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Author Topic: Teslas >20% more efficient than iPace or eTron  (Read 2447 times)
Countrypaul
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« Reply #15 on: February 25, 2019, 09:12:21 AM »

It seems odd to me that they are, at times, blaming the poor consumption on the lack of regenerative braking when travelling a constant speed on motorways.

They conveniently forget that, to brake, one must first accelerate and that uses more power.  To capture more power from regenerative braking than expended in the initial acceleration is against the 2nd law of thermodynamics.

It also seems odd that they put emphasis on the weght when travelling at constant speed the weight is almost irrelevant, it mainly affects the energy in acceleration and braking.
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DonL
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« Reply #16 on: February 25, 2019, 09:24:15 AM »

It seems odd to me that they are, at times, blaming the poor consumption on the lack of regenerative braking when travelling a constant speed on motorways.

They conveniently forget that, to brake, one must first accelerate and that uses more power.  To capture more power from regenerative braking than expended in the initial acceleration is against the 2nd law of thermodynamics.

It also seems odd that they put emphasis on the weght when travelling at constant speed the weight is almost irrelevant, it mainly affects the energy in acceleration and braking.
Only true if the road is flat. Going up a hill, work done is proportional to the weight (also going down the energy available for potential braking).
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« Reply #17 on: February 25, 2019, 09:25:46 AM »

it would be nice to see some numbers from a rolling road test - I googled but couldn't find any... I'm surprised because there's so many rolling roads round it would be easy to do?


maybe the tuning places that have rolling roads aren't setup for that kind of test, or maybe they can't do long tests where cars sit on the rollers for an hour? (or few hours?)
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Philip R
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« Reply #18 on: February 25, 2019, 09:33:23 AM »

 Mass is not weight. Mass in kg and weight in Newtons. In normal parlance we measure weight in kg too, but gravitational force g in N/kg is not constant.
Mass effects acceleration and braking, weight affects the rolling resistance of the tyres on the road. Weight is the force on a mass due to gravitational acceleration.
Philip R
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JohnS
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« Reply #19 on: February 25, 2019, 09:41:03 AM »


It seems odd to me that they are, at times, blaming the poor consumption on the lack of regenerative braking when travelling a constant speed on motorways.

They conveniently forget that, to brake, one must first accelerate and that uses more power.  To capture more power from regenerative braking than expended in the initial acceleration is against the 2nd law of thermodynamics.

Only true if the road is flat. Going up a hill, work done is proportional to the weight (also going down the energy available for potential braking).


Fair point, but it does not lessen my point about the authors amnesia.
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DonL
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« Reply #20 on: February 25, 2019, 06:07:04 PM »

Mass is not weight. Mass in kg and weight in Newtons. In normal parlance we measure weight in kg too, but gravitational force g in N/kg is not constant.
Mass effects acceleration and braking, weight affects the rolling resistance of the tyres on the road. Weight is the force on a mass due to gravitational acceleration.
Philip R
I stand corrected on loose use of english.
To be more scientific Work =  Mass*Gravity*Height. We seem to be looking at drag and acceleration and rolling resistance and ignoring the work done simply going up a hill which is very significant in my experience of driving an electric car. In any event the lower weight (common english usage) of the Jaguar, thanks to extensive use of aluminium, is an advantage for all the variables mentioned but not drag which becomes more significant at higher speed (square law?).
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« Reply #21 on: February 25, 2019, 07:09:44 PM »

I don't pretend to understand this, but when the Monroe team stripped down a TM3 they mentioned that the motors were cheaper but more efficient than that in the Bolt (and a n other (I forget)), but then explained that they were confused as to why the magnet(s) had 3 fine lines on it, so they hit it with a hammer and found it was 4 magnets stuck together, and (I understand nothing now) by aligning multiple magnets you can effect they way they work in motors and improve efficiency, something about the magnetic field ? ? ? ? ? ? ? ? ? ? ?
Two ways of doing that, either might be of value.
  • By segmenting magnets you reduce the potential for eddy currents, i.e. electricity currents going around in circles in the magnets as a result of the motor turning. That improves efficiency a bit - more segments are better (I'm working on a design with about 120 segments at the moment), but make manufacturing it more expensive.
  • Depending on how the magnets are arranged, you can create something called a Halbach Array. Essentially this reduces the amount of iron you need to have behind the magnets to carry the flux, while strengthening the field in front of the magnet. Building these is a right pig, so I'd be very surprised if it was done on a mass-market car like the Model 3 (and would really like to know how it was done).
It might also be simply a cost saving, depending on exactly the magnetic material used - larger shapes can be very difficult and thus expensive to make in some materials.
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« Reply #22 on: February 26, 2019, 07:07:41 AM »

I don't pretend to understand this, but when the Monroe team stripped down a TM3 they mentioned that the motors were cheaper but more efficient than that in the Bolt (and a n other (I forget)), but then explained that they were confused as to why the magnet(s) had 3 fine lines on it, so they hit it with a hammer and found it was 4 magnets stuck together, and (I understand nothing now) by aligning multiple magnets you can effect they way they work in motors and improve efficiency, something about the magnetic field ? ? ? ? ? ? ? ? ? ? ?
Two ways of doing that, either might be of value.
  • By segmenting magnets you reduce the potential for eddy currents, i.e. electricity currents going around in circles in the magnets as a result of the motor turning. That improves efficiency a bit - more segments are better (I'm working on a design with about 120 segments at the moment), but make manufacturing it more expensive.
  • Depending on how the magnets are arranged, you can create something called a Halbach Array. Essentially this reduces the amount of iron you need to have behind the magnets to carry the flux, while strengthening the field in front of the magnet. Building these is a right pig, so I'd be very surprised if it was done on a mass-market car like the Model 3 (and would really like to know how it was done).
It might also be simply a cost saving, depending on exactly the magnetic material used - larger shapes can be very difficult and thus expensive to make in some materials.

Hiya, found a video of Munro talking about the TM3, and they say it is the Halbach effect/array, so they too were surprised at just how 'advanced' this mass market motor is, Munro describes them as having magic. See from around min 10 onwards, worth watching to min16 at least. Just a quick note, they are very critical of the additional strengthening and mass of the car. It seems Tesla designed it to be safe in a crash, before the additional strength from 'bolting' all the components together is taken into account.

Munro Talks Tesla Model 3 Motor Magic And Profit Potential
« Last Edit: February 26, 2019, 07:13:45 AM by M » Logged

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« Reply #23 on: February 26, 2019, 07:24:40 AM »

OK, thanks. Looks like they aren't making any allowance for the fact that Halbach arrays are normally quite expensive to make, so they might be underestimating the cost of the Tesla motor. We use them quite a bit in aerospace applications, because they're the lightest way of making a permanent magnet rotor. Most people don't use them however because the additional assembly cost of putting it together is more than the raw material cost of more NdFeB material. That's why I'm curious about Tesla - they have form for choosing a more expensive solution which looks better technically, but they occasionally come up with something really clever and I'm wondering which is the case here.

Just for clarity, Halbach arrays are neither new or magic, they're just rarely seen because they're a pig to make and so very expensive except in niche applications. If they're doing a semi-Halbach array instead (a true array has a continuous ring of magnets, which doesn't sound like what they've done from the description) that might do it, but you'll obviously lose some of the weight advantages.
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« Reply #24 on: February 26, 2019, 07:29:56 AM »

OK, thanks. Looks like they aren't making any allowance for the fact that Halbach arrays are normally quite expensive to make, so they might be underestimating the cost of the Tesla motor. We use them quite a bit in aerospace applications, because they're the lightest way of making a permanent magnet rotor. Most people don't use them however because the additional assembly cost of putting it together is more than the raw material cost of more NdFeB material. That's why I'm curious about Tesla - they have form for choosing a more expensive solution which looks better technically, but they occasionally come up with something really clever and I'm wondering which is the case here.

Just for clarity, Halbach arrays are neither new or magic, they're just rarely seen because they're a pig to make and so very expensive except in niche applications. If they're doing a semi-Halbach array instead (a true array has a continuous ring of magnets, which doesn't sound like what they've done from the description) that might do it, but you'll obviously lose some of the weight advantages.

Slight (complete actually) tangent, but whilst we have your science head on line, is it true that a 'full flow rocket engine' is the Holy Grail of rocketry, it's just that SpaceX's Raptor engines are full flow, and I've no idea how impressive (or not) this is?
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« Reply #25 on: February 26, 2019, 08:40:49 AM »

Full flow rocket motors are considered the holy grail of engine design as all of the fuel ultimately gets the opportunity to go through the main combustion chamber (instead of some being wasted by having a separate exhaust for the fuel that was used to power the turbo pumps - trivially like a wastegate on a turbocharged engine lets out some exhaust energy) and so is potentially more efficient. This is hard to do as to have to have very high pressure pre-burners, and it’s  particularly nasty on the oxygen side of the motor as you have hot high pressure gaseous oxygen present - which would really like to react with all the elements it can find in the engine as quickly as it can - so the metallurgy here is groundbreaking.  There is a lot more complex plumbing to make, and also you can’t test the pre-burner side of the motor without the rest of the engine also present as that’s how it works. So the whole engine has to be built before you can test each stage - scary stuff.

Additionally for the Raptor, they have just exceeded the world record for rocket chamber pressure previously held by the Russian RD-190 motor, and also they’re doing it using methane as the fuel rather than the until now standard fuel of rocket-grade kerosene.  Again this is the cutting edge of rocket science.   They also have not yet run with supercritical temperature fuels - which SpaceX does in its current Merlin/Falcon9 rockets- one of the only rocket motors to do this - the ultra low temperatures increases fuel density by about 15% over regular cryogenic temperatures and so gives a proportional increase in overall rocket performance.



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« Reply #26 on: February 27, 2019, 06:59:45 AM »

Thanks Dan, I understood what they'd done was impressive, but wasn't sure if it was really, really impressive. No wonder the company has gone from 0% to around 65% of commercial space launch business in a decade (recent tweet from Elon - "SpaceX commercial launch market share went from 0% in 2010 to 65% in 2018.).

And on the BEV side have even impressed Munro (and pdf) with their motor technology. But Elon's tweet on Tesla's success (sister tweet to Space X success) now has him being investigated by the SEC (again).

He posted - "Tesla made 0 cars in 2011, but will make around 500k in 2019"

then corrected it 4hrs later with - "Meant to say annualized production rate at end of 2019 probably around 500k, ie 10k cars/week. Deliveries for year still estimated to be about 400k."

 .... even though the original tweet was after trading hours, the SEC are still 'doing him' for it.

The ironic thing though is that TM3 production has a broad range of estimates for 2019 and could hit 400,000, which would take Tesla to 500,000 vehicles anyway. I suspect the shorts are using, or should that be miss-using, the SEC and complaints process just to cause trouble and further their aims. Silly and sad.
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« Reply #27 on: February 27, 2019, 07:29:47 AM »

Slightly off topic still but SpaceX has had final sign off from NASA for its “Commercial Crew Programme” - so SpaceX will be doing the first test flight of their human-rated capsule Dragon 2 in the next couple of days as part of the plan to allow NASA to fly astronauts to the International Space Station on non-Russian, privately developed rocket hardware.
If the two demonstrator flight last go smoothly (the second one will include an in-flight emergency capsule launch abort) then SpaceX will fly Astronauts to the ISS by the end of the year.

Another major achievement for SpaceX is how they have made the concept of landing, reusing and reflying the first stages of a rocket stack basically routine. They’ve made 27 landings now and have a clutch of first stages which have been flown twice with 2 I think having had 3 flights now.  The first stage alone is estimated to be about 70% of the overall cost of an orbital rocket mission.
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« Reply #28 on: February 27, 2019, 09:24:03 AM »

So I watch Mr Musk's ideas quite closely.

I was disappointed to find that his battery packs were made by whacking a load of small batteries in a box. Seemed very crude...,but then understanding slowly dawned. Easy to make millions of them, good surface area to volume ratio, allowing heating and cooling. Simple design, very sophisticated management. This is exactly NOT what other EV companies are doing, most of them supplied by LG flat packs with much less  flexibility of design, heating and cooling abilities.

Then there's the electric motor. With it's Halbach array magnets (not done normally, 'cause it's just too hard to do), it is way ahead of most other designs.

Add these two together, miles ahead of competitors.

The new rocket engine follows a similar thread. What's the best we can do? let's do it.

Pity about the tweets though!
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« Reply #29 on: February 27, 2019, 10:02:06 AM »

This video is well worth a watch explaining full flow rocket engine cycles - in fact Scott Manley is one of the best channels on YouTube in my opinion for rocket science nerds

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