see that now. that makes more sense.

The display stunt with the C5 powertrain and fragments of the chassis is like the Tesla Model S display pieces, or the similar set of components from a Mazda Miata/MX-5: none of them are structurally sound or driveable, but if you bracket together some bits are that not actually connected in the real car, you can make it stay up for display (and even to roll it around). For example, the suspension spring-shock units of the Tesla and Mazda hold up the (missing) body, not the subrames, and the C5 upper control arms and shocks are attached to the (missing) frame rails, not to the subframes (which is why the they're just flopping around unattached in the photo).

This set of Miata components looks almost as much like a backbone chassis as the similar set of C5 components... but it's not, just as the C5 example is not:

Notice that the springs are not holding anything up, and there is a floor jack under the back which is holding it up. That webbed bit in the middle is the Power Plant Frame.

 

[428RC]

You can do that, and some builders essentially do that with sets of battery modules from plug-in hybrids (such as the Chevrolet Volt and Chrysler Pacifica Hybrid), because each set only holds about 16 kWh. Each set (or "string") runs at the desired overall battery voltage, and the sets are connected in parallel. This is valid whether the sets are packaged as separate packs, or all in one box.

The issues with parallel packs are that each one needs a complete BMS, and they will never quite equally share current (either when discharging or when charging). These can be manageable, but they are why production EVs don't use parallel sets of modules.

Although people talk about starting with one set and adding more later, I haven't noticed anyone actually doing it... which doesn't mean that it wouldn't work.


But Tesla modules are not small; if you string 16 of them together you get the full 350 volts. There is a somewhat dicey modification to change a Model S module from 6S to 12S (with of course half as many cells in parallel), but for a set of four modules to have the 96S configuration required to give the full 350 volts, each one would need to be reconfigured to 24S, and there's no reasonable way to do that.

I am sorry, I have not had a chance yet to study the battery side of this. I was thinking that if I could reduce the initial cost and start with 4 batteries then add later as things are worked out. range is not an immediate priority, but I also do not want to make crazy battery mods. So If I understand, to use 4, then that means major mods, and then adding others means they would be in parallel which is bad. In the end I need to chose the number I need for the correct voltage and capacity and build that. It would be nice if I could do 8 then 8, but that would end with 2 8's in parallel again... Ok, so best to either plan for 16 ( I think the S has 16) or fix the number and build that. thanx

 

[remy_martian]

The display stunt with the C5 powertrain and fragments of the chassis is like the Tesla Model S display pieces, or the similar set of components from a Mazda Miata/MX-5: none of them are structurally sound or driveable, but if you bracket together some bits are that not actually connected in the real car, you can make it stay up for display (and even to roll it around). For example, the suspension spring-shock units of the Tesla and Mazda hold up the (missing) body, not the subrames, and the C5 upper control arms and shocks are attached to the (missing) frame rails, not to the subframes (which is why the they're just flopping around unattached in the photo).

This set of Miata components looks almost as much like a backbone chassis as the similar set of C5 components... but it's not, just as the C5 example is not:

Notice that the springs are not holding anything up, and there is a floor jack under the back which is holding it up. That webbed bit in the middle is the Power Plant Frame.

It's not a display stunt. The upper control arms and shocks are not connected, but the C5 has transverse leaf springs that are loaded and holding a ride height, unlike your stunt photo with the jacks. The C5 suspends the drivetrain and the crossmembers via the lower ball joints and lower control arms attached to the crossmember and on the wide tires.

No jacks, no brackets...you pull a C5 apart like this and it will stand, as shown in that pic. You'd be challenged to kick the tires over from vertical.

And, to my point, that torque tube will react through the engine mounts and the very stiff rear diff mounts, not the front center diff mount that was originally shown here that serves to react to axle torque, to chassis twist of the front and rear crossmembers relative to each other. Both crossmembers being attached to the suspension.

 

[remy_martian]

I am sorry, I have not had a chance yet to study the battery side of this. I was thinking that if I could reduce the initial cost and start with 4 batteries then add later as things are worked out. range is not an immediate priority, but I also do not want to make crazy battery mods. So If I understand, to use 4, then that means major mods, and then adding others means they would be in parallel which is bad. In the end I need to chose the number I need for the correct voltage and capacity and build that. It would be nice if I could do 8 then 8, but that would end with 2 8's in parallel again... Ok, so best to either plan for 16 ( I think the S has 16) or fix the number and build that. thanx

You can get a dozen Tesla modules in place of the engine for about the same weight. Add two more elsewhere, ideally behind the driver longitudinal position for balance, and you're done.

 

[brian_]

... I was thinking that if I could reduce the initial cost and start with 4 batteries then add later as things are worked out. range is not an immediate priority, but I also do not want to make crazy battery mods. So If I understand, to use 4, then that means major mods, and then adding others means they would be in parallel which is bad. In the end I need to chose the number I need for the correct voltage and capacity and build that. It would be nice if I could do 8 then 8, but that would end with 2 8's in parallel again... Ok, so best to either plan for 16 ( I think the S has 16) or fix the number and build that.

Right... and the number of 22 volt Model S/X modules is 14 or 16, depending on variant, and is 16 for full performance of the drive unit.

You could start with 8 modified (12S) modules - if anyone is still doing that modification - then replace (not supplement) them with 16 unmodified modules later (for the same 350 V but twice the energy capacity and power capability), but that seems like a lot of effort and expense just to delay part of the battery purchase.

 

[remy_martian]

I am not 100% following you here, can you sketch something?

as far as how I will drive, its not an autocrosser or a drag car, just normal get into it on paved roads every once in a while type of driving

What if I cannot triangulate like a roof would, where would you strengthen the frame in that case. even a flat plate will not bend if it is strong enough right, if this was a 2 " thick steel plate then no torque in the auto world would flex that.

Orville Wright supposedly was twisting a bicycle inner tube box to come up with "wing warping". Roadholding is the reason for torsional stiffness, not occupant protection you are envisioning in autocrossers and drag cars. You can take a 4x10 sheet of 1/2 inch steel plate and it'll twist.

The "4x4" frame drawing you have shown needs to be coupled into the A and B pillars and trans tunnel of the body to resist twist, which could crack it from suspension loads....iirc, the '62 used an X-frame layout?

There's no easy answer here - engineering is all about tradeoffs and optimization for a constrained problem set. If you don't care about road holding, what you have may work.

One good pothole could write off the fiberglass-bodied car, though, especially with you having redistributed the front suspension mass along the full length of the car.

Provoking thinking here. You're The Decider.

 

[428RC]

Orville Wright supposedly was twisting a bicycle inner tube box to come up with "wing warping". Roadholding is the reason for torsional stiffness, not occupant protection you are envisioning in autocrossers and drag cars. You can take a 4x10 sheet of 1/2 inch steel plate and it'll twist.

The "4x4" frame drawing you have shown needs to be coupled into the A and B pillars and trans tunnel of the body to resist twist, which could crack it from suspension loads....iirc, the '62 used an X-frame layout?

There's no easy answer here - engineering is all about tradeoffs and optimization for a constrained problem set. If you don't care about road holding, what you have may work.

One good pothole could write off the fiberglass-bodied car, though, especially with you having redistributed the front suspension mass along the full length of the car.

Provoking thinking here. You're The Decider.

Right... and the number of 22 volt Model S/X modules is 14 or 16, depending on variant, and is 16 for full performance of the drive unit.

You could start with 8 modified (12S) modules - if anyone is still doing that modification - then replace (not supplement) them with 16 unmodified modules later (for the same 350 V but twice the energy capacity and power capability), but that seems like a lot of effort and expense just to delay part of the battery purchase.

thanx. I guess I need to keep working on battery layout and capacity. I imagine even 14 modules will yield more capacity than I need. What is the next logical step down in QTY to get the correct voltage for the tesla LDU, and work from there for a layout. i was able to crawl under the frame to verify the height of the frames under the floor and it will only support one thickness of battery, so that and Remy's structure concerns may be pushing me to no batteries under the floor after all. It does allow some more welded in support for the under floor area, as well as maybe adding back a spine in the trans tunnel, so I think its progress.

 

[57Chevy]

The best use of the Tesla battery imo is selling it to someone else for a powerwall and using the funds to buy something more suited to your application. There is so much out there and new ones coming available regularly that I'm just making a black box where the engine was and leaving the contents until I'm ready to make that decision, rather than trying to retrofit existing gear in.

Multiple batteries spread apart are more difficult as you need a way to isolate each one for maintenance. If you can keep it all in one block with the contactors etc then it'll make for a simpler installation

 

[428RC]

The best use of the Tesla battery imo is selling it to someone else for a powerwall and using the funds to buy something more suited to your application. There is so much out there and new ones coming available regularly that I'm just making a black box where the engine was and leaving the contents until I'm ready to make that decision, rather than trying to retrofit existing gear in.

Multiple batteries spread apart are more difficult as you need a way to isolate each one for maintenance. If you can keep it all in one block with the contactors etc then it'll make for a simpler installation

thanx, that makes sense. I am not seeing any deals on wrecked Teslas. If this takes 2-3 years there may be a new tech that makes the currents cells cheaper anyway. its just hard for me to plan an empty black box A big box is getting in the way of my steering rack right now, so I have a lot of work to do.....

 

[remy_martian]

Yes...that pesky steering rack and shaft.

As long as the solar and grid storage crowd keeps their valuation relative to lead acid, we're pretty much screwed on battery pricing, imo

 

[brian_]

... A big box is getting in the way of my steering rack right now, so I have a lot of work to do.....

Yes, there's a reason that the classic front-engine high performance car layout, in which the engine occupies space from roughly the axle line rearward, has the steering rack in front of the axle line ("front steer"); transverse-engine cars, with the engine ahead of the axle line, have the rack behind the axle line ("rear steer"). Some vehicles have really interesting rack positions to work around the powertrain - check out Citroen's Rube Goldberg style system in the DS for amusement.

The steering column is another challenge, typically not causing any conflict with the engine in a rear-steer configuration, but likely to be a problem for any large underhood battery pack.

The C1 is rear-steer (and with a traditional box and links, not rack and pinion); the SRIII chassis converts it to the C5's front-steer, making the steering column longer, although that also allows the battery box to drop lower behind the axle line.

 

[brian_]

2. I see that there are many large DC and AC motors like a warp9, warp11, warp13. I could either attach this directly to the front of the differential or to the front of the 6sp transmission, however the best fit by far would be to eliminate the transmission.

... trying to add a reducer to the C5 diff, or keeping the 6spd seems counter productive...

If you use a separate motor (instead of a complete drive unit) with the original final drive, you could possibly get the advantage of retaining the Corvette's original electronically controlled limited slip differential... although that would be an electronic control system management challenge.

I ran across an adapter which is intended to allow a drive shaft to connect to the input of the C5 final drive, without the transmission:
Corvette Differential Driveshaft Adapters

It appears to be a bearing carrier which also closes off the front end of the final drive housing, and a pinion shaft replacing the stock shaft.

This could be used (with a more appropriate coupler instead of the U-joint yoke) to couple the final drive closely (with a housing adapter) to a motor, or to a reduction gearbox and motor. That would certainly fit in the chassis, although a complete EV drive unit (such as the various Tesla units discussed) would be a more straightforward choice if it fits.

If using the C5 final drive, there is a limited choice of ring-and-pinion ratios; the motor speed and any added reduction gearing need to work with what is available. From the factory that was probably only 2.73:1 (base automatic), 3.15:1 (optional auto), or 3:42:1 (manual or optional auto). Of course C6 or C7 parts might interchange (I think they're all similar but not all interchangeable) and might have different ratios, and in the aftermarket there are a few more choices, including 3.73:1, 3.90:1, and 4.10:1.

 

[428RC]

I ran across an adapter which is intended to allow a drive shaft to connect to the input of the C5 final drive, without the transmission:
Corvette Differential Driveshaft Adapters

It appears to be a bearing carrier which also closes off the front end of the final drive housing, and a pinion shaft replacing the stock shaft.

This could be used (with a more appropriate coupler instead of the U-joint yoke) to couple the final drive closely (with a housing adapter) to a motor, or to a reduction gearbox and motor. That would certainly fit in the chassis, although a complete EV drive unit (such as the various Tesla units discussed) would be a more straightforward choice if it fits.

If using the C5 final drive, there is very little choice of ring-and-pinion ratios; the motor speed and any added reduction gearing need to work with what is available. From the factory that was probably only 2.73:1 (base automatic), 3.15:1 (optional auto), or 3:42:1 (manual or optional auto). Of course C6 or C7 parts might interchange (I think they're all similar but not all interchangeable) and might have different ratios, and in the aftermarket there are a few more choices, including 3.73:1, 3.90:1, and 4.10:1.

thanx yeah, I was thinking this at first, but after the initial round of answers, one of which was the need to add gearing before the differential, I think the LDU is an easier solution. Part of this thought process was to take the planetary gear set from a 4wd transfer case and make a box for it bolted where the above plate would be. But sourcing splined shafts and being responsible for strength and hardening makes this too much effort.

my effort now is to start laying it out and to get my block diagram populated, then split off the blocks to detail each with how and what. A lot of planning left .

 

[remy_martian]

Wild thought, looking at your CAD drawing....hard mount a 2 module metal Battery box between the LDU and rear face of the torque tube, which is about the horizonal CG of the two gas tanks in a C5 (same weight as a full tank of gas as well). Bolt that "bellhousing" face to the box. Hard mount the front steel battery box of 12 modules, also attach the face of the torque tube to it.

You can thicken up the torque tube with weldments if needed.

I may do this to my C5. Thanks for the view I never had 🤓

Edit: you're going to have to source custom axles for the LDU, so six of one, half dozen of the other. Unless Brian can ferret out C5 axles for an LDU 😂

 

[brian_]

thanx yeah, I was thinking this at first, but after the initial round of answers, one of which was the need to add gearing before the differential, I think the LDU is an easier solution. Part of this thought process was to take the planetary gear set from a 4wd transfer case and make a box for it bolted where the above plate would be. But sourcing splined shafts and being responsible for strength and hardening makes this too much effort.

That makes sense. If you go back to that - perhaps by buying a customized unit from a commercial supplier of reduction boxes like this - just be careful with bearing and seals, since the highest input speed from an electric motor is likely to well above the intended operating speed range. Torque Trends makes these units for both EV applications and as underdrives in engine-driven vehicles, and they use a different input bearing for the EV version to handle the higher speed.