# Planning Senior Project Design/Build



## ZSharpell (Jun 28, 2016)

Hello Everyone,

My name is Zachary Sharpell, I am a fourth year Mechanical Engineering undergraduate at Cal Poly San Luis Obispo. For my senior project I am designing and building an electric vehicle. Before I begin purchasing parts, I would like to request more experienced help for my design (specifically motor/controller at this moment).

Initially, I planned on attaining a range of 100 miles at 60 mph on level ground with no wind. Based only upon losses from aero and rolling resistance drag (using the following values: Cd = 0.3, A = 25ft^2, rho = 0.0765 lbm/ft^3, V = 60 mph = 88 fps, mu (rolling) = 0.02, W (weight) = 4360 lbf), I determined that I need at least 25 hp (18.6 kW) to maintain 60 mph. From the DIY electric car forums, it was recommended that a vehicle has at least 35 kW per 1000 kg (46.9 hp per 2200 lbs, http://www.diyelectriccar.com/forums/showpost.php?p=187927&postcount=2) to allow for adequate acceleration and passing ability. Using an AC-20 motor with Curtis 1238-6501 controller at 72 V (http://www.thunderstruck-ev.com/hpevs-ac20-motor-conversion-kit-en.html) and a single gear reduction (2.65:1), I could attain 62.6 hp and 164 lb-ft of torque at a vehicle speed of 60 mph (motor rotational velocity of 2000 rpm; tire size P245/35ZR20).

I realize the hp (kW) output of the motor changes with motor rpm (almost linearly for the first 4000 rpm of the AC-20 motor at 72 V), and that I do not have enough acceleration/passing power for a 4360 lb vehicle based upon the recommendation I found within the forums. Based solely on calculations, I need to choose a different motor; however, individuals with experience may provide different recommendations. Also, motors/controllers which provide greater power also have a higher price tag (AC-35, AC-50). Can anyone provide me with recommendations for motors/controllers for my project (and recommendations for the project in general - batteries, chassis design, BMS). I would like to stick with Thuderstruck Motors since they have a package deal (http://www.thunderstruck-ev.com/ac-motor-kits.html), but if there are better options I am absolutely willing to change suppliers.

As a final note, I have chosen not to purchase a donor vehicle because my university will not provide me space to work on a full sized car; however, if part of my project involves _building_ a full sized car chassis, they will provide me space (I don't quite understand how the school makes these decisions).

Thank you to anyone willing to help me and provide me with advice. I am new to the electrical aspects of the car world (most of my electrical involvement has been in research for PEMHFCs and Aluminum based batteries), but I am eager to learn.


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## miscrms (Sep 25, 2013)

Sounds like fun. AC-20 definitely sounds too small, I usually think of that as more a motorcycle/cart motor  Even AC-50 may be a bit lean for your weight.

Can I ask what your goals are? IE what are you trying to achieve? At this point production EVs are becoming fairly common place, so just building one is not trivial but not all that novel anymore. No offense intended.

I'm probably biased, as I'm basically taking on the same project, but I think a great thesis project would be to see just how much improvement could be made in the efficiency/performance of a standard production EV by optimizing weight and aerodynamics. By taking a production drive system from something like a wrecked Leaf, there is basically no work to do developing the drive system. It's all down to base-lining the performance of the existing platform, designing / modeling an ideal platform and predicting improvements, tearing down the donor to harvest your "kit", and then building it to see how your predictions compare to reality. The resale prices on used Leafs are so depressed at this point you could probably just buy a used 2011 for around the $7k I paid for a wrecked one a year ago. The battery will have lost some capacity, but you would be able to do your own base-line testing on the same battery and drive system and show the delta in range / efficiency / acceleration etc and extrapolate the improvement on a brand new one.

My goal is to cut both the weight and CdA roughly in half relative to the stock Nissan Leaf, but I'm going with an existing chassis as the mechanical side is not my forte. I would think you could do at least that well if you are building something from scratch. When I was considering scratch built I was looking heavily at the Locost 7 concept. Taking the same idea with lots of Miata running gear, a custom space frame chassis, a lightweight aero shell, and maybe the Leaf motor/transaxle used in a rear engine RWD configuration I would think you could build something pretty phenominal in terms of both efficiency and performance at a very reasonable cost.

You can check out the links in my sig if you are interested in my (slowly) ongoing efforts to re-use the Leaf drive system in its entirety.

Best of luck,
Rob


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## ZSharpell (Jun 28, 2016)

Thank you for the reply, miscrms!

The goal for my senior project is to create a full sized prototype vehicle for testing aluminum air and aluminum ion batteries I am researching/further developing. The batteries, according to the laboratory test cells, have an energy density about 2-3 times that of lithium ion. The end goal is to use this prototype vehicle as a test bed and proof of concept to gain a better understanding of electric vehicles, how to improve them, and eventually get a car to market (we all have our crazy goals, right?). I take no offense, and I agree that creating an electric car is not the most novel act anymore, but that is why I want to improve the battery technology.

I like your idea of taking the drivetrain from a Leaf, and the prices for wrecked Leafs (or is it Leaves... who knows) are not bad. Would I be able to use the Leaf's motor controller, or would I need to make/purchase one? I planned on building a battery pack using Panasonic NCR18650B cells (good price and capacity), and have done quite a bit of searching/inquiring as to how the Tesla pack is made. I have also been reading pages and pages from the forums about constructing a pack with a BMS, and have a general idea of how to construct one. That being said, a "general" idea needs refining and acutal design; however, I needed to start somewhere.

I would like the prototype vehicle to have a range of ~100 miles at a constant 60 mph, and from some quick calcs, I need around a 30 kWh of capacity (I took into account aero and road losses at 70% DOD for the cells). Those numbers were for the AC-20, so I am sure they will change with a more powerful motor. One thing is for sure, the battery pack cost adds up quickly.

In terms of the design for the vehicle, I designed and tested on exterior concept in the wind tunnel/cfd already, and as expected for a first try it was not great... at all. I went back to pencil and paper, literally, and started off with a new design. I made a rough shape (see picture below), and hope to test in in a water tunnel and wind tunnel this coming September/October.

I know I have a lot of work to do ahead of me, but that's what makes it worth doing!


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## ZSharpell (Jun 28, 2016)

Here is a screen capture from the rough exterior design of the car. Please let me know your thoughts of how I can improve the design!


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## Duncan (Dec 8, 2008)

Hi
You have two goals
Investigate new battery technology using a car as a test bed
Investigate improving the "car" they go in

I would suggest that you stick to one of them as a primary goal

Developing a mass market car is not rocket science BUT it is thousands of engineer man years - look at how much Tesla spent on developing the S Type

Doing it yourself is roughly the equivalent of proposing to carve a double sized copy of the Mount Rushmore statues using only a spoon


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## ZSharpell (Jun 28, 2016)

I agree with you, Duncan, in the fact that I have two overarching goals, and that I need to focus on one primary goal at a time. I am first furthering the development of the battery technology (after the prototype test bed car is built), and then (with a team) the car will be improved. I know it is impossible for me to develop a mass market car alone - it would take my entire life, or longer (by the way, good metaphor to Mount Rushmore).

On the focus on creating the test bed (think of it as part one of the first goal), I will be working with at least six other students at Cal Poly SLO to develop the prototype, so I will not be alone. My specific focus of the prototype vehicle is to choose the motor/controller (likely from a Leaf donor car from what I've read and been told) and create a temporary battery pack made of lithium ions (I'm leaning towards Panasonic NCR18650B cells). 

Being that it is summer time most students want to take a break from school and projects, but I want to get as much done in those two areas as possible prior to the end of summer break. Does that seem reasonable (choose a motor/controller, and have a rough design of a battery pack) to do over summer? This is something I have not done before, so please tell me if it's a crazy idea to do that over summer (~10 more weeks).


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## Duncan (Dec 8, 2008)

Hi Zachary

In your shoes I would be trying to get hold of a Nissan Leaf - or Chevy Volt
With a bad battery pack and or cosmetic bodywork damage

Then you could concentrate on developing your battery pack - you could try and make it fit in the Leave/volt box or you could ditch the rear seats and use that area

I am currently fitting most of a Chevy Volt battery pack in my home made two seater
"Duncan's Dubious Device"
I am most impressed with all of the bells and whistles that came with my Volt battery

You could start backwards and get a Volt or Leaf pack from the scrappers - mine was $1800
And work on developing a pack that would replace that - (then get your $1800 back by selling the modules)


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## ishiwgao (May 5, 2011)

ZSharpell said:


> Here is a screen capture from the rough exterior design of the car. Please let me know your thoughts of how I can improve the design!


this post is a little long, but please bear with it till the last part which is the main point haha. as what Duncan mentioned, you are indeed working on 2 different goals, of which I might add that are actually not all that related to each other. 

Batteries and their performance can be tested independently without a vehicle, or if you want to see real world performance, then the cheapest way to do it is to put them in an existing electric vehicle where your only point of failure is the batteries themselves (which your school's rules on the doner vehicle is indeed a little queer)

on the other hand, building a vehicle to improve on its efficiency in driving is a totally different subject that maybe a good battery will help, but that battery is only one part of tens of different points where you can improve efficiency. you also showcased a design in the post that I've quoted and asked for improvements, which is now an aerodynamics matter rather than a drivetrain.

in short, building a whole new vehicle to test a whole new battery is not only redundant in a way, but it also requires too much effort, and at the end of the day if you do indeed get a good efficiency in terms of driving energy per km, how do you say exactly what gave the improvement? was it the batteries, or was it the new design that you did? 

you mentioned that you are a mechanical engineering student, which means that probably the aluminium battery project you are working on is not something you have a major role in I'm guessing. I'm not belittling you in any way, and it's great if you are indeed one of the key players in the research of the battery. I'm just saying that as a mechanical engineering student, first get what you are supposed to do right (which is to build an awesome electric vehicle, preferably with standard batteries so that you have one less problem to deal with, plus a base for getting a norminalised results for the efficiency of the car), and then AFTER that get those aluminium batteries in to see how they work. 

please correct me if i got any facts wrong. I merely skimmed though all the posts but what got me to reply was the "I am a fourth year Mechanical Engineering undergraduate" followed by "aluminum ion batteries I am researching" because these 2 don't really make sense together. Do keep up your spirit in putting in more than the required effort in school, because this will get you to learn a lot more than your peers, and will help you in your career in your future.


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## dain254 (Oct 8, 2015)

I admittedly skimmed as well - for purposes of learning I wouldn't recommend using salvaged components from a Leaf. You will spend the majority of the time fighting to maintain a wiring harness and ECU designed for another vehicle. 

Instead use off the shelf components and learn how to design a BMS for the ~3000 18650 cells you will need to get 30kw (including becoming a master at soldering...), program a controller, integrate a charger, and program/create a control system, instrument cluster, and data logging for all of the above mess I described! Part of engineering is also dealing with supply management... Source a motor and controller based on available performance data AND take into account supply chain stability. There are plenty of more powerful units out there aside from the AC-20, and some of them a lot cheaper (there is a huge thread on here about forklift motors). From an instructors point of view all of this would earn you a much higher grade than simply reusing Leaf parts.


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## ZSharpell (Jun 28, 2016)

Duncan said:


> I would be trying to get hold of a Nissan Leaf - or Chevy Volt with a bad battery pack and or cosmetic bodywork damage





dain254 said:


> You will spend the majority of the time fighting to maintain a wiring harness and ECU designed for another vehicle.


Would it be possible to salvage just the motor from the Leaf/Volt and purchase or make a compatible motor controller? The Leaf's motor looks sufficient on paper, and I have not found another 80 kW motor elsewhere. I have looked at the forklift threads, and will look further into those. Does anyone know of a motor (preferably AC 3 phase) that outputs around 80 kW, or more?



dain254 said:


> ...design a BMS for the ~3000 18650 cells you will need to get 30kw (including becoming a master at soldering...), program a controller, integrate a charger, and program/create a control system, instrument cluster, and data logging for all of the above mess I described!


Sounds like a good challenge to me! There are a few projects on Instructables regarding these, so I will take another look at those.



ishiwgao said:


> please correct me if i got any facts wrong.


Your facts are correct, as an ME I should not be working on the aluminum based cells, but I have been reading a lot of research and experiemental papers about these cells to learn. I admit I have very little knowledge of advanced chemistry, so I am searching for more knowledgable students to work on the batteries.

Thankfully, I do not need to make a full on aluminum based battery for the vehicle for my senior project, I merely want to experiment with various electrolytes and cathodes in single cells to gather data (voltage, current flow, etc.) for future battery development. I completely agree with you that I need to focus on the car first (with standard batteries) just to get a working prototype and a base for getting normalised results of efficiency.

The exterior design of the car in terms of aerodynamics will be handled by other students (those who enjoy external flow in fluid mechanics/dynamics). I created the CAD model to provide a starting point for the students who take over that section of the project.


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## miscrms (Sep 25, 2013)

Dain, I agree for the most part. Using the Leaf system certainly comes with its own headaches. OTOH, if cost/performance is an important factor at this stage, it is a way to get a complete 80kW drive system with 24kWh battery, BMS, charger, gear reduction transaxle, etc that is all engineered to work together for probably $5-8k. This might work very well for phase 1, where the focus seems to be on building and demonstrating a platform. The downside may come in phase 2, where you will be stuck making your new test battery talk to the Leaf BMS or creating a custom BMS that can impersonate the Leaf BMS.

There are some promising controllers being developed by folks on this board that should be able to drive the Leaf motor, which might be another option. The challenge there is the more creative you get with mixing and matching components, the more time you will have to spend getting them all working the way you want them to. Using a fully thought out kit off the shelf from a vendor will save you a lot of that time, but will cost more money for a given level of performance.

As to the vehicle design, it certainly looks cool. But again, I'd encourage you to think about what your goals are. IMHO Tesla has done a pretty outstanding job in the big heavy expensive sporty electric car space. Trying to beat them at that is probably pretty pointless. If you think you can make a better battery, focus on that and plan to sell it to them once its proven. I think the opportunities are more in revolutionizing the performance (range / efficiency / acceleration) at an affordable price point. IMHO those all point toward smaller and lighter. 

All that being said, keep up the energy and don't let the nay-sayers get you down  If we knew the answers we'd all be millionaires and we'd have flying cars by now


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## dcb (Dec 5, 2009)

ZSharpell said:


> Does anyone know of a motor (preferably AC 3 phase) that outputs around 80 kW, or more?


two AC15's would be more than 80kw fyi (i.e. one motor and one controller per rear wheel).
http://www.hpevs.com/Site/images/to...s/ac-15 96 volt 650 amp metric peak graph.pdf

note, there are a ton of motor options and diy controller options, though hopefully you can recruit the EE folks to deal with the controller side of it and focus on the ME side.

i.e. if on a budget, there are AC24ls for $300 on ebay which should make 40kw each with enough volts (and a controller made from surplus IGBT). There are some w/weird splines too which is an ok ME challenge to sort out.
(i.e. if you had a controller that could do 170v, then that would get you close to 40kw) http://www.hpevs.com/Site/images/torque-curves/baldor-ac24/Baldor AC-24 metric peak.pdf

plus quite a few affordable DC motors that can make 150hp (simpler controller as well).

but there are a billion engineering tradeoffs with every choice, and building a whole car from scratch with no experience during your senior year isn't realistic.

You ARE going to have to focus on one aspect, and presumably it will be related to your degree. Even a two speed gearbox can be a challenge, Tesla tried and failed there.


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## ZSharpell (Jun 28, 2016)

dcb said:


> two AC15's would be more than 80kw fyi (i.e. one motor and one controller per rear wheel).


In this Instructable, the guy states that using two motors to independently drive the rear wheels (one motor per wheel) does not require a differential or torque vectoring device ("There is no interconnection between the two driveshafts or motors - each drives completely independently of the other. The torque characteristics of the electric motors inherently distribute torque between the driven wheels, thus there is no requirement for any differential."). 

This may be a dumb question, but wouldn't going around a corner cause the inner motor to sense a greater load because it is rotating slower than the outside wheel? If so, the inner wheel motor would pull more power than the outside wheel and produce more torque than the outside wheel. From what I recall about diffs/torque vectoring, the goal (most of the time) is to provide more torque to the outside wheel to facilitate cornering ability. If I have this backwards, please let me know.

If I were to use a dual AC24ls or AC15 motor setup, the performance would be pretty good (based on the excel calculator I am using).



miscrms said:


> it is a way to get a complete 80kW drive system with 24kWh battery, BMS, charger, gear reduction transaxle, etc. that is all engineered to work together for probably $5-8k.


I do like the idea of using the Leaf parts so that I can focus on just building the prototype; however, creating a new BMS, battery pack, etc. would be more difficult later. It's a tradeoff. I'll keep searching for inexpensive Leafs and comparing other options such as a dual setup of smaller motors.


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## dcb (Dec 5, 2009)

ZSharpell said:


> This may be a dumb question, but wouldn't going around a corner cause the inner motor to sense a greater load because it is rotating slower than the outside wheel?


the foot pedal in a typical ev controls torque, so with separate controllers they should be pretty much the same load despite being at different rpm. If you want to get into torque vectoring (don't know if it is all that or not) then conceptually you can have a device (i.e. mircocontroller) that takes the throttle and a steering angle input and generates separate throttle signals for the separate controllers.


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## ZSharpell (Jun 28, 2016)

Got it. Since it doesn't matter that the motors are traveling at different rpms while cornering corner, I can make each axle independent and with its own gear reduction? This makes me like electric motors even more now.

When connecting both controllers to the battery pack, do I simply use a splitter so each terminal of the battery becomes 2? If so, I'll need the battery to provide 2x the amps since the splitter puts the controllers in parallel (just a sanity check).

With the excel sheet I used to calculate estimated acceleration, I found that a 2000kg vehicle with a 4:1 reduction and two AC24ls motors w/ Curtis controllers yielded a 0-60mph time of 21.225 seconds. That seems pretty darn slow, so I suspect something is incorrect with the way the hp and torque are calculated. Does that number seem off?


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## ZSharpell (Jun 28, 2016)

Here is the excel file I am using (I found it within the forums). Credit for the excel macro goes to Wesley Taylor.


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## dcb (Dec 5, 2009)

off the cuff it sounds high
http://www.060calculator.com/
[email protected] rwd ~ 13.5sec

but I've not messed w/that spreadsheet.

fyi, it does have a traction limit section, no point in gearing up more than the tires can handle, yay more Mech Eng problems!  It is actually good to know the traction limit (IIRC 0.8 x axle weight as a swag) since it sets a high limit to gear ratio. And of course drag(cda) and rr set the lower limit based on power. 

more volts on that ac24ls will keep the hp climb linear for longer (maintain torque before breakdown to higher rpm). There is a whole thread on them here. They are TENV though, whereas the HPEVS are ODP (air flows through them, more constant power but more environment concerns), and there are industrial conversions as well.


basically you want the highest ratio (assuming single speed) that just barely spin the tires for best off the line performance, then lower it as needed if you need more top speed and can live with reduced acceleration, otherwise you need more power (or less weight, or drag, you get the idea).


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## ZSharpell (Jun 28, 2016)

13.5 seems more reasonable for that amount of power. I'll check to see what's wrong in the spreadsheet. Thank you for finding that online calculator!



dcb said:


> more volts on that ac24ls will keep the hp climb linear for longer (maintain torque before breakdown to higher rpm). There is a whole thread on them here.


I read in one of the forums that the AC24ls is designed for a 156 V input but no more than 300 A. I will search for more info within forums tomorrow (are there any specific ones you recommend?), but in general would it be bad to up the voltage by 50 or so to maintain torque longer?


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## dcb (Dec 5, 2009)

the ac24ls is pretty weak still at 156v
here is the thread, 
http://www.diyelectriccar.com/forums/showthread.php/azure-dynamics-ac24ls-motors-81166.html

the datasheet says (with the right controller, in delta) 240v max, but the graph is at 156v here.
http://wiki.berkholtz.net/_media/vehicles/ac24ls_dmoc445productsheet.pdf
which in that graph would move the knee from [email protected] to 6krpm (minus some losses). The dmoc445 controller it is based on can only do 280 amps rms FYI (~400 amps peak).

I've noted a discrepancy between the hpevs graph and the azure one (hpevs is different by a factor of 2, twice the torque at 1/2 the rpm), I've asked but I don't know which one is right. Also they said it will not survive on 500A current (rms?). So still some ambiguities on it, unless you find something in that thread. I'm not recommending it, just noting it as an option for your consideration fyi.


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## ZSharpell (Jun 28, 2016)

From what I have read in the 81166 forum and this forum, it seems reasonable do use a dual motor setup with two controllers. The main question I have, and there may not be a definitive answer for it, is which controller would best suit a dual rear motor setup? The Curtis 1238 seems to be the most user friendly in terms of having the controllers "talk" to eachother (forum post here), but the problem with those controllers is their inability to supply greater than 156 V to the motor. Could I program a Curtis controller or replace an internal part to make it handle greater voltage?


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## Duncan (Dec 8, 2008)

It is possible to do a dual motor/controller setup

But as an engineer you should be looking at "why" - 
There are obvious cost disadvantages 
two motors, two reduction gearboxes, two controllers
And weight disadvantages (same)

What are the advantages? - what will that setup do better than a single motor and a diff?


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## ZSharpell (Jun 28, 2016)

The main reason for using a dual motor configuration with the AC24LS is that the motor is not very powerful, even if capable of attaining 40kW. From rough estimation from the 0-60 calculator (see quote), a single motor setup would yield a time of ~ 22.7 sec. 



dcb said:


> http://www.060calculator.com/
> [email protected] rwd ~ 13.5sec


I know the real time will differ, but in comparison with increasing the possible power by a factor of 2 (80 kW available), the single motor doesn't stand in comparison. I understand weight, cost, complexity, etc. increase; however, a single AC24LS motor doesn't seem like it will provide enough power.

I could get a more powerful motor, like the AC-35or AC-50, but those motors are more expensive than a $300-400 AC24LS (especially if we look at the AC-35X2). Also, miscrms was hesitant about the AC-50 being enough for the vehicle (post).

A dual motor setup would eliminate the need for a diff since the motors are able to cope with differing speeds around a corner (from what I understand). I'm not against a single motor setup (I actually favor the idea of using a single setup), but finding a powerful single motor usually coincides with a higher price tag. Then again, I would save money on the battery pack since only one motor would be drawing power instead of two.

There are advantages and disadvantages to both. Doing some number crunching will provide a better comparison.


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## brinkhamer (Jul 8, 2016)

ZSharpell said:


> Then again, I would save money on the battery pack since only one motor would be drawing power instead of two.


Just fyi, I think it doesn't matter to the battery if it is feeding 1 80kw motor or 2 40kw motors, as long as the voltage and current capacity is right. battery horsepower is a limit to keep in mind.


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## ZSharpell (Jun 28, 2016)

That is very true. Thank you for pointing that out. I will keep that in mind!


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## Duncan (Dec 8, 2008)

_There are advantages and disadvantages to both. Doing some number crunching will provide a better comparison._

I am pretty sure that the requirement for two reduction boxes will mean that there are NO advantages to two motors!


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## ZSharpell (Jun 28, 2016)

Duncan said:


> I am pretty sure that the requirement for two reduction boxes will mean that there are NO advantages to two motors!


In regards to weight, inertia, and simplicity, I agree with you. The dual motor was appealing due to the low cost of the AC24LS motors; however, it seems that I need to consider paying more for a more powerful single motor. This brings me back to the Leaf donor idea. I spoke to a Cal Poly EE professor today, and he said it should not be a great deal of trouble to interface the Leaf motor with another motor controller so long as the controller is rated for proper volts and amps.

I have read about using the Leaf motor in the forums, and I did not see anything about the ease of using a non-stock controller for the Leaf motor. Is there a forum I didn't read that explains interfacing an existing motor controller to the Leaf motor (_and it actually worked_)?


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## Duncan (Dec 8, 2008)

There are two (at least)

http://www.diyelectriccar.com/forums/showthread.php/re-using-complete-leaf-drive-system-151458.html

http://www.diyelectriccar.com/forums/showthread.php/any-ac-motor-any-inverter-umc-152234.html


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## ZSharpell (Jun 28, 2016)

Thank you, Duncan!


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