Will Electric Vehicles Be Viable? When?

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gruntguru
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Re: Will Electric Vehicles Be Viable? When?

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Tommy Cookers wrote:
Thu Nov 04, 2021 2:34 pm
gruntguru wrote:
Thu Nov 04, 2021 12:32 am
... Stu. I assume you mean handling characteristics and not power/torque characteristics as suggested by Tonmy. You would be crazy not to take advantage of the enormous power spread of the electric motor and eliminate the mass of the gearbox (allowing more batteries). (That also moves the electric motor back for better weight distribution and lower polar moment of inertia.) Locate battery mass low and close to the CG. If you can achieve 50:50 weight distribution, lower CG and reduce polar moment from stock you will have improved handling.
the power spread of the EM is essentially the same (as the ICE could be today if that's what people wanted)
EM torque is (current) capped at low rpm for thermal reasons and (voltage) capped at high rpm for energy reasons

a gearbox is fundamentally beneficial to the EM as it is to the ICE an automatic transmission is very helpful to an EM retrofit eg in starting, accelerating, and hill climbing ....
and potentially much simplifying and improving in efficiency the electrical side a DIY job (avoiding the 3 year waiting list)
It only requires a small increase in electric motor power rating (over the original ICE) to obtain superior thrust at all (sane) speeds with a single gear ratio and no clutch. If motor choice is relatively open, retaining the gearbox is a very inefficient choice.
je suis charlie

gruntguru
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Re: Will Electric Vehicles Be Viable? When?

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Tommy Cookers wrote:
Thu Nov 04, 2021 2:34 pm
gruntguru wrote:
Thu Nov 04, 2021 12:32 am
... Stu. I assume you mean handling characteristics and not power/torque characteristics as suggested by Tonmy. You would be crazy not to take advantage of the enormous power spread of the electric motor and eliminate the mass of the gearbox (allowing more batteries). (That also moves the electric motor back for better weight distribution and lower polar moment of inertia.) Locate battery mass low and close to the CG. If you can achieve 50:50 weight distribution, lower CG and reduce polar moment from stock you will have improved handling.
higher polar M of I increases the margin between heave and pitch natural frequencies - improving the ride short wheelbase cars like the MX5 (and the 911, VW beetle, Morris Minor etc) could benefit from this (on EM retrofit) what people often call PMI is really the relationship of PMI to 'fixing moment' (wheelbase squared) ie so-called low PMI cars are also mostly shorter wheelbase - so aren't truly low PMI .... but swb's increased weight transfer both in corner exit and entry is beneficial to expert drivers truly lower PMI departs quicker even in steady cornering (without the above benefits) and PMI is really the inertia about the PM centre not the cg anyway low PMI is unlikely in this retrofit case
How many cars would not benefit from a reduction in PMI?
I think a reduction in PMI is very likely. Stu's comments are a guide to how it is done.
je suis charlie

Tommy Cookers
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Re: Will Electric Vehicles Be Viable? When?

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gruntguru wrote:
Mon Nov 08, 2021 1:46 am
.... If motor choice is relatively open, retaining the gearbox is a very inefficient choice.
it's an extra cost to manufacture - but not inefficient
(consider some EV makers do use a gearbox - and eg the Tesla 3 is 'only' 80% efficient)

in this case there's already an automatic transmission
£25000 is the starting rate for a conventional ie non-DIY conversion


btw
nowhere can I find anything that sounds like a description of how or if the electric car has a .....
seamless relationship from control pedal to output over the range from max drive torque to max braking torque
so it's not like F1
control-wise regenerative braking is apparently always independent of any friction braking so ....
people are likely to choose a low regen setting as it will make driving easier/smoother off-accelerator so getting ....
less energy recovery than ideal

btw 2
the 'trolley-truck' concept has quite poor efficiency - because the line losses will be high (c.10-15%)
due to the necessarily rather low voltage/high current and the lack of rails for the circuit return-side (its not a tram)
so no better efficiency than a BEV equivalent

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Zynerji
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Re: Will Electric Vehicles Be Viable? When?

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Big Tea
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Re: Will Electric Vehicles Be Viable? When?

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This is very low efficiency, and not very far along in development, but very light and flexible so could be mounted in so many places and ultra cheap. For instance, the roof of a truck, house roof, factory roof etc.

It is made from the same 'stuff' crisp packets are made of. A long way to go, but looks encouraging

https://www.youtube.com/watch?v=sGQAOeSnErs&t=689s
I saw two shooting stars last night, I wished on them but they were only satellites. Its wrong to wish on space hardware I wish, I wish...

Just_a_fan
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Re: Will Electric Vehicles Be Viable? When?

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Zynerji wrote:
Mon Nov 08, 2021 9:30 pm
https://scitechdaily.com/compact-fusion ... roduction/

Like I mentioned last week...
We're hoping fusion becomes realistic, but many aren't holding their breaths.

It's a technology that has been long in the promise and short in the reality. Not surprising, of course, because it amounts to running a small star in a shed, and that is, understandably, jolly difficult to do.
Turbo says "Dumpster sounds so much more classy. It's the diamond of the cesspools." oh, and "The Dutch fans are drunk. Maybe"

Just_a_fan
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Re: Will Electric Vehicles Be Viable? When?

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Big Tea wrote:
Mon Nov 08, 2021 10:14 pm
This is very low efficiency, and not very far along in development, but very light and flexible so could be mounted in so many places and ultra cheap. For instance, the roof of a truck, house roof, factory roof etc.

It is made from the same 'stuff' crisp packets are made of. A long way to go, but looks encouraging

https://www.youtube.com/watch?v=sGQAOeSnErs&t=689s
A nice looking development and one that would be great on the roofs of very large buildings such as warehouses. 10s of kW of capacity with little structural weight added to the building is "a very good thing indeed". =D>
Turbo says "Dumpster sounds so much more classy. It's the diamond of the cesspools." oh, and "The Dutch fans are drunk. Maybe"

gruntguru
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Re: Will Electric Vehicles Be Viable? When?

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Tommy Cookers wrote:
Mon Nov 08, 2021 4:37 pm
gruntguru wrote:
Mon Nov 08, 2021 1:46 am
.... If motor choice is relatively open, retaining the gearbox is a very inefficient choice.
it's an extra cost to manufacture - but not inefficient
(consider some EV makers do use a gearbox - and eg the Tesla 3 is 'only' 80% efficient)
I was referring moreso to the inefficiency of retaining a transmission (which was designed for a very different application) along with the mass and volume penalties. The performance penalty associated with eliminating the transmission could be offset by choosing a motor with a rating (just guessing) 10-20% higher. Most EV makers go this way.

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Zynerji
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Re: Will Electric Vehicles Be Viable? When?

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gruntguru wrote:
Mon Nov 08, 2021 10:56 pm
Tommy Cookers wrote:
Mon Nov 08, 2021 4:37 pm
gruntguru wrote:
Mon Nov 08, 2021 1:46 am
.... If motor choice is relatively open, retaining the gearbox is a very inefficient choice.
it's an extra cost to manufacture - but not inefficient
(consider some EV makers do use a gearbox - and eg the Tesla 3 is 'only' 80% efficient)
I was referring moreso to the inefficiency of retaining a transmission (which was designed for a very different application) along with the mass and volume penalties. The performance penalty associated with eliminating the transmission could be offset by choosing a motor with a rating (just guessing) 10-20% higher. Most EV makers go this way.

https://i.imgur.com/BtgyM7E.png
In a small road car, how do you feel about an electric motor mounted directly to one of these new vector torque differentials? Would you speculate that you could virtualize the gears using the "electronic slip" they generate?

gruntguru
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Re: Will Electric Vehicles Be Viable? When?

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True torque vectoring (which unlike any passive differential, can supply more torque to the faster wheel) is a huge benefit to handling and grip. Several makers (eg McLaren) apply braking to the inside wheel. The ultimate technique is an electric motor for each wheel. Works out OK weight wise - two smaller motors weigh more than one big one with the same power but - you can eliminate the differential.
je suis charlie

Greg Locock
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Re: Will Electric Vehicles Be Viable? When?

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I'd always recommending eliminating the diff and using one motor per wheel. Diffs are amazingly inefficient, especially at low torques.

This gives the added advantage that you can have great fun emulating an open diff, by using a common demand torque, or a spool, by using a common demand speed, or anything in between by mixing the two inputs.

Tommy Cookers
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Re: Will Electric Vehicles Be Viable? When?

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gruntguru wrote:
Tue Nov 09, 2021 4:58 am
.... The ultimate technique is an electric motor for each wheel. Works out OK weight wise - two smaller motors weigh more than one big one with the same power but - you can eliminate the differential.
2 smaller motors won't weigh less than one big one with the same power
if the one big one is driving at high rpm and low torque via eg CWP reduction
and this OBO is a lesser burden on the whole electrical system upstream
torque costs current (and money) - and current (more than voltage) is the burden on the electrical system design
there's no free lunches - all design approaches have their adverse consequences

F1 uses the 8 speed gearbox to maintain the MGU-K at high rpm and low torque
the migration to higher torque with lower rpm is formally capped - more than the torque capping in road EVs


presumably the open differential gets at low torque disproportionate friction from its internal preloading
this in part to prevent whine - but this wouldn't matter in an EV would it ?
Last edited by Tommy Cookers on Fri Nov 12, 2021 4:51 pm, edited 1 time in total.

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Andres125sx
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Re: Will Electric Vehicles Be Viable? When?

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Stupid question probably but I´ll do it anycase :mrgreen:

Instead of a gearbox, what if they use two motors with very different rpm/v so one is used for first meters from still and slow speed, and the second with higher rpm/v is engaged at higher speed to overcome that torque-rpm problem?

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Zynerji
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Re: Will Electric Vehicles Be Viable? When?

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Greg Locock
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Re: Will Electric Vehicles Be Viable? When?

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"presumably the open differential gets at low torque disproportionate friction from its internal preloading"

No, it is to do with stiffness, and hence weight, of the casing.

As the torque is applied the casing flexes, forcing the hypoid gears out of mesh and increasing friction. At high loads this is worse. So, in order to stop the diff oil from boiling the gears are meshed incorrectly at low torques, and then come into alignment at high torques.

This means that at low torques the %efficiency is lousy, but at least in terms of watts into the oil (Torque *(1-efficiency) *rpm*2pi/60) you take the hit where it does the least damage.