# Open wheeled tandem seater



## ishiwgao (May 5, 2011)

it looks like a cool build!

Not to spoil the fun though, my first impressions were "are you sure you wanna use battery boxes as front and rear crash structures...?"


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## brian_ (Feb 7, 2017)

Darxus said:


> View attachment 124224
> 
> 
> ...
> Motor (output shaft) is bolted directly to the differential (pinion shaft, I'll need to get a coupler made). Changed ring and pinion gears to match motor RPM limit with, I don't know, 90mph? Looks like I need to use a front diff, to avoid problems with oil flow, since I have the diff oriented backwards. Not sure exactly which would be best. Definitely need an LSD. And one of the bigger problems is a lot of front diffs are significantly more lopsided than rear diffs, but possibly due to removable stub axles?


Whether they are live beam axles or final drives for independent front suspension, those front axles are only offset so that the propeller shaft can clear the engine. You can use the same centre section in a non-offset configuration. You might also not need a specifically front unit - the differential internals are the same, and some ring-and-pinion sets can run either way.


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## brian_ (Feb 7, 2017)

Darxus said:


> View attachment 124222
> View attachment 124224
> 
> View attachment 124225
> ...


I understand the tandem seating arrangement, but there's no one I would want and be able to sit with this way. You may find it works, but a serious mockup (with sides, not just two spots marked on the floor) would certainly be required.


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## brian_ (Feb 7, 2017)

ishiwgao said:


> Not to spoil the fun though, my first impressions were "are you sure you wanna use battery boxes as front and rear crash structures...?"


Perhaps just an energy-absorbing nose cone would be a wise addition.


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## brian_ (Feb 7, 2017)

Darxus said:


> Everything fun seems to use a NetGain Warp 9 motor.


That may have been true several years ago.


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## Darxus (May 10, 2010)

ishiwgao said:


> it looks like a cool build!
> 
> Not to spoil the fun though, my first impressions were "are you sure you wanna use battery boxes as front and rear crash structures...?"


Thank you. Yup, safety is not a high priority in this design. I figure it's significantly safer than my motorcycle, and I'm comfortable with that.


brian_ said:


> Whether they are live beam axles or final drives for independent front suspension, those front axles are only offset so that the propeller shaft can clear the engine. You can use the same centre section in a non-offset configuration. You might also not need a specifically front unit - the differential internals are the same, and some ring-and-pinion sets can run either way.


That is very helpful, thank you. Do you know of any specific examples that would work? Or how best to find them?

Seems like something that came with an LSD would be nice, but maybe not, since I need to change the gear ratio anyway. It would also be nice to use a rear diff that can handle the rotation / oil flow, so I can use the original axles (without removing the stub shaft(?)).

Are there any with a centered pinion, equal length half shafts, and an offset ring gear? (Not important, but I'm curious, I like symmetry.)


brian_ said:


> I understand the tandem seating arrangement, but there's no one I would want and be able to sit with this way. You may find it works, but a serious mockup (with sides, not just two spots marked on the floor) would certainly be required.


Yeah, I'm thinking just passengers I'd ride a motorcycle with. And definitely need a mockup with walls and a roof.


brian_ said:


> That may have been true several years ago.


Can you give me examples that are fun without a Warp 9 motor now? Other than snowdog's electric supercar, with a Tesla subframe, which I believe would be too wide for this body, and cost $56,499.37 for the build as of March?


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## brian_ (Feb 7, 2017)

Darxus said:


> Can you give me examples that are fun without a Warp 9 motor now? Other than snowdog's electric supercar, with a Tesla subframe, which I believe would be too wide for this body, and cost $56,499.37 for the build as of March?


There are many swaps using Tesla drive units or any other common modern EV (e.g. Leaf), and all will have more power available than any WarP 9 can produce; they don't need to be as expensive as snowdog's car, but none will be the $1,000 that some people seem to think an EV can be built for with a free forklift motor, homebuilt controller, and some miracle deal on a salvaged battery.


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## brian_ (Feb 7, 2017)

Darxus said:


> Seems like something that came with an LSD would be nice, but maybe not, since I need to change the gear ratio anyway.


Since the same ring and pinion gears worth with limited-slip and open differentials of the same final drive model, you can change the ratio without losing the LSD. You can also find something with the right ratio and replace the open diff with a limited-slip, but it would have to have a limited-slip available.


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## Electric Land Cruiser (Dec 30, 2020)

It's not my style but it looks like fun! I say build it but I agree I'd go with a modern EV motor. Maybe LEAF motor and transaxle with custom controller. The LEAF motor is small and 100-150lbs or something so pretty light. Can make 300+kw with custom inverter (and the right batteries).


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## Rusted B&B (Nov 6, 2020)

this is pretty cool concept - I like the fighter jet style seating but I would do a mach up of the fitment of the seating but design an real are very different. I tried this and was like, oh, that is way to close.


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## Darxus (May 10, 2010)

brian_ said:


> There are many swaps using Tesla drive units or any other common modern EV (e.g. Leaf), and all will have more power available than any WarP 9 can produce; they don't need to be as expensive as snowdog's car, but none will be the $1,000 that some people seem to think an EV can be built for with a free forklift motor, homebuilt controller, and some miracle deal on a salvaged battery.


Thank you. Is there any way to get a Limited Slip Differential with a Leaf motor?


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## Electric Land Cruiser (Dec 30, 2020)

Darxus said:


> Thank you. Is there any way to get a Limited Slip Differential with a Leaf motor?


Yes Quaife has quoted people for some amount of money I forget. I would pull one apart and measure the parts it may be the same or close enough to something available for other Nissan FWDs that would be less expensive.


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## brian_ (Feb 7, 2017)

Darxus said:


> Are there any with a centered pinion, equal length half shafts, and an offset ring gear? (Not important, but I'm curious, I like symmetry.)


Looking for examples, it appears that all conventional (not high pinion) front differentials have the ring and pinion gears cut the same as at the rear, so a rear unit can simply be turned around (and the motor rotational direction set appropriately). Typically rear final drive units are set up for equal-length half-shafts and a centred pinion shaft.

In a discussion of Dennis Palatov's 2019 Pikes Peak Racecar, we had a look at the complete chassis:


brian_ said:


> ...
> A 2020 article mentioned that the car was run on the salt flat at Bonneville (in 2019) and included this interesting view of the D2EV without bodywork or battery packs:


I'm reasonably certain that the front final drive unit is normally used at the rear, and is simply turned and placed in the front. Some members of this forum worked on that car, so they might know what was used, but as far as I know they were not on the mechanical side.


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## MattsAwesomeStuff (Aug 10, 2017)

brian_ said:


> but none will be the $1,000


1000 euro was the challenge. Bit more wiggle room.



Darxus said:


> I could really use some more people telling me "That looks fun, you should build it."


Doesn't matter what we think, if you think it looks fun, then go build it. It's certainly different, which means, maybe almost no one would think it's cool except you. That's okay, you build the car that's perfect for you, not us.



> The Soliton 1 became unavailable, the Zilla 1k came back.


So... Damien threw together a quick 1000+ amp DC mod board for the stupidly-cheap salvaged Prius Gen 2 controller ($150 at most, lots are grabbing them for $50).

Though, he never really finalized or produced the design. EV8 over on the OpenInverter forums was smart enough to read that design and build a quick sample board of it on some perfboard... without writing any of it down, just keeping it all in his head. I think he stuck it into his RX8, and was disappointed by _only_ 265 hp out of it or somesuch before he I think melted his motor or something (controller was fine). He's moved onto an AC build now.

So a couple of us said "Stop, wait... can you share what you built?" and he's too busy to get around to doing it, said he'd have to write it all down. So I was like "No, just, share what you did, whatever you used to build it" and he was like "Oh, I just built it in my head". And then with some slight nagging, he's come around to "Okay fine, didn't think anyone was still doing DC builds... I'll try to get around to it sometime after the next couple weeks." That was, yesterday.

Anyway, point being, for something close to almost free, you can repurpose a Prius Gen 2 inverter and go melt a motor if you want to, depending on how good you are about reading schematics or, how patient you are and gambling that EV8 will find time to publish something more crowd-friendly.



> Everything fun seems to use a NetGain Warp 9 motor.


Don't pay for a Warp 9. Use a forklift motor if that's where you're at. Pretty much same thing, and you can get one for ~$150 in scrap value, (I got several for free). Some people say they have trouble finding these, but, I'd say the massive majority are still able to do so without much hassle at all. Call up forklift repair places in your city, ask if they have any old traction motors around "Just in case" that you could buy from them, or any junkers in the yard you could pull the motor off yourself. There's a massive 130-page thread in the motor forums here about how to do this.

Seems to me you can easily get both motor and controller for a DC build for well under $500. Under $200 if you're persuasive.


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## Darxus (May 10, 2010)

brian_ said:


> Looking for examples, it appears that all conventional (not high pinion) front differentials have the ring and pinion gears cut the same as at the rear, so a rear unit can simply be turned around (and the motor rotational direction set appropriately). Typically rear final drive units are set up for equal-length half-shafts and a centred pinion shaft.
> 
> In a discussion of Dennis Palatov's 2019 Pikes Peak Racecar, we had a look at the complete chassis:
> 
> I'm reasonably certain that the front final drive unit is normally used at the rear, and is simply turned and placed in the front. Some members of this forum worked on that car, so they might know what was used, but as far as I know they were not on the mechanical side.


That's great, thank you. So I should be able to use a Ford 8.8" rear diff, which seems very popular for custom things, just oriented as a front diff? Its pinion is horizontally offset by 2", are you considering that centered? 

Wow, I used to follow Palatov's stuff a lot when he was working on the DP1, I had no idea he won Pikes Peak a bunch of times.


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## brian_ (Feb 7, 2017)

Darxus said:


> So I should be able to use a Ford 8.8" rear diff, which seems very popular for custom things, just oriented as a front diff?


Yes, that's in most Ford cars with IRS, RWD/AWD, and a longitudinal engine. There is a range of ring-and-pinion sets for it to change the ratio. Stronger versions built since 2015 are called the "Super 8.8"; some parts are not interchangeable between the versions (apparently pinion bearing etc. for the "super" come from the Ford 9.75 unit) so get the one you want from the beginning. The Mustang has used a Super 8.8 with IRS since 2015. It comes in both aluminum and iron housings.



Darxus said:


> Its pinion is horizontally offset by 2", are you considering that centered?


Yes, that's what I was thinking of as close enough. There's no good reason for an auto designer to require the propeller shaft to be exactly centred, so I'm not surprised that they vary by that much.


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## MesquiteTim (Sep 30, 2021)

A miata donor, or at least the rear sub frame with diff and suspension would be MUCH easier to start with than a Ford rear end. Check out the Exocet for clues. The electric motor could be directly coupled to the diff and still be behind the rear seat


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## Darxus (May 10, 2010)

brian_ said:


> Yes, that's in most Ford cars with IRS, RWD/AWD, and a longitudinal engine. There is a range of ring-and-pinion sets for it to change the ratio. Stronger versions built since 2015 are called the "Super 8.8"; some parts are not interchangeable between the versions (apparently pinion bearing etc. for the "super" come from the Ford 9.75 unit) so get the one you want from the beginning. The Mustang has used a Super 8.8 with IRS since 2015. It comes in both aluminum and iron housings.
> 
> Yes, that's what I was thinking of as close enough. There's no good reason for an auto designer to require the propeller shaft to be exactly centred, so I'm not surprised that they vary by that much.


Great, thank you. Yeah, I had a feeling. In such a narrow bodied and symmetrical car, it's noticable, but I can cope. You can't see it because this quick render has a black background, but the offset gives me a fine place to tuck the charger.










MesquiteTim said:


> A miata donor, or at least the rear sub frame with diff and suspension would be MUCH easier to start with than a Ford rear end. Check out the Exocet for clues. The electric motor could be directly coupled to the diff and still be behind the rear seat


Many possibilities in life would be much easier than attempting this project. But using the Miata rear suspension... would not give me the inboard coilovers I want. I want to do the suspension much like an FSAE car (with outboard brakes). 

But I do often think about building a regular locost 7 or T-bucket for practice.


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## brian_ (Feb 7, 2017)

MesquiteTim said:


> A miata donor, or at least the rear sub frame with diff and suspension would be MUCH easier to start with than a Ford rear end. Check out the Exocet for clues.


Yes, it would be easier, but the Miata subframe would be wide compared to the desired body; the Exocet is not a narrow tandem-seat vehicle. 



MesquiteTim said:


> The electric motor could be directly coupled to the diff and still be behind the rear seat


Yes, but the final drive unit would be facing the wrong way... although the suspension with an early Miata subframe would probably be usable turned around.


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## MesquiteTim (Sep 30, 2021)

No, Brian I said it correctly. Connect the motor directly to the input of the diff. with the motor sitting under the back of the rear seat. A hyper 9 is only 14 inches long so it would tuck under the slant of the rear seat while sitting IN FRONT of the diff. I thought I made it perfectly clear the first time. 

I have an exocet in my garage. If you want dims, just ask me and I will give you data.

The width of the Miata subframe bolts are about 30 inches. It widens out at the seats to allow for two 17 inch wide seats and a narrow tunnel. The reset hangs out in the wind on the exocet. If he designs a frame too narrow, he will lose stability in turns. inches wide will give him at least a chance for a decent battery pack. Anything narrower than a sports car will be a disappointment. There is a mountain of go fast parts for the Miata to give you the performance you want.

Pic of the off road version showing how narrow the Miata subframe is. He could easily narrow his frame at least 8 inches narrower than the Exocet. He would have proper suspension geometry, diff, brakes, shocks all in place for $500 to $1000.

I like the design. If I was interested in a tandem seat car, I would start from an Exocet layout and narrow the cabin.


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## piotrsko (Dec 9, 2007)

Late to the party but series of observations:

Back 10 years ago, brushed DC was the fastest way to get massive hp for cheap using basically a pwm source and a igbt. Not so much anymore as there are more options since power silicon is pretty cheap. There were a bunch of Sol Jrs made that are slightly less powerful than a 1 but I think you want AC

The Volt packs are 40 mile capable in a volt (or 1988 ranger) each and structural overkill, but they are a T and about 30" wide unless you cut the backbone. If you go to 4.2v a cell you get another 2KWH capacity.

Why not cut down a modern AWD front diff (not the tube style dana but say 2000 chevy s10)

Build it, to me it looks like a morgan stayed overnight with a chrysler and this was the kid.


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## brian_ (Feb 7, 2017)

MesquiteTim said:


> No, Brian I said it correctly. Connect the motor directly to the input of the diff. with the motor sitting under the back of the rear seat. A hyper 9 is only 14 inches long so it would tuck under the slant of the rear seat while sitting IN FRONT of the diff. I thought I made it perfectly clear the first time.


That's not the design which Darxus has been consistently showing, but it is an alternative... one which would force the wheelbase to be much longer. In the existing design the rear seat back is already over the final drive; adding 14 inches of motor would force the axle 14 inches further back. 14 inches of wheelbase is the difference between a small sports car a medium-sized sedan.

Obviously the suggested placement was not "perfectly clear", and I misinterpreted the intention.


MesquiteTim said:


> The electric motor could be directly coupled to the diff and still be behind the rear seat​


​Sure... a rear motor as Darxus plans is behind the seat, and so is a motor between the seats and the axle. But this suggestion said "behind the seat", not "under the back of the rear seat".​


MesquiteTim said:


> I have an exocet in my garage. If you want dims, just ask me and I will give you data.
> 
> The width of the Miata subframe bolts are about 30 inches.


That dimension is helpful. Obviously 30" (plus more, as the subframe extends beyond the bolts) would correspond to a tandem body built for a very wide pair of occupants, and (as I noted) would not likely be suitable as-is.

For anyone interested in details, the NA/NB Miata rear suspension and subframe are so popular for projects that 3D models are readily available. The GrabCAD presentation includes a 3D viewer in the web page so that it can be examined without even loading it you your 3D software.



MesquiteTim said:


> ... If he designs a frame too narrow, he will lose stability in turns. inches wide will give him at least a chance for a decent battery pack. Anything narrower than a sports car will be a disappointment. There is a mountain of go fast parts for the Miata to give you the performance you want.
> 
> Pic of the off road version showing how narrow the Miata subframe is. He could easily narrow his frame at least 8 inches narrower than the Exocet. He would have proper suspension geometry, diff, brakes, shocks all in place for $500 to $1000.
> 
> ...


The width of the frame in the passenger area is unrelated to the track width. Yes, the Miata subframe can be narrowed to fit a narrow frame. The spring/damper units do not attach to the subframe, and would still be out past the body, although they could be radically inclined to bring the top mounts in.

Yes, the track width should not be narrowed significantly (and that would require custom axle shafts if it were done), so that means narrowing the subframe *and* fabricating all new longer control arms to make up the difference. Lengthening the arms changes the geometry, so mounting points might need to change... and that's about all that the subframe provides. At that point, there is little left from the Miata other than the uprights... but yes, building a custom suspension using stock uprights and hub components is an option.


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## brian_ (Feb 7, 2017)

One good point out of the Miata discussion arc:
If you use the final drive (differential in housing) and suspension uprights (hub carriers or knuckles) *from the same donor vehicle* - one that has a suitable track width and keeping that stock track - you can use the stock axle shafts with CV joints intact and unmodified. This is true whatever you do with the suspension, even if you can't use the donor subframe (which you don't need, since you're building a tubular frame anyway) and even if you build all new control arms (of the same general design so they work with the upright, of course).

The donor could be the rear of a Miata, or a recent (IRS) Mustang or Camaro (although they're both heavier and thus stronger than you need), or one of an almost endless variety of RWD and AWD cars... just not anything mid-engine or rear-engine or just front wheel drive. Of course some hub carriers will be easier to work with, depending on the type of suspension for which they are designed; double wishbone and multi-link suspensions would be the most desirable.

This all applies to any vehicle in which you are custom-building the structure (such as the LoCost style), not just the tandem layout.


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## MesquiteTim (Sep 30, 2021)

rolls eyes, walks out, closes door on the way out


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## MesquiteTim (Sep 30, 2021)

To the OP, consider the track width in your design. You are a motorcycle guy and we don't know if you have 4 wheel car design and performance. Obviously your tandem won't lean so it's a different calculation. The Miata is the lightest smallest narrowest production donor. It's cheap and plentiful. 

Good Luck which ever way you go...


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## TT-Man (May 28, 2015)

Hi Darxus,
You Americans do think big, .... I guess that it is your horizons are so very larger.
I fancied a mini version of yours as my horizons are limited to a 40 x 12 miles island. The vehicle that I would buy (if manufactured for sale at an acceptable cost ) would be the VW Nils. But it is not made for sale .... yet?.. Look it up it is lovely.
I am at a cross roads do I commit to going ahead with a build? It would be to the European L7e regulations, this limits motor power to 15kW continuous, and 800 (?) Kg without batteries.
Brian has also made suggestions on my proposed project. He has a lot of good advice.
I have a frame builder lined up, and am sorting various bits of running gear. The Mazda mx5 differential, and BMW Mini wheel & suspension components seem possible. Like you would like inboard springing and shock aborbers, but have decided on the KISS principle, so will (if it happens) take a pragmatic view, keeping it simple.
Good luck with your project, Joe


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## brian_ (Feb 7, 2017)

Darxus, just to be clear about your plans, what are the wheelbase and track (width between tire centres) of the current proposal? It looks like it might be a bit long for a small sports car (due to the engine-sized front battery pack between the front axle and the driver's feet, and the extra passenger), and a reasonable but perhaps slightly narrow track (with substantial suspension arm length beyond the narrow frame).

With a very low centre of mass (typical of "sit on the floor" sports car configurations like this), the track can be relatively narrow.


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## Duncan (Dec 8, 2008)

Hi Darxus
You will find that you can't narrow a car down very much before its too narrow for performance
So you may as well use the normal side by side seating

The tandem seating would be a good idea if you built a leaning machine!!

My car 








Duncan's Dubious Device


The floor and bulkheads have been brazed into the chassis Shouldn't that read "bronzed"? ;) Any updates?




www.diyelectriccar.com




Is a side/side version of your car - using a Chevy Volt battery and a DC motor

If I was starting again now I would put something like a Nissan Leaf power unit in the back


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## brian_ (Feb 7, 2017)

Duncan said:


> You will find that you can't narrow a car down very much before its too narrow for performance
> So you may as well use the normal side by side seating


Again, the passenger cell and frame of this vehicle is very narrow, but the track is not. And again, Darxus, what is the currently planned *track* dimension? If it's a little too narrow, just extend the suspension arms (assuming that they're custom-built anyway).

Even single-seat race cars have big side pods now, but half a century ago Indy and Formula cars had a narrow body and separate wheels like this project. The historic Lotus 29 Indy car (that started the end of the traditional Indy cars) and the Lotus 33 (that dominated F1 in 1963 of the same time) were about the same width and track as the Lotus 23 sports racer, despite the 29 and 33 being narrow-body single-seaters while the 23 being a full-body car with "two seat" cockpit. The body width does not constrain the track.



Duncan said:


> My car
> 
> 
> 
> ...


Yes, I think they're similar, too... except that the narrow body and central seating forces the motor to be differently located. I'll note that even with side-by-side seating, there's still no room for the motor between the backs of the seats and the final drive unit, so the Device has it forward, between the occupants' legs.


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## Duncan (Dec 8, 2008)

brian_ said:


> Yes, I think they're similar, too... except that the narrow body and central seating forces the motor to be differently located. I'll note that even with side-by-side seating, there's still no room for the motor between the backs of the seats and the final drive unit, so the Device has it forward, between the occupants' legs.


If you use a longitudinal engine/motor then it has to go forwards a bit
But if you use a transverse unit then you only have to move the occupants forwards a bit - and you then have more width available for the occupants

My car is quite tight - I could not buy seats for it I had to make/modify seats to fit it


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## Darxus (May 10, 2010)

brian_ said:


> Looking for examples, it appears that all conventional (not high pinion) front differentials have the ring and pinion gears cut the same as at the rear, so a rear unit can simply be turned around (and the motor rotational direction set appropriately).


Can you tell me how you checked that?


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## Darxus (May 10, 2010)

brian_ said:


> Again, the passenger cell and frame of this vehicle is very narrow, but the track is not. And again, Darxus, what is the currently planned *track* dimension? If it's a little too narrow, just extend the suspension arms (assuming that they're custom-built anyway).


At the moment I'm looking at stock diff / axles / hubs of a 2015+ (6th generation / S550) Mustang, rear hub face to hub face = 62.5", with 18x7" wheels with a 4.25" backspacing (therefore 0.75" offset). I believe track is tire center to center, so that should work out to a track width of 61.0"?

Yes, custom suspension arms. And yes, I've spent some time drooling over the Lotus 29 and 33.


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## Darxus (May 10, 2010)

Sorry, that was a 5th gen axle measurement. 2015+ is 66.25" hub face to hub face, so 64.75" track width?


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## brian_ (Feb 7, 2017)

Darxus said:


> Can you tell me how you checked that?


Read online discussions and descriptions from gearing vendors.


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## brian_ (Feb 7, 2017)

Darxus said:


> At the moment I'm looking at stock diff / axles / hubs of a 2015+ (6th generation / S550) Mustang, rear hub face to hub face = 62.5", with 18x7" wheels with a 4.25" backspacing (therefore 0.75" offset). I believe track is tire center to center, so that should work out to a track width of 61.0"?





Darxus said:


> Sorry, that was a 5th gen axle measurement. 2015+ is 66.25" hub face to hub face, so 64.75" track width?


Yes, that's track... and using the stock track of the donor vehicle for the hubs/carriers and final drive allows use of the stock axles. Thanks for the dimensions.

For those concerned that the vehicle has narrow track.... it certainly does not.  Even with components from a smaller donor (such as a Miata) the same approach still leads to the same track as the donor, not narrower just because the passenger cell is narrower.



Darxus said:


> Yes, custom suspension arms. And yes, I've spent some time drooling over the Lotus 29 and 33.


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## Darxus (May 10, 2010)

I feel like it would be useful if track was measured at the outside of the tire, instead of its center.


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## brian_ (Feb 7, 2017)

Darxus said:


> I feel like it would be useful if track was measured at the outside of the tire, instead of its center.


The overall width is important to fender width, and staying within legal vehicle width limits, but is otherwise not important. It is the track width which is relevant to everything about vehicle dynamics.


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## Darxus (May 10, 2010)

I don't know how I missed all these posts, sorry. 


MesquiteTim said:


> Connect the motor directly to the input of the diff. with the motor sitting under the back of the rear seat. A hyper 9 is only 14 inches long so it would tuck under the slant of the rear seat while sitting IN FRONT of the diff.


The rear seat is right up against the diff, there is not room for a motor there. I'm using rough dimensions for the diff, but the passenger's head is nearly centered over the axle:








At the widest, the body is 87.5cm = 34.4", it would be interesting to see how that lines up to the back of an Exocet. It doesn't have the inboard suspension, but that could probably easily be converted to push rods. 



MesquiteTim said:


> I like the design.


I appreciate that.


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## Darxus (May 10, 2010)

TT-Man said:


> Hi Darxus,
> You Americans do think big, .... I guess that it is your horizons are so very larger.
> I fancied a mini version of yours as my horizons are limited to a 40 x 12 miles island. The vehicle that I would buy (if manufactured for sale at an acceptable cost ) would be the VW Nils.


Yeah, most people I know live about 35 miles = 56km away.

I was similarly interested in things shaped like the VW L1 for a while, one of mine (ICE):


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## Darxus (May 10, 2010)

brian_ said:


> what are the wheelbase


Wheelbase is 291cm = 114.6".


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## Darxus (May 10, 2010)

Darxus said:


> 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
> ...


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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## brian_ (Feb 7, 2017)

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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## brian_ (Feb 7, 2017)

Darxus said:


> Wheelbase is 291cm = 114.6".


Plenty long enough without any further stretching!


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## Darxus (May 10, 2010)

brian_ said:


> 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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## Duncan (Dec 8, 2008)

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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## Darxus (May 10, 2010)

Duncan said:


> 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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## brian_ (Feb 7, 2017)

Darxus said:


> 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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## Electric Land Cruiser (Dec 30, 2020)

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


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## Darxus (May 10, 2010)

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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## brian_ (Feb 7, 2017)

Electric Land Cruiser said:


> 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


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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## Darxus (May 10, 2010)

brian_ said:


> (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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## Darxus (May 10, 2010)

I haven't done composites in... years. 4k 30fps video loop: https://www.eternalmachinery.com/ecar/ebucket96+98crf31fps30.webm


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## Duncan (Dec 8, 2008)

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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## Darxus (May 10, 2010)

Duncan said:


> 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
> 
> ...


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


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## Duncan (Dec 8, 2008)

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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## Darxus (May 10, 2010)

Duncan said:


> My battery compartment is 950 mm long and 590 mm wide


Awesome, thank you very much. That fits in the space I've been modelling! Er, without the steering column. Can you tell me how much height you need, from the bottom of a battery, to have space for wiring?


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## Duncan (Dec 8, 2008)

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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## Duncan (Dec 8, 2008)

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


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## Darxus (May 10, 2010)

Duncan said:


> 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!


Duncan said:


> 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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## Darxus (May 10, 2010)

I thought of a problem: Windshield wiper vs. front opening canopy. I can mount the wiper and mechanism to the front of the canopy, there's room for that, no problem. The annoying part is running power and fluid. Which I could do through the hinge at the rear. But are the aesthetics of the direction it opens worth that to me? Or do I hinge it at the front?
















It seems like everything remotely similar opens at the front, often with two pairs of arms:
(from 20 Weirdest Car Doors Ever )








Hah, there's a wikipedia page: https://en.wikipedia.org/wiki/Vehicle_canopy


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## Darxus (May 10, 2010)

I feel like I finally got a handle on lighting.


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## Duncan (Dec 8, 2008)

Hinged at the rear means that if it pops open when diving it will rip straight off


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## brian_ (Feb 7, 2017)

Duncan said:


> Hinged at the rear means that if it pops open when diving it will rip straight off


Just like the majority of engine hoods, and many aircraft canopies. This is an issue, but a manageable one - use a two-stage catch.


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## brian_ (Feb 7, 2017)

Darxus said:


> Hah, there's a wikipedia page: https://en.wikipedia.org/wiki/Vehicle_canopy


As there is for almost everything. 
Feel free to improve it after your canopy research.


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## brian_ (Feb 7, 2017)

Darxus said:


> I thought of a problem: Windshield wiper vs. front opening canopy. I can mount the wiper and mechanism to the front of the canopy, there's room for that, no problem. The annoying part is running power and fluid.


Power for the wipers and mounting the weight of the wiper assembly to the canopy are issues regardless of the hinge direction. A front-hinged canopy may be able to use a body-mounted wiper motor if the wiper arm can hinge with the canopy as it opens.

Regardless of hinge location, the washer nozzle can mount on the hood ahead of the windshield (as they normally are) - it doesn't need to move with the canopy unless the canopy includes substantial bodywork ahead of the windshield.


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## brian_ (Feb 7, 2017)

Darxus said:


> It seems like everything remotely similar opens at the front, often with two pairs of arms:
> (from 20 Weirdest Car Doors Ever )
> View attachment 124811


I think the forward hinging is normally done simply because the body is lower ahead of the canopy than behind it. The four-bar linkage in that example helps by moving the canopy forward when opened, and lifting it away from the front edge area which makes the canopy to body seating easier.

The Holden Hurricane from the same article was much better styled rendition of the same idea as that Nova.


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## saxere7 (Nov 19, 2021)

We are getting a tandem for our wedding present (hopefully) and I’m looking at the various options. I’m interested in the convenience of the smaller wheeled ones, but am not sure how comfortable they are over several hours. Any opinions from owners?


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## Duncan (Dec 8, 2008)

saxere7 said:


> We are getting a tandem for our wedding present (hopefully) and I’m looking at the various options. I’m interested in the convenience of the smaller wheeled ones, but am not sure how comfortable they are over several hours. Any opinions from owners?


Hi saxere7 - I think there is some confusion - a "tandem" is completely different to an "Open wheeled tandem seater"


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## Darxus (May 10, 2010)

Duncan said:


> Hi saxere7 - I think there is some confusion - a "tandem" is completely different to an "Open wheeled tandem seater"


Google images does decently with it: Open wheeled tandem seater - Google Search

It's funny that right now the third image is one of mine, from this thread, and it's the only image I posted here that I created that is not open wheeled.


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## brian_ (Feb 7, 2017)

Duncan said:


> Hi saxere7 - I think there is some confusion - a "tandem" is completely different to an "Open wheeled tandem seater"


Do you really think that account is anything other than a bot establishing an account to later post spam? No human functional enough to use a keyboard could possibly read any of this thread, or even the forum name, and think that the discussion is about bicycles built for two.


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## Darxus (May 10, 2010)

I have a room that I'm not really using, which has an external door. It occurred to me that the body of this thing might be about the width of a door. So if I took the wheels, suspension, and axles off, it would fit through a door. I just measured, and within my accuracy, they're the same width. I can do it.

As long as, you know, I can verify that people will fit in that width.


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## piotrsko (Dec 9, 2007)

Well the Piper Pacer I used to own was 41 inches wide with cramped* side by side seating......SO you need 20 ish inches which is less than a standard entry door of 36 and gives you 9 inches a side unless there's a doorstop moulding which will kill an inch and a half

*I was 6'2" & 275 lbs back then.


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## Darxus (May 10, 2010)

piotrsko said:


> Well the Piper Pacer I used to own was 41 inches wide with cramped* side by side seating......SO you need 20 ish inches which is less than a standard entry door of 36 and gives you 9 inches a side unless there's a doorstop moulding which will kill an inch and a half
> 
> *I was 6'2" & 275 lbs back then.


Passenger's knees. Plus various body mechanics to get them to fit around me. Very inconvenient.


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