Seeking opinions on independent Twin motors with different gearing

Open for any sort of non-technical discussion regarding EVs
Post Reply
Armstrod
Noobie
Posts: 1
Joined: Fri, 14 Dec 2018, 09:10
Real Name: Dave

Seeking opinions on independent Twin motors with different gearing

Post by Armstrod »

Hi Everyone,

I'm looking at a conversion for a Daihatsu Cuore, l700 chassis. Super quick summary, 2 door 4 seat, 700kg "super mini" hatchback. FWD layout, but chassis is capable of AWD, which is what my query is centering around.

Goals are:
a commuter that can cover an approx 60km round trip each week day, roughly 20km of that will be on 100km/h highways, rest in stop start, 60km/h stuff.
  • I'm setting my minimums at 100km range, 120km/h top speed.
  • Primary objective is performance in handling and acceleration, secondary is developing environmentally friendly alternative for my commute.
  • I have other vehicles available for longer trips, so am willing to sacrifice range for performance as long as the vehicle is capable of handling my commute distance with a reasonable safety margin.
  • Down the road I believe I would look at using partially degraded batteries for home storage from solar, so while I don't want to kill lifespan by overtaxing the batteries, I dont want weight penalties involved in over sizing the battery pack to accommodate future degradation.
I've been looking at options for achieving this, and after identifying that the chassis does have AWD hardware available I could bring in from overseas, I'm wondering if a direct drive layout, using two independent motors feeding front and rear diff's that have different ratios (low ratio at rear for acceleration, high at front for top speed) would achieve my goal, while overcoming the gearing difficulties involved with home-built direct drive setups. Hoping using direct drives will give me an overall larger pool of motor power/torque, and traction to utilize, with weight penalties being partially offset by the removal of the gearbox.

My concerns at this stage are:
Over speeding the rear motor, I'm hoping that a control solution can be found that will transfer the load from the low geared rear to the higher geared front as speed increases, but am unsure how far a motor can be spun beyond its rated speed.

Motor selection. Cost is an obvious factor when doubling down on everything, so that is steering me towards a DC setup. By sacrificing on range requirements I'm also thinking that Regen and other major benefits of AC wont have the same value to my application as others.
Did briefly consider DC rear, AC front to try for the strengths of each type, but I cant really see a realistic way forward on that once practicalities of controllers etc come into play. Am keen on opinions though.

If I did go DC throughout, do folks have thoughts on benefits/drawbacks of mismatched motors? I'm thinking I'd want most of my torque from around 0-80, if 80-120 is achieved in an "acceptable" time frame by a smaller motor through higher gearing, I could be tempted if there is weight/cost savings to be had. Conversely I might have some opportunities to "over-boost" the rear motor and run it hot, with the knowledge that I have the front motor taking the load at mid to high speeds or when a thermal cutout comes into play.

Brief thought bubble also in back of mind is two smaller motors upfront connected direct to axle. Very high gearing ratio, but I'd have the rear to get it up to speed, think I'm opening a whole can of worms from a handling/stability control perspective which is steering me towards running through mechanical diffs. Again interested in opinions of the current state of stability control for the home builders. Are these just simple algorithms that transfer torque or hugely complicated? I flip flop between all the various scenarios I can imagine a car getting itself into at speed, needing extremely complicated control software to deal with each of them, to mechanical diffs aren't exactly intelligent decision making machines, are two motors with a lookup table in their control software performing basically the same function, and after that it's up to the driver?

Thanks all, apologies for long post.
User avatar
brendon_m
Senior Member
Posts: 1315
Joined: Sat, 28 Oct 2017, 11:00
Real Name: Brendon McCarrol
Location: Perth, Western Australia

Re: Seekign opinions on independent Twin motors with different gearing

Post by brendon_m »

Getting diff ratios right might be tricky with direct drive. You'll need a larger motor to get the torque and if you then get 2 motors to fill the gap you are going to fast run into weight limits.
Any ideas on motors? And what sort of budget?

I have a diahatsu sirion that's been converted with a DC motor and the original gearbox, has about a 80km usable range (maybe push it 100km in a real emergency) By the time the conversion was done one of the seat belts had to be pulled out to get get the weight down for it to be licenced.
User avatar
Richo
Senior Member
Posts: 3737
Joined: Mon, 16 Jun 2008, 00:19
Real Name: Richard
Location: Perth, WA

Re: Seeking opinions on independent Twin motors with different gearing

Post by Richo »

Sorry I don't see what benefit you would get stuffing around with AWD.
If you take 1st gear ratio + diff and add about 20% ie if was a turbo etc then using that torque direct drive you end up with around 200kW.
So as if you were stuck in 1st gear with a turbo but still goes up to 150kph+
Estimated is 0-100 in 2.5 with one motor.
This is stage 2 of the Handi...

The Cuore only has 40kW and is still pretty nippy due to weight and gear ratios.
My "acceptable" performance may differ to yours.
How much power were you hoping to have?
Are you hoping to get 400kW in a torque vectoring AWD Cuore?

Also I have doubts that doing a dual motor in a Cuore would work due to the GVM.
You could get the performance but the pack would have to be LTO and you'd only have a range of 20km.
Which is why I have the Handi...
So the short answer is NO but the long answer is YES.
Help prevent road rage - get outta my way!
francisco.shi
Senior Member
Posts: 826
Joined: Mon, 17 Sep 2018, 16:30
Real Name: Francisco
Location: Brisbane, Strathpine

Re: Seeking opinions on independent Twin motors with different gearing

Post by francisco.shi »

Having a motor for each wheel is not difficult to manage if you want to emulate diffs. If you want to get good performance with low weight you need to have motors running at very high speed which means a gearbox. It is generally lighter to have one motor gearbox and diff than two smaller motors and two smaller gearboxes. Depending on the power you want. I am using a motor with (custom using off the shelf gears) gearbox which will give you 660Nm @ 2745rpm (189kw) peak and the package including inverter weighs around 65kg. It uses all off the shelf parts and it is designed to drive a diff.
To do The same with two motors you would need everything half the size which would get difficult to find parts off the shelf so you would have to custom make everything.
QUT made an AWD race car with 4 motors. Each motor with gearbox was about 6.5kg and would put out 16kw and would drive the wheel directly but they had to get gears cut and buy some special motors.
In the end it depends on how much money you want to spend.
User avatar
brendon_m
Senior Member
Posts: 1315
Joined: Sat, 28 Oct 2017, 11:00
Real Name: Brendon McCarrol
Location: Perth, Western Australia

Re: Seeking opinions on independent Twin motors with different gearing

Post by brendon_m »

If you could get it through engineering, something like 2 of these may work.
http://kellycontroller.com/96v-dual-car ... p-810.html
The motors seem to be about 10kw each on the 72v graph.
Don't know how accurate /reliable the specs are.
francisco.shi
Senior Member
Posts: 826
Joined: Mon, 17 Sep 2018, 16:30
Real Name: Francisco
Location: Brisbane, Strathpine

Re: Seeking opinions on independent Twin motors with different gearing

Post by francisco.shi »

I think they are a bit under powered.
I guess your first step would be to determine how much power you need.
Do you have a target 0-100kph time?
User avatar
brendon_m
Senior Member
Posts: 1315
Joined: Sat, 28 Oct 2017, 11:00
Real Name: Brendon McCarrol
Location: Perth, Western Australia

Re: Seeking opinions on independent Twin motors with different gearing

Post by brendon_m »

Most reviews on hub motors tend to be negative as well. If they live up to their ratings then 10kw a corner would be the same as the original 40kw ice. (I assume it's 10kw peak not continuous, if continuous then you could theoretically push 200kw)
However I doubt they'd live up to their ratings without melting into a pile or be licensable from an engineering /suspension point of view, but it is an avenue to explore.
User avatar
Richo
Senior Member
Posts: 3737
Joined: Mon, 16 Jun 2008, 00:19
Real Name: Richard
Location: Perth, WA

Re: Seeking opinions on independent Twin motors with different gearing

Post by Richo »

I had a look around for some pics of the L710 AWD running gear but haven't found anything yet.
Must be rare if I can't even get a picture of one.
Possible only on the auto import bid sites that have them.
I doubt importing a whole L710 would be cost effective.

I still think a beefier version of the AT1200 for direct drive from one motor is better value for money.
Image
So the short answer is NO but the long answer is YES.
Help prevent road rage - get outta my way!
Post Reply