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Discussion Starter · #21 ·
thanx, I am looking at the AEM and that looks reasonable. is there an EV block diagram posted somewhere? It seems there are a lot of small components to support the power and control and it would be nice to have a graphic of the parts and connections.

the LDU posted 3D files I have found are from a scan and have some surface knitting issues. I am trying to heal them but for now 3D printing is not possible as it is group of zero thickness surfaces. If I can get it converted to a solid then I might be able to section and print it in my printer. the 3D looks good for virtual fitting though, so I may be modelling my chassis rear suspension as it is more straight forward.

the scanner is too much for me to spend. maybe I can find one used or lease one for a week or two if I get to that need. We have a scanner at work and the results have never been that great, but that is with small very detailed parts, maybe large parts are easier.

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Discussion Starter · #22 ·
this is a beginning of a rough block diagram as an illustration of my lack of knowledge :). I would be greatly appreciative if anyone can please list any and all components you can think of so I can add them to my poorly populated diagram.

thanx

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A reminder: this is a C5 powertrain (to be converted) and C5 suspension under a C1 body, with an aftermarket frame.

tube chassis, torque tube is moot...
The torque tube takes the reaction torque between the engine and the transmission; the frame isn't exposed to any drivetrain torque around the tube axis, which is longitudinal. It would be appropriate to retain the torque tube or an equivalent in any conversion approach which places the electric motor where the engine was... but that's not the current plan.

The other torque to consider is reaction to the axles. In the C5 design, the torque tube acts as a beam or lever, pushing down at the final rear end (final drive housing) and up at the front (engine mounts), in both cases essentially at the suspension, so the vehicle structure doesn't have to handle this. With any powertrain configuration that is packaged only at the rear (salvaged EV drive unit, motor directly attached to final drive or transaxle) the reaction is taken through the much more closely spaced front and rear mounts of the drive unit; the aftermarket frame is not designed for that, but it's no worse than with the original frame. Some care would be required in the design of the drive unit mounts to the frame.

Up front, the original frame would have mounted the engine and transmission assembly at the motor mounts (on each side of the engine) and a transmission mount (at the tail housing); the aftermarket frame has the motor mounts, but not the transmission mount because the torque tube is acting as a beam to support the back of the engine. The logical location for a battery pack is in place of the engine, as indicated in post #2; a pack there would presumably be supported by the motor mounts, but would also need a rear mount. Again, this will put bending load on the frame that was not intended, but would likely be acceptable with a suitable mounting bracket design.

The frame-bending part of this situation is similar to the many conversions of the Mazda MX-5/Miata to other engines (commonly GM "LS" V8s): the Mazda has a Powerplant Frame which bridges the transmission to the final drive (but doesn't take any significant torque), and the conversions usually omit this, requiring the body to support a transmission mount and the rear subframe to support the front of the final drive and thus to take axle torque. Even with 400 horsepower V8's in this light compact car structure, this seems to work. :)


Regardless of the powertrain configuration, the vehicle structure - the frame in a Corvette - has to handle torsion due to suspension loading. The aftermarket tubular steel frame is likely somewhat better than the original C1 frame in this respect, although it's still just a flat platform, but that isn't directly relevant to EV conversion. It does suggest that massively increasing performance while retaining the platform configuration isn't a great idea, but the aftermarket frame supplier apparently finds it adequate for the far greater power and traction of the C5 powertrain and chassis (compared to any real C1), so an EV conversion is unlikely to be any worse.

Overall, the aftermarket frame is greatly inferior to a stock C5 structure, because it is limited to fitting under the C1 body, but it should still handle the conversion, just as stock early (pre-C4) frames have handled other conversions.
 

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this is a beginning of a rough block diagram as an illustration of my lack of knowledge :). I would be greatly appreciative if anyone can please list any and all components you can think of so I can add them to my poorly populated diagram.

thanx

View attachment 126804
  • Unless your trips are limited to the endurance of the 12 V battery and you charge it when you charge the main battery (not kidding, some people do this), you need a DC-to-DC converter between the traction (drive) battery and the 12 V battery.
  • Depending on your system modelling approach, you may want to show multiple battery modules.
  • Once you show the battery modules you have started detailing what is inside the traction (drive) battery system, and that need to include overcurrent protection (one or more fuses) and a disconnect provision (contactors).
  • In the area of control devices (or "human interface" if you prefer that), you have the accelerator pedal but you also need a directional (forward/reverse) selector, probably with a "neutral" (electrically, not mechanically) selection. If you use a non-Tesla drive unit with a parking pawl, you'll probably want to select that as well.
  • If you want to DC (fast) charge, you need the device which manages connection between the external equipment (EVSE) and the battery - this does not go through the charger.
 

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Since you are considering the old Tesla Model S / Model X induction motor drive units, you might also consider the Tesla Model 3 rear drive unit, as I mentioned at the beginning of this thread. The Model 3 drive unit can be controlled with a VCU in the same way that the earlier LDU and SDU are. tiger82 switched his Cobra-style race car from an LDU to the Model 3 drive unit. Model 3 drive unit 3D models are available in the GrabCAD library; the one from Matt Brown shows it in the Model 3 rear subframe and suspension - you would presumably not use that subframe but it provides context for the drive unit mounting.
 

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... how many Tesla battery modules would be needed for say 150 miles range with the Tesla large drive unit?
There's no need to tie the choice of specific battery modules to the choice of drive unit, although depending on your other choices it may make the electronic controls easier.

The real requirements are for energy, power, and voltage, constrained by mass and packaging restrictions. In the Tesla Model S/X case, all versions until recently used externally identical 6S (22 V nominal) modules. For early Tesla Model S performance, 14 modules in series (for about 308 V) as in the those cars are sufficient; for later Model S performance, all 16 modules (again in series, for 350 V) would be required. If using other modules, the voltage requirement remains and you would need enough energy for the desired range and enough power capability for the desired performance.

here is a quick sketch using a view from SRIII webpage. this is the chassis I have.

View attachment 126794
This shows the majority of the battery volume in the area of the original engine, which makes sense.

... the batteries will be under the floor. I do not plan to use 16 packs but it remains to be worked out.
The illustration indicates some battery under the floor, apparently stuffed into the spaces between tubes which are currently empty or occupied by the exhaust system. The problem is that most EV battery modules are too large to fit in those spaces, and the Tesla Model S/X modules in particular are very wide and long. Realistically, I don't think any battery modules will fit there, at least without some significant re-working of the structure, although this frame for the C1 has more room than with the lower floor of later Corvette generations.

Terminology note: a component part of an EV battery consisting of several cells which are handled as an assembled unit and combined with others is normally called a "module". "Pack" usually refers to one or more modules with supporting devices (e.g. contactors and fuses) in a housing. The entire battery of any production EV car is a single pack (although conversions may be forced to split the battery into front and rear packs to fit enough in); among production vehicles only heavy commercial trucks and buses have batteries so large that they are built as multiple packs.
 

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Discussion Starter · #27 ·
A reminder: this is a C5 powertrain (to be converted) and C5 suspension under a C1 body, with an aftermarket frame.


The torque tube takes the reaction torque between the engine and the transmission; the frame isn't exposed to any drivetrain torque around the tube axis, which is longitudinal. It would be appropriate to retain the torque tube or an equivalent in any conversion approach which places the electric motor where the engine was... but that's not the current plan.

The other torque to consider is reaction to the axles. In the C5 design, the torque tube acts as a beam or lever, pushing down at the final rear end (final drive housing) and up at the front (engine mounts), in both cases essentially at the suspension, so the vehicle structure doesn't have to handle this. With any powertrain configuration that is packaged only at the rear (salvaged EV drive unit, motor directly attached to final drive or transaxle) the reaction is taken through the much more closely spaced front and rear mounts of the drive unit; the aftermarket frame is not designed for that, but it's no worse than with the original frame. Some care would be required in the design of the drive unit mounts to the frame.

Up front, the original frame would have mounted the engine and transmission assembly at the motor mounts (on each side of the engine) and a transmission mount (at the tail housing); the aftermarket frame has the motor mounts, but not the transmission mount because the torque tube is acting as a beam to support the back of the engine. The logical location for a battery pack is in place of the engine, as indicated in post #2; a pack there would presumably be supported by the motor mounts, but would also need a rear mount. Again, this will put bending load on the frame that was not intended, but would likely be acceptable with a suitable mounting bracket design.

The frame-bending part of this situation is similar to the many conversions of the Mazda MX-5/Miata to other engines (commonly GM "LS" V8s): the Mazda has a Powerplant Frame which bridges the transmission to the final drive (but doesn't take any significant torque), and the conversions usually omit this, requiring the body to support a transmission mount and the rear subframe to support the front of the final drive and thus to take axle torque. Even with 400 horsepower V8's in this light compact car structure, this seems to work. :)


Regardless of the powertrain configuration, the vehicle structure - the frame in a Corvette - has to handle torsion due to suspension loading. The aftermarket tubular steel frame is likely somewhat better than the original C1 frame in this respect, although it's still just a flat platform, but that isn't directly relevant to EV conversion. It does suggest that massively increasing performance while retaining the platform configuration isn't a great idea, but the aftermarket frame supplier apparently finds it adequate for the far greater power and traction of the C5 powertrain and chassis (compared to any real C1), so an EV conversion is unlikely to be any worse.

Overall, the aftermarket frame is greatly inferior to a stock C5 structure, because it is limited to fitting under the C1 body, but it should still handle the conversion, just as stock early (pre-C4) frames have handled other conversions.

thanx for your input, this is the way to discuss :)

the C5 is also open on the top, it looks like the same flat plane, I agree the torque tube is to keep the motor and diff from twisting the frame like a biscuit tube :). with rubber mounts on both ends, I am skeptical it added much more than that. since the motor is now in the back, I believe it is moot for my car.

the SRIII frame has main support members with 3 tubes run parallel along the sides and then spreading wider as they go up over the rear axle and similarly in the front. this increases the frame sectional boundaries and I think makes it stronger than the mass produced rectangular tubes. the front and rear both have aluminum cradles.these are substantial and I think they add a lot of "racking" prevention as well. left and right is connected with removable aluminum members that are under the torque tube. The same frame design is available to guys who opt out of the torque tube by putting a pinion adapter on the C5 rear differential and moving the transmission up to the back of the motor, so the design is already proved for that implementation. I am happy with the design.

However, I am considering cutting out the entire center section of the frame leaving the outer triangular rails, then I will design the battery box with that structure in it to replace the center portion of the frame. I haven't modeled it yet, but in my minds' eye I think the top portion of the frame center section may stay and the battery box will double that and replace the lower portion. This is all contingent on the battery selection and number of batteries. If I can work out a way to compartmentalize the batteries I could leave the center structure welded in, if it needs to be one large box than I will figure that out a different way. Since there is no longer a driveline to work around, i am sure more cross bracing will find it way in the design.

if the LDU is used, the whole rear structure will need to be addressed to handle that torque. It is all conjecture until I chosse, the model 3 is an option, I will see if I can import that model as well. I think it might fit, but there is a lot of frame in the area around the current 6spd so the width will be the key.
 

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Discussion Starter · #28 ·
  • Unless your trips are limited to the endurance of the 12 V battery and you charge it when you charge the main battery (not kidding, some people do this), you need a DC-to-DC converter between the traction (drive) battery and the 12 V battery.
  • Depending on your system modelling approach, you may want to show multiple battery modules.
  • Once you show the battery modules you have started detailing what is inside the traction (drive) battery system, and that need to include overcurrent protection (one or more fuses) and a disconnect provision (contactors).
  • In the area of control devices (or "human interface" if you prefer that), you have the accelerator pedal but you also need a directional (forward/reverse) selector, probably with a "neutral" (electrically, not mechanically) selection. If you use a non-Tesla drive unit with a parking pawl, you'll probably want to select that as well.
  • If you want to DC (fast) charge, you need the device which manages connection between the external equipment (EVSE) and the battery - this does not go through the charger.
thanx, I will adjust my diagram. :)
 

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the LDU posted 3D files I have found are from a scan and have some surface knitting issues
Sorry yes, I forgot about that. I'll have a play and see if I can get it watertight. Recently did a traditional wood carving that is over a hundred years old and it had about 30,000 non manifold faces and ended up printable so has to be possible.
We have a scanner at work and the results have never been that great
The results are never great, they are more "death stars" with large ragged edges of the bits that didn't scan. I just clean up a little and align the planes to something sensible and drop them in the cad. It uses up ram like crazy but that's about all.

For your layout you'll need contactors, one in the 0V rail and one in the HV rail for redundancy plus a fuse. Contactors microweld closed as a common failure mode (beat with a hammer to fix) and so the second one in the 0V line is there to handle this situation. You'll need an insulation resistance monitoring device too which ensures no HV connection to the frame. The MCU is likely redundant as that is the logic board inside the LDU, the VCU provides the higher level stuff, at least with AEM anyway. Getting wheel speed into it is fairly basic presently, I don't think it can take ABS CAN data yet. Hopefully in future it can because I'd like to run the Tesla ABS module. The VCU should be able to output analog gauge signals to interface to older dashes, but presently it isn't configured to do that. There aren't any progammable can to analog converters out there that I can find so it might be a dirty Arduino hack until something better comes out. There are motorised speedo drives that spin the OEM cable based on pulse or can input, the LS crowd use them. If you want AC then it has to run of the HVDC so using the Tesla compressor is a good option. You'll need a HV Junction box, could recycle the Tesla one possibly.

For the torque, the limitation is the tire, not the power source. The difference is that the peak torque of dropping the clutch gets spread out and so the area under the curve is much bigger- which is the fun aspect- however the frame doesn't see any increased forces from that.
 

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the C5 is also open on the top, it looks like the same flat plane...
The C5 incorporates the passenger cell cage (windshield pillars, roof, and roll hoop); even in a convertible, the front and rear hoops are significant. Convertible or coupe, there is a substantial structural central tunnel. It doesn't really matter, since the relevant comparison would be to the flexy C1, but the C5 structure is much more than a flat platform.
 

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Discussion Starter · #31 · (Edited)
The C5 incorporates the passenger cell cage (windshield pillars, roof, and roll hoop); even in a convertible, the front and rear hoops are significant. Convertible or coupe, there is a substantial structural central tunnel. It doesn't really matter, since the relevant comparison would be to the flexy C1, but the C5 structure is much more than a flat platform.
thanx, that's true, I think I will try to plan for a roll bar of some kind as well as maybe something under the dash. I could bolt these on after the body maybe? I plan to use tall seats, I know sacrilege in a 62 :), but I have a special top cover that is like the C5 with head rest bumps. So maybe I could come up with a fancy roll bar design as well. I am warming to it. Most likely I will have the hard top on most of the time anyway, AC is much better than top down in FLA.

I have adjusted the block diagram to add the things suggested, if I understood right thanx Brian and 57, and some things from my reading as well.

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Discussion Starter · #32 · (Edited)
for reference, here is the C5 stock frame
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and this is Art Morrison's 1962 corvette retro-mod frame.

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and similar frame as I have from SRIII Motorsports, however mine has the c5 cradles. still looking for my actual pictures.

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thanx for your input, this is the way to discuss :)

the C5 is also open on the top, it looks like the same flat plane, I agree the torque tube is to keep the motor and diff from twisting the frame like a biscuit tube :). with rubber mounts on both ends, I am skeptical it added much more than that. since the motor is now in the back, I believe it is moot for my car.
You blew off some major elements in the C5's chassis.

The C5 uses the torque tube's tunnel as a torsion resistant element between two large shear plates (firewall and backrest) that transmit those shear loads into the roof through the A and B pillars (which your floppy chassis has none of and the only remaining suspension reactor is the torque tube itself).

In development, the car was tuned by the number of bolts used to close off the torque tube tunnel, resulting in a bazillion bolts to close it off, which shows the sensitivity to suspension reaction in a chassis, even with A and b pillars and the torque tube in place.

The rails are high strength hydroformed steel rectangular section pieces, which move suspension loads to the shear plates efficiently and at high frequency with minimal bending and almost no torsion at all. Your gokart pipes do none of that in the absence of a roll cage.

Given you're doing an early 60's car where straight line acceleration and "look at me" is the goal and roadholding is not important, maybe none of this matters.
 

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Discussion Starter · #35 ·
You blew off some major elements in the C5's chassis.

The C5 uses the torque tube's tunnel as a torsion resistant element between two large shear plates (firewall and backrest) that transmit those shear loads into the roof through the A and B pillars (which your floppy chassis has none of and the only remaining suspension reactor is the torque tube itself).

In development, the car was tuned by the number of bolts used to close off the torque tube tunnel, resulting in a bazillion bolts to close it off, which shows the sensitivity to suspension reaction in a chassis, even with A and b pillars and the torque tube in place.

The rails are high strength hydroformed steel rectangular section pieces, which move suspension loads to the shear plates efficiently and at high frequency with minimal bending and almost no torsion at all. Your gokart pipes do none of that in the absence of a roll cage.

Given you're doing an early 60's car where straight line acceleration and "look at me" is the goal and roadholding is not important, maybe none of this matters.
try using less you's and your's and terms like "floppy"

I am having a hard time understanding how this rubber mount located on the bottom center of the diff is providing any torque resistance to the rear frame? If it was meant to stabilize the frame, I would think these would be on the outboard sides of the differential.

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It's not... in the C5. In your chassis, without a roll cage, it contributes something, though granted and to your point, not much. You neglected the lower mounting bolts in the back, btw.

Put a properly triangulated roll cage in and you can do as you've planned - send the suspension load chassis torsion through it.

Unless you DGAF about handling, which is the C5's coup de grace
 

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Discussion Starter · #37 ·
It's not... in the C5. In your chassis, without a roll cage, it contributes something, though granted and to your point, not much. You neglected the lower mounting bolts in the back, btw.

Put a properly triangulated roll cage in and you can do as you've planned - send the suspension load chassis torsion through it.

Unless you DGAF about handling, which is the C5's coup de grace
what are your suggestions to shore up the frame I have, using your understanding of mechanical design, automotive suspension, on-road performance charactoristics, and EV battery requirements?
 

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Discussion Starter · #38 ·
Hi, battery question. It looks like the batteries will not layout the way i originally thought. 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? This is assuming Tesla S batteries and a Tesla LDU.
 

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what are your suggestions to shore up the frame I have, using your understanding of mechanical design, automotive suspension, on-road performance charactoristics, and EV battery requirements?
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.
 

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I am having a hard time understanding how this rubber mount located on the bottom center of the diff is providing any torque resistance to the rear frame? If it was meant to stabilize the frame, I would think these would be on the outboard sides of the differential.

View attachment 126827
It doesn't. The torque tube transmits reaction torque between the transaxle and the engine; it does not contribute torsional stiffness to the vehicle structure. The tunnel contributes torsional stiffness to the vehicle structure. The torque tube is in the tunnel of the C5 structure; the tube and tunnel are not connected. The single mount - instead of a pair of widely spread mounts - illustrates the point of the torque tube: it does not require engine reaction torque to be transmitted through the frame.

An all-in-one motor and transaxle assembly will also not require any transmission of torque about the longitudinal axis through the frame. (y)
 
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