# New Build, 2005 Lotus Elise EV!



## LotusEV (Sep 8, 2012)

I have a 90% completed project, it is a Lotus Elise.

I am looking for assistance and advice for the last 10% of the project which is mostly the motors and controller!

Specs so far:

20 x 19.2V nominal (384V nominal pack) UEV-18XP batteries by Valence with a U-BMS XP system (keeps batteries balanced and works on CANbus to report information on battery status). Batteries are 69Ah, giving a total of ~26.5kwh.

2 x CurrentWays 3kw chargers, these chargers can work in parallel to provide 6kw of charging power, which equates to a 4.5 hr maximum charging time from 100% DOD.

There is an Opto 22 Industrial I/O computer board which monitors the independent vehicle systems and contactors providing control and data to the driver via a 7" touchscreen in dash (needs further programming)

Now here is where I am looking for help:

The car is built at this point to be used with in-hub motors which I am realizing aren't going to be an option for me, they don't produce enough power and are too expensive to adapt to my budget! What this means though, is that the battery pack is installed in a carbon fiber box mounted right between the rear wheels, there is no direct axle option! So my solution (after many ideas being shot down) is to mount 2 6.7" DC motors, one for each wheel, just behind the battery box, which is about 10" offset from the "axle line" with the wheels. My thought is that a small 12 tooth gear directly on the motor shaft which is on a chain connected to a short shaft coming out of the wheel with either a 48 or 60 tooth sprocket; this is either a 4:1 or 5:1 gear drive reduction.

The advice I'm looking for:

1. do you guys think this motor setup will work and that 2 6.7" D&D ES-31B motors @ 144V each motor (and 250A peak current) through a 5:1 or 4:1 will provide adequate performance? (I mean Lotus-esque, 0-60mph in under 5 seconds)... My thought is that the motors are rated at 72V to peak torque at 75 lb/ft, this would be 300 or 375 lb/ft of torque at EACH wheel or 600-750 lb/ft of torque total peak, I don't know what the torque curve for these motors at 144V input is though?

2. The best controller I can find for this high-performance and high-voltage application is the Netgain Warp Drive 360V, it is the only DC controller which provides the high voltage input I need (which will peak at 418V at 100% SOC). It also has CANbus communications (so I can get RPM data, current data, error data, etc. on my data-center inside of the car), reversing contactor (essential for direct drive) and the ability to drive the motors at a lower voltage than the input voltage (reduce our 400V to 288V). Does anyone have experience with these controllers? Is there a way to do traction control with the controller?

3. Motors, I am thinking of D&D ES-31B b/c of its robust ratings @ 144V, one of the few 6.7" motors which can work @ 144V... Does anybody think there is a better motor option? (I don't want to go too big or too heavy b/c it will be outside of the wheel-base and space is somewhat limited)

Any advise???


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## LotusEV (Sep 8, 2012)

Some pictures, excuse the messy garage I had to clean house recently and we stashed everything at the front of the garage...


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## skooler (Mar 26, 2011)

Dual 6.7s should be adequately powerful but how do you plan on spinning them at the same speed?

What about going front wheel drive?

Rebuild the rear battery box to alow for an axel and diff?


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## LotusEV (Sep 8, 2012)

Do you think they won't spin close enough to the same speed being wired in series? Shouldn't their internal resistance be basically the exact same (to a very small tolerance) and if so when wired in series they should receive the same voltage and current? Am I making bad assumptions here? I was thinking of using just one controller to accomplish this.


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## somanywelps (Jan 25, 2012)

I would keep the motors on the same shaft. Things get tricky otherwise.

Make sure the 360V warp drive actually supports 415 Volts.

Also look at the Scott Drive thread in the motors subforum.


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## major (Apr 4, 2008)

LotusEV said:


> ........... if so when wired in series they should receive the same voltage and current? Am I making bad assumptions here? I was thinking of using just one controller to accomplish this.


Hi Lot,

Yep, bad assumption. Motors in series are forced to have equal current but the voltage will divide according to the speed. So when you corner, the respective motor voltages can be quite different. And investigate what happens when one of the two loses traction. 

Speaking of bad assumptions, I think you made a serious mistake loading the car with batteries like that. I'd say you're just getting started instead of a 90% complete project. Back off and design a propulsion system to meet your goals and then figure out how to package it and the battery onboard.

Welcome to forum,

major


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## Batterypoweredtoad (Feb 5, 2008)

Wire the motors in parallel and use bigger motors. At least 9". Parallel gets you limited slip behavior. Stock final drive is 4.53 so if you want to match stock acceleration with your similar gear reduction you need to match the stock torque of 138 fl/lbs and then multiply by whatever gear you would normally be in at that speed. Ex: first gear you would need 3.17*138=437 ft.lbs. Second gear would need 2.05*138=283 ft.lbs. Third would need 1.48*138=204 ft.lbs. After that you are probably getting into the point where you can't feed enough voltage to keep the amps/torque up but you are ahead of stock at that point anyway. You should be able to get around 300ft.lbs. of torque with 1000 amps and two 9" motors from Netgain or Kostov should be able to handle that load easily.


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## skooler (Mar 26, 2011)

As major said, the issue with one motor per wheel is that as soon as the car cocks up its hind leg under some spirited driving and one wheel loses traction that motor will speed up and quite likely over-speed.

You really need an axle to join the wheels together (differential with half shafts). That way, in the above scenario the wheel in the air is still attached to the other wheel and won't over-speed.

In summary, I would advise you remove the rear box and install a differential, either with or without a gearbox and couple a single or dual motor directly to the gearbox or attach it to a shortened propshaft in turn attached to the diff.

Have a look at some of the RWD projects on this site for a better idea.

Cheers,

Mike


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## Batterypoweredtoad (Feb 5, 2008)

Series=motor/wheel with least traction gets more voltage and you spin the tire and overspeed the motor. 

Parallel=motor/wheel that turns slower pulls more amps to try to equalize speed. 

See Brute Force's car for an example of someone making the independent motor per wheel setup work. I think one of the Mini builds is doing the same thing but I am not sure if it is completed.


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## Ace_bridger (Nov 22, 2011)

Welcome and many congrats on chossing a great British sports car for your conversion! It will be awesome I have no doubt.

I'm with Major on this. I would just take a step back and start with the motors and controller(s) and then fit the batteries around them.

What was wrong with keeping the original gearbox and connecting an appropriate (9 inch?) motor?

Awesome project which needs some re-think I think to make it totally awesome.

Cheers,

Adam


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## Batterypoweredtoad (Feb 5, 2008)

Yeah, Batteries may be a large chunk of the build cost but the battery box is a small part of the project. Relocating the batteries and using the stock transmission would make everything easier and probably better.


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## Ziggythewiz (May 16, 2010)

I'd say the box is a good chunk of the job, but it's location is less important, and pretty flexible usually. Definitely don't compromise the rest of the build on account of the box's location.


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## sunworksco (Sep 8, 2008)

You can use two independent front drive motors with two ESCs that can communicate for limited slip. This is how I am planning to build my reverse trike car. Front-wheel drive would balance the car's CG. It is too bad that you started with the battery pack before designing the propulsion system. Batteries in a couple of years are going to make leaps and bounds in technology. I will bet that a Tesla battery pack could reduce in weight by 1/3. That is 500Lbs.!
I have always believed that an efficient ev chassis is one that has the batteries on one end and the motor on the other.
You do have one of the lightest and most aerodynamic. The chassis also has 10,000psi of torsional rigidity. I'm using the same chassis fabrication for my reverse trike but using aluminum foam sandwich panel instead of aluminum sheet.
Take a look at the Inrekor chassis technology.

http://www.youtube.com/watch?v=7QBsA3UX69o&feature=youtube_gdata_player

http://www.youtube.com/watch?v=p0Bc6t96jPA&feature=youtube_gdata_player


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## LotusEV (Sep 8, 2012)

Fantastic advice from everyone so far.

I think it seems that if I go with parallel wiring for the motors I'm a better situation altogether.

As far as redesigning/locating the batteries, it is not quite that simple, the rear-end of this car was designed originally (and not by me, btw) to be dual in-wheel motors, in this regard the rear sub-frame was rebuilt to accomodate the increase in unsprung mass at the rear wheels, in doing this the frame is now inconveniently located between the wheels, I would have to drill out holes for the axle to go through to the wheels, this would compromise the frame in ways that I am not confident in... I think, unless there is no way to make it work otherwise, I am better to leave those components as is.

BatterypoweredToad: I'm not sure what you mean, are you saying the total output of the two motors needs to add up to those numbers before the drive-train gearing? I think you are saying is that I reallly need to focus on the torque/RPM curve with the idea that at 0-1200 RPM (1st gear speeds) I want 437+ lb/ft of torque (at the wheels, so multiply motor output by (4 or 5), at 1201-2400 RPM I want 283+ lb/ft, from 2401-3600... etc, etc... to match the performance of the Lotus engine/tranny setup... Is that right?

If I'm interpreting this correctly then I should be less focused on a peak at wheel torque of 750 lb/ft and more focused on a wider torque band with a lower peak, this makes sense... Anyone know the best 6.7" motors to do that?


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## LotusEV (Sep 8, 2012)

Here are a couple pix of the area just behind what would be the axle, the area where I am planning on mounting the motors. It is not really shown but the sides of the battery box near the wheels is also covered by aluminum frame of the car.


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## MalcolmB (Jun 10, 2008)

LotusEV said:


> the frame is now inconveniently located between the wheels, I would have to drill out holes for the axle to go through to the wheels, this would compromise the frame in ways that I am not confident in... I think, unless there is no way to make it work otherwise, I am better to leave those components as is.


I'm not sure I understand, if there are no holes in the subframe for drive shafts, how would you drive the wheels? To isolate the chain drive from the vertical movement of the wheels you would need two half shafts (each with a pair of CV joints) each connected to a stub shaft on which a sprocket is mounted. There's no way to fit all that in outboard of the subframe.

It sounds as if you're thinking of mounting a stub shaft and sprocket on each wheel outboard of the subframe and simply driving those directly from motors? But if you did that the chain would have to constantly change length as the wheels move up and down... Sorry if I've misunderstood.


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## LotusEV (Sep 8, 2012)

I think you understand the idea... I was thinking of doing it just like a motorcycle drive train, the motor would be mounted "center" of the up/down motion and the drive chain would be on a static brace that runs between the two sprockets (stubby shaft from wheel and motor)... The up and down shouldn't stretch the chain very much, I think, I guess I am just thinking of however motorcycles do it! Maybe a spring tensioner on the chain would be necessary?


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## toddshotrods (Feb 10, 2009)

That might work but there are some things you need to look into, and plan for. The biggest is whether or not there is camber gain and, if so, how much. Camber gain (positive or negative) will cause misalignment with your chain as the front sprocket's angle changes. Ideal would be a really short CV axle to a fixed sprocket.

Also, if you don't have a CV axle and fixed front sprocket, you need to be able to adjust the chain at the longest distance, so that as the suspension moves it won't tighten the chain. That would probably be disastrous for your motor bearings.

Finally, motorcycles don't usually spend as much time in the types of extreme weather a car might. If your car will be exposed to this, make sure you can get to the chains easily for maintenance, or build sealed chain cases.


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## LotusEV (Sep 8, 2012)

Weather is probably not a huge deal, I'm in Phoenix, heat is the biggest issue here and the chain drives will have forced air cooling (design of car for the forced air to the brakes) plus I'll put blowers on both motors. I will likely build a guard for the bottom of the chains to prevent too much rocks/debris from getting caught in them. Also, I am probably not going to drive it in the rain (which is rare here anyways) too much, if at all.

The chains would be easily accessible by just taking the wheel off...

I like the idea of a short CV joint though, but that may allow too much flex (in the wrong direction, rather then up down, cambering in/out) on the motor shaft? The stock Elise axle has CVs right next to the wheels so I can use those shafts and just machine them to the appropriate length with a sprocket attached!

Thanks for the advise!


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## Arlo (Dec 27, 2009)

very nice car can't wait to see it done.


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## MalcolmB (Jun 10, 2008)

Aside from the other difficulties, it doesn't look as if you could fit a large enough sprocket outboard of the subframe. A 48-tooth 1/2" pitch sprocket is roughly 8" in diameter.

I know you're not keen on the idea, but the way I would do it would be to cut holes in the subframe for standard drive shafts. The holes would be reinforced with collars of thick-walled tube. That would give you the choice of a conventional diff (if there's enough height inside the subframe), a chain-drive diff, or dual motors driving sprockets on the inboard ends of the drive shafts.

A chain-drive diff would give the most compact solution, since the motor would be transverse.


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## LotusEV (Sep 8, 2012)

You are right, 8" diameter may be a little too big for the available space, our ratio may need to be knocked down a bit unless there are 8 tooth sprockets that would work on the motor... then just a 32 tooth needed on other end...


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## LotusEV (Sep 8, 2012)

UPDATE:

I have solved some of my problems today when I tried to reinstall the stock Lotus rear suspension system and found that all of the mounts on the rebuilt rear subframe were left in the same locations!!! So now I have the rear wheels/suspension worked out better and have a little more space to work with outboard of subframe but before hubs (about 11")... 

So current plans are:

2 x D&D ES-31 motors (I know there are a lot of haters on these motors but the rated RPM, voltage and size are all within project parameters) w/ 14 tooth ANSI #40 sprockets (smallest size w/ 1 1/8" bore is 15 tooth unfortunately)...

These will be chained with a second sprocket which is ANSI #40 @ 36 tooth... This second sprocket is on a shaft which also has an ANSI #40 @ 12 tooth (1" bore on this shaft)...

This 12 tooth sprocket will be chained to a 20 tooth ANSI #40 sprocket which is shafted to the hub of the wheel (1" bore on shaft)...

From my calculations this should be a 1:2.57 followed by 1:1.667 gearing ratio which should multiply to give appx 1:4.3 as our direct drive gearing ratio... If we capture the appx. 90 lbft of torque peak from each motor that means we will have about 390 lbft of torque (@ peak RPM only) in each of the rear wheels, or 780 lbft peak total... 

This should also equate to an appx. 100 mph top speed (circumference of wheels is 6.5', so wheel RPM of ~1360 is needed as peak (based on 13.6(wheel)RPM/MPH by the following equation: 13.6r/m*6.5ft/r/m*60min/hr=5300ft/hr), motors peak RPM is 6000, divided by 4.3 that is 1400, so our peak RPM on the motors will be just above the RPM they will be spinning at @ 100MPH in this scenario (which is a speed I will likely never actually go up to aside from that one time just to see if its possible!).
Typical highway driving of 60-70 MPH will equate to 800-950RPM (of wheel itself) or motor RPM of 3500-4100. So the motors will stay below 70% of peak RPM all the time. 
Typical street driving of 40MPH will equate to 550RPM @ wheel or ~2350RPM @ motors...

Please correct me if I'm wrong on these RPM correlations and how the gearing will effect our speeds...

Also, any advice on how a 2*(4.3xTorqueOutputofMotor) as overall torque will look on a torque curve (which I haven't seen for these motors)...

I hope this makes the project more clear!

My next action step is mounting a short axle to the hubs and anchoring the other side to the subframe with a bearing/joint and mounting a sprocket on that short axle (for each side)... Then comes the mounting of the motors and the mid-point sprocket ratio reducer...

Thanks for any advice in advance!


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## tylerwatts (Feb 9, 2012)

A quick interjection, all those chain reductions don't sound favourable.

Also, your "Peak torque" is a constant up to the rated RPM which will be proportional to the voltage fed to the motors and their specs.

Additionally, though these may be specced to 144V, you can over volt most DC motors, forklift motors rated at 48V or 96V have been over volted into the hundreds, the brush timing simply required advancing.

Can you show some pictures with the stock sub frame please.

My first thoughts would be to move some of the batteries to the front to fit a chain driven diff underneath the batter box at the rear and fix your 2 motors together onto the drive sprocket for the diff, or better yet have a gear driven diff housing manufactured (this can be done from reclaiming the gears in a stock transmission and placing them on a couple custom shafts in a custom milled housing.) if this fits into your budget.


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## toddshotrods (Feb 10, 2009)

I don't like the sound of #40 chain for the amount of torque you're looking at, and accelerating a car with it. My _motorcycle_ uses #50...


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## Ziggythewiz (May 16, 2010)

LotusEV said:


> Typical highway driving of 60-70 MPH will equate to 800-950RPM (of wheel itself) or motor RPM of 3500-4100. So the motors will stay below 70% of peak RPM all the time.
> Typical street driving of 40MPH will equate to 550RPM @ wheel or ~2350RPM @ motors


The most efficient band for these motors is 2400-3600 rpm, so I like how your numbers crunch out.


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## LotusEV (Sep 8, 2012)

toddshotrods said:


> I don't like the sound of #40 chain for the amount of torque you're looking at, and accelerating a car with it. My _motorcycle_ uses #50...


#40 chain is rated at 810 lb working load and 3125 lb tensile strength.
#50 is 1430 lb working and 4880 lb tensile.

I suppose I'm not certain what those ratings mean as it relates to vehicle propulsion but it would seem that 810 lb working load would correspond to a peak torque of 810 lbft... If that is the case it is rated more than double what it will actually see (since its only half of the system and peak torque is 380 lbft or so for each)... Perhaps I'm off as to interpreting these values as they apply to the project though...

I could use #50 ANSI but that makes the diameters of every sprocket increase which may lead to space problems (I'll see if its doable though, more built-in safety is always better).


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## LotusEV (Sep 8, 2012)

tylerwatts said:


> A quick interjection, all those chain reductions don't sound favourable.
> 
> Also, your "Peak torque" is a constant up to the rated RPM which will be proportional to the voltage fed to the motors and their specs.
> 
> ...



The batteries are in a custom Carbon fiber box, this box is mounted right between the rear sub-frame and using that space would require not only removing 4 batteries but also cutting through the walls of the subframe, these are 2 things I don't want to do. Also, the front end of this car is incredibly compact and there isn't space for more than 1 or 2 batteries to be moved up there...
I have certainly considered the option but I keep circling back to why not just try the chain drives, if it works (which I'm 80% certain it will) then problem solved and unique/fun system built!


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## Bowser330 (Jun 15, 2008)

You used your direct drive ratio to show your multiplied torque value of 780fltbs (4.333 * 180ftlbs from the dual motors)

This is significantly lower then what a stock (ICE) 2005 Elise delivers in first gear...

http://www.lotustalk.com/forums/f25/baseline-dyno-plots-post-your-dyno-plots-here-22741/


First gear = 2.923 * 4.20 final drive = 12.28:1

http://www.automobile-catalog.com/auta_details1.php

The dyno shows the torque is pretty flat from 1500 to 8500rpm @ ~100ftlbs

First gear = 12.28 * 100ftlbs = 1,228ftlbs all the way to 42mph...

Your starting multiplied torque of 780fltbs is close to what a stock (ICE) Elise starts with in second gear...1.75 * 4.2 = 7.35 * 100ftlbs = 735ftlbs
7.35 * 110fltbs = 808fltbs
7.35 * 120fltbs = 882ftlbs

If you are going direct drive you want to use motors with higher torque values....Impulse9's with 160V can draw 1000A up to 5000rpm+
@1000A they deliver ~230fltbs...


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## LotusEV (Sep 8, 2012)

Bowser330 said:


> You used your direct drive ratio to show your multiplied torque value of 780fltbs (4.333 * 180ftlbs from the dual motors)
> 
> This is significantly lower then what a stock (ICE) 2005 Elise delivers in first gear...
> 
> ...


Agreed, however the space limitations at the rear end of this car prohibit the use of dual 9's... Also the battery pack has a peak discharge rating of 200A (Pack Voltage is 345 nominal, so around 70kw peak power availability which equates to around 500A peak @ 144V, this is 250A peak per motor in parallel and 500A peak in series(@72V per motor), a motor that can go higher then that is great for safety but may not be as beneficial as it is on paper.

I appreciate the information on the stock ratios though, that is helpful to look at what our potential specifications will be, an elise starting in 2nd gear may lack that fast 0-30 but past that it is a very quick car! I think I will be satisfied with performance, it may not blow me away but it will be sufficiently quick and "fun", I think... We aren't going to get the sub 5 seconds 0-60 like the ICE elise but anything less than 8 seconds is sufficiently quick for me!


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## Bowser330 (Jun 15, 2008)

LotusEV said:


> Agreed, however the space limitations at the rear end of this car prohibit the use of dual 9's... Also the battery pack has a peak discharge rating of 200A (Pack Voltage is 345 nominal, so around 70kw peak power availability which equates to around 500A peak @ 144V, this is 250A peak per motor in parallel and 500A peak in series(@72V per motor), a motor that can go higher then that is great for safety but may not be as beneficial as it is on paper.
> 
> I appreciate the information on the stock ratios though, that is helpful to look at what our potential specifications will be, an elise starting in 2nd gear may lack that fast 0-30 but past that it is a very quick car! I think I will be satisfied with performance, it may not blow me away but it will be sufficiently quick and "fun", I think... We aren't going to get the sub 5 seconds 0-60 like the ICE elise but anything less than 8 seconds is sufficiently quick for me!


best of luck to you...please continue to share information and your results!

Have you already purchased your motors and controllers, sorry If you already posted that, I didnt go back and read the previous pages...


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## LotusEV (Sep 8, 2012)

I have purchased a few motors, have not purchased the controller yet, having a heck of a time finding suitable ones... only one I can see that is capable of what I need is the netgain warpdrive, the Zilla 2k EHV would work but is at least $1000 more then the warpdrive and both have overkill ratings as far as amperage.

The biggest specs for me are:
-capable of 345V nominal (400V peak would be good so I can add a battery if desired since there is a space for one more)
-programmable output voltage (ie. 144V output to motors from the 345V input)
-Series/Parallel switching
-Reverse capable (w/out getting too complicated with external contactors would be nice)
-CANbus communication (to hook into our I/O system interface)

I think that is all that is absolutely necessary for me, any suggestions?

I've only found 3 controllers in total: warpdrive 360V, zilla EHV (only 2k available these days), Soliton Shiva (way too pricey @ $10K though)...


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## Jesse67 (May 12, 2009)

Your chain tension load guess is a bit off sorry to say. If your motor can produce 100ft lbs then the chain tension depends entirely on the pitch diameter of the motor sprocket. So say you have a 1.5" pitch diameter sprocket (.75" radius), 

Chain tension = 100 ft lbs x (12 in/0.75 in) = 1600lbs chain tension.
100ft lbs torque is 100lbs of force at the end of a 12" lever so if your lever is a lot shorter (your sprocket radius) the force is a lot higher.

My example is a very small sprocket which gives a high chain tension but that's how you need to do the calculation. The pitch diameter would be measured from the center of the shaft to the center of one of the pins on the chain as its wrapped around the sprocket. 

Looks like quite the project you've acquired there! What I would do is use a small differential mounted just behind the subframe with chain or toothed belt drives to your half shafts and then a single motor driving the pinion of the diff. If that sticks back too far you can point the diff up and mount the motor vertically. This way you should have more motor and controller selection and less cost on electronics, although machine work could be a bit more involved. 

Or could you mount the diff behind the subframe and just run the halfshafts at an angel forward to the wheels? I'm not sure what the offset is and if the angles would be too steep.

Good Luck!

Jesse


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## dtbaker (Jan 5, 2008)

quick read thru this thread.... seems like you have backed yourself into a 'muscle car' build and trying to squeeze it into a tiny car. limited return as you add more and more weight. why don't you go back to the Lotus theory of LIGHT to build a giant killer? keep it simple with a Warp9, Soliton/Zilla1k, and go a little crazy with 200v super light pouch cells and use the controller feed a max of 160v to the motor if you have extra money? you'd get plenty of zap if you keep the weight and complexity down....


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## Tesseract (Sep 27, 2008)

LotusEV said:


> ...
> The biggest specs for me are:
> -capable of 345V nominal (400V peak would be good so I can add a battery if desired since there is a space for one more)


What was the reason for picking such a high battery pack voltage in the first place?

EDIT - nevermind; I see you acquired this as an almost-completed project. Good luck with the controller, as your requirements have ensured that NONE of what is on the market today will satisfy all of them.


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## LotusEV (Sep 8, 2012)

I believe the netgain Warp Drive suites the needs of this vehicle, it is rated up to 360V nominal so the voltage is no problem and has CAN-bus, etc. But basically it is the only controller which is powerful enough for this application, I haven't found any others to compete with it at this level (voltage)... I was just wondering if anyone else was aware of one that could?


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## Tesseract (Sep 27, 2008)

LotusEV said:


> I believe the netgain Warp Drive suites the needs of this vehicle, it is rated up to 360V nominal so the voltage is no problem and has CAN-bus, etc.


That appears to be the case, though I would hasten to add the caveat that "nominal" voltage is a bit nebulous and technically undefined these days. Is that nominal for lithium, or lead-acid, or Ni-Cd, or Ni-Mh, etc.?

I would also caution you that just because a product has a CAN bus interface doesn't mean it will listen to commands from some other CAN bus device, nor provide any particularly piece of data over the CAN bus that you might need. CAN is just a hardware signalling standard with some rough guidelines on how the data should be formatted (ie - the protocol). That is to say, just because a charger and a controller use CAN to communicate doesn't necessarily mean they will listen to each other, much less interact in a desired manner.

Two of the other requirements you specified (elsewhere, perhaps?), series/parallel switching and "reverse without using contactors", are mutually exclusive and/or impossible. Reversing a series DC motor requires contactors to flip the polarity of the field relative to the armature while s/p switching requires contactors to rewire two motors from being in series to being in parallel; these two functions, together, require a boat-load of contactors, to the point that it defies all sense, particularly when a regular old transmission - like the one that was in the car to begin with - will provide all of the same functionality with none of the costs/reliability problems.


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## MalcolmB (Jun 10, 2008)

Tesseract said:


> Reversing a series DC motor requires contactors to flip the polarity of the field relative to the armature while s/p switching requires contactors to rewire two motors from being in series to being in parallel; these two functions, together, require a boat-load of contactors, to the point that it defies all sense, particularly when a regular old transmission - like the one that was in the car to begin with - will provide all of the same functionality with none of the costs/reliability problems.


OK, I'll bite  I know you don't like contactors in the motor circuit and I realise this approach wouldn't make much sense in this high-voltage application. But there are a few applications where this can still be a reasonable option. For low-voltage conversions (100V or so) all you need is three DPDT contactors. And in cases where space is restricted or where no suitable gearbox is available it can be a lot easier (and cheaper) to install a few extra contactors than it would be to modify the vehicle structure or an existing transmission. It worked quite well for White Zombie for several years.

Back to the Lotus. Do you have any better photos that show the construction of the subframe just inboard of the wheels? I've used enclosed single-stage chain drives on my own car and I know how much work is involved in setting them up. I think it would be easier and ultimately more reliable to modify the subframe so you can run the original drive shafts to a diff.


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## Rustybkts (Sep 27, 2009)

Great installation so far but a pity the drive wasn't installed before the cells!

My own Elise S1 conversion (www.evalbum.com/1454) has been on the road for over three years now and is fun fun fun!
Tesla chose well for the Roadster as the Lotus chassis is perfect for an EV sports car.

Have you thought of putting cells in the fuel tank space between the seats and rear bulkhead?
It would give you some space and lower the weight. I also managed to squeeze 10 cells in the front although my Series 1 car may be different.

For simplicity, I used the standard gearbox with an AC motor mated to it and locked it in third gear. No clutch needed of course.

The voltage you are working with is ideal for an AC motor.

Best of luck and I hope you get mobile soon.


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## LotusEV (Sep 8, 2012)

Rustybkts said:


> Great installation so far but a pity the drive wasn't installed before the cells!
> 
> My own Elise S1 conversion (www.evalbum.com/1454) has been on the road for over three years now and is fun fun fun!
> Tesla chose well for the Roadster as the Lotus chassis is perfect for an EV sports car.
> ...


Your car is one of the inspirational EV out there for me!!! I have been a huge fan of it for a while and it is one of the reasons I bought this project! I can't wait to get on the road with it soon, I'm hoping by December, the only thing left is machining the mounting system and putting it all in there, design is done (basically)... 

I wish we could use an AC motor d/t to the voltage but unfortunately the space doesn't allow for much more then a 7" diameter motor in the rear and the AC motors have gear-boxes which (from what I have found) are just a hair too big for my space...

I hope I can achieve around 200 Wh per mile like you but I don't think it will happen d/t DC motors and no regen, but hopefully around 220 Wh efficiency will be attainable (and give me 120 miles range)...


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