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abebarker

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People truly don't deserve what they have.
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Crissa

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Why would they need to do that? They usually just throw more motors at something to get more torque. That's where that crazy acceleration comes from.

-Crissa
 

Crissa

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https://theconversation.com/heres-why-electric-cars-have-plenty-of-grunt-oomph-and-torque-115356

Electric motors have a very broad curve of power. You can mix and match motors to get a nearly flat torque curve. That's why the Plaid (tri-motor) drive train is so good at what it does, and needs no shifting gear ratios.

My motorcycle goes from 0-95 with nearly no loss in efficiency with only the belt (small gear in front, big in back) acting as a reducer. There's no need to change gears in normal speeds at all. Changing loads are more easily dealt wih more motors because more motors can spread out the amperage without melting.

-Crissa
 
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John K

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Compared to Tesla’s current setup, what benefit in cost, manufacturer, performance and reliability would Tesla achieve converting to a planetary gear system?
 

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I don't see the performance gain, personally. Literally there's programming in my motorcycle that tamps down the available power at low RPM. It doesn't have the logic and sensors for traction control, so it does this rough thing.

Because the moment it breaks loose of friction, it can totally spin up to an amazing rotational speed almost instantly. No ICE powered wheel can do that.

-Crissa
 
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John K

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I am familiar with the process. I am acting as Tesla in this hypothetical conversation.

Quantify performance pulse with a trade off on reduced reliability and greater difficulty manufacturing thus greater cost, is that enough to motivate me as a company to change?

If my intention was to create a vehicle solely on performance, my decision path would be different. If my goal was to create an efficient manufacturing process to create a reliable EV while making it fun to drive, I would have other decision criteria.

Since I am not part of Tesla, the nerve of them never responding to a resume I never sent. I cannot speak for them. I do not see the lure to change current design. Granted, I ,at be missing something.

Regardless of Tesla, nobody can say the gear system is not cool. If they do, they are square.
 

Bill906

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An inverter powered induction motor with decent vector control and motor feedback can deliver 100% motor torque at zero speed.

Although I don’t know how Tesla controls their inverters I feel extremely confident in assuming they use vector control and have motor feedback.
 
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ajdelange

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Why would we want a kluge like that? We want the simplest gear train we can have which is, in the case of the tri motor, just a conventional gear or 2 at the right ratio and, in the case of the AWD, a simple differential at the rear. Of course the front motor requires a differential. The reason for simplicity is to eliminate drive train loss thus increasing efficiency.'

No "gear shifting" is required. A fixed ratio suffices because we can get full torque down to 0 speed with induction or synchronous motors using FOC (vector) control which, of course, Teslas (and all other BEV AFAIK, have. FOC permits independent control of flux and torque via separate PI (feedback) controllers. Clearly the art is in the tuning of the controllers.

Now while it is true that we don't need to "shift gears" and that the efficiency curves are very flat with speed and torque they are not completely so thus the motor control scheme may rely more on the front motor in some regimes and more on the rear motor(s) in others and the front and rear motor gearing ratios may be slightly different.
 

JBee

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John K, I get you.

The amount of cost is really limited to a minimum as is the difficulty and reliability problem. The amount of performance gained will be enormous. The torque delivered at a stand still can be increased by 4 times (not sure of the actual difference in starting torque vs full speed torque for Tesla) and the efficiency goes up as well, to near maximum. The increase in weight would be the weight of a planetary gear set, if two motors are already being used. Planetary gear sets are notoriously reliable and long lasting.

It may not be necessary for all situations. A families first car may not need it. Although, it is cheap enough to be a serious consideration.

If Tesla's reputation as a leader is going to hold out into the semi truck market, or even the light truck market, then they may need to adopt this technology. It is ideal for the induction motor. (If you ask me, it almost looks like the drive train was designed to have this planetary gear dropped right in, if you replaced the round inverter with another motor.)
The Models S Plaid has the reverse problem, in that they have to reduce power to the wheels on launch because the electric motors have too much torque, meaning the tyres will break traction up until fairly high speeds. Despite this low ratio gearing they still have to carbon wrap the rotors to stop it from flying apart at high RPM. A higher ratio, which is the primary benefit from a planetary gear would just make the problem worse, not better.

Theres also the problem of gear tooth size to adequately transfer power and torque, a planetary gear would be a fair bit bigger as a result and add a whole bunch of bearings that could fail. Even for semi I don't think it will be necessary as a simple gear on the motor would suffice, have less parts and last longer.

If you're into "cool" gearboxes have a look at the moon rovers harmonic drive.
 
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ajdelange

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The Models S Plaid has the reverse problem, in that they have to reduce power to the wheels on launch because the electric motors have too much torque, meaning the tyres will break traction up until fairly high speeds. Despite this low ratio gearing they still have to carbon wrap the rotors to stop it from flying apart at high RPM. A higher ratio, which is the primary benefit from a planetary gear would just make the problem worse, not better.
The torque is easily reduced by reducing the magnitude of the d-q vector. It can be switched anywhere within its reachable range to anywhere else in that range (magnitude and phase) within milliseconds. The only gearing that is necessary is that necessary to get the most efficient design motor speed down to range of tyre speeds that typify cruise. There is no need to shift gears (though some designers do have a second gear). Tesla has done the trades and found this un-necessary while outperforming the vehicles that do shift gears.
 

JBee

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The torque is easily reduced by reducing the magnitude of the d-q vector. It can be switched anywhere within its reachable range to anywhere else in that range (magnitude and phase) within milliseconds. The only gearing that is necessary is that necessary to get the most efficient design motor speed down to range of tyre speeds that typify cruise. There is no need to shift gears (though some designers do have a second gear). Tesla has done the trades and found this un-necessary while outperforming the vehicles that do shift gears.
My argument was that it is unnecessary for Tesla electric motors to use a "planetary gear" because there is a need to increase the deliverable torque to the wheels.

My comparison was that the Model S Plaid actually has to reduce the torque (as you described) because it had too much torque, and that in fact the coefficient of traction of the tyres was the limiting torque factor (otherwise the tyres spin), not the overall motor gear ratio.

As for if more gears is necessary primarily depends on the level of acceleration performance required and the the top speed of the vehicle. The limit there being the rotational velocities of the rotor, which is why we got the CFWIM in the Plaid. It could well be that the Tesla Roadster either has to add some RPM to the CFWIM or that they do actually add a gear to reach top speed. Either way a planetary gear would unlikely help...except if they used is as a CVT transmission like they did in the Prius. using two motors rpm and direction to change the overall ratio.
 

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We can be more efficient than either the induction motor or the reluctance motor because we can choose what speed the motors are running at. We can run them near their most efficient speed most of the time. You don't get a choice.
Nope because planetary gear systems necessary to give the assortment of ratios that would be necessary to stay at the peak efficiency would required several stages as was done in the automatic transmissions of the days of yore with ICE vehicles where what you are thinking does apply because those engines have narrow torque and efficiency peaks. Electric motors have very broad ones.

We can get a lot more torque at 0 rpm than the motor can put out at 0 rpm because the motors are running at full speed.
ELectric motors can put out full torque at 0 rpm and they do it with nothing more than a garden variety reduction gear. This is how the 2500 kg Teslas are able to get to 60 mph in a few seconds.

Say the field speed needs to run at 5 Hz when the shaft is at 0 rpm, in order to maximize the effect of the induced current in the rotor.
To "maximize the effect of the induced current in the rotor" the flux linkage component of the vector current is increased to whatever it needs to be. Torque is controlled through slip in an induction motor and through field angle relative to the rotor in PM motors..


The linear distance that field can travel is fixed distance based on the radius of the rotor.
That's got nothing to do with it. The torque produced depends on the magnetizing current and the torque current, independently controllable, and either the slip or the angle depending on whether the motor is IM or PM.


If the motor is able to get up to speed and the field can operate at say 400 Hz that is an additional 395 pulses of similar amounts of energy delivered per second. That is why this system is MUCH more powerful than a simple motor.
Again you reveal that you know little about AC machines (disclaimer: I don't know that much either - it is a very complicated subject) or about 3 ø systems. Power is not delivered in "pulses" (these are not DC brushless motors - they are 3 ø AC motors). It is delivered continuously.



Perfect for the Semi (and my truck, I want it in my truck).
Un necessary in either which is why Tesla, who believe it or not know considerably more about these matters than you do, have not elected to use it.



[But wait, that's not all.] This system also allows you to get effective and efficient regeneration down to 0 rpm. You get all that for the price of a planetary gear set (and the additional weight of the aluminum case that will need to be beefed up to handle the torque).
It is not necessary to use such a kluge for good regen braking as is demonstrated by the fact that the modern crop of Teslas already have it, with nothing more than simple (relatively) reduction gearing, to the point where one pedal driving to a full stop is available to the driver.
 
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ajdelange

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My argument was that it is unnecessary for Tesla electric motors to use a "planetary gear" because there is a need to increase the deliverable torque to the wheels.
Wasn't disagreeing. Just trying to amplify.

My comparison was that the Model S Plaid actually has to reduce the torque (as you described) because it had too much torque...
Any car does in the sense that the maximum torque is seldom required i.e. when coming out of the blocks or passing. At any other time the motor(s) can supply more torque than is necessary and so we turn the toque knob to a setting less than 11.
 

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