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Discussion Starter · #1 ·
I am creating this new thread for my second EV project.

I am still competing in my first EV (The Batt mobile). I will continue to update that thread until I decommission that car (probably at the end of 2017)
http://www.diyelectriccar.com/forums/showthread.php/autocross-ev-special-166009.html


This new thread is to share my progress on the new project. My direction has changed a few times during the planning phase.

Originally it was to be a totally new car, single seat, Front wheel drive, with a target weight of around 300kg.

I have now decided it will be single seat but a bit bigger than the previous idea and will be mid engined and rear wheel drive. I am confident the weight will be less than 430kg but I am not sure exactly what it will end up being.
 

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Discussion Starter · #2 ·
Here are a couple of pics of the progress so far.

The idea is to take maximum advantage of the torque by making it rear wheel drive. I have decided to re-use my existing motor, gearbox, controller and batteries to ensure I still have the same power but with reduced weight.

Another key improvement will be the rear suspension geometry which I got totally wrong on the first car.
 

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Discussion Starter · #3 ·
These mockups are using a spare gearbox that is identical to the one in my first car. The bucket represents the motor (I tell people it will be a 20L motor :) )

As you can see I will still sit on the right side of the car with a gear shift in the centre. The batteries will sit down the left side and as close to the firewall as possible.

I will have passive steering on the rear wheels. I will have the ability to dial it up or down. I will increase it for motorkhana where you want the back end to slide sideways. I will decrease it for khanacross where you want maximum grip through corners.

I have purchased a reversing contactor and I have programmed an Arduino to control it and the throttle. This will allow me to switch it fast but in a controlled sequence to protect the key components.

The car is 160mm narrower than the old car and 50 mm lower. The length will be about the same.

As I mentioned I am aiming for sub 430kg. Some people are thinking it will be more like 330kg but I think that is too optimistic.
 

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Discussion Starter · #4 ·
Its a little dificult to form a mental image of the finished product from these pictures. But if you think of a rather squarish / agricultural, single seat version of a Ford Indigo without the front wing and add a full roll cage.
 

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Hi
Looks like fun - I do like RWD - but then my old mini FWD was also great fun

What was your gearbox again?

Did you think about going to the layout I used with the Subaru diff and direct drive?

I can spin my rear tires - and I got an LSD with the Subaru bits

Looks like you will be sitting about a foot further forwards (compared to the rear wheels) than I do
What front suspension are you going to use?
 

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Discussion Starter · #6 ·
Hi
Looks like fun - I do like RWD - but then my old mini FWD was also great fun

What was your gearbox again?

Did you think about going to the layout I used with the Subaru diff and direct drive?

I can spin my rear tires - and I got an LSD with the Subaru bits

Looks like you will be sitting about a foot further forwards (compared to the rear wheels) than I do
What front suspension are you going to use?
Going purely by stats FWD is quicker in my sports. But I don't think it is true for EVs. One reason is there is less weight over the front wheels and the other is that I am losing the advantage of the torque through wheel spin.

So I have decided to take full advantage of the launch by makign it rear wheel drive.

The gearbox is a 5 speen Nissan N13 box (LSD variant).

Yes I have a couple of the Subi diffs. But goign down that path would have meant a lot more expense and tiem to achieve the correct outcome. Mostly because of the custom drive shafts required and some way of bringing the gearing down to what I need. But it is still on the cards for my next project using my 8 inch motor.

The lower control arms will be pulsar n13 on all 4 corners. The upper control arms will be home grown same as last time. All 4 corners will be similar to the front of the last car with the shocks sitting up over the top. The new front will sit a lot lower as they won't have to sit over the motor and gearbox.

I will be concentrating a lot more on Aero too. with no motor and gearbox out front I can make the airflow much better from front to rear. The floor plan will be entirely flat (not even a bolt protruding through). I will also have a cover over the left side of the car from the dash all the way back over the motor. Eventually I will also add my big GTR wing over the back.

The current car is fairly quick so I can't wait to experience a lighter version with the same power and even better launch.
 

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Going purely by stats FWD is quicker in my sports.
I'm not sure how you are analyzing the data, but I think autoslalom is dominated by front wheel drive simply because the vast majority of small and light cars are front wheel drive.

The gearbox is a 5 speen Nissan N13 box (LSD variant).
I think the transmission could be valuable, compared to a single-speed configuration, even if it is never shifted during a competition run. The gear can be chosen to suit the course... like changing gearsets in a quick-change, but much cheaper.
 

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Discussion Starter · #8 ·
The data I am refering to is the outright record times for all the Australian Motorkhana championships. 90% of the records are held by front wheel drive cars.

But 100% are held by specially build motorkhana vehicles (front or rear wheel drive). In other words when we choose to build a motorkhana car we get to choose between front or rear wheel drive. So its not really driven by car manufacturers at all.

I think you hit the nail on the head regarding the gearbox. If money were no issue of course it would make sense to remove the weight of the gearbox and have quick change gears. But I am on a super tight budget so the whole car (The current car) is cobbled together based on whatever I can find from wrecked cars and whatever I can make myself. The new car won't be too different from this. But there are a few things that will be a little less aggrecultural like the suspension mounts where I will be using a fair amount of Rose joints.
 

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The data I am refering to is the outright record times for all the Australian Motorkhana championships. 90% of the records are held by front wheel drive cars.

But 100% are held by specially build motorkhana vehicles (front or rear wheel drive). In other words when we choose to build a motorkhana car we get to choose between front or rear wheel drive. So its not really driven by car manufacturers at all.
Interesting! :) Thanks for the insight.

In every form of motorsport I've seen - including autoslalom - front wheel drive is distant third choice of drive configuration for purpose-built competition vehicles, behind rear wheel drive and all wheel drive. Motorkhana does appear to be unusual - I had not heard of this sort of event as competition (with reversing, etc) in recent decades, although there was gymkhana before my time.

I see that in a random set of motorkhana rules that I found online (for Western Australia), FWD and RWD specials are in separate classes. Often people choose a class for the competition, rather than choosing a design and falling into a class as a result. If the fast cars are in any class, those wanting to race against them choose the same class.

Our autoslalom events (in Canada) have no reversing and are on paved surfaces; rallycross runs on mixed surfaces.
 

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Discussion Starter · #10 ·
Interesting! :) Thanks for the insight.

In every form of motorsport I've seen - including autoslalom - front wheel drive is distant third choice of drive configuration for purpose-built competition vehicles, behind rear wheel drive and all wheel drive. Motorkhana does appear to be unusual - I had not heard of this sort of event as competition (with reversing, etc) in recent decades, although there was gymkhana before my time.

I see that in a random set of motorkhana rules that I found online (for Western Australia), FWD and RWD specials are in separate classes. Often people choose a class for the competition, rather than choosing a design and falling into a class as a result. If the fast cars are in any class, those wanting to race against them choose the same class.

Our autoslalom events (in Canada) have no reversing and are on paved surfaces; rallycross runs on mixed surfaces.
Yes it is a bit unusual and I believe it also may be a dying sport unfortunately. As it relies on a decent piece of sealed suface in an area where engine and tyre noise is not an issue. Once upon a time a shopping centre car park was perfect. But these days they are open on weekends and usually have the carpark all divided up with gardens, shade sails etc.

Motorkhana can be held on dirt or grass but usually those are more for fun rather than championship status as the surface changes so quickly.

So I am trying to cover off hillclimbs, autocross and khanacross in the same vehicle. But it would be nice to get in the record books as the only electric to win the championship if the sport does die. Don't get me wrong I hope it doesn't die as it is a great entry level sport and is awesome for kids learning to handle a car.

All wheel drive in not allowed in motorkhana unless it was manufactured that way as a production car. WA run under the same rules as us. Yes we have front and rear wheel categories. Rear wheel drive actually get a handicap advantage to level the playing field a little. The stats I am refering to are outright (not allowing for handicap)

You can see the stats here: http://motorkhana1.webs.com/AMC_Times.pdf

The official rules are managed through the Confederation of Australian Motor Sport (CAMS)

I do think that any advantage that I might stand to gain by being front wheel drive is then more than lost through front wheel spin on launch thus losing all the advantage of the torque. By makign the new car rear wheel drive I can take better advantage of the torque during the launch.

Google "Full Charge Motorsport" to see some of my videos.
But make note there is a mix of motorkhana and khanacross in there.
 

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Discussion Starter · #11 ·
Here are the latest pics of my latest project. It is basically the same concept as last time except it is totally different :)

This time it will be around 440KG, rear wheel drive, mid engined, narrower, better aero, better suspension design. I can't wait to drive it.

I still have a fair amount of work to have it ready for the first event on Feb 11. I will provide another update soon.
 

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Excellent
Half the weight of the Device - and it looks like a bit more rear biased

I look forward to seeing the front and rear weight and what it goes like

I sit a good bit further back and my front wheels are a good bit further forwards - I suspect that your layout will be gentler on the driver
 

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Discussion Starter · #17 ·
Thanks guys.

I think the weight distribution is misleading. The motor and gearbox sit just infront of the rear axle. The batteries are roughly the same weight and sit between the half way point and the front axles (somewhat compensating for the motor and gearbox). Then my weight will be just to the rear of the centre point. The really good news is that there is almost no weight hanging out past either axle. So as long as I can get enough weight on the front wheels to hold them down I think it will work well. It has been concerning when it severely understeers as I push it around my yard. But that was without the batteries, without me and also without a wheel alignment. So I hope to see a fair improvement as I load up the front half of the car.

It's not fully complete just yet. If I am lucky it will be finished in the next two weeks. I am not sure I will get a chance to weigh it before Feb 11 but I am sure I will get to weigh it soon after then.
 

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The motor and gearbox sit just infront of the rear axle. The batteries are roughly the same weight and sit between the half way point and the front axles (somewhat compensating for the motor and gearbox). Then my weight will be just to the rear of the centre point. The really good news is that there is almost no weight hanging out past either axle.
Centralized mass, for a low polar moment of inertia, is great for transient response. That and short wheelbase seem well-suited to this type of competition. It should be good. :)

The layout is similar to the road racing Cobra described in this forum... but improved by placing the motor ahead of the axle rather than behind it. All of the components are different; it is only the layout which is similar.

A rear-biased weight distribution is good for drive traction, and not necessarily a problem for handling, depending on tire selection and suspension design. Too extreme is bad, of course.

It's not fully complete just yet. If I am lucky it will be finished in the next two weeks. I am not sure I will get a chance to weigh it before Feb 11 but I am sure I will get to weigh it soon after then.
There's no rush on the weighing, of course; it's just curiosity. I am looking forward to hearing about both the weight, and the weight distribution (both front:rear and left:right).

I am also curious about wheelbase, track, and tire sizes. Sorry if those details were already given somewhere - I may have missed them.
 

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Discussion Starter · #20 ·
Thanks Itchy.

Brian, The front track is slightly wider than the rear track. This is to minimise the chance of the rear wheels taking out a flag as I turn around it (more so for tighter corners). Also I will usually be running larger tyres on the back than the front, so the difference between the two won't be much.

The wheels and tyres on it in those latest photos are just to move it around during construction.

I have 3 pairs of semi slicks (think super soft road tyres). These are all 205 wide and on 15 inch wheels. I will use these in the wet or for events that don't matter.

For the serious events I have 1 set of slicks (uncut wets). The fronts are Hoosier 205 wide and the rear are Dunlops and are 250 wide. All are 15 inch wheels.

Weight bias L to R will be firmly to the right as I am 120KG and the batteries are about 60KG. I am putting the Auxilliary battery up in the nose on the left side to help compensate. But the chassis is quite narrow so all the weight is close to the centre line. I don't expect this to be much of a factor.
 
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