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Discussion Starter · #42 ·
Zilla 1k:
· Maximum Battery Current at 200V: 950 Amps = 190kW
· Maximum Battery Current at 300V: 885 Amps = 266kW
· Maximum Battery Current at 400V: 800 Amps = 320kW

So, yeah, looks like running the two packs in parallel for 395V 860A would be best?
I was concerned that I was exceeding that amps spec a little. I'm comforted by this: "Max Current 1000 Amps Continuous With Liquid Cooling" - EVWest
That all works out nicely then.
 

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The current Mustang is a bit challenging as a donor when using the hub carriers / uprights / knuckles, because they are designed to work with the car's "integral link" suspension design. It's an effective and common design, shared with several makes and many models, including the original Tesla Model S and X; however, the lower arm is a large thing with complex loads that will make custom fabrication more difficult - in production cars it is always done in cast aluminum because it's not practical to build otherwise. A tour of this design is included in this Edmunds article:
2015 Ford Mustang GT Long-Term Road Test - Suspension Walkaround

There are many possible donors of all of the parts needed, but the most obviously similar to the Mustang are GM's Camaro and various Cadillac models, using the (earlier: Camaro 2010-2015) "Zeta" or (later: Camaro 2016+, various Cadillac) "Alpha" platforms. These rear suspension designs (which are similar but not identical) are more like a straightforward double wishbone (the Zeta design has an upper A-arm, two angled lower links, and a track rod; Alpha has a five-link) and should be easier to work with; the final drive they use is common and well proven at substantial power. Again from Edmunds:
2010 Chevrolet Camaro SS: Suspension Walkaround (Zeta)
 

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Discussion Starter · #45 ·
The current Mustang is a bit challenging as a donor when using the hub carriers / uprights / knuckles, because they are designed to work with the car's "integral link" suspension design.
Wow, that's incredibly helpful, thank you. Yeah, the current Mustang's suspension does look pretty complicated. And the example options are really great.

Honestly, I was leaning toward the Mustang because of how historically popular Ford diffs have been. And I know lighter cars don't need as sturdy a diff, but I'm not sure if the reduction in weight is enough for the Miata's diff to handle extremely roughly 330 ft-lbs of torque from 0rpm.

"The torsen is good for around 250 hp and close to that much torque." - a Miata forum

It might also be worth it to be able to brag about breaking a Miata diff, if it happened. So, maybe I don't care if it's strong enough. But I have gotten attached to the wide track of the current Mustangs.
 

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When you are worrying about the diff remember that in the donor the torque is multiplied by the gearbox
AND
The limit on the torque is the amount of grip your tyres have
A Miata is about 1200 kg - my Device is a bit heavy at 800 kg - if you have half the weight then you are limited to half the torque
 

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Discussion Starter · #47 ·
When you are worrying about the diff remember that in the donor the torque is multiplied by the gearbox
AND
The limit on the torque is the amount of grip your tyres have
A Miata is about 1200 kg - my Device is a bit heavy at 800 kg - if you have half the weight then you are limited to half the torque
That makes sense, that's great, thanks. So if a Miata diff can handle extremely roughly 250 ft-lbs, and weighs about 2372 pounds, and mine ends up weighing 1500 pounds, then if I used Miata tires it could handle roughly 395 ft-lbs. But I'm using much larger tires. But the Miata has a transmission. They mostly break in second gear, which is 2.991:1 reduction.

I'm having difficulty wrapping my brain around how much the transmission thing matters. If you're getting 330 ft-lbs at the ground both ways (ICE with gearbox, electric without), the input torque at the diff would need to be the same with both, right? So the gear reduction = increase in torque at the transmission isn't relevant?
 

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I'm having difficulty wrapping my brain around how much the transmission thing matters. If you're getting 330 ft-lbs at the ground both ways (ICE with gearbox, electric without), the input torque at the diff would need to be the same with both, right? So the gear reduction = increase in torque at the transmission isn't relevant?
Correct, except that you'll have far more than 330 lb-ft at the axles (even a HyPer 9's torque multiplied by a typical ring-and-pinion ratio is several times that); did you mean 330 lb-ft at the pinion shaft (into the final drive/diff)? As far as the final drive is concerned, it doesn't matter if a transmission is used or not... just how much torque is applied to the final drive input.

Online remarks about how much torque a final drive can take are probably all talking about engine torque and assuming some transmission gearing.

For an extreme case you could assume that there is enough traction to accelerate the mass of the vehicle at the acceleration of gravity (which you won't acheive), so the force at the tire contact patches totals the weight of the vehicle (1500 pounds.... but it's not likely to be that light). Multiply that by the tire radius (about half of the 27" tire diameter) to get 1690 ft-lb (total of both axle shafts). Divide by the final drive ratio (roughly 4:1 for an early Miata, less for a typical Mustang) to get the highest input torque to the pinion that the tires could possible support: 420 ft-lb or so. Any Miata can produce that in first gear.
 

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My Miata makes over 340ft-lbs at the wheels and the rear end has held up fine (ICE). "They say" 400-450whp is the limit for the Miata Torsen diff. You can get Miata diffs in a variety of final drives from 3.3:1 to 5.x:1. I have a 3.6:1 in mine with a 6-speed so it's geared for 170 MPH :cool:
 

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Discussion Starter · #50 ·
Awesome, so it sounds like a Miata Torsen diff will work. So it would be better, due to being lighter. So how do I do that while accomplishing the wider track of a recent Mustang / Camaro (which are similar)? And is that worth just sticking with a Mustang / Camaro diff+axles+hubs+brakes for simplicity?
 

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My Miata makes over 340ft-lbs at the wheels and the rear end has held up fine (ICE).
...
I have a 3.6:1 in mine with a 6-speed so it's geared for 170 MPH :cool:
Presumably what this means is that it produces over 340 lb-ft of torque at the engine output, as estimated from measurement at the tires by a dynamometer... which really means that the measured total axle torque, divided by the final drive ratio (3.6 in this case), and divided by the gear ratio used in the test, equals over 340 lb-ft. That's double the stock torque of any non-turbo Miata/MX5, so I assume that this is a modified or swapped engine. In first gear that's more than the weight of the car in drive force at the tire contact patches.

Actual 340 lb-ft literally at the wheels would only be about 340 pounds of forward force (because the tire radius is about one foot).
 

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Discussion Starter · #52 · (Edited)
(1500 pounds.... but it's not likely to be that light)
Yeah, I keep seeing Duncan mentioning his being 800 kg = 1764 pounds, and thinking there's no reason mine would weigh less than that plus another Chevy Volt battery pack, totalling 2196 pounds = 996kg. Slightly more than the first gen (heavier) Miata.

I expect I'll build it with a single Volt pack initially. But I also don't expect to get better mileage than Duncan's 50km (31 miles) at 100kph (62mph). And my girlfriend lives 40 miles away. And I want to actually drive the thing.

So I guess I'll estimate 2200 pounds until I get better info. I'm always interested in guesses.
 

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When you throw away all of the clutter a Chevy Volt Battery is 152 Kg - 336 lbs - I have 133Kg of batteries - my batteries are all on the floor -
I have one of the two 1 kWh modules + three of the seven 2 kWh modules as a single "lump" - and two "lumps" under the bonnet - leaving one 2kWh module left over
if the chassis had been a bit longer I could have fitted four 2 kWh modules on one side and three 2 kWh + two 1 kWh modules on the other

You can double stack the batteries but that would raise the height of the center of mass

At 800 kg my car is a bit overbuilt - also my motor is 102 kg - If I rebuilt it I would hope to lose 100 kg
 

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Discussion Starter · #55 ·
When you throw away all of the clutter a Chevy Volt Battery is 152 Kg - 336 lbs - I have 133Kg of batteries - my batteries are all on the floor -
I have one of the two 1 kWh modules + three of the seven 2 kWh modules as a single "lump" - and two "lumps" under the bonnet - leaving one 2kWh module left over
if the chassis had been a bit longer I could have fitted four 2 kWh modules on one side and three 2 kWh + two 1 kWh modules on the other

You can double stack the batteries but that would raise the height of the center of mass

At 800 kg my car is a bit overbuilt - also my motor is 102 kg - If I rebuilt it I would hope to lose 100 kg
Thanks, I'd love to get measurements from you of what space you took to fully plumb and wire them. It would be really nice to be able to make a first pass at a frame before buying the batteries.

Yeah, I'm planning on two layers of batteries. Do you still have roughly 0 body roll after softening your suspension? I think raising the center of gravity less than half the height of a battery won't kill me :p
 

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My battery compartment is 950 mm long and 590 mm wide
The battery is snug fit

The last video on my site is the event on the 16th - I had the new springs fitted - still negligible roll

You can see from the picture that I have an intrusion into the battery box for the steering - the big grey piece is the Subaru front subframe
The two slots in the grey piece at the bottom of the picture are where the Subaru engine would mount
 

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I took the bottom plate from the Chevy - and by drilling out about 300 spotwelds I was able to get the bits that actually clamped the batteries
(first picture) - this shows the mounting plates - you can see where I welded together a couple of pieces to get two that were the right length
Then I welded them to a couple of cross members - 19mm square steel tube
You can see these in the second picture
The water pipes were before I trimmed to length!
The actual modules are 275 mm tall - and the main wiring is below that level
The wires/connectors for the individual cell BMS will take up another 20 mm

So in total from the floor
About 22 mm for the mountings
275 mm for the modules
20 mm for the BMS wiring
 

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Discussion Starter · #60 ·
So in total from the floor
About 22 mm for the mountings
275 mm for the modules
20 mm for the BMS wiring
Wonderful, thank you! Double that 317mm also fits in the space I've been modelling!
If my space had been 120 mm longer then I would have been able to squeeze the whole 16 kWh - rather than the 14 kWh that I did
That doesn't quite fit. I'll have to re-check cell counts, since I'm putting some in the back for weight balance.
 
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