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Which System for an Electric Car?

Posted: Jan 22 2020 5:49am
by rg12
I have been recruited to a team that plans to build a road legal car.
I made it clear that I'm more of a battery guy than an electrical system guy but they still want a general direction from me but I want to consult with you guys first.
The car is just a first draft so nothing is certain yet but they are aiming for a sporty light weight coupe that weighs about 1300kg including passengers and needs to reach 0 to 60 in about 6 seconds.
I'm thinking of dual motors in the rear (one for each wheel), no gearbox, dual controllers (one for each motor) and many other people will be in charge of the many other systems on board.
The main question is, what kind of power (in kw) will I need to move something that heavy, that fast.
I need to know that in order to plan the right battery for the car and calculate capacity, weight etc...

Re: Which System for an Electric Car?

Posted: Jan 22 2020 6:08am
by jonescg
100 kW will do that quite smartly.
Dual motors and controllers is a lot of headache, so my recommendation is stick with one.

Re: Which System for an Electric Car?

Posted: Jan 22 2020 4:17pm
by rg12
jonescg wrote:
Jan 22 2020 6:08am
100 kW will do that quite smartly.
Dual motors and controllers is a lot of headache, so my recommendation is stick with one.
but then I have to have a differential and a whole system to take the power from the motor to the rear wheels.
It's not a go-cart with a single shaft connecting the two rear wheels while a single motor with a chain spins them...

Re: Which System for an Electric Car?

Posted: Jan 22 2020 5:41pm
by Hillhater
Dual motors will require 2 complete sets of drive train components.
Controllers, motors, reduction transmissions to the wheel....all complexity and weight, likely needing design, development and custom manufacturing to suit your application.
A reduction differential and axle is existing, proven, technology.
How much “development” is planned ?
Why wouldnt you build around a modified, uprated, Leaf powertrain hardware ?

Re: Which System for an Electric Car?

Posted: Jan 22 2020 6:17pm
by amberwolf
yeah, you could just go to arlo1's leaf drivetrain thread, i think it is, and copy that. ;)

Re: Which System for an Electric Car?

Posted: Jan 22 2020 6:21pm
by amberwolf
if you're insistent upon independent rear wheel motors and want something mechanically simple, you should contact places like qsmotor that sell car-sized hubmotors and controllers, and see if they ahve something powerful enough for you.

if you can't find motors powerful enough to allow only two motors and two controllers to acclerate quckly enough for you, then just use four of them (and four controllers).

Re: Which System for an Electric Car?

Posted: Jan 22 2020 6:59pm
by rg12
Hmm...sounds logical then to have one big motor...
About that leaf setup, any ready/semi ready platform is welcome but needs to be performance oriented rather than a be the heart of a small family car.

Re: Which System for an Electric Car?

Posted: Jan 22 2020 7:08pm
by amberwolf
arlo1's is not a "family car". go read his thread, easy to find. ;)

Re: Which System for an Electric Car?

Posted: Jan 22 2020 7:20pm
by rg12
amberwolf wrote:
Jan 22 2020 7:08pm
arlo1's is not a "family car". go read his thread, easy to find. ;)
Went through it just now but it's 500+ posts that I really don't have time to go through.
All I want to know is if it's a kit that can be bought or is it a log of a home made project to turn the Nissan Leaf drivetrain into a performance drivetrain.

Re: Which System for an Electric Car?

Posted: Jan 22 2020 7:37pm
by spinningmagnets
Soon, you will read responses about "unsprung weight". This means you want the wheels to be as light as possible. The famous Jaguar rear-end moved the disc brakes from the rear wheels to the sides of the differential to reduce the weight at the wheels.

It is actually reasonable to use two rear hubmotors when the speeds are fairly low. Golf carts are a slam dunk, but when considering a road-car, there are two categories, highway speeds (70-MPH+) and city speeds (50-MPH max).

The ideal system uses a central motor between the wheels, but you can "get by" using hubmotors at the lower speeds, if you must...

Re: Which System for an Electric Car?

Posted: Jan 22 2020 7:50pm
by amberwolf
rg12 wrote:
Jan 22 2020 7:20pm
Went through it just now but it's 500+ posts that I really don't have time to go through.
your loss.

if you want to develop a drivetrain you're gonna have to know how they work and what kind of problems you may have to overcome, and possible solutions.

so if you don't want to learn anything, and expect someone is just going to hand you everything you need on a platter all the time, i wish you good hunting, and good luck.

Re: Which System for an Electric Car?

Posted: Jan 23 2020 2:36am
by j bjork
As I understand it, without any experiance of any of the parts:

Leaf= defenetly not a performance car.

Leaf motor and transmission= good for performance.

Arlos controller with some leaf controller parts= good for performance.

Leaf controller with just parts to be able to use it in other vehicles =?

Re: Which System for an Electric Car?

Posted: Jan 23 2020 6:28am
by rg12
amberwolf wrote:
Jan 22 2020 7:50pm
rg12 wrote:
Jan 22 2020 7:20pm
Went through it just now but it's 500+ posts that I really don't have time to go through.
your loss.

if you want to develop a drivetrain you're gonna have to know how they work and what kind of problems you may have to overcome, and possible solutions.

so if you don't want to learn anything, and expect someone is just going to hand you everything you need on a platter all the time, i wish you good hunting, and good luck.
It's more the engineer's job to do this, I'm in no way an expert to drivetrains nor going to plan one.
I'm in for helping the team by providing directions to where there might be a ready to use platform and think which general idea might be the best one to go to but am not going to learn everything from scratch as it isn't my job in this team.
spinningmagnets wrote:
Jan 22 2020 7:37pm
Soon, you will read responses about "unsprung weight". This means you want the wheels to be as light as possible. The famous Jaguar rear-end moved the disc brakes from the rear wheels to the sides of the differential to reduce the weight at the wheels.

It is actually reasonable to use two rear hubmotors when the speeds are fairly low. Golf carts are a slam dunk, but when considering a road-car, there are two categories, highway speeds (70-MPH+) and city speeds (50-MPH max).

The ideal system uses a central motor between the wheels, but you can "get by" using hubmotors at the lower speeds, if you must...
Hub motors are too heavy as you said, a sh** load of unspung mass so it's very bad for the performance part.
Plus, if you wanna have nice sporty rims you will end up with two giant ugly hub motors for the rear wheels making it look like a chinese cheap car and that's not what we are going for.

Re: Which System for an Electric Car?

Posted: Jan 23 2020 9:27pm
by Hillhater
j bjork wrote:
Jan 23 2020 2:36am
As I understand it, without any experiance of any of the parts:

Leaf= defenetly not a performance car.

Leaf motor and transmission= good for performance.

Arlos controller with some leaf controller parts= good for performance.

Leaf controller with just parts to be able to use it in other vehicles =?
Missing the point...
Jonescg ( experienced EV engineer) suggested 100kW should br enough for the target performance.
A stock leaf motor was 80/110 kW..newer ones 150kW...
RG was contemplating dual motors etc to avoid the “complexity” of a single motor +diff.
Leaf motor power can be boosted with mods to , or alternative controllers..and suitable batteries
There are several companies working with modification to the leaf controller.
The Leaf drive train solves the hardware problem and avoids the complications of developing and manufacturing a dual motor drivetrain.
Maybe RG12’s team should just consult with Arlo ?

Re: Which System for an Electric Car?

Posted: Jan 23 2020 9:43pm
by jonescg
Hillhater wrote:
Jan 23 2020 9:27pm

Maybe RG12’s team should just consult with Arlo ?
He's a very approachable and knowledgeable guy. Highly recommended.

Re: Which System for an Electric Car?

Posted: Jan 24 2020 2:58pm
by rg12
Thanks guys, will forward this to the person in charge of the mechanics of this project :)