rear engine EV conversion.

[Clev]

Originally Posted by Frank Lee

A most intriguing thread.

It's like the EV conversion equivalent of an HHO thread.

[some_other_dave]

Originally Posted by Clev

At least with everything in the front you'll get predicable understeer.

Spoken like someone who hasn't autocrossed...

2. CRX. You might be able to adapt the FWD transmission to the rear. You'd have to swap the ring gear so you don't end up with five reverse gears and one forward. You're also cutting out a big chunk of the floor to fit the motor/tranny package in there, adapting drive axles and rear suspension from an AWD Civic to fit. And then you have no room for batteries in the back at all.

I know something about CRXes, having owned and worked on two of them since 1993. So a few points.

- The CRX (and all Civics, and most Hondas) have transverse drive-trains. You can just pick the whole thing up and stick it in the back of the car and everything will turn the correct way. That's how the Fiero, the MR-2, and the X1/9 were all made, with FWD drivetrains behind the front seats. So no R&P flipping required.

- The AWD Civic rear diff and power transmission setup is horribly flimsy. It won't even take 100% of the torque that a Civic engine can put out, let alone an electric motor. The AWD Civic could only send a max of something like 15% of its power to the rear diff, so they sized the components for that. But putting the trans in line with the rear wheels will work just fine.

- The front compartment, where the engine used to sit, can be used for batteries. There is also a goodly amount of space in the back of the CRX, including the area taken up by the fuel tank. IMHO there is more than enough for an electric motor and batteries and the transmission.

- There have been mid-engine'd CRXes made. Or at least one, with an NSX drivetrain. It was made by chopping out the rear of the car and adding a partial tube frame to handle the loads. Something similar would be required for the electric motor and transmission in this case.


It would be a whole lot of work. Doable, certainly, but you'd have to really like fabrication and have some pretty good equipment to use.

It would be much simpler to start with a Fiero. Possibly an MR-2 (the later ones may have more of the look you want; the early ones are very small indeed). You could also use a Porsche 914; there are a number of electric conversions of that car around. Google can show them to you. It has a lot of room for batteries...

-soD

[Clev]

Originally Posted by some_other_dave

It would be a whole lot of work. Doable, certainly, but you'd have to really like fabrication and have some pretty good equipment to use.

Interesting. How many batteries can you fit just behind the driver with the motor/transaxle back there?

It would be much simpler to start with a Fiero. Possibly an MR-2 (the later ones may have more of the look you want; the early ones are very small indeed). You could also use a Porsche 914; there are a number of electric conversions of that car around. Google can show them to you. It has a lot of room for batteries...

Again, how many batteries can fit behind the driver? The flaw in his plan is that he wants everything at the back: engine, transmission and batteries.

[vskid3]

Originally Posted by Clev

1. AWD Eclipse. You're going to throw out the drivetrain and couple the motor/tranny directly to the rear diff, I assume. That means that you'll have to mount the motor/tranny to the suspension as unsprung weight; otherwise, there will be no provision for the motor to move relative to the suspension. (On RWD cars, the driveshaft takes care of this; on FWD cars, it's the CV shafts.) Throw a 200 pound motor and 125 pound tranny on your suspension as unsprung weight, and you'll probably crack a rim every time you hit a pothole.

I really doubt the AWD Eclipse has a solid rear axle, so the argument about adding unsprung weight is void. Everything else looks good, though. The only efficiency to be gained by putting everything in the back is wheelies per mile.

[Frank Lee]

What I find intriguing is someone who thinks they are up to the job of building an EV asking these sort of questions. I mean, if you can thread a nut onto a bolt, why are you asking these things? Don't you know?

Clev: your assumptions are equally strange. Do you think a solid axle is banging around under the rear of that AWD? Really? Does a rearward weight bias spell instant highway death?

I can see what he's getting at with the rear MOTOR (engine ) rear battery layout, and it makes perfect sense to me, and I think it's worth pursuing. As I've explained in the XL1 thread, added weight at the rear of a vehicle is much more manageable than added weight at the front. He is thinking he wants the batteries right next door to the motor for "cleaner" wiring. But I seriously doubt that as this thing goes forward (if it does at all) that the final solution will be all the batteries in one spot. There will be some in the back and some in the front. That should even out any *overblown* handling concerns, but then it negates the "clean" power cable theory.

I wonder if Winfield's IP is the same as that of the guy who was going to mod his old Jeep to get 50 mpg? Same sort of, "I'm gonna do this but I don't have any idea how"? I feel like, if ya have to ask, it ain't gonna happen anyway.

[Ryland]

The main reason that converted electric cars use a transition is that it's an easy part to hook the electric motor up to so with a rear wheel drive vehicle like a pickup truck or a vehicle that has a 4 wheel drive version that you can bolt the rear suspension and drive train in to the car you have, then you have a really simple drive train with the motor connecting to a drive shaft stub connected to the rear differentail, only draw back with this set up is that it has been pointed out that some cars don't have a strong enough rear end to handle an electric motor, but either way the electric motor is going to take up alot less space then a gas engine and transmision grafted in to the rear of a normaly front wheel drive car.
Also, once you take the gas engine out of the front, what are you going to do with that large empty space? seems like a great space for batteries to me.

[Clev]

Originally Posted by Frank Lee

Clev: your assumptions are equally strange. Do you think a solid axle is banging around under the rear of that AWD? Really? Does a rearward weight bias spell instant highway death?

I can see what he's getting at with the rear MOTOR (engine ) rear battery layout, and it makes perfect sense to me, and I think it's worth pursuing. As I've explained in the XL1 thread, added weight at the rear of a vehicle is much more manageable than added weight at the front. He is thinking he wants the batteries right next door to the motor for "cleaner" wiring. But I seriously doubt that as this thing goes forward (if it does at all) that the final solution will be all the batteries in one spot. There will be some in the back and some in the front. That should even out any *overblown* handling concerns, but then it negates the "clean" power cable theory.

And that's exactly the point. He insists that the motor, transmission and batteries are all at the rear of the car. Do you think that having 300+ pounds of motor/transmission and 1,000+ pounds of battery hanging over and behind the rear axle, with an empty compartment up front, isn't going to screw with the handling of a car that wasn't already designed that way? And I might add that his whole stated reason for doing it wasn't for handling, but for efficiency. Having your steering tires completely unloaded and your drive tires heavily loaded does nothing for efficiency.

I wonder if Winfield's IP is the same as that of the guy who was going to mod his old Jeep to get 50 mpg? Same sort of, "I'm gonna do this but I don't have any idea how"? I feel like, if ya have to ask, it ain't gonna happen anyway.

Which is why I compared it to an HHO thread. "Hai guyz, I'm gonna buy a 4,350 pound car and put everything behind the rear axle because I'm doing it for the mpgs. Hey, why are you picking on me?"

[Frank Lee]

Everything in back ain't gonna happen anyway; there isn't enough room.

[some_other_dave]

Originally Posted by Clev

Interesting. How many batteries can you fit just behind the driver [in a CRX] with the motor/transaxle back there?

Depends on how much space is required for the motor, tube-frame, etc. Also how much of the rear luggage space you're willing to turn into battery storage, and how you separate the engine compartment from the rest of the car. Figure using the CRX transmission, a relatively compact electric motor, using not much space for the tubes and walls, and that you're willing to go all the way up to the height of the stock cargo divider. Also, ignore whatever structure you need to hold all of the batteries.

At a guess, I'd say you could get 10-20 full-sized batteries in the available space, including taking up at least some of the space for the fuel tank.

Again, how many batteries can fit behind the driver? The flaw in his plan is that he wants everything at the back: engine, transmission and batteries.

I don't know for the Fiero or MR-2, or the X-1/9 for that matter. In the 914, there's a ton of space. You can easily fit a half-dozen batteries in the rear trunk, if you really want to expose the batteries to road hazards you can stuff up to another half-dozen next to the transmission. Plus the electric motors take up a whole lot less space than the stock ICE motor does, so there's easily space for another half-dozen batteries in the engine bay itself! Then, if you're willing to put batteries elsewhere, you can fit another four or six in the fuel tank compartment, and at least six and possibly up to ten more in the front trunk!!

So in the 914, figure you can fit 12 batteries easily in the space available behind the driver. Maybe 18-20 with a bunch of work. And there's the possibility of a lot more if you use space up in front...


Of course, all of the numbers I'm throwing around require the design and fabrication of systems to hold and connect all of those batteries. And some of that is probably not that easy, even if there is sufficient space.

-soD

[Clev]

Originally Posted by some_other_dave

At a guess, I'd say you could get 10-20 full-sized batteries in the available space, including taking up at least some of the space for the fuel tank.

20 T-105 batteries are 1240 pounds. Add 300 pounds for the motor/transmission, and you're talking about over 1,500 pounds on and behind the rear axle of a CRX, not counting wiring and battery boxes. Face it: it's possible, but massively impractical, and provides no benefit to an EV, which was the whole point.

I don't know for the Fiero or MR-2, or the X-1/9 for that matter. In the 914, there's a ton of space. You can easily fit a half-dozen batteries in the rear trunk, if you really want to expose the batteries to road hazards you can stuff up to another half-dozen next to the transmission. Plus the electric motors take up a whole lot less space than the stock ICE motor does, so there's easily space for another half-dozen batteries in the engine bay itself! Then, if you're willing to put batteries elsewhere, you can fit another four or six in the fuel tank compartment, and at least six and possibly up to ten more in the front trunk!!

So in the 914, figure you can fit 12 batteries easily in the space available behind the driver. Maybe 18-20 with a bunch of work. And there's the possibility of a lot more if you use space up in front...

Which he completely refused to consider. He wants everything over the back axle.