# Direcgt drive or manual trans



## koya (Oct 26, 2012)

I've been doing a lot of reading and watching a lot of youtube, I decided on a Boxster. I use to have one and I would like to have another but electric. Now the question is, either go direct drive or stay with the OEM manual. I am thinking of dual warp 9 or single warp 11 with Soliton 1 controller.


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## Caps18 (Jun 8, 2008)

Go with the OEM manual. It is more efficient.

I would also go for the 11" if it will fit, and if it will produce more power than the 9". I really don't know what difference the 9" and the 11" have in terms of Watts/mile or acceleration... I blame vendors and Netgain for not properly advertising the benefits and real world performance of the different motors.


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## major (Apr 4, 2008)

Caps18 said:


> Go with the OEM manual. It is more efficient.
> 
> I would also go for the 11" if it will fit, and if it will produce more power than the 9". I really don't know what difference the 9" and the 11" have in terms of *Watts/mile* or acceleration... I blame vendors and Netgain for not properly advertising the benefits and real world performance of the different motors.


A transmission is not more efficient than direct drive. In fact is adds components into the driveline which introduce extra loss. It is possible that the ability to alter the gear ratio can allow you to select a more efficient operation region of the motor for a particular condition, but this is likely just at low speed and low load where the overall loss would be small compared to the overall duty cycle. The main benefit, efficiency wise, for the transmission is sustained low speed high load like climbing hills slowly. For accelerations and highway cruising, the direct drive will probably be more efficient.

The Warp9 and Warp11 will produce nearly equal peak power which is determined by the battery and controller. And also will dual W9s. The motor torque/RPM curve is different and may influence the choice of gearing. The larger motor(s) will have larger thermal mass and possibly higher power rating.

There is no such thing as Watts/mile. Motor and driveline efficiency will affect the energy consumption (Watt hours/mile). The direct drive choice will likely be a winner in this regard unless the car's duty cycle has a lot of low speed hills.

The choice between direct drive and transmission depends a lot on the performance and type of driving you expect. Typically you would look at larger motors and higher current limits for direct drive.

Another factor to consider is reverse. It comes free with the tranny. Direct drive needs reversing contactors.


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## Caps18 (Jun 8, 2008)

Don't you have RPM limits with the direct drive and that limits the top speed? And I thought the Watt hour/mile thing drops the time part because you don't care how long it takes to travel a mile, it will use the same amount of power if it takes the same amount of time.

Here is another Porsche that is well done and well photographed for some inspiration.
http://www.zwheelz.com/Vehicles.html


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## major (Apr 4, 2008)

Caps18 said:


> Don't you have RPM limits with the direct drive and that limits the top speed?


Say you had a 4 speed tranny. 4th gear is 1:1. Same as direct drive. Same RPM to mph ratio.



Caps18 said:


> And I thought the Watt hour/mile thing drops the time part because you don't care how long it takes to travel a mile, it will use the same amount of power if it takes the same amount of time.


You're right that time does not enter into it. But Energy units do not infer time. Think of Energy as Joules. The Energy consumption is Joules per meter. Wh/mile is just a units conversion handy for us westerners.


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## Coley (Jul 26, 2007)

*Re: Direct drive or manual trans*

I would and did go with the manual trans, instead of direct drive.

With direct drive, you have NO disconnect with the wheels in case of a controller going on full blast. (had that happen twice)

You have to react very fast to keep from having an accident.

You also have no neutral for test running the motor to check out things that you change.

The trans also makes mounting the motor easier.
The small added weight and drag are not worth the risk of direct drive.

And as noted, reverse is much easier.


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## Jesse67 (May 12, 2009)

My mini truck EV is direct drive, because of this it's initial acceleration is somewhat limited as is the top speed. The initial acceleration is determined by the motor torque, the gear ratio and the weight while the top speed in this case is determined by the motor's power available at high rpm to overcome aero drag, it happens to be 85km/hr at 5500rpm but even if it had more power I would be limited by the max motor rpm of ~6500 at about 100km/hr. Direct drive can be done and by picking the right gear ratio your vehicle can be very efficient over a certain speed range. For the most part I'm quite happy with the mini truck's performance and efficiency, 140Wh/km from the wall at city speeds.

BUT in your case with a boxter, unless you're prepared to build a custom differential you will still have to keep the transaxle (likely locked in 3rd gear or so) in order to get the right direct drive gear ratio and doing this is no more efficient than just using the transmission normally. 

The only way you can gain significant efficiency by going direct drive is if you have a vehicle layout where the transmission and diff are separate and you can eliminate the transmission entirely by hooking the motor directly to the differential (assuming it has the correct ratio). Were the mini truck 2wd this is what I would have done as it has a conveniently low differential ratio of 6.83:1, but to keep 4wd operational I had to keep the transfer case. The transmission here is just an empty case with a shaft running through it as I did not need to use any other reduction gearing to get the correct final drive ratio where as you almost certainly would need to use some of the transmission gearing with a boxter due to it's larger tires and higher final drive ratio. And in hindsight even though I reduced some drag and lost a bit of weight by stripping out the transmission I should have left it intact and functional which would have given more low speed gear options and avoided the hassle of tearing it apart and trying to make it work in direct drive with the transfer case. 

So my advice after my ramble, don't bother with direct drive for your boxter unless you replace the entire transaxle with a seperate differential with the correct ratio.... which would probably just add a lot of extra complexity to the built for minimal efficiency gain and weight loss. 

Here's a porsche 944 with a Soliton 1 and a warp 11HV, sounds like it's pretty quick!
http://electricporsche.ca/


Good Luck and have fun!


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## Duncan (Dec 8, 2008)

Hi
I am a fan of direct drive - especially with a fairly light car

However as the Boxster has a trans-axle rather than a separate gearbox and diff it would make sense to use the manual gearbox


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## koya (Oct 26, 2012)

Thank you everyone, I think my ages is showing here; from what i remember the diff and trans on the Boxster are somewhat a single unit. hence I would need to do a lot of fabrication and ended up adding some weight. I elected to focus on a direct drive system because most of the reading I've done on factgory produced EV are direct drive. I guess I need to re-think my approach on a Boxster. I did find this site for a conversion, very nice.

http://www.rp-eng.com/

The other donor I am looking at is to and from work car for my wife, 2000 Lincoln LS 3500 curb weight car. Back to the calculator for figure out what it will take to do this one:


Range; 50 miles
speed 0-60 mph on signle charge.


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## Jesse67 (May 12, 2009)

All of the factory produced EVs use direct drive because they have AC or some type of brushless motors with very high rpm ranges. I know the tesla model s for example goes over 10,500rpm. Because of this they can still have low gearing for good off the line acceleration and with the high redline they can spin very quickly for a reasonable top speed. That said the tesla roadster initially was designed with a two speed gearbox which provided better acceleration and top speed performance but it wasn't durable enough in the end. 

With DC motors and most of the available DIY AC motors you really only have about half of that rpm range so in order to have the same top speed you can only have half the gear reduction, eg 4:1 vs 8:1. So using a DC motor to produce the same off the line acceleration and the same top speed as say a model S you would need a motor with twice the torque, (roughly, assuming same curb weight etc. etc.). You can make it work but you will have compromises in off the line acceleration, top speed or both. This is why most DIY conversion keep the transmission unless they are very lightweight and have a layout and gear ratios that works well for direct drive or very large motors and controllers are used.

The heavy Lincoln can certainly be converted but expect a lot less range and performance for the same cost in parts as something lighter in weight like a boxter.

Jesse


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## Hollie Maea (Dec 9, 2009)

I would go with direct drive, and use the dual warp 9s so you can switch series to parallel and get what amounts to two gears. Anyway, that's what I am planning on my conversion.


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## Richard Wood (Jun 27, 2008)

I am also hoping to do direct drive, for a 95 BMW 318ti. My aim is to put the motor in the tunnel to leave more room for batteries at front and a better weight distribution. I would also like to benefit from the lighter weight of removing the gearbox.

On the question of safety raised, I am aiming to use an AC motor - is it the case that this removes the risk of the motor running away on one? I am still required under the local rules to have an emergency disconnect for the battery regardless - are these fullproof?

If there was any convenient simple two speed gearbox that would help with the spread of gearing I'd love to know about it as I suspect I might have an issue with our local geography.

My car will be purely a commuter car. There are three different scenarios on the way to and from work. Firstly some short steep hills below 50km/h at the start that I can avoid if necessary, a 100km/h limited motorway, and a sustained 2km of 8 degree incline that is limited to 80km/h but I want to be able to go at that speed up also.
The car weighs about 1200kg before conversion and final drive ratio on this car is apparently 4.44 but there are many like cars with a whole range of gearings that look like can be swapped in if needed. It is the sustained hill climb that concerns me and it will be very inconvenient also if I can't hit 100km/h on the more gentle motorway inclines.

Thoughts, calculations anyone?

Also, how does two motors help compared to putting in a bigger motor? Can you do that with AC?


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## Jesse67 (May 12, 2009)

You could potentially make that work with your BMW with the separate transmission and differential. I'm not sure if 4.44 would be a low enough gear ratio but it might be close, it will really depend on what motor you pick.

Here's what looks like a good page with the calculations required to figure out your power requirements for climbing that hill. They have a similar example, just pug in your numbers. 
http://arachnoid.com/gravitation_equations/power_energy_gravity.html

Two small DC motors may have the same continuous power handling and torque as a single larger DC motor but generally being smaller diameter they can handle a higher max rpm without self destructing which makes them somewhat better for a direct drive application where you need the bigger rpm range. Two DC motors can also be run off the same controller, but I don't believe two AC motors can, you would need two motors and two controllers.


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## Hollie Maea (Dec 9, 2009)

Richard Wood said:


> Also, how does two motors help compared to putting in a bigger motor? Can you do that with AC?


The "Series to Parallel" trick is really a brushed DC thing. By running two motors from a single controller, you can maximize the output of the controller at both low and high speeds. But for AC, you need separate controllers for each motor anyway, from what I know. And the limitation that you are getting around--limited RPM due to voltage limits across the brushes--is a DC only problem.


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## Richard Wood (Jun 27, 2008)

Jesse, what about a larger AC motor, does that achieve the same as a larger DC motor might in addressing the low end power and top speed? 
I've also been reading about air cooled AC vs water cooled and wondering if might be better to go water cooled for a more efficient motor or instead go air cooled and include a two-speed gearbox. Thoughts?
Richard


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## Jesse67 (May 12, 2009)

The problem with AC motors is availability, there are a variety of smaller air cooled low voltage options like the AC50 from HPEVS with some bigger ones on the way but other options seem to be a bit scarce or very expensive. If you can find one that someone is willing to sell you for a reasonable price other than the AC50 family I think you're doing pretty good. There are lots of DC options though.

A large DC motor will have more torque but a lower top speed, that's why people use two smaller DC motors together, similar torque and power to one larger one but higher rpm capability. Water cooling for any motor will allow more continuous current capability, doesn't affect top speed.

Jesse


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## Richard Wood (Jun 27, 2008)

Thanks Jesse, I plugged in numbers into the calculations in the document you referenced. I had the angle wrong as it is 8 percent not 8 degrees. I also went with the GVMR of 1555. I came out with 36 hp at 80km/h, and 46 at 100km/h (that is above the speed limit for that road).
Work energy came i at 2.44 megajoules for the lift.
I just need to understand now what the hp means. I imagine I need to add that to a calculation of what hp is needed to drive the car forward at 80km/h on the flat.
EDIT: Found this equation: Required Hp = Hp (Rolling Resistance) + Hp (drag) + Hp (Hill Climbing) + Hp (acceleration) , and explanation here. 
Cheers
Richard


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## mizlplix (May 1, 2011)

*Re: Direct drive or manual trans*

A direct drive application is a tricky one. It requires compromises on all fronts.

"What can you live with?"

In my case, decent performance is a direct drive AC50 in a vehicle no more than 2,000 Lbs in flat terrain with no head wind and gearing in the 10:1 region (with my tire diameter, 32").

Outside of that, you will need at least two gears. Three if you are dealing with over 3,500 Lbs.

In a 1,900 Lb. car and two gears, I could do zero -60 MPH in 10.5 seconds.
In the same car using high gear only, I could do zero-60 in 12.3 seconds.

A properly geared DC motor could beat that easily as the AC50 is soft on torque in the zero-3,000 RPM range.

If you have your heart set on direct drive....Go DC
and pick a top speed and gear for that. It will give 
you your best performance.

I still recommend 2 or 3 gears in any commuter car. 
Traffic, terrain and other conditions are not 
predictable and you need to be able to adapt easily.











The best 2 speed transmission I ever found is this one:
http://www.colemanracing.com/Lightweight-2-speed-
Transmission-P6179.aspx

It weighs 37 lbs.
It has low-high and reverse.
When in high gear it is a straight through power 
flow and does not turn the lower cluster for low
friction.
It shifts on-the-fly without any clutch, so you Clutchless guys are in heaven.

Miz


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## Jesse67 (May 12, 2009)

*Re: Direct drive or manual trans*

That's it Richard, what it's missing is drivetrain drag and motor and controller efficiency to get the continuous battery and motor current you'll need to design for. 

As estimates, for a rear drive car drivetrain efficiency is a bit lower because of the hypoid gears in the diff, say 90% for a manual trans newer car like your bmw, ~95% or so for a DC controller (depends on which one) and ~85% for a DC motor depending again on model and what rpm and torque you're running at. Multiply that together and you end up with about 72% of your battery current actually making it to the road! So the HP number you get from rolling resistance (this is different than drivetrain drag) aero drag, and your hill and divide that by ~.72 (or whatever number your components give you) for continuous battery current to climb that hill. Those efficiency numbers are why small details make a big difference for an EV's range and overall efficiency. Things like synthetic drivetrain oils, a proper wheel alignment and running your motor at it's most efficient rpm can have a big impact.

That's a pretty slick 2 speed trans there, but for $1800 I think I would live with the slightly heavier stock manual! For a totally custom build or if you didn't have a trans to start with that starts to look pretty sweet though.


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## Hollie Maea (Dec 9, 2009)

*Re: Direct drive or manual trans*



Jesse67 said:


> if you didn't have a trans to start with that starts to look pretty sweet though.


That's me! Definitely something I would be interested in for my Opel GT. Miz, do you know how robust this thing is and what kind of torque it can handle?


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## dougingraham (Jul 26, 2011)

Hollie Maea said:


> I would go with direct drive, and use the dual warp 9s so you can switch series to parallel and get what amounts to two gears. Anyway, that's what I am planning on my conversion.


The series parallel trick is one of those things that adds complexity where you dont need it anymore. The only time there is an advantage to doing this is if for some reason you can't get enough battery voltage but you can get twice the current. An example would be a single WarP9 motor has a max voltage rating of 170v. If you want to run two motors you should put them in series with a 340v pack feeding the controller and then you dont need to switch them since you can already get full current and full voltage. In series you have full torque but the torque band is about half of what it is in parallel. But when you switch to parallel you only have half the torque you had when you are in series. So you get a big hit in output when you switch to parallel at the higher speeds. Switching between series and parallel requires three high power contactors and you need to remove power briefly during the change over. If one of the contactors shorts then the result could be a shorted motor controller unless some provision to detect this is provided.

I am pretty sure that no serious drag racers are still doing the series parallel trick because there is no advantage to it. It seems to me you have four choices.


You can series the motors and run the pack at twice the motor voltage or the controller max voltage whichever is lower.
You can parallel the motors and then each motor sees half the of the controller current which might not give full torque. 
You can run each motor with its own controller.
You use a single larger motor.

My first choice would be to use a single larger motor and size the battery pack so the charged voltage is at the controller voltage limit and the battery capacity so it can sustain the full current for the time you need it to last. For a Soliton this would be 340volts or about 100 cells. You configure the controller to limit the motor voltage to the motor limit. In the case of the Warp9 or Warp11 this is 170v with the old brushes and maybe 192volts with the Helwigs. With interpoled motors this limit is generally quite a bit higher. But since the controller is regulating the output voltage the motor may never see the battery sag. Since the Soliton 1 can do 1000 amps this would be 10C for a 100AH pack and that would be the minimum capacity. A 130AH would be better with prismatic cells. With 100AH cells this would be a 32kwh pack and with 130AH cells it would be 41.6kwh. There are overall less issues with this. Because the motors can generally stand enough current paralleling them would cause you to run into the current limit of the controller so neither motor will put out full power in that configuration. In series you will probably just run into the voltage limit of the controller but the motors will see battery sag which will result in a loss of torque at the top end. Two motors and two controllers is good second choice if your batteries are sized to handle the large currents possible. In this situation for a passenger street car with a pair of WarP9's I would go with 200AH cells so they can do 2000 amps and 80 cells to get the voltage high enough to overcome sag at full current. This is a huge pack at 51.2kwh.

The real question is how much power do you really need? A single WarP9 is certainly more than is necessary for a 2400lb car. It is essentially a street racer because of all the low end torque. I can leave my car in 4th gear (direct drive through the transmission) and start out from a stop pretty easily on the level. It is a really neat sensation to start out on an interstate on ramp from a stop in 4th gear and accelerate up to 70mph without shifting. I can easily keep up with typical traffic and nobody knows its an EV. The problems with this are at low speeds the internal fan is not moving much air so cooling could be a problem in stop and go traffic. An external forced air blower is probably essential. You may have situations where you are stressing things trying to start up a steep hill that would be no issue at all with a gearbox.

The optimum for me would be an AC motor with an RPM limit of at least 10k rpm with a controller limit of 1000 amps and a voltage limit of about what the Netgain, Soliton, and Zilla controllers have. With an RPM band like that you can really do no transmission drives with plenty of torque at the low end. Plus you get the ability to regen if you want it and the only wear part on the motor itself is the bearings.


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## Hollie Maea (Dec 9, 2009)

Thanks for the insights, Doug. Until very recently I had mentally ruled out DC, but I started looking at it again very recently but I'm still working on understanding everything, and was trying to find a way to get out of having a transmission (the old school automatic I have in my car now isn't going to cut it). At the same time, I don't want a slow or sluggish car (I already have a slow and sluggish EV  ). I certainly haven't settled on anything yet. If I understand what you are saying, the series/parallel thing was used more due to controller limitations that more recent controllers don't have. My belief had been that it was to be able to go to higher voltages (and RPMs) than the brushes were rated for since at high speeds you wouldn't have your full voltage drop over the brushes because of back EMF. But like I said, I don't really know what I am talking about, and I appreciate all the input I can get!


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## dougingraham (Jul 26, 2011)

*Re: Direct drive or manual trans*



Hollie Maea said:


> That's me! Definitely something I would be interested in for my Opel GT. Miz, do you know how robust this thing is and what kind of torque it can handle?


You want to put 2 Warp 9's in an Opel GT?!? You will twist it in half!

Unless you want to drag race this car you will be plenty happy with a single Warp9, Soliton Jr and use the stock transmission with clutch with an appropriate battery pack. Or an AC-50 Curtis setup would be great plenty. It won't be a street racer but nobody will know its an EV either.


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## dougingraham (Jul 26, 2011)

Hollie Maea said:


> Thanks for the insights, Doug. Until very recently I had mentally ruled out DC, but I started looking at it again very recently but I'm still working on understanding everything, and was trying to find a way to get out of having a transmission (the old school automatic I have in my car now isn't going to cut it). At the same time, I don't want a slow or sluggish car (I already have a slow and sluggish EV  ). I certainly haven't settled on anything yet. If I understand what you are saying, the series/parallel thing was used more due to controller limitations that more recent controllers don't have. My belief had been that it was to be able to go to higher voltages (and RPMs) than the brushes were rated for since at high speeds you wouldn't have your full voltage drop over the brushes because of back EMF. But like I said, I don't really know what I am talking about, and I appreciate all the input I can get!


I think the series parallel thing happened because it seemed like a good idea at the time. I believe the Zilla has it built in to operate the contactors and I am pretty sure the White Zombie used this for a couple of years. I remember reading he stopped using it one year and his times improved. Maybe Otmar will read this and comment. He would know as well as anyone why it was used and why it no longer is. But I suspect it was trying to keep the battery light and when they switched to Lithium all that changed.

My car is a heavier than the Opel GT. I think about 400lbs. I wish you had been at EVCcon so you could drive my car even a little. If Jack has one this year I am planning on going again and I will be happy to let anyone drive my car that wants to (and can fit in it.)


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## mizlplix (May 1, 2011)

No, but they would.
http://www.colemanracing.com/Lightweight-2-speed-Transmission-P6179.aspx

But, it is made and raced in 3,100# asphalt cars with 500+ HP V-8 engines.

So, I think it is about twice the strength you need.

Miz


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## Hollie Maea (Dec 9, 2009)

dougingraham said:


> You want to put 2 Warp 9's in an Opel GT?!? You will twist it in half!


Haha...yeah a bit overkill. I was just trying to find a way to not have to find a transmission  I wasn't going to hook up a Zilla2K though.
Anyway, I know that a Soliton Jr kit, or an AC50 would be "plenty", but I want a bit more than plenty. I've noticed that most of the people on this forum are either people trying to keep costs as low as possible while barely meeting their absolute minimum needs OR they are people with endless money and lots of sponsors building dragstrip rockets to race against alcohol powered supercars. I think I'm a bit in the middle. I'm not making a dragster, but I want great performance, one that would not ever make anyone wonder whether or not they would want an electric car. The way I see it, if I spend about as much as it would cost to buy a LEAF, I'd be pretty happy to trade in all the modern accoutrements that come with such a car for an older hotter faster car. So that's where I'm coming from. Probably won't go with the dual warp9s though  I'm pretty much changing my mind every day, which is fine since I just got my job a month ago and haven't accumulated all the money I need yet 



mizlplix said:


> But, it is made and raced in 3,100# asphalt cars with 500+ HP V-8 engines.


Yeah, that would work just fine.


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## Duncan (Dec 8, 2008)

Hollie Maea said:


> Anyway, I know that a Soliton Jr kit, or an AC50 would be "plenty", but I want a bit more than plenty. I've noticed that most of the people on this forum are either people trying to keep costs as low as possible while barely meeting their absolute minimum needs OR they are people with endless money and lots of sponsors building dragstrip rockets to race against alcohol powered supercars. I think I'm a bit in the middle. I'm not making a dragster, but I want great performance, one that would not ever make anyone wonder whether or not they would want an electric car. The way I see it, if I spend about as much as it would cost to buy a LEAF, I'd be pretty happy to trade in all the modern accoutrements that come with such a car for an older hotter faster car. So that's where I'm coming from. Probably won't go with the dual warp9s though  I'm pretty much changing my mind every day, which is fine since I just got my job a month ago and haven't accumulated all the money I need yet
> .


_I think I'm a bit in the middle. I'm not making a dragster, but I want great performance,_

Yep me too

I am being a real cheapskate
Motor - $100
Controller - $600
DC-DC - haven't got one
Charger - Bad Boy - $100
Batteries - 92 Headway 16Ah (4S for auxiliary + 2P x 44S for main pack) ~$2000

And I hope for enough pep to not embarrass myself at the track

http://www.diyelectriccar.com/forum...-dubious-device-44370p6.html?highlight=duncan

Your Opal GT should make a fast little car with a single 9inch and a Soliton1

I suspect that 1000 amps into a 9 inch will give enough torque to spin your tires in top - in which case why bother with a gearbox?


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## mizlplix (May 1, 2011)

> I suspect that 1000 amps into a 9 inch will give enough torque to spin your tires in top - in which case why bother with a gearbox?


If all you do is race, ok.

But if you street drive the increased amps in the lower RPM s will be a stress on your pack and reduce your range as well as increasing motor and controller heat.
(More than a two speed set up) Especially if there are any hills where you live.

To each, his(her) own.

Miz


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## major (Apr 4, 2008)

mizlplix said:


> But if you street drive the increased amps in the lower RPM s will be a stress on your pack and reduce your range .....


Hey miz,

How does lower RPM increase battery stress (amps)? 

If you're driving on the street at like 10 mph and it requires 5 kW, it is the same current from the battery if the motor is operating at 1000 RPM or at 4000 RPM. The battery would not know the difference of what the gear ratio is.

Now the motor would see higher current at the lower RPM, but not the battery.

Regards,

major

edit: miz, could you please leave the source in your quotes. Thanks.


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## dougingraham (Jul 26, 2011)

Duncan said:


> _I think I'm a bit in the middle. I'm not making a dragster, but I want great performance,_
> 
> I suspect that 1000 amps into a 9 inch will give enough torque to spin your tires in top - in which case why bother with a gearbox?


I am in the middle too which is why I went with a WarP9. I was on the edge between a Soliton 1 and Jr and decided I didn't want to buy twice so I got the 1. I would have been happy with the Jr as it turns out. I haven't done it yet but I plan to have a race button on the dash like the super cars do which will unlimit the Soliton for those special times at street lights.

From the EVTV dyno tests a while back the WarP 9 does 277 ft-lb of torque at 1000 amps. This isn't enough to spin the wheels in the direct drive gear in my car (4th). It is enough in 2nd gear however. It is also enough to get me to 25 in less than a second. And to break motor mounts.

The Opel GT originally had 67, 83 or 103 HP depending on year and selected motor. I haven't found a torque spec for these engines but as these things go the torque peak is similar to the horpsepower. So a WarP9 with 1000 amps and say 60 100AH cells would have perhaps three times the torque and maybe twice the wheel horsepower of the original car with only a little increase in weight. Electric horsepower and torque is very different than ICE horsepower and torque. It is generally better because of the flatter curve.


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## Hollie Maea (Dec 9, 2009)

Yeah a single warp9 will do the trick, I think. I am definitely looking with interest at that two speed transmission. I need one anyway, it would cost the same as the second warp9 but would be more practical overall.


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## mizlplix (May 1, 2011)

Accelerating from a stop in high gear shows a higher amp draw from my pack than accelerating from a stop in low. The only difference is the overall ratio, which suggests a greater effort from the motor.


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## Duncan (Dec 8, 2008)

mizlplix said:


> Accelerating from a stop in high gear shows a higher amp draw from my pack than accelerating from a stop in low. The only difference is the overall ratio, which suggests a greater effort from the motor.


I would expect a higher draw as the motor is probably further from its "sweet spot"
So this is a CON

On the PRO side eliminating the gearbox saved a lot of space enabling the whole "engine bay" to be used for the battery

Also on the PRO side you lose the clutch and the weight of the gearbox

The smaller and lighter the car the more the important these "PROs" become - and the less important that CON is

An Opal GT is a lovely car - very small and very light


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## major (Apr 4, 2008)

mizlplix said:


> Accelerating from a stop in high gear shows a higher amp draw from my pack than accelerating from a stop in low. The only difference is the overall ratio, which suggests a greater effort from the motor.


 Greater effort from the motor, but not the battery, assuming all other conditions equal except the gear ratio. It would be interesting to examine your data from the aforementioned test to see why the results differ from the physics 

KE=½Mv². No mention of gear ratio there. So from, say, zero to 30 mph, in the same time interval, there will be equal change in Kinetic Energy, equal change in battery energy, equal power from the battery, therefore equal current. Granted there may be small differences due to different system efficiency at different speed and motor loads, but these should not be too great and the time spent at those conditions short, so for normal driving, the difference in battery energy small.

The exception is conditions requiring excessive slow speed accelerations and low speed high load conditions like hill climbing where the high motor current will cause inefficiency which adds substantially to wasted energy. Such conditions are normally outside the usual street duty cycle for a reasonably geared vehicle.


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## Jesse67 (May 12, 2009)

The differences will come from motor heating due to the motor not operating at it's most efficient point. If you can shift to keep your motor in it's band of maximum efficiency you'll use less energy to accelerate at the same rate. If you are in direct drive, as in a gear high enough to go from a stop all the way up to your target speed your motor may not hit it's "sweet spot" until you are halfway up to speed. But how much you lose depends on the motor and your gearing. Does anyone have a low speed graph of say a warp 9 showing efficiency at full torque below 2000 rpm as an example? The Netgain graph only goes down to ~2000rpm.

Acceleration = Force/Mass, a lower gear ratio at the start gives you higher wheel torque and thus higher initial acceleration potential than if you start off the line with a with a higher gear ratio.


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## major (Apr 4, 2008)

Jesse67 said:


> The differences will come from motor heating due to the motor not operating at it's most efficient point. If you can shift to keep your motor in it's band of maximum efficiency you'll use less energy to accelerate at the same rate. If you are in direct drive, as in a gear high enough to go from a stop all the way up to your target speed your motor may not hit it's "sweet spot" until you are halfway up to speed. But how much you lose depends on the motor and your gearing. Does anyone have a low speed graph of say a warp 9 showing efficiency at full torque below 2000 rpm as an example? The Netgain graph only goes down to ~2000rpm.
> 
> Acceleration = Force/Mass, a lower gear ratio at the start gives you higher wheel torque and thus higher initial acceleration potential than if you start off the line with a with a higher gear ratio.


That sweet spot for the motor efficiency may be from 300 to 9000 RPM and the time you spend out of the sweet spot so short and at such low power that the overall energy loss is insignificant.

Yes, F=Ma, but that does not change the Energy requirement, which is the argument I am making. I am not saying a lower gear won't provide greater acceleration.

Answer me on how the transmission eases stress on the battery, since miz apparently won't  The motor efficiency sweet spot argument is good for only a few percent which is likely spent accelerating the mass and polar moment of inertia of the transmission itself along with the frictional loss in the tranny.

And another point in my favor.......no production BEV uses a multiratio transmission. The OEMs have undoubtedly considered it. Battery stress (range, durability and life) is a major concern, if not THE main concern with production BEVs. If the use of a transmission (which they know how to make cheaply) could enhance the battery, don't you think we'd see it in the production BEVs hitting the market?


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## Jesse67 (May 12, 2009)

I'm not sure what the sweet spot is, it completely depends on the motor and controller and what torque is being applied. The efficiency varies widely with operating conditions though as for all motors it has to start at 0% at full stall where full motor current is applied but no mechanical work is being done. 

You are correct that aside from efficiency differences due to different rpms the energy and thus battery current are theoretically the same to provide the same rate of acceleration when comparing different gear ratios. Power is power. 

Aside from efficiency and energy though most DIYers retain the transmission because the motors available to DIYers do not have a high enough rpm range to provide both reasonable acceleration and a high enough top speed with direct drive. OEMs have access to AC motors which spin up to 12,000rpm on the other hand. 

Even if you have a light enough vehicle to go direct drive, like my mini truck, you still have to pick a gear ratio that will compromise both starting wheel torque and top speed. The mini truck has a reasonable off the line acceleration of about 0.5G, not fast but enough to be fun to drive, however the top speed is only 85km/hr at 5500rpm which is close to the max speed for that motor anyways. I could pick a higher gear ratio (lower numerically) to raise my top speed but I would need a larger motor (or controller) to provide more torque to make up for my lost gear reduction. This would be more expensive, hence most people keep the transmission which will give the best of multiple fixed gear ratios at a slight cost of extra weight and powertrain drag. For my case I'm fine with the compromise in top speed.


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## major (Apr 4, 2008)

Jesse67 said:


> I'm not sure what the sweet spot is, it completely depends on the motor and controller and what torque is being applied. The efficiency varies widely with operating conditions though as for all motors it has to start at 0% at full stall where full motor current is applied but no mechanical work is being done.
> 
> You are correct that aside from efficiency differences due to different rpms the energy and thus battery current are theoretically the same to provide the same rate of acceleration when comparing different gear ratios. Power is power.
> 
> ...


Yes Jesse, I agree with most of what you say, but that was not the issue. When you say "efficiency varies widely with operating conditions", it is of course true. The efficiency varies from zero to, say, 90%. But unlike some power plants, the efficiency of the electric motor (and controller combination) is very high for a large region of the map of RPM and load. And where the efficiency is low is at very low RPM and/or very low load, so the actual loss is low. Add to that the fact that operation at those low efficiency regions is typically for very short duration, the amount of energy is quite low. All this means there is little to gain with respect to battery stress by changing gear ratios.

There are plenty of reasons to use transmissions with electric motors and I am not against it. I just don't like seeing invalid reasons tossed out there for doing so  Someone please show me how the transmission eases stress on the battery.


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## Jesse67 (May 12, 2009)

Your point is correct it doesn't ease battery stress, and yes the efficient range is much larger than a gas engine, hence people who do use their transmissions only generally use 2 or 3 gears at the most. A transmission can certainly provide increased acceleration with a smaller motor though which is why I'll be using one for my next conversion.

Cheers!


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## vmrod (Jul 2, 2010)

I have a 1973 electric Opel GT. It has been driven a couple times on a test battery pack, but I can still give you some insight.

First, if you intend to throw lots of power into the drivetrain, you will need to replace the rear axle (which is a weak spot in the car). The manual transmission would need replacing as well, as the car's original torque was not so high.

I plan on using the stock tranny and rear end for maybe the life of the vehicle. Only if it gets destroyed will I upgrade it.

Charlie Rickman (in Texas) has been driving his electric Opel daily for over 2 years now. He has videos on Youtube of him at the track. (see below)

http://m.youtube.com/watch?v=HAoxM6UHPD0
I'm guessing he is starting off in 3rd gear, but not sure. He told me that his car is clutchless, so although he could shift gears, it would not be something to do while at the track. He also has a Zilla1K-LV (limited to 156V), and a 156V-100aH battery pack. We each are using the Warp 9 motor.

I have a Zilla1K-EHV. It can handle up to 850 amps up to 375V. I plan on a 192V-100AH LiFePO4 pack (Calb gray cells) at least for now. My car has a clutch in it, so I can shift quickly. I am confident that I will get better performance in my Opel than Charlie's due to my clutch and higher voltage battery pack. However, after viewing Charlie's car at the track, I would be very satisfied with that in my Opel.

My XR3 trike will be my fast EV and the Opel is to be my daily driver, until the trike is one day completed.

So, what I guess I'm getting at, is I would put a sngle Warp 9 in the Opel, and enjoy it with the stock drive system. Once you get bored or break it, then upgrade the drivetrain.


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## Hollie Maea (Dec 9, 2009)

I'm really looking forward to seeing your GT when it is completed. It's nice to have a coulple of people with them. I am starting to firm up in my mind what I want. I am thinking a single warp9, soliton1, and grey 100 ah Calbs with total pack voltage in mid 200s (I want decent range). I'll need to get another transmission since my car is automatic; I like the looks of that racing 2 speed tranny linked earlier in this thread.

Any ideas what torque that back axle can handle? Is there a common one that customizers often use for an upgrade?


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## vmrod (Jul 2, 2010)

I don't know what the original axle can handle, but the forum at Opelgt.com may know.

There are a few rear ends that racers use, it depends on the power and what is available. I think chevy has a 7.5" or 7 bolt or something like that. Whatever the choise, you have to shorten the axle and do all sorts of stuff to it. You would need new brake parts, maybe new rims....it's a big thing to do.

That tranny in the pic is not good for what you want at all. I had seen it before. It is for Oval track racing. Yes, it is 2-speed, but to shift to low gear, you have to first shift in low gear, then press and hold down the clutch while the car continues to move. Once you are moving, you let off the clutch and shift into high gear. The clutch wears out quickly too. Just google info on a Brinn transmission.

Maybe a chevy S-10 would work? There is also a Getrag 240 tranny that Opel guys sometimes use, cuz it has 5 speeds instead of 4. However, I don't think it is much tougher than the original Opel tranny. You may find an original Opel tranny and parts cheap anyway.

You could probably put 240V of batts in an Opel, but you would lose your cargo space Charlie has a useable range of 50 miles, I think. I should get about 60. My daily commute is 25 miles or less, and I can likely charge at work. My batts should last!


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## Hollie Maea (Dec 9, 2009)

Thanks for more information. I'll keep looking on the transmission front. It doesn't make any sense to go to a 5 speed transmission--4 gears is already more than I need. Anyway, I'll find something.

I know my battery pack is going to fill the car up, but for me personally, I would rather have 100 mile range than to have cargo space. I'm not going to be hauling much around in this thing 

I don't think I'll need a new axle, but I'll keep in mind that that is the limiting component.


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## vmrod (Jul 2, 2010)

On that 5-speed tranny (Getrag 240), the 5th gear is an overdrive. If you have sufficient battery power, this would allow for higher top-end speed.


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## DanGT86 (Jan 1, 2011)

Those racing 2 speed transmissions are extremely light and ultra low drag. The thing you have to watch out for is that most of them are not designed to be run in low gear for any more than a few seconds. Almost all of them I have seen are used in circle track racing where they stay in direct drive (2nd gear) for most of the race. First gear has a clutch pack that is engaged for taking off from a dead stop. This also allows first gear to disengage when in second which keeps the drag very low. The clutches burn up and are replaced very often. First gear is there just to comply with racing classes that require cars to be able to take off from a stop and or have a factory style clutch. Just be careful buying one since "can I drive in first gear?" is not usually the first question you ask when buying a transmission. 

Old american manual transmissions like the muncie and saginaw are commonly modified for racing by removing gears to keep rotating weight and drag low. Although heavier (around 70lbs) they are pretty cheap. There are also cheap splined couplers to run them with no clutch. Circletrack racing suppliers like coleman and speedway motors carry lots of this stuff. 

Now for a personal opinion: If you don't have access to a machine shop and cheap materials,and your car has a transaxle, don't try to go direct drive. Unless its a transwarp type motor hooked directly to a driveshaft it will be very expensive and require lots of engineering. A transmission is an easy place to bolt a motor to and its designed to transmit lots of torque to the wheels. The benefit of that engineering is well worth the slight driveline drag.


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## Hollie Maea (Dec 9, 2009)

Thanks again for all the insights. I am leaning towards a more standard transmission like everyone else does. Haven't decided on clutch vs clutch less. In general, I don't want to make things needlessly difficult, but on the other hand I am doing this for the experience, am not afraid to dig into some engineering and don't want to rule things out just because they are difficult. And I want my car to perform as well as it looks! So that is where I am coming from.


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## mizlplix (May 1, 2011)

The 2 speed racing transmission I linked to earlier has a 2:1 low gear so they race in low on the 1/4 mile tracks then use high gear on the 1/2 mile tracks. So torque in either gear will not be a problem.

It also says in the ad that it is for use with an external clutch (No internal clutch to wear out)

Other than the price, the straight cut gears make more noise than helical ones do, but that is why they are straight cut...much lower friction and drag.

They do shift easier than regular transmissions. Something a clutchless car would benefit from.

If you want a good clutchless coupler, Buy a regular clutch type electric motor hub for a Chevy V6.











Then the Speedway direct coupler "button" will just bolt it together.









Miz


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## major (Apr 4, 2008)

I saw this posted on the EVDL and thought I'd drag it over here. 



> In the April edition of Road and Track in "Tech Advice" a reader asks why transmissions aren't employed with electric motors in mainstream EV's to increase efficiency.
> 
> R/T says:
> 
> While there are advantages to torque multiplication from combining an electric motor with a transmission, they are so small relative to the cost, complexity, and packaging constraints of such an arrangement that it's better to simply vary the electrical flow to the motor to gain the desired speed or power. If nothing else, leaving out the transmission and it's added weight leaves room for more batteries, which addresses the real issue with electric vehicles: range.


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## Arlo (Dec 27, 2009)

major said:


> I saw this posted on the EVDL and thought I'd drag it over here.


 Yes or leaving the transmission out leaves you room for a bigger motor which gives the same performance results as a rule of thumb and means there is less moving parts to break or maintain.


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## Jesse67 (May 12, 2009)

True in theory and especially for factory vehicles but in any DIY front wheel drive vehicle at least you generally need to keep the transmission which provides the differential as well as a way to hook the motor to the wheels. Custom single speed gearboxes are not exactly common.

RWD on the other hand definitely has this advantage if you can hook the motor direct to the differential. While I'm happy with the mini truck as is my next conversion will still keep the transmission intact. I like options as I'm driving!

Jesse


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