[LargoEV7]

Hi Guys, first post, thanks for adding me.

I am a long time car builder, have built around 10 cars from scratch for road and race, and built 3 over the last few years of my own design, albeit one similar, but not the same, as an Ariel Atom.

The last one I built 2 years ago, but not quite finished, is a Lotus 7 inspired, but larger open sports car. I had been busy for a while, now I'm going to complete it now, and as I own a Tesla S70 and a JAC iEV6S (small suv, 110hp) http://jacen.jac.com.cn/showroom/iev6s.html and am smitten by electric cars, I am going to make this sports car as a EV.

It's named after the well known Locost 7 homebuilt car from a well know book "Build Your Own Sports Car for as Little as £250" but larger (and completely different structure design) so ended being called the Largo, and now the Largo EV7.

Anyway, enough of the boring stuff, even with my long background with cars and owning 2 EVs, I know nothing about EV powertrains. I'm sure I'm not the first here to say that!

I am Australian but I reside permanently in China with my own business (hence the JAC). The variety of electric motors here is bewildering, albeit most look heavy and industrial.

My question is seeking a suggestion where to start with motors? The car will be around 1600lbs total weight I figure as an EV, and I thought for moderately exciting acceleration, 60 to 75KW (80 to 100 HP)? The 2900lb JAC certainly gets punched along nicely by 110hp, shocks a lot of cars at traffic lights.

Is there motor numbers/model types I should be searching for?

AC or DC? Voltage?

Water cooled or air cooled?

What's the difference between one of those big heavy looking industrial motors with all the cooling fins, and one for an EV? Just weight or more?

Info for controller?

Any suggestions would be greatly appreciated and I promise to start a build log and share, I have already started stitching a new and updated chassis together the last few days, can't go further until all the layout and what goes where is now decided on.

Thanks guys, and Happy New Year to you all.

Picture is the older ICE build, but am re-figuring that design.

Mark.

 

[Duncan]

Hi Mark

Sounds like my Device - but a bit nicer looking
http://www.diyelectriccar.com/forum...dubious-device-44370p15.html?highlight=duncan

Industrial motors are not usually useful - far too heavy at useful power points

You can go DC
Primitive - no re-gen - but cheap and very powerful - 500 Hp

And the other option is motor/gearbox from an OEM electric car

Normally Tesla/Leaf - but sounds like you will have others to choose from

Have fun!

 

[brian_]

Someone will be along soon to suggest using all salvaged Tesla Model S components. Someone else will suggest salvaged Nissan Leaf components. They're similar in many ways, and both make sense to me.

My question is: Why build a vehicle from scratch of a layout designed specifically to fit a traditional longitudinal engine and transmission, if it is being built for an electric drivetrain? Why not proportion it more like the Atom, to fit an integrated drive unit in the back and the battery between the rear axle and the driver, instead of planting the huge and heavy battery pack at the front of a high-performance rear-wheel-drive car?

I do understand converting an existing front-engine/rear-drive car (considering this for our Triumph Spitfire brought me to this forum), but I don't understand building from scratch in that format... particularly if using an integrated drive unit (motor and transaxle, like all production EVs). I can sort of see the old layout if adapting some separate motor to a salvaged rear end unit (differential/final drive); for an example of that, see Duncan's Dubious Device (his name, not mine ).

As it is, building the chassis without having chosen the motor and related components seems backwards... like building a foundation for a house, then designing a floor plan and being stuck with the outline of the foundation instead of what would work best for the plan.

Perhaps if I understood the intent of the vehicle, the chassis choice would make more sense.

 

[LargoEV7]

Duncan and Brian, thanks for replying.

I will not use a Tesla Leaf etc power unit, can not get them. Crashed cars here are recycled and components not available to public. Also individual new components are very cheap.

Duncan, that's awesome, will start reading your blog over the next few days, grats on have a finished vehicle.

I'm not overwhelmed by the Tesla or JAC's regen, I actually find the JAC's aggressive regen bloody annoying in traffic and wish there was an off switch, so if a DC has more power then I would steer that way without regen.


Brian, as mentioned, I am a considerably experienced car builder, not just my 10 or so over the years, but involved in numbers of others. The car you see pictured has a Toyota 2JZ in it and it is staying like that, I am not converting that car, I'll finish that one another day. I have started a new chassis with plenty of allowance for component fitment, they call me Billy, not Silly. If there is issue, it takes a mere few hours for me to cut out chassis members and rework them. Among other things I have a light metal engineering business so it's not a problem.

I am looking at my choices, yes, you are correct, I could get a hold of front wheel drive unit that can be fitted 'mid engined' and batteries up front, or I can put a motor up front and retain closer to original Lotus 7 character with a 4 link live rear end. This is a more viable option for me with the components I can easily obtain locally due to the amount of Hi-Lux and Navara pickup copies around here, the Largo above already has those components so I am working with a known design quantity the 2nd time around. I have it all in 3D on my computer.

Either method doesn't change the premise of my questions though, but appreciate your input.

This is the Finnish companies MG MGA conversion layout, I quite like it ..

 

[LargoEV7]

Well I have been trying to understand the relationship of petrol engine's HP to electric engines output, and it's hard to get it around my head when it's jammed with 40 years of playing with ICE HP!

But anyway, what does the crew think of this as a starting point for moving 1600lbs/750kgs down the road? Thanks again.

 

[brian_]

Well I have been trying to understand the relationship of petrol engine's HP to electric engines output, and it's hard to get it around my head when it's jammed with 40 years of playing with ICE HP!

Engines are always rated in continuous output, and don't put out any more for brief periods. Electric motors are normally limited by heat, so the peak power (which it can't take for extended periods) is typically substantially higher than the continuous power (the level that can be sustained with a stable motor temperature). I suppose peak electric motor power is a bit like the extreme power output for an engine quoted by some guy with a nitrous-injected or highly boosted engine that you know will blow up that power is kept up for a whole minute. If you only drag race, only the continuous power might matter.

Both have power output which is dependent on shaft speed. While engine torque is best in the midrange, so power climbs until near the top of the operating range then drops off quickly, electric motor power depends heavily on motor type. A motor power rating at one speed (maybe even a unspecified speed) without the context of the rest of the speed range doesn't mean much. In the example shown, there is a power rating and a speed range (3200 - 5000), but it may not be able to sustain that power over that entire speed range... which is not a very broad range anyway.

The Golden Motor products seem to be fairly well known... is that graphic the only source of performance data for these things (in the "20 kW" size)?

 

[brian_]

I have realized that I have been through this stupidity with Golden Motor and their data before...

• @72 volts (tabular): https://www.goldenmotor.com/eCar/HPM-20KW-72V%20Data.pdf
• @96 volts (graph): https://www.goldenmotor.com/eCar/HPM-20KW-Performance%20Curve.pdf

Unfortunately, these are the plots with torque on the X-axis and tabular data for a similar datasets, a style more commonly seen for brushed DC motors, so they provide no information about the range below the peak torque speed.

Imagine if an engine manufacturer put their engine on a friction brake, spun it up to redline with no load, then left the throttle open and measured torque data as they applied ever-increasing brake force until they got down to the torque peak and thus immediately stalled the motor... then published that as a power curve? They would be laughed out of the business. Standards are lower in the electric motor business.

 

[brian_]

This is the Finnish companies MG MGA conversion layout, I quite like it ..

I assume that's E-Drive Retro's MGA-EV.

Perhaps it's just poor website design, but this really looks like a company which hasn't produced anything, but has a slick business proposal package, including one non-running demo chassis.

Their MGA-EV has a completely aftermarket four-wheel independent suspension, so it doesn't really retain any of the MGA character other than the body and the general layout. With the motor taking much of the engine compartment, they were driven to stuffing battery boxes in the trunk, under the floor (so the floor is presumably too high), and in the front... sort of a stuff-'em-everywhere approach that is understandable in a conversion, but not very slick for a professional package in a car retaining nothing of the original car except the frame and body.

Since it abandons the original rear axle anyway, the MGA-EV could have had a rear motor, allowing much more battery in the front and better mass distribution of the drivetrain. The most interesting feature to me is the use of a relatively high-torque/low-speed YASA motor to enable effective operation with only an off-the-shelf final drive unit (differential with ring and pinion gears) for gearing - no additional transmission.

 

[Duncan]

Hi Mark

In a modern car you simply can't use continuous power - especially in a sporty car

You hit full power and in seconds you are over the speed limit
Or if you are on a track the next corner is upon you

If you live near one of the BIG racetracks like the Nurburgring Ring then you may be able to apply a lot of power for a bit longer

Next
Gear Shifts
In the old days even a FAST car took quite a long time to accelerate and shifting gear was normal

Modern cars have got so damn fast that there is no time to shift

With an electric car you can simply use a single gear - which makes understanding how it all works easy

Basically - Torque is proportional to current

Power = Torque x Speed - what that means in an electric car is that

Torque is constant - until you get power limited - then as you go faster Torque reduces

So you want lots of torque - ideally enough to break the tires loose = current

But you want to maintain that torque as log as possible = Voltage

My car is 900 Kg with me in it and has 55% on the rear wheels
I can break traction - so I need to lift off a bit
As I accelerate the torque drops off - at about 130 kph I only have about 70% of my initial torque

This is GREAT on the track
On the road I use 45% of max (switch on the dash) - which is pretty damn quick but not as scary - because I'm using less current I still have that same current available at higher speeds

All of this is with a DC motor

I can drive at a continuous 100 Kph - I am NOT very aerodynamic - but I draw less than 200 motor amps - which is in the continuous power zone for my motor - BUT my motor will be producing closer to 20 Kw (same torque twice the rpm)

If I was going to tow something - then I would have to worry

That 20 kw motor is probably as good as my 10 kw motor
The problem is that it is matched to a controller that can give 20 kw and a burst of 50 kw

I'm feeding my 10 Kw motor with a controller that can deliver 400 kW

I think that you will be disappointed - your car won't go as well as it looks like it should

 

[LargoEV7]

Thanks for your replies Brian.

I have lived in China for 13 years, not getting solid information or the actual questions you ask is normal, as frustrating as it is.

They advertise 20KW motors, but in 120V, 96V and 72V at the same price, what is the real world difference between the 3 please?

 

[LargoEV7]

Hi Mark

Not yet!

Hi Mark

In a modern car you simply can't use continuous power - especially in a sporty car

Hey Duncan.

Can't use continuous power?

https://www.youtube.com/watch?v=LJXgqYE_0VI&t=18s

Luckily I now live in a country of freedom and don't fear candy paint Commodores every 500 meters when I drive. When I say drive, I mean spend half the time staring at my speedo in fear, I'm sure you know what I mean.

Hi Mark

I think that you will be disappointed - your car won't go as well as it looks like it should

Interesting, thanks, it's only been a day of learning, chipping away at it.

Ok you have a 10KW motor, but can get a burst of 400KW due to the controller? But there must be a limit to the motor, they come in different sizes and that's one thing I'm having trouble understanding. That 20KW motor above is quite small and can only have X amount of windings(?) where I have seen huge industrial motors also 20KW. I don't know what i am talking about here by the way!

I am back in Oz for annual holiday in Feb, I might pop over and see you?

 

[brian_]

In a modern car you simply can't use continuous power - especially in a sporty car

You hit full power and in seconds you are over the speed limit...

Good point - the current horsepower war in automotive marketing is generally pointless, as few drivers ever use full power even in their ordinary and relatively lower-powered cars. The real power users are those towing trailers, and even then they rarely use more than half the power available for more than a few seconds.

However...

Or if you are on a track the next corner is upon you

If you live near one of the BIG racetracks like the Nurburgring Ring then you may be able to apply a lot of power for a bit longer

Not only "BIG" tracks, and not only a bit longer. From ordinary street cars to purpose-built racers, cars on all road race tracks spend a large portion of their time at full throttle, and at high engine speeds they are at a substantial fraction of full power. Yes, it may only be a few seconds to the next turn, but after brief braking (a second or two is typical) the power is back on, and usually soon after that it's full-throttle time again. A single lap of the track we used with our Honda meant more full-throttle time than a typical day's driving on the street; we burned fuel at four times the rate of highway cruising, which corresponds to an average power level of at least half of the engine's peak.

Due to higher speeds, road race track lapping uses higher power - and more on-throttle time - than lower-speed competitions such as autoslaloms.

Nürburgring (the "ring" or track near Nürburg, Germany) has become well-known to the general public in recent years, and it's difficult to drive because it is difficult to remember all of the many corners, but as far as power demand is concerned it is just like any typical road race track (albeit a hilly one... some are quite flat). Instead of spending several minutes doing one lap of the 20.8 km and 154-turn Nordschleife, running at a more typical track means spending less than two minutes doing a dozen turns; either way, in an hour a car on any of these tracks covers a similar distance and number of turns... averaging well over half of full engine power.

A motor which can produce its peak power for a few seconds, then needs minutes of cool-down, cannot handle that peak power level under road racing (or fast recreational lapping) conditions. Most high-power "tuner" gas-engine cars can't handle actual track conditions, either. It is really important to understand the intended use of the vehicle.

 

[Duncan]

I disagree with Brian
On club tracks - basically anything short of the real big boys tracks the organisers know that if they let the speeds get too high then they won't be able to actually use the tracks

As a general rule the slower the track the lower the level of safety gear

So on a club track while you will use MORE power than on the road you won't be using anywhere near continuous power, assuming that you have a powerful car - if you have low power car then you will be using a lot higher percentage all the time

The tracks that I go to have limited length straights - If I want to go on a faster track I would need a race license and the appropriate safety gear - and I do not want to get into the arguments about what type of fire extinguisher I need!

The ring is NOT like "any typical road race track" as it has some very high speed sections - much much higher than 90% of road race tracks

 

[Duncan]

If you are in NZ - drop in - I'll put the kettle on!

I could not do that run at full power in my car - after about 8 seconds I would have to lift off at 140 kph or else my motor would explode

As far as the motors are concerned - for old technology stuff like mine it's the weight - my motor is 102 Kg - so when you overload it it has some mass to heat up

The Industrial motors and that one you reference are a generation more advanced than mine

BUT they are low voltage and low rpm

The OEM motors work by spinning a LOT faster - and a much higher voltage

Torque is proportional to motor weight (roughly roughly)

So my 10 Kw is 1400rpm and 102Kg

A Tesla motor is 14,000 rpm - this not only means 10 times the power for the same torque but a LOT more cooling

I've got a single gear reduction - a Subaru Diff - 4.1:1
Which is OK and gives me about 140 kph as a max speed - more than enough here in the land of the Jam sandwiches

 

[LargoEV7]

If you are in NZ - drop in - I'll put the kettle on!

I meant if conveniant I will nick over while I'm in Oz (you know that land you call West New Zealand) for the sole purpose of visiting you and learning something, and I can meet Baabara too.

I could not do that run at full power in my car - after about 8 seconds I would have to lift off at 140 kph or else my motor would explode

In what manner is "explode"?

Do you mean overheat, or literal case damage/shatter, or other etc?

As far as the motors are concerned - for old technology stuff like mine it's the weight - my motor is 102 Kg - so when you overload it it has some mass to heat up

I don't care about the weight first time around, as it's a learning curve and I'm not going to spend up big first time and then find I have to change out.


Anyway, the new chassis is ready to be played with, I started this with a few hours here and there last week and threw it up on a bench today to start doing a bit of thinking about next moves.

And that's a plane I have designed myself and scratch building in the background.

 

[brian_]

The point about race tracks is just that road racing does involve high power a substantial fraction of the time (whether it is accelerating out of slow corners or building high speed), so if your drivetrain can only handle drag races or brief spurts of power on the street, it won't handle lapping a track.

 

[Duncan]

Hi Mark

Explode as in over rev and explode - it's used at 1,400 rpm in the forklift - at some higher rpm...
At the end of the 1/8th it's at 4,700 rpm - the general feeling amongst the experts is that it MIGHT be OK at 6000 rpm....

The extra weight is a good thing - it is more mass that has to be heated up before the whole things melts into a puddle

How did you design that chassis?
I started out by laying out the suspension on my board and building the chassis around it

I see you have triangulated - I decided to braze sheet steel to the frame instead - in hindsight I would NOT do that again

What I fancy for a later project is the folded composite type chassis

http://www.autospeed.com/cms/article.html?&A=112925

Not that design - but the idea of buying honeycomb panels and folding them to make a chassis does appeal

 

[LargoEV7]

Explode as in over rev and explode - it's used at 1,400 rpm in the forklift - at some higher rpm...

Ok, understood thanks.

Have you ever known of one to separate in use?

The extra weight is a good thing - it is more mass that has to be heated up before the whole things melts into a puddle

Putting a water jacket around it wouldn't be that hard. Possibly wrap aluminium tube or copper brake line tube around it and send water through.

How did you design that chassis?
I started out by laying out the suspension on my board and building the chassis around it

What I fancy for a later project is the folded composite type chassis

Been building them for a long time and just know where to start in general. I use Sketchup because it's so fast and easy to lay everything out and make changes in hours on the computer rather than days in the shop. Then I get a friend to FEA the structure and make changes according to his suggestions if practical. That chassis is over 5000 lbs per inch in torsion and will be closer to 8000 when it's paneled.

Take time to learn Sketchup, it's a powerful tool and so easy to use.


So question time;

We have a 10KW 1500 rpm motor, lets just say it's 24V.

Layman's speak, if I give that motor 48V, will it have 20KW at 1500 rpm? ..

or

Will the 48V simply allow it to spin to double, 3000 rpm, at which point I will have 20KW?

Maybe the 48V does both, and at 3000rpm we have 40KW?

Or is it other? Thanks again.

 

[Duncan]

Talking DC here!

First - Overspeed - yes a number of people have blown up their motors - BUT it's normally been under no load and GOK rpm

We have a 10KW 1500 rpm motor, lets just say it's 24V.

Layman's speak, if I give that motor 48V, will it have 20KW at 1500 rpm? ..

That motor will take 24v and 416 Amps to produce 10 Kw

If your controller can feed it more amps you will be able to give it more amps at low rpm - so more torque

BUT if you have a 24 volt battery - that's it for power - higher rpm will be less current

If you have a 48 volt battery you will be able to feed it its 400 amps until 3000 rpm - for twice the power
Also if you can feed it 800 amps at 1500 rpm you will have the 20 kw there! current will drop reducing your torque as you accelerate

If you have a 96 volt battery then you will be able to feed it's 400 amps at 6000 rpm - if it does not self destruct!


My motor is 10 Kw at 206 amps 1400 rpm and 48 v

When I feed it 1200 amps I get about six times as much torque!

When I had a 130v battery I was limited to about 3300rpm and 200 amps - about 60 kw