# Kitcar conversion



## MadMacs2020 (Jun 10, 2013)

Hi, 
after introducing myself I thought I would post my questions which are the main thrust of my joining the forum and not just lurking anymore;

I have been considering building an EV kitcar, but I want it to be usable as a commuter vehicle and hopefully able to make it to my nearest kitcar show in Exeter if possible.

The car I had in mind was the Mirach Roadster http://www.totalkitcar.com/wp-content/uploads/2012/09/news_mirach.jpg, but I was wondering about space requirements for the EV equipment. I know the roadster is rear wheel drive and uses a BMW 3 series as the normal donor, but the engine bay will take up to a V6 as far as I understand, unusually the Mirach does have a fairly large boot but I'd like to leave some of this for stowage.

My question is basically, compared to say a normal ICE V6 engine and it's various accoutrements like petrol tank and such how does an EV install compare?

I've seen pics of the Warp9 electric motor for example and it looks nearly as big as a 4-stroke ICE, is this true? how big are these controllers? Is it something like an ECU or are we talking something like Doc Brown strapped to the bonnet of the DeLorean in Back to the future 3?

It would be good to know the sizes of some of these items so that I can work out if there would be enough space in the vehicles I fancy. 

Also, could someone recommend the best way to work out if it would be possible to create a motorway capable car from something like the Mirach or if I wouldn't have the space requirements to store enough battery power to make a sustained run of 60mph for approximately 40 miles.

Finally, is there any strength to the in-wheel motors being developed these days, could they provide me with an option instead of going with a transmission, propshaft and differential?

I realise that a number of these questions are n00b queries and I'm sorry to bombard you with all of them, I have tried to perform a search of the forum to investigate if these questions have been answered but I haven't been able to find quite the right answers, any help would be much appreciated, even if it is to point me at the right forum thread. 

Thanks in advance MM


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## dougingraham (Jul 26, 2011)

MadMacs2020 said:


> My question is basically, compared to say a normal ICE V6 engine and it's various accoutrements like petrol tank and such how does an EV install compare?
> 
> I've seen pics of the Warp9 electric motor for example and it looks nearly as big as a 4-stroke ICE, is this true? how big are these controllers? Is it something like an ECU or are we talking something like Doc Brown strapped to the bonnet of the DeLorean in Back to the future 3?
> 
> ...


As for size, the electric components are overall a little more bulky than the stuff you remove if you use lithium batteries. I removed the gas tank muffler, and spare tire from the rear and was able to install about the same weight in batteries and the charger as what was removed and this consumed none of the normal storage space. Under the hood I remove the ICE and cooling system and replaced all of that with warp 9 motor, soliton 1 assorted support components and another battery box. The car weighs just a few pounds more than factory with a full tank of gas and has a range of somewhere between 60 and 80 miles depending on how one drives and temperature.

The WarP9 is about 9 inches in diameter and 16 inches long excluding the shafts. Quite a lot smaller than an ICE. The motor controllers vary in size and shape but the high power ones require quite a lot of space and the lower powered ones much less. It is easy to find the dimensions of devices online.

Your desire to go 40 miles at 60mph is modest with lithium batteries. The car will weigh about the same as it did with the ICE gear installed.

Lots of threads about wheel motors. In a nutshell they don't exist in a form that you can buy and may never be practical for a number of reasons. They seem like a good idea but are not really.


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## Duncan (Dec 8, 2008)

Hi MadMac

http://www.diyelectriccar.com/forum...-dubious-device-44370p8.html?highlight=duncan

This is my car
Suggestions
Lose the gearbox - go direct drive
This frees the entire engine bay for batteries

I have a very small battery pack 144v x 32Ah - 50Kg 
But there is room in my battery box for three times as many cells

I had a look at a similar car here that is being built with a turbocharged 4cyl - my God what a lot of stuff he was having to shoehorn in!
Tons more space with an electric!


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## MadMacs2020 (Jun 10, 2013)

Thanks for the responses, if I were to go direct drive, how would that work for things like speedo and peddle boxes, could I just go with and auto peddle box and then do away with a gear changer altogether?

If I went direct drive with an RWD BMW 3 series rear axle, would it be best to mount the motor direct to the rear diff or should I try to use the drive shaft to maintain weight distribution? or could I balance out any differences with battery weights?

Just trying to get my head around the conversion details. Your help and advice is always appreciated.
MM22


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## dougingraham (Jul 26, 2011)

MadMacs2020 said:


> Thanks for the responses, if I were to go direct drive, how would that work for things like speedo and peddle boxes, could I just go with and auto peddle box and then do away with a gear changer altogether?
> 
> If I went direct drive with an RWD BMW 3 series rear axle, would it be best to mount the motor direct to the rear diff or should I try to use the drive shaft to maintain weight distribution? or could I balance out any differences with battery weights?
> 
> ...


If you go direct drive: The speedometer is almost always a tap off the transmission so you would need to do something else for that. You could leave the clutch pedal in place, it just wouldn't connect to anything. Gear changer would go away as well of course.

You usually can't connect the motor directly to the rear differential. There is no good way to mount it directly and stuff does move around. Having a short driveshaft with U joints and the sliding splined shaft like is currently between the transmission and differential is a good idea. If there is room in the transmission tunnel for the motor you could do that.

Having all the space under the hood would make mounting batteries there easier in many cases.

I usually recommend against removing the transmission. You need a lot more motor to go direct drive and be satisfied with the performance. Gearboxes let you match the motor to the car and speed. A two speed gearbox with the correct ratios would let you drive around town most of the time and you would use the high gear only when on the highway. For me third gear is just slightly too high for driving around town. If it is level I can start off nicely. And then I switch to 5th gear on the highway. 2nd gear is show off gear. It is just about right to scare anyone. First gear is too low such that the motor never gets to full load before you have to shift. With direct drive you will probably want to be able to change the rack and pinion in the differential to match the motor. With a transmission this is not such a concern Your transmission will correct any mismatch.

Best wishes!


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## Duncan (Dec 8, 2008)

MadMacs2020 said:


> Thanks for the responses, if I were to go direct drive, how would that work for things like speedo and peddle boxes, could I just go with and auto peddle box and then do away with a gear changer altogether?
> 
> If I went direct drive with an RWD BMW 3 series rear axle, would it be best to mount the motor direct to the rear diff or should I try to use the drive shaft to maintain weight distribution? or could I balance out any differences with battery weights?
> 
> ...


Hi Madmacs
I am using a Cycle Analyst 
http://www.ebikes.ca/drainbrain.shtml
as my main instrument - speedo, current, volts, amphours, distance
This just needs a pickup on the motor shaft or one of the wheels

Your diff will be rubber mounted - best to use a short drive-shaft - mine is a Subaru propshaft cut down to about 1 ft

Direct drive/gearbox
If you can spin the tires in top a gearbox is totally unnecessary
I can't quite do that - with my current controller but when I upgrade I will definitely be able to
Most kit cars are a bit tight where the pedals are - only having two pedals means you can drive in your wellies


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## MadMacs2020 (Jun 10, 2013)

That's interesting, however, if I were to keep a gearbox, wouldn't I need a clutch to change gear? if not how do I disengage the driving wheels whilst the engine is running or am I getting confused?


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## Duncan (Dec 8, 2008)

MadMacs2020 said:


> That's interesting, however, if I were to keep a gearbox, wouldn't I need a clutch to change gear? if not how do I disengage the driving wheels whilst the engine is running or am I getting confused?


This is something that causes some controversy

The clutch is used for two things
Starting from stationary
Required because an IC engine needs to be kept running 
For an EV - totally unnecessary (not controversial) as the motor has lots of torque from zero rpm

Changing gear when driving
When you change gear on a conventional manual gearbox 
(1) - disengage - need to take off the load - zero throttle
(2) - engage
Inside the gearbox there are two parts spinning at different speeds - syncro cones cause the speeds to match before slotting the dogs together

With an IC car the mass of the flywheel makes this slow or not possible so the clutch allows the gearbox parts to match speed without involving the flywheel

IC motorbikes don't normally use the clutch for changing gear while driving 

An electric motor will have a lot less rotational inertia than a flywheel but more than a gearbox input shaft

So if your gearbox shifts well with strong syncros - don't need a clutch
If your gearbox has weaker syncros - a clutch is a good idea

I believe this is less a case of individual gearboxes and more of type of gearbox, Ford, Honda...

Flywheel
This is needed on an IC car because the engine operates by discrete pulses - totally unnecessary on an EV AND it will reduce your acceleration


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## skooler (Mar 26, 2011)

MadMacs2020 said:


> That's interesting, however, if I were to keep a gearbox, wouldn't I need a clutch to change gear? if not how do I disengage the driving wheels whilst the engine is running or am I getting confused?


I kept the clutch in my RX8 conversion.

I find shifting up in normal driving very easy without the clutch. Shifting down is a bit harder but you get the hang of it.

Its handy to have when you want to just shift rather than line up synchros.

Added benefit is that it is a mechanical disconnect should something go wrong.


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## dougingraham (Jul 26, 2011)

With an ICE equipped with a heavy flywheel you can shift clutchless reasonably quickly. You take your foot off the gas while placing slight pressure on the shifter mechanism. When the load on the drivetrain is close to zero it will pop into neutral. You quickly move the stick to the next gear and apply light pressure. When the engine decelerates to the point where the input and output speed matches the stick will usually just drop in. This is still possible with an EV but I have found that it takes quite a lot longer because there is almost no drag to slow the motor down and allow the gears to match speed. Down shifts are also more difficult for the same reason. You need a really gentle touch on the throttle to spin the motor up and match the speeds. I might be making this sound difficult and it isn't, just different than with an ICE. You have to be patient. I kept my clutch so I still have a flywheel but it is a 12lb aluminum racing flywheel instead of the 24lb steel one originally on the ICE. I would need to be really patient if I still had the original flywheel. Eliminating the 12lb flywheel would help but I suspect it would still be a waiting game.

There is one situation not mentioned when going clutchless. And this is when someone wants coast down regen. Since the mass of the motor is so low when you disengage the gears the motor will stop very quickly making it very difficult to match the speeds to allow you to reengage the transmission. This might sound like what is missing from my up shift scenario above but without a flywheel you would need a really small amount of coasting regen to prevent the motor from slowing too quickly. You either can't effectively use coasting regen or you need a way to deactivate the regen when shifting. This adds another hand or foot control and pretty much adds back in the complexity you were trying to eliminate when you got rid of the clutch. You might be able to train yourself to feather the throttle manually to allow you to match speeds. Is anyone using that approach?

I kept the clutch which allows me to shift in a manner very similar to with the original ICE. Now all that being said, when driving around town in traffic I never shift and never use the clutch at all. I put it in 3rd and use the throttle pedal to go faster and the brake when I need to stop. I would say that this is probably close to 90% of my driving. So clutchless would almost always have worked the same for me.


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