Factory Five Project 818 4wd EV

LSB · Jul 25, 2012

Greetings Folks,

Long time lurker, first time poster, due to my humble request for help from your great community.

I have a 2007 Subaru WRX sti which my wife recently rolled into a ditch. I went to Google to help me come up with an idea to salvage what money I could from this catastrophe.

I stumbled upon this kit car

http://www.factoryfive.com/kits/project-818/

This mid-engined, rear-wheel drive layout leaves ample room around the front axle for an electric motor/controller/battery setup.

GOAL

600+ HP in a <1000kg vehicle designed to optimize 1/4 mile Drag time.
(400 from combustion engine + 200 from electric)
After researching many types of electric motor capable of delivering the desired 200HP of electric power needed to reach this goal I have come up with some questions I havent solved.

Due to the application of the electric motor, a long range will not be required.

The first question is: If using Li ion batteries, what would be the estimated minimum weight of the battery array required to power a capable electric motor to 200HP

Secondly I am not sure which of the popular motor designs would best suit my application. I am interested in installing the best technology available to reach my weight/power goals.

eg. will an ac asyncronous motor handle that power?
Will a bldc setup like the scott drive be able to stay under the weight limit?

The initial weight of the car is 818kg, leaving 182kg to play with....

jk1981 · Jul 25, 2012

25-30kg of high power (50C) Lipo is about as light as you can realistically go for a 200Hp capable pack and that will deliver for about 1 minute (though rated for continuous 50C discharge they're unlikely to actually deliver that for 1min without something overheating). Pack life will likely be in the 10s not 100s of cycles if you push it that hard!

There's no point in going for top of the range high tech motor/control for this sort of job, you might as well get something that can take the power for short bursts without cooking and is simple/robust. Efficiency is less important than ability to handle big overloads for 10-12 seconds. Series DC might be the best bet since big power controllers are relatively cheap. Still, it's not going to be simple once you start looking at gearing, diffs etc. Two small motors, one per wheel might be a relatively neat solution eliminating the diff and offering the possibility of series/parallel switching to introduce some electrical 'gearing'.

Personally I'd go the other way: Sell the Scoobie motor, keep the weight down, install a big power (200-300kW), low-medium energy (maybe 5-6kWH, 50-60kg Lipo) electrical system with a very small motorcycle ICE providing maybe 10-15Hp of parallel hybrid cruise power. That way you get good fuel efficiency, normal range and very good peak performance.

Or just build it with simple Scoobie power and enjoy it

LSB · Jul 26, 2012

jk1981 said:
Personally I'd go the other way: Sell the Scoobie motor, keep the weight down, install a big power (200-300kW), low-medium energy (maybe 5-6kWH, 50-60kg Lipo) electrical system with a very small motorcycle ICE providing maybe 10-15Hp of parallel hybrid cruise power. That way you get good fuel efficiency, normal range and very good peak performance.

This is an excellent idea for an 818 build if you didnt have an sti and started from scratch because the end result for the cost of the build would be phenomenal.

With a 15kw ICE and high powered netgain you would have a car that would equal the standard build in power, weight and range without using a drop of dirty fuel. And all for maybe a 15k premium, taking the build cost to around 30k.

For me, the loss I would take from selling the unneeded parts from my car would be too great. The motor, although on stock internals is very high output and I consider a total weight of 2200ish pounds is still very lightweight for a hybrid, or any performance car for that matter.

Due to the info I gathered from the advice you gave I think the scope of the project can be extended somewhat.....

The current estimate of weight distribution is 38/62 meaning that the front has 200kg less on it.

Going the netgain 9" route with a decent controller etc will leave plenty of room for battery weight while being able to maintain a 50/50 weight distribution.

If the Subaru motor output is increased to 500hp through a $6000 turbo and computer system upgrade I cab purchase, with the 300+hp input of the netgain we would have a p2w ratio of 800hp per tonne for acceleration/top speed purposes.

If you then add in the instant torque characteristics of the Electric motor, you will be able to eliminate wheelspin at launch. Being able to get that much power to ground at launch will leave any supercar for dead.

The Lambo Aventador has a p2w of 400hp per tonne, 4wd and sophisticated launch control and completes the 1/4 in 10 odd seconds.

Depending on proper calculations, the battery pack could weigh as much as 90kg while delivering this performance.
If you chose to drive only the electric motor you could still commute on a day to day basis (50km max range?) for the running cost of a chevy volt.
Start the ICE and the car's acceleration potential exceeds any other car on the road.

The first orders are expected to be available "Before Autum" according to factory five which leaves plenty of time to agonize over final decisions and design front axle setup...

dougingraham · Jul 25, 2012

I looked at this when it was in the contest stage. I thought it would make a good roller for a conversion. I wasn't thinking about augmenting the ICE with electric. My own preference would be to just make it a rear drive EV. It is so light that it will make an excellent EV. However here are my thoughts on the electric portion of your idea.

A single Netgain WarP9 at 1200 amps and 192 volts will be about 65% efficient. This would be 309 input horsepower and about 200 HP output. It can do this for at least 10 seconds, maybe 20. To get 192 volts after sag you would need around 256 volts so a pack of 80 LiFe type cells or a pack of 70 LiCo or LiMn configured with enough guts to do the job. Using A123 cells this means an 80S3P pack. This would weigh 119kg (262lbs) for just the cells. Using the 6AH Haiyin cells would require something like a 70S3P arrangment. This would weigh 36kg (79lbs) for just the cells. You would need to use a Netgain Warp drive controller or a Zilla 2K to reach these power levels. (Or a Soliton Shiva which would be overkill.)

Haiyin Batteries 79+ lbs.
WarP9 156lbs.
Netgain Controller 16.5lbs.
Total 252+lbs.

Additionally you will need a transaxle that can handle 200hp with an appropriate final drive ratio.

If you don't want a transmission on the electric portion of the drive system you need to pick an appropriate reduction ratio. Knowing what this would be has too many unknowns. It would be something around a 3.5:1 final drive ratio. You would need to tweak it in at the track.

LSB · Jul 26, 2012

dougingraham said:
A single Netgain WarP9 at 1200 amps and 192 volts will be about 65% efficient. This would be 309 input horsepower and about 200 HP output. It can do this for at least 10 seconds, maybe 20. To get 192 volts after sag you would need around 256 volts so a pack of 80 LiFe type cells or a pack of 70 LiCo or LiMn configured with enough guts to do the job. Using A123 cells this means an 80S3P pack. This would weigh 119kg (262lbs) for just the cells. Using the 6AH Haiyin cells would require something like a 70S3P arrangment. This would weigh 36kg (79lbs) for just the cells. You would need to use a Netgain Warp drive controller or a Zilla 2K to reach these power levels. (Or a Soliton Shiva which would be overkill.)

Haiyin Batteries 79+ lbs.
WarP9 156lbs.
Netgain Controller 16.5lbs.
Total 252+lbs.

Additionally you will need a transaxle that can handle 200hp with an appropriate final drive ratio.

If you don't want a transmission on the electric portion of the drive system you need to pick an appropriate reduction ratio. Knowing what this would be has too many unknowns. It would be something around a 3.5:1 final drive ratio. You would need to tweak it in at the track.

Thank you so very much, this is exactly the type of info I was hoping for!

In respect to the electric motor drive setup, my thoughts are this. Because the electrical system willl only be able to output maximum torque for a short period of time, I feel my best approach is to use a 'no transmission' design with a final drive ratio that with allow the motor to power the car to around 170 km/h(limit of 3rd gear).

This should allow a drive ratio that will really pull off the line which is needed to assist the ICE to get all of its power to the ground off the mark, while keeping weight and moving parts to a minimum.

After researching more I found that this design (called Heavy Hybrid?) has been around for a while in motorsports.

The 2011-2012 Le Mans winning Audi A18 drives the front wheels with Electric motor and uses kinetic force to charge the batteries.

Porsche 918 spyder being released soon also used this concept of 4wd.

Im sure you guys know that though. I am always a little slow.

Joey · Jul 26, 2012

Whatever you decide on, please post lots of pictures of your build. This has potential to be really cool.

LSB · Jul 26, 2012

Managed to find some pics that may be of interest.

This is the Porsche 918 drivetrain design in top down:

And for comparison's sake, I sourced a top down view of the project 818 and roughly estimated where a netgain warp 9 would fit. Bit worried about fitting 192 batteries in...

Is it worth posting other views of the 818 to give some notion of whether this will even be viable due to size constraints?

This option is obviously direct drive with a fixed ratio, I'm not sure if there is any other method that would fit in.......

LSB · Jul 26, 2012

jk1981 · Jul 26, 2012

You'll not satisfactorily be able to exploit the regenerative braking potential using the DC series motor, I suggested that because this appeared to be a project focused on using some bits you already had plus minimal spend to build a drag car.

Also, the sketch you posted has no option for a differential and you'll need to ensure whatever motor you fit can physically hold together at Vmax even if it has long since given up generating any torque. Looking at the CAD rendering it's not very clear exactly where the front shock absorber mounts but since it appears to clash with the (not shown) track control arm I can only assume it's mounted further rearward than it appears where the front CV will need to be <edit> Looks from the plan view like there might be room </edit>. There's also a fair bit of triangulation in the way of your potential driveshaft runs.

If you're willing to spend some more serious money on this It might be worth looking at high performance motorcycle hub motors. Using two gets away from the diff problem, they're much lighter than a 9" DC*, the big ones used (modified) for racing can probably handle around 80kW peak, they're generally AC so open up regen braking possibilities and they're wound for direct drive at very roughly the speeds you're looking at. However, you'd need to make sure the controller and battery could not be damaged by excess back emf at Vmax on ICE power alone. If you're looking at 400+ HP that's going to be what, 160mph+? Two big AC inverter drives wont be cheap though.

*the downside to light weight is less overload capability.

Your battery volume won't be huge, I suspect you could slot a lot of it into a 'transmission tunnel' box between the legs of the passenger and driver which is low and close to the desired COG.

The other thing to look at is how much traction will you have. The COG should be fairly low with the flat Scoobie motor and no roof but the weight transfer rearwards is still going to be dramatic with 400 HP+ launching you forwards. I doubt trying to push another 200HP out through the front wheels will do much for you until you're in 2nd or 3rd besides generate smoke.

It has potential to be very cool but I still think I'd go one way or the other: Aim to get the high performance from the ICE OR the electric, not both. It's your project though, I'm sure there are solutions to all the problems so it'll be cool to watch

jk

LSB · Jul 27, 2012

jk1981 said:
You'll not satisfactorily be able to exploit the regenerative braking potential using the DC series motor, I suggested that because this appeared to be a project focused on using some bits you already had plus minimal spend to build a drag car.

My initial scope was for a streetable drag car, but I had overestimated the weight of batteries needed, meaning the scope can be broadened.

With respect to the DC motor, the main attributes are the overload capacity and the price which are both relevant. The downsides are very significant too though, including no regen braking.

jk1981 said:
Also, the sketch you posted has no option for a differential and you'll need to ensure whatever motor you fit can physically hold together at Vmax even if it has long since given up generating any torque. Looking at the CAD rendering it's not very clear exactly where the front shock absorber mounts but since it appears to clash with the (not shown) track control arm I can only assume it's mounted further rearward than it appears where the front CV will need to be <edit> Looks from the plan view like there might be room </edit>. There's also a fair bit of triangulation in the way of your potential driveshaft runs.

This shot gives a better idea on an actual running car of where the clash points are. I found it in this testing video
http://www.youtube.com/watch?v=uN_jVWlSPmk&feature=related

jk1981 said:
If you're willing to spend some more serious money on this It might be worth looking at high performance motorcycle hub motors. Using two gets away from the diff problem, they're much lighter than a 9" DC*, the big ones used (modified) for racing can probably handle around 80kW peak, they're generally AC so open up regen braking possibilities and they're wound for direct drive at very roughly the speeds you're looking at. However, you'd need to make sure the controller and battery could not be damaged by excess back emf at Vmax on ICE power alone. If you're looking at 400+ HP that's going to be what, 160mph+? Two big AC inverter drives wont be cheap though.

The problem I initially conceive with hub motors is the unsprung weight they add. Also the motors will be much more susceptible to the elements and the disc brake setup is also an obstacle.

The advantage is that more weight on the wheel=more grip in a drag race as well as the lightweight setup.

I just think that the unsprung weight issue and the other complications that are connected to that are just too big a hurdle to choose this method.

In respect to traction, it is the main reason i chose the 4wd EV setup. It is of the utmost importance that the front wheels can be driven past the point of traction otherwise maximum potential hasnt been reached.

How much grip there will be and how to adjust both motor's output accordingly will be a trial and error thing. There will definately be much more grip than leaving the car RWD.

Another thing that is exciting about this setup is the manual gearbox. While the ICE transmission is disengaged during gear changing, the electric motor is still pulling.

jk1981 · Jul 27, 2012

Sorry, I wasn't clear. I don't think mixing hub motors and big brakes in a car wheel is a good idea for the reasons you've also picked up on, inertia vibration and heat. I meant mount them inboard driving a shaft each.

Thinking more about it without some out of the ordinary sophistication (field control of some sort or electrically isolating the battery/controller from excessive BEMF at speed) you're not going to find a motor/controller pair capable of significant torque output and 150mph+ direct drive.

dreamer · Jul 27, 2012

Using a differential to get a 3.5x final drive ratio is not going to get very much torque on the ground, is it ? Torque from a series DC motor may be instantaneous, but it isn't huge. A multiplier of 3.5x isn't much compared to transaxles that yield 12x-15x in low gear. A 200hp vehicle should put something like 3000 lb-ft to the wheels after multiplication thru first a trans and then a diff, right ? The Warp9 might provide 250 lb-ft at 1000amps, so just 3.5x through a diff is pretty weak torque to the ground.

On the other hand, even such a low ratio is going to destroy the motor's bearings at speeds of 150+mph. Figure each wheel revolution will cover 6' of ground. At 150mph (150*5280/60/6) they will be turning at 2200rpm, and any motor attached to a 3.5 diff will be forced to turn at 7700rpm. A Netgain Warp9 may not survive 7700rpm. It is spec'ed at 5500rpm max which would barely get you to 100mph with a 3.5x diff.

Cars like the Tesla get away with only a single gear because they are running AC motors that can take 14000rpm, which means they can use a higher drive ratio than 3.5x.

Have you considered using a lightweight automatic transaxle from a Honda ? Get your 15x torque multiplier at launch and an overdrive final ratio under 3x that will keep rpms low enough the Netgain won't fly apart. Without ever shifting. Just put it in Drive, idle the Netgain via software in a Soliton Jr. just shy of stall converter speed. The efficiency loss in idling the automatic to keep the clutch packs ready shouldn't be a big deal in a hybrid where you aren't trying to eek out every last bit of range from the battery.

Bowser330 · Jul 27, 2012

+1, a lot of good points here.

There are trade offs to direct drive when you have a motor with lower redline.

I like the idea of hooking up an auto transaxle w/Idle but spend the extra 1000$ and get the Soliton-1, Impulse9 ~230ftlbs e-TQ * 85% eff = 196 m-tq, the honda transmission should be able to handle that.

dreamer · Jul 29, 2012

"Batteries would have to be fit in the cockpit, as close to the front as possible."

You could also think about a battery box that is under the cab of the vehicle. Using A123 pouch cells lying flat in 3P packs, laid out 9x7, you could create a 60"x60" box from aluminum diamond plat and extruded aluminum channels that was only 1" thick and bolted covering the bottom of the seating area. 63S3P would easily produce the 200hp you are looking for. That's a $7500 battery with 10kwh capacity. The advantage being low center of gravity and a smooth aero belly pan for the vehicle. The disadvantage being you have to drop the battery box to diagnose battery issues or possibly even to access the bottom of the engine depending on how far forward the engine sits.

LSB · Jul 30, 2012

Thanks again for input, lots of food for thought. I recently saw the movie "Revenge of the Electric Car" Which shows exactly how they use their batteries, including the active and passive safety measures.

One of the passive attributes of their model S battery pack is that it sits under the floorpan of the car In a similar setup to that which you described. They use 18650 form factor which are of similar height to the A123's. The battery unit acts as part of the rigid structure which theoretically increases strength.

While the 63S3P is slightly more weighty than I had envisioned, when you estimate range under heavy load, any less than 20kw would limit its usefulness in racing as the charge that the kinetic charging or the ICE can produce will not be able match the output.

The effect that a battery unit like this will have on the desired weight distribution will be interesting. Using some very basic estimations I'll assume that the torque needed to surpasses tractable force of a 16 by 7" radial tyre to the front wheels (in a 1100kg vehicle) is around 2100nm. While this is easily achieveable with a 9" motor + 2.9:1 gear ratio and 3.5:1 diff ratio, we need to consider that this figure will be raised by the fact that the rear wheels are helping with forward thrust. The same obviously goes for the ICE powering the rear wheels. Due to this, because the ICE generates more torque in addition to the forward thrust of the vehicle sending many more forces to the back wheels, weight over the front would be well served to be kept as close to 50 50 as possible.

The advantage in this respect to using an electric motor at the front is that you can determine the exactly amount of torque to send to the wheels instead of having to mechanically input this using the clutch and accelerator like you would with the ICE. Therefore, in a drag race you just need to concentrate on launching at the top of the torque curve of the ICE.

I received an email from someone at Factory five about the specific dimensions of the chassis and body, but they are unable to produce it at this time as the car is still in development. However, they mentioned that the large area in the front where I had envisioned placing the electric engine has fiberglass channels running through it and up throught the bonnet (for downforce) which will mean bonnet modification will be needed.

Factory Five Project 818 4wd EV

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