Forum Project - Electric D2?

[Goran]

Thanks Steven for the reccomendation their site looks very professional.
Rather than a personal project, I was hoping for this to be more of a forum project, for whoever is interested, to bring together forum skills and so we all learn something. A bit of electronics, engineering, design, machining, etc.

The finished car could then be donated to A8parts as a demo car for the forum and for A8parts, and to show off how versatile a D2 platform is.
The ideal of course would be to have a two motor set up one driving the front axle one driving the rear axle to stay true to Audi's design. But to start with Mikki's idea is best just to go with FWD or RWD for simplicity. They spent $20k on the Maserati! that's nuts, I'll have to watch that episode.

I think weight wise it may be ok. Nissan leaf weighs around 1535kg. A rought back of the cigarette packet calculation for a D2

1730kg for a manual S8 so to get down to the bare platform:
1730
-198 engine
-85 gearbox + flywheel
-66 fuel
-10? fuel tank
-10? front shafts
-10 prop shaft
-11? various other engine bay parts
1340 chassis

+218 Nissan battery equivalent
+58 Nissan leaf motor (not clear if Power module is included)
+23? other random stuff to mount battery and motor
1630kg total

So it seems it would only be 100kg heavier than a standard Leaf. Should be able to move along

There are a few Leafs being broken on UK ebay already, if this project got serious I would be happy to buy a Nissan Leaf motor + power module for around £1300 and donate it to the project. It would probably be easiest to fit it in the engine bay to drive the front wheels and just adapt half shafts to fit the D2 drive shafts.

http://www.ebay.co.uk/itm/2014-Nissa...UAAOSwI2xX8l2y

Alternatively, we could get creative and look for other cheaper solutions such as motors from the various Renault electric cars, Kangoo, Zoe, etc. Or even build our own control module.

Battery cost would be the major hurdle.

I know its all a bit pie-in-the-sky thinking, it would be cool to see a electric D2 though. Or a D3 for that matter (only if we could get rid of the complex air suspension ). To me it seems the lighter weight of aluminium platforms is well suited to electric powertrains.

[MikkiJayne]

The 2.8 FWD 5-speed with velour interior barely tips the scales at 1500Kg Its a passenger heavier than our TT!

Why do most conversions hook the motor up to the original gearbox (as WD did)? I would have thought direct drive to the diffs would make more sense, like the Leaf unit appears to do. With a motor having max torque from 0 rpm it seems like a gearbox is pointless.

Doing direct drive, you could easily put two motors in place of the gearbox, one driving the rear diff and one driving the front (use a rear diff flipped over). Then, all the power control and batteries go under the bonnet to keep the weight balance right. A pair of 150hp motors would push it along nicely

[MikkiJayne]

Interestingly, the Leaf has a single reduction gear of 7.9377. The motor has a top speed of 10,390 rpm, so with the D2's tyres that would give a top speed of 100mph which is probably adequate

I still think you'd need two of them to have acceptable performance in a D2 though, since 11 seconds to 60 is a bit embarrassing for a car like that. It'd be relatively simple to fit in the front, but a little tricker to put in the back unless you decouple the controller hardware on top from the drive system. You could probably just extend the cables and put that in the boot though. The subframe may need a chunk of work to fit the drive in it too, since it looks quite wide.



If you could use an aftermarket controller with it then it'd be relatively simple to tie both drives together, electrically.

Two of these are a little heavier than the 5HP24, but the fuel tank goes as does the propshaft and rear diff so I reckon that's about even, leaving a good 250Kg left for batteries. The Leaf battery is 300Kg, so thats not far off.

Range would be a bit pants - probably only 50-60 miles. It'd be a good commuting car though

[MikkiJayne]

And now I have this stuck in my head, so you lot can too

https://www.youtube.com/watch?v=MK1g5dMYR3s

[Goran]

Some great ideas there Mikki, keep em coming

Yes unfortunately the Leaf and Tesla motors need a single speed reduction gearbox, in order to attain motorway speeds. Interestingly both are roughly 8:1
There are exotic motors out there that have the torque at low rpm and high rpm capability that don't need a reduction gearbox at all, but I don't think they have made it into any cars yet.

Before I found out that Leaf and Tesla need 8:1 reduction gear, I thought about just using the D2 rear diff for front and back wheels and splining a motor directly into it. After all it is a bit like a reduction gearbox. If a more torquey motor can be found it could do alright with a 4.111:1 reduction?

Definitely two motors all the way. I don't know how it would work electronically though, do they need to be run from one controller so that traction can be controlled between front and back axles.

Great idea about space under the fuel tank, maybe a whole Leaf unit could fit under there if tilted at an angle?

Wow the Leaf unit is quite heavy with the trans included, that's around 80kg. With the control module its probably over 100kg?

Yeah! I'd rather have a D2 with 60 miles range than a Leaf!

[MikkiJayne]

The WD car used a two-motors-in-one-housing unit to get the most power it could (link here), but even that only had 120hp peak, so the Leaf motor is quite impressive. The power curve for their motor looks just like a 40V S8's torque curve, but the torque for the motor looks like a steam engine

AC-35x2 Torque Curves

68Kg for that, so 80 for the Leaf including the reduction gear isn't bad. I reckon it would work with a 4:111 reduction based on the graph. Its just like being in 4th all the time which would be fine since you're not going for top speed. Using the 3.7 final drive from the 4.2 A8 would probably be better actually since you'd make better use of the torque spread up to 3000rpm - 64mph, vs 58mph with 4:111.

Koenigsegg can do 0-248mph with no gears using a torque converter and an MGU on the crankshaft! https://www.youtube.com/watch?v=glf_k4qGBAA. They're effectively in 7th gear all the time!

Controlling two motors with aftermarket controllers appears to be simple - one controller for each motor, both being fed the same speed signal input. Thats what the WD car did, albeit both motors were built in to the same casing. It would be interesting to see if the control device talks can-bus, then you could still run the ESP You'd need it with all that torque.

[Goran]

Oh yes I saw that, amazing what they can do with just a torque converter, pure genius!
Good point I forgot that ESP is an independent system using the brakes.

[Ameiseuk]

Curtis Instruments or Zapi will do a controller (or matched pair) that will do your job.
The use a fly-by-wire input and simple voltage input for direction control.
Would be a lot easier to use a stand alone black box from these guys rather than trying to bodge a Nissan Leaf controller

A lot of 3-wheel electric forklifts use a single motor controller with dual motor outputs (one for each drive wheel on the front of the truck). They use a steer angle input to vary the motor speed (and even reverse drive) in tight turns. We wouldn't need that input but if you were getting creative you could use it as a form of traction control.
If the rear wheels were spinning you could theoretically cut output to the rear motor while maintaining the required power to the front axle (or vice versa) restoring it when the abs sensor inputs match

I can put a call in to either of those suppliers if needed

[tintin]

Originally Posted by MikkiJayne

Interestingly, the Leaf has a single reduction gear of 7.9377. The motor has a top speed of 10,390 rpm, so with the D2's tyres that would give a top speed of 100mph which is probably adequate

I still think you'd need two of them to have acceptable performance in a D2 though, since 11 seconds to 60 is a bit embarrassing for a car like that. It'd be relatively simple to fit in the front, but a little tricker to put in the back unless you decouple the controller hardware on top from the drive system. You could probably just extend the cables and put that in the boot though. The subframe may need a chunk of work to fit the drive in it too, since it looks quite wide.



If you could use an aftermarket controller with it then it'd be relatively simple to tie both drives together, electrically.

Two of these are a little heavier than the 5HP24, but the fuel tank goes as does the propshaft and rear diff so I reckon that's about even, leaving a good 250Kg left for batteries. The Leaf battery is 300Kg, so thats not far off.

Range would be a bit pants - probably only 50-60 miles. It'd be a good commuting car though

That Leaf motor looks a bit bigger than the Tesla ones, I'll see if I can find some pictures.

[Goran]

Only because it is a part of the transmission. Its actually quite small, unfortunately I am not sure that it can be used on its own outside the housing which is part of the transmission casting.

Of course I would take a Tesla motor any day, much more powerful and no permanent magnets. They are not so easy to come by especially not for £1300 inc controller and transmission.