# RX8 Project - KERS type system.



## RotaryKing (Jan 25, 2011)

Hi everyone, I was reccomended to this site by a friend when I told him I was tossing around an idea for converting my car to a bit more efficient one. I was thinking something similar to a mild hybrid to help around town and highway. Currently, driving conservatively I am averaging around 15-17mpgs in town and about 22mpgs highway and has seen as low as 13mpgs running premium. I understand that having a rotary causes a few issues but I thought about it a bit and concluded that a mild hybrid is the way to go because the rotary cannot be submitted to constant restarting especially in stop and go traffic. The KERS system comes in for track use. I read up a bit about it but I am still confused in some areas. I know that it can ether generate power from braking or off of the flywheel. It gives them a temporary boost in power per lap. The energy is stored and discharged as a boost in power. If I were to venture a guess, it would probably be a large capacitor that can store it and discharge it. I don't need a huge boost in power, just a quick surge when my RPMs drop too low to get back into my power band above 6000RPMs. I am not quite as sure as to where to start with something like this and how to go about doing it. I don't quite know if it is even possible with a FR setup with a manual gearbox on a rotary. Any help would be greatly appreciated.

I am quite a stickler for weight too so I am really weighing this in my mind. Its either this so that I can drive it more on a daily basis or go another route and make it a strict weekend fun car.


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## Nathan Atkins (Mar 22, 2012)

I had exactly this same idea for my rx8 email me and we can share ideas. Ive found lots of good info online.

The basic idea...

Section the driveshaft and use the existing powerplant frame to mount a NetGain WarP 7 motor
it has 55lb ft of torque to offer tapering off to 0 at about 70mph and can be spun to 80 mph or so with no worries

This is tedious typing on the kindle fire, id like to make a proper message later when my son is done with the laptop

I'm very excited to see I'm not the only one thinking of this, I'm curious to see what you've found out so far

Nate

[email protected]


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## skooler (Mar 26, 2011)

There are 3 other RX8 conversions on the forums at various stages.

Have a search and a read if your interested.

Cheers

Mike


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## RotaryKing (Jan 25, 2011)

Hey guys,

I haven't done much over the past year. Med School was a royal pain. Over Christmas, my car decided to die out on me. I am in the process of rebuilding it and haven't decided on the electric motor or what rotary engine to go with. So far I have a 20B in the running but its a long haul right now. I have a build thread made on another site.


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## Nathan Atkins (Mar 22, 2012)

I wasnt able to open up your build thread unfortunately.

what i had in mind was similar to this:
http://www.netgaintechnologiesllc.com/the-solution.html

but scaled down for my car, i havent measured yet but i think the warp7 will fit inline on the drive shaft system and mount to a bracket welded to the powerplant frame. I basically want a mild hybrid system, I dont even need the regeneration system, i just want to ease the load on the gas engine whenever possible.

The RX8 i found on here was a full electric conversion. I'd like to retain the ICE


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## RotaryKing (Jan 25, 2011)

http://carfanaticsforum.com/thread-122.html

Check the last couple pages.
That is my build thread. I have yet to figure out what I want to do with it. I didn't even look at electric motors but I will take a peak. I was thinking about a flywheel motor but I haven't looked at or know about much else. I guess I should start looking.


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## Nathan Atkins (Mar 22, 2012)

I see why the link in your signature doesnt work, the url doesn't include the "forum"

I didn't know that flywheel systems were available, maye from Williams Hybrid Power?


Anyway, here's a cut and paste of the post i made over at RX8club.com about the electric system:

I'm right now looking into making a KERS system using a Netgain WarP 7 and a switchable 48v/72v battery pack. 

It would provide peak torque of 65 ft lbs from 1500 drive shaft rpm (about 26 mph with a 4.444 diff) tapering off linearly to 20 ft lbs at 3600 drive shaft rpm (62mph)

The basic idea is to section the factory drive shaft and install the warp7 inline with the remaining first half of the drive shaft. Netgain uses a similar system on freight trucks, but the warp7 is small enough to be mounted to a bracket welded onto our power plant frame.

Power from the engine can be driven through the electric motor even when the system is off (If you wanted to remove the battery pack for say an autocross, to save weight) The electric motor stops providing useful torque at about 4000rpm (70mph)but can be spun to 5500 continuously (about 95mph, a more than adequate limit for a street/autocross car)

Motor weight is 93 lbs and couldn't possibly be situated lower in the car, so CoG impact is negligible and the battery pack can go either in the well in the floor of the trunk or up against the rear seat backs in the forward part of the trunk. battery weight depends on what type of cells but for my power requirements in Lithium Ion it's about 100 pounds. So a total weight gain with wiring and controller heads of about 200-225 pounds (the weight of a fat friend)

Maintaining speed at 45-50 mph, as I do commuting and running by sons to school, requires minimal engine torque, I think this system would allow you to basically let the engine idle along for much of the commute ( you'd need to keep it on for accessory drive, EAPS, brake vacuum, etc.) 

Power recovery through this motor is possible and with as much uphill/downhill as there is on my commute, it would be very useful, but for starters I'm interested in just topping off from the garage every night)

So there you have it, additional torque at the speeds I travel most often with relatively easy setup using off the shelf components.

All told this project should come in below $5000 (the cost of a nice turbo setup) At least that's the optimistic figure i pitched to my wife...

Motor Specs:
http://www.go-ev.com/motors-warp.html

and a cartoonish depiction of the system they use on freight trucks:
http://www.netgaintechnologiesllc.com/the-solution.html


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## skooler (Mar 26, 2011)

Nathan Atkins said:


> I see why the link in your signature doesnt work, the url doesn't include the "forum"
> 
> I didn't know that flywheel systems were available, maye from Williams Hybrid Power?
> 
> ...


 
So the motor goes beteen he gearbox and the differential?

Effecively shortening the propshaft?

Makes sense although I'd go for a 9" motor instead of a 7"

There isnt a lot of space down there as the exhaust and a structual member between the gearbox and differential(keeps the straight and alligns the prop shaft) sit in the tunnell.


Just a thought.

Could you replace the differential with one that takes an input (output?) from both sides such as those used on a 4x4

That way one side can take the original propshaft and the other can take the motor. so the motor goes right at the back of the car beneath the boot/trunk where the exhaust backbox is.

As an added bonus. If you can find a box that does fwd/rwd/4wd you could have the option to switch between engine, motor and aengine and motor.

If you want pictures of the rx8 theres is some on my build thread that may be of use to gve you an idea.
http://www.diyelectriccar.com/forums/showthread.php/good-motoriii-p291682.html#post291682

Cheers

Mike


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## Nathan Atkins (Mar 22, 2012)

You're right, there isnt too much room there, the idea was to modify that girder that goes between the gearbox and the diff to hold the Warp7, I chose that over a 9 because of it's smaller diameter and the fact that it doesn't need to power the car independently.

Gotta go for the afternoon school run!

thanks ttyl


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## RotaryKing (Jan 25, 2011)

I need to get the time to actually look at those. I'm going to be super busy this weekend so I don't know if I can get to those, but I promise I will give them a look. I honestly like your idea so much better. I don't have to worry about space in the engine bay for it your way and you make an excellent point about the CoG. The only thing that is alarming is the 220lbs of weight. The other thing is, rotaries need to be revved. I'm sure you know why but just wanted to remind you as to why it might not be so great to let it idle that much. I'll look at this and let you know where I might head with this project. I should have the engine out on Sunday so it'll finally give me time to take a look at the links you posted and do some research so we can swap ideas and thoughts.


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