# AWD conversion



## z80 (Dec 18, 2011)

I have a front wheel drive gasoline vehicle that is available as an AWD variant.

I was thinking of acquiring the rear axle from a wrecking yard since it just bolts straight onto the chassis.

This I would then drive with an electric motor.

-the rear axle has a limited slip differential with a flange.
-there is plenty of space underneath the vehicle for an 8 inch wide 15 inch long motor.
- I propose to bolt the electric motor directly to the differential flange with no other gearing apart from the 3.11 reduction in the differential.



my newbie question is...

Since the differential ratio is 3.11, I calculated that the engine RPM range would be in the *0-3000 rpm* range (0-120mph)

what electric motor is suited for low rpm high torque?


I prefer a DC engine as a first project.

The electric motor would be used for launching the vehicle, thereby massively improving traction.

After 10 seconds or so the gasoline engine would have 100% of the workload and the electric motor disconnected from the power source.

(Eventually i would seek to employ a cruise control hybrid setup if possible)


If anyone has any recommendations i would appreciate it.


thanks in advance.

I have been thinking about this little motor...

http://www.evmotors.com.au/products/8inch.html


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## major (Apr 4, 2008)

z80 said:


> I have a front wheel drive gasoline vehicle that is available as an AWD variant.
> 
> I was thinking of acquiring the rear axle from a wrecking yard since it just bolts straight onto the chassis.
> 
> ...


Hi z80,

Welcome. For my sake and future clarity, please call the electric machine a motor and use the engine term for the smelly thing or ICE (internal combustion engine) 

First off, there is either a typo or a mistake in the math. 0 to 300 RPM is not realistic. And a 3.11 ratio will be tough. A higher numerical ratio will be needed if you want to launch the vehicle with a motor of that size with reasonable current.

Direct mount of the motor to the diff will work if you have independent suspension. Otherwise the motor will be unsprung mass and suffer from excessive vibration.

Another thing to beware of is that brushes on DC motors work well when passing current. But running dry so to speak can result in excessive wear. Without declutching the motor, the axle will back drive it with zero current and that may wear the brushes quickly. I can't say if they will last 1000 miles, 10,000 or 100,000. But it is something not usually done.

Hybrids are tough to do. And for your first EV conversion, even tougher. But what the heck. It's your project.

Regards,

major


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## z80 (Dec 18, 2011)

major said:


> Hi z80,
> 
> Welcome. For my sake and future clarity, please call the electric machine a motor and use the engine term for the smelly thing or ICE (internal combustion engine)
> 
> ...


 
thanks for the rapid reply Major.

Yes it was a typo...LOL...I did mean 3000 rpm...(editted now)

As for the brushes I am not concerned about the wear rate, since the primary objective is to make it work first, but thanks for mentioning something i will indeed watch out for.
(perhaps i could periodically cycle some current through them to reduce wear or use regenerative braking)
Yes it does have full independent suspension, in the US it is known as a Galant and I propose to use an Endeavour rear axle.

I basically want the traction and launch of an AWD but without the ongoing 20% extra emmissions penalty.

The Lithium cells is what I was thinking of using since they are significantly lighter (LIFeP04)?

Since I would only need approximately 10-30 seconds at a time I suspect the battery cell amperage need not be very high?

Being a complete noobie is there a way to determine vehicle mass versus required/recommended amperage?

Since this is more of an EV assist drive scheme it should be less complex than a full hybrid setup?


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## Ace_bridger (Nov 22, 2011)

Tomorrow's technology is going on right now in people's sheds...tinkering and trying new ideas and systems. I think it's a great idea and one that can develop in complexity as required.

All the very best of luck and I'll follow your progress closely.

You could create the car details and build in the 'garage' on this site...top right hand corner of the screen. We could follow your build...


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## Gary B (Jun 2, 2011)

z80 said:


> I have a front wheel drive gasoline vehicle that is available as an AWD variant.
> 
> I was thinking of acquiring the rear axle from a wrecking yard since it just bolts straight onto the chassis.
> 
> ...


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## z80 (Dec 18, 2011)

What i was thinking of doing to keep it simple (the KISS method) was to not have any manual control of the electric motor driving the rear wheels.

Just an electronic "window" pulse comparator hooked up to the ABS sensor.

It would detect movement in the front wheels and apply current to the electric motor to match the rpm, and keep applying power until the rpm was in a user selected band.

Also when it detects the rpm pulses are reducing, then apply regenerative braking.

I know the purists will think i am crazy not dispensing with the dirty engine, but the car runs on propane which is very cheap at around a third of the cost of gasoline.


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## Bowser330 (Jun 15, 2008)

z80, i think its a damn good idea...

As Major has mentioned, DC might not be the way to go for the running "dry" reason, also DC is a pain to do regen with, so the best thing would be to use a slightly more expensive, however more applicable motor+controller setup....
The HPEVS AC-50 (~4500$) ~70hp & 110ftlbs, the motor is AC without brushes, so it can spin with less wear, it also has easier to apply regen. There are cheaper less powerful versions of the setup, but the AC-50 is king (at the moment)

You also asked about battery, now, torque is limited by amps and the amount of amperage a specific lithium battery can SAFELY put out over a short period of time is a specific range/value. what you need to look for is the C-rating of the lithium battery. How many amps can be burst/temporarily drawn from the battery safely. So for example an A123 battery is 3.3V and 2.3AH, but its burst C-rating is 50C, so it can push out 115A safely, the C-rating on a 40AH Thundersky is 4C(this is from personal experience from members on the forum), so 160A safely. one battery was 40A the other was 2.3A...all im saying is make sure you take note of the C-rating and get feedback from the forum on your battery selection. Headways, might make a great pack for your application.

As for Regen, If/when I get around to building such a conversion I would have the regen be activated by the brake lights, but have the regen turn on and stay on until the throttle is pressed. That way you can tap the brakes, regen turns on, you can remove your foot from the analog brakes and you will still slow and store via regen, if you aren't slowing down fast enough, you can always re-press the analog brakes for extra stopping power.

I myself have been pondering such a setup, however I have had some concerns...

(1) How will you ensure the front and rear axle's are at the same rpm, will the e-motor controller talk to the ICE engine management? OBDII?

(2) How will you control the throttle of the e-motor controller, will it be proportional to the ICE throttle, e.g. ICE pedal is pressed 20%, e-motor pressed 20%, or maybe it would be better on fuel economy to have the e-motor have more responsibility of the torque upfront, so 20% ICE = 40% e-motor?


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## z80 (Dec 18, 2011)

Thanks for the reply, I was thinking of the setup only being active in the 0-25 mph speed window, thereby being a traction launch system.

Once the vehicle has launched (due to slippery road surface or performance demand) then the rear wheels need no electric drive.

The power required to do that is not huge,though the current is, i was thinking that seeing as how it would be a short duty cycle then the overall battery count would not need to be large. As you have mentioned though, the C rating would be critical.

The way I envisaged controlling it would be through tapping into the ABS magnetic pickup sensor.

The sensor has 52 lobes on the pickup ring.

That means if i should be able to monitor a variation of 1/52 of one wheel rotation discrepancy between the front gasoline drive system and the rear electric drive system.

If a proportional digital analogue system was employed, where as the count of lobes sensed variation increases, this could be used in an DA conversion to proportionally control the motor voltage.

So...the moment 7 degrees of tyre/wheel spin is detected the rear drive system could proportionally engage for say a 10 second lock and hold current unless reset by further wheel spin.


it's just tossing ideas about the control system around at the moment.

The car has drive by wire throttle already, which essentially is twin variable resistors producing a 0-5v swing as you press the accelerator pedal.

It should not be too difficult.


Thank you for the battery info....what is the best Lithium battery manufacturer for say 600amps at 70 volts demand taking into account the C rating with the smallest footprint and weight and base AH?


I think you have mentioned an A123 and a company called Headways as being a good C rating?

sorry for all the questions....


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## Gary B (Jun 2, 2011)

z80 said:


> What i was thinking of doing to keep it simple (the KISS method) was to not have any manual control of the electric motor driving the rear wheels.
> 
> Just an electronic "window" pulse comparator hooked up to the ABS sensor.
> 
> It would detect movement in the front wheels and apply current to the electric motor to match the rpm, and keep applying power until the rpm was in a user selected band.


I really like this idea. - Believe me. - It sounds like you might be into designing your own "controller". - Good fun ! - As i have been warned here by others: keep your eye on "fault" modes and what happens "if". - 



> Also when it detects the rpm pulses are reducing, then apply regenerative braking.


I'm interested in finding out how you are going to do that.



> I know the purists will think i am crazy not dispensing with the dirty engine, but the car runs on propane which is very cheap at around a third of the cost of gasoline.


I do not think you're crazy. If (when ?) your electrical system breaks down you'll still have a way to get home. - (As long as you still have your propane.) - Best to you. Gary B


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## Batterypoweredtoad (Feb 5, 2008)

This conversion is an interesting concept that many people have considered but I have never really given much thought to whether it would work well. I think it can. If I were to try it, here is what I would do: 

1) Use a 13" motor. You need lots of torque for the direct drive rear and you need very little in the way of RPM's. A big 13" gives you exactly that. Using Kostovs motors as an example their 13" provides about 2-3x the torque per amp when compared to the 9". Space may be limited, but enlarging a tunnel isn't really that big of a deal. 

2) Drive the EV motor just like you would in an EV. Have it tied directly to the throttle just like you would if the ICE wasn't present. You will get a varying amounts of assistance from the Electric motor as you go through the gears, but don't worry about the whole lack of syncronization bugaboo that is the darling of the internet. Whats pushing one end couldn't car less about what is happening on the other. The only issue I can see is if you have a manual transmission up front. Slipping the clutch to get the ICE drivetrain going would cause the EV motor to push the car which could be fairly disconcerting. An automatic drivetrain should make this a non issue. 

I would be really curious to drive something converted in this fashion. I am curious though what would happen as you run out of charge. I don't really see any easy way to make the EV drivetrain disconnect as you drive so you can go long distances purely on the ICE. Being limited by the EV range eliminates one of the main benefits of a Hybrid. Maybe a smarter controller could drastically cut back the battery amp limits as the pack dies so you get just enough juice to spin the motor fast enough to keep it from becoming a generator. Such a low draw should allow a pack to get a lot of miles out of the lower end of a charge. I don't know of any readily available cheaper controllers that want to be a charger unless you go AC. Maybe the biggest curtis AC controller/motor setup would work? It wouldn't get you near the torque of a big 13", but it would allow regen. In the end though, you still end up with a heavier more complex vehicle for you daily trips with your only advantage being long distance capability.


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## z80 (Dec 18, 2011)

I have already started this project, and am up to the electric stage.

The donor car is the equivalent of the US galant with 3.8L V6 engine.

My brother worked at Mitsubishi for 15 years and got me all the service manuals.

It turns out that the US built Endeavour has a rear axle and differential that looked like it would bolt on to both the US galant and our australian 380 cars.

I took a gamble and had the rear axle from a wrecked Endeavour shipped across.

I got ripped off by seedy people who didn't deliver evrything i paid for but I got enough major bits to do a basic proof of concept.

The biggest hurdle is in the engineering/safety issues with a major modification....this, unbelievably, just bolted straight in.

The differential has a 4 inch flange that shouldn't be too difficult to mate to an electric motor...it's even a limited slip differential!

Here is how well the rear axle from an Endeavour SUV bolted to a FWD galant/380.


Uploaded with ImageShack.us


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## Bowser330 (Jun 15, 2008)

My conversion would be more of a performance conversion and would be used all the time, or whenever I had juice! 

It seems your conversion wouldn't be used as much, only during periods where you needed AWD for a short bit. If that is the case then your battery AH can be small, as the system wouldn't need to operate very much.

72V 600AH smallest weight...hmmm
Check out Cell Man @ http://www.emissions-free.com/catalog/c1_p1.html

He can make customs packs and the price seems to be about $6.50 per cell with BMS...So that would mean 23 series = 75V & 9 parallel = 600A burst @ 30C, which is pretty safe for those cells, especially over a short 10 sec period. So you would need about a 207 cell pack @ 6.5$ = $1,345$
each cell weighs 70g so the weight of the pack without BMS would be 32lbs, total pack = 1.55 KWH

I am not really sure about a cheap/safe source of Headways, maybe someone else can chime-in...I know that they retail for about 18$ each, they come in a 10A variety that can burst 15C so 150AH, they are 3.2V and 300g each... so you would need 23 series (~75V) and 4 (40AH) in parallel = 600A burst, 92 cells needed @ 300g = 61 lbs, cost = 1,656$, energy = 3 KWH, I am not sure what the cost of a BMS would be, maybe 100$ or so, and you would need to assemble the pack yourself, so...a bit more of a manual method, but for a little more weight, cost and time you get double the energy...


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## z80 (Dec 18, 2011)

Bowser330 said:


> My conversion would be more of a performance conversion and would be used all the time, or whenever I had juice!
> 
> It seems your conversion wouldn't be used as much, only during periods where you needed AWD for a short bit. If that is the case then your battery AH can be small, as the system wouldn't need to operate very much.
> 
> ...


I am very grateful for your reply with the link.

I would happily pay more for professional assembly for my first battery pack because then i can focus on other things.


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## Bowser330 (Jun 15, 2008)

Batterypoweredtoad said:


> .... but don't worry about the whole lack of syncronization bugaboo that is the darling of the internet. Whats pushing one end couldn't car less about what is happening on the other. ....


Can you please elaborate on this a bit more? 

Will the e-motor axle's wheels normalize "through the road" to the ICE driven wheels?


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## Batterypoweredtoad (Feb 5, 2008)

Bowser330 said:


> Can you please elaborate on this a bit more?
> 
> Will the e-motor axle's wheels normalize "through the road" to the ICE driven wheels?


They should. The only effect having a motor on the other end should have is that the e-motor shouldn't have to work as hard. Its similar to going down hill or pushing a car of half the weight. It all just adds up to the e-motor having an easier time or accelerating the car faster. 

To be my own devils advocate: I have seen one example of non linked front and rear drive wheels with separate motors possibly being a problem in one of the Tiger twin bike engine powered cars. The show 5th gear blew the front motor. It's possible the front engine blew because it was drastically oversped due to spinning the front wheels while the rear wheels had traction. I also heard a valid argument that in a twin engine car with turbos you might have one engine come on to boost mid corner while the other was out of boost and upset your cornering balance.


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## Bowser330 (Jun 15, 2008)

Batterypoweredtoad said:


> They should. The only effect having a motor on the other end should have is that the e-motor shouldn't have to work as hard. Its similar to going down hill or pushing a car of half the weight. It all just adds up to the e-motor having an easier time or accelerating the car faster.


cool, that makes the hybrid much easier.

One thing though is that the e-motor wouldn't have the benefit multiple gear ratios...so the e-motor's peak power would be dialed in to a specific speed.


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## Batterypoweredtoad (Feb 5, 2008)

Bowser330 said:


> cool, that makes the hybrid much easier.
> 
> One thing though is that the e-motor wouldn't have the benefit multiple gear ratios...so the e-motor's peak power would be dialed in to a specific speed.


I agree completely. That is what makes me think a big low rpm motor would be great. It would mate nicely with the factory diff to allow you to spend most of your driving in the big motors sweet spot.

This thread makes me want to revive my search to see if anyone has figured out a good controller for the Toyota Highlander rear E-motor/differential yet. Heck, does anyone know if the aftermarket has come up with kits for the bigger pack conversions on the highlanders?


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## z80 (Dec 18, 2011)

The car I am using has traction control which will in theory limit the disparity between front and rear wheelspin over a certain value.


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