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JBee

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This must be what you are talking about, being able to produce lots of torque at low end.

So power is the product of torque and speed. At low speed the motor is delivering low power but full torque. Ok. At high speed the motor is still delivering full torque but it is now delivering more power.

I am saying that with a power split you can get MANY times the low end torque than the motor can deliver at that speed by itself. The motor is delivering more power at high speed. Torque is power divided by speed. Deliver a lot of power at low speed and you will have lots of torque. Again, many times more low end torque can be produced with the power split than with the motor alone.




Also, being able to extract all the energy, even at low speed even though there is not much power there, is a big deal. No need to tell me that it is not a big deal.
You need to include the final drive through a differential (if you have one) and realise that the limiting factor on many EVs is the traction of the tyres at any given speed. So adding more torque in any of the Tesla drivetrains just means it can spin the wheels easier, not that it would produce a meaningful increase in performance or efficiency.

Using it as a power split device, like the Prius does, was done so that the Prius doesn't need a clutch and can be essentially "direct drive" but with a ICE attached, which is not normally possible. There one electric motor would spin in reverse at the same speed the ICE would spin forwards, meaning that the wheels would have 0rpm through the planetary gear. That is also why the Prius had a limited speed and power in reverse, in fact they won't reverse up a steep hill well because of this.

But in a electric only situation the variable gearing is not that beneficial if your motor already has full torque from 0rpm and has enough motor rpm to reach the vehicle top speed through a simple single gear ratio.

One idea I had ages ago was to use the powerspilt device and two motors as a flywheel storage for acceleration purposes on smaller EVs. There you could preload the motors by spinning them in reverse of eachother at the lights, then on launch they would both slow down putting both the power of the motors and the power of the decelerating motor mass/flywheels into the wheels for faster acceleration. In reverse you could do the same for regen to spin up the flywheel. But now I have a version of that idea that doesn't use a planetary gear at all and does it all electro-mechanically instead which also allows for higher flywheel rpm without the friction. The primary reason for it is to reduce peak power on smaller battery packs and to use it as a more "mechanical" voltage converter.
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Crissa

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The Semi can benefit the most. Running high torque at low speeds is not efficient for the induction motor and they produce a lot of heat.
Heat production is a direct connection to power applied - so more speed equals more heat.

As pointed out earlier, static motors push air away from them through centrifugal force, which means are higher speeds you have more cooling.

This just doesn't apply to EV motors at all.

-Crissa
 
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Heat production is a direct connection to power applied - so more speed equals more heat.
Although the power applied does have some connection to the amount of heat generated it is not exactly a direct connection. The efficiency determines how much of the power applied gets converted to heat. With a simple motor you can't change the efficiency in any way so your job is done. With the power split we can do all sorts of tricky things to get better efficiency.

This just doesn't apply to EV motors at all.
Do I need to explain why that statement is completely false?
 

JBee

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Heat production is a direct connection to power applied - so more speed equals more heat.

As pointed out earlier, static motors push air away from them through centrifugal force, which means are higher speeds you have more cooling.

This just doesn't apply to EV motors at all.

-Crissa
Crissa are you doing ok? I'm genuinely getting concerned now. :-(

"so more speed equals more heat" and " which means are higher speeds you have more cooling".

You're going to have to decide which one it is.
 

Bill906

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You're going to have to decide which one it is.
If you read the entire sentence she was referring to a type of motor I pointed out earlier. A static (meaning mounted in a factory, not in a vehicle) motor that is fan cooled where the fan speed is based on motor shaft speed. In this type of motor, the cooling is increased with speed.

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JBee

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If you read the entire sentence she was referring to a type of motor I pointed out earlier. A static (meaning mounted in a factory, not in a vehicle) motor that is fan cooled where the fan speed is based on motor shaft speed. In this type of motor, the cooling is increased with speed.

A7602407-4A81-4C47-A25E-CB511DA33ECC.jpeg
So what does a static motors have to do with planetary gears in a electric semi or truck as per the OPs comments?

None of the EV motors in production cars that I know of are "static" (stationary?) neither are there many that are air fan cooled directly from its own driveshaft. Especially Teslas, that are all water jacket cooled motors with seperate water pumps and with fan driven radiators. Further heat generation is not dependant on motor speed (rpm?) rather motor load, which is not rpm dependant. A stalled motor also produces heat, and water jacket cooling works while the vehicle is stationary as well, like on a car dyno at full power.
 

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So what does a static motors have to do with…
Well, when I brought it up earlier it was when you claimed high torque low speed motors created a lot of heat. I explained that the only time I knew of where low speed caused excessive heat is in this fan cooled type of motor. I was pointing out that unless you have this type of motor, (which EV’s most likely do not), low speed has virtually no effect on motor temperature. I believe we’ve gone full circle and now you are also claiming speed has virtually no effect on the motor temp.

Yes, load affects motor temperature. More accurately, current (amps) is the most relevant factor in temperature and depending on the type of motor, application, etc. motor current can be considered proportional to load. (with some exceptions).

Maybe you’re right. Maybe Tesla will find that a complex system of two motors with a planetary gearbox per axis is more efficient enough to outway the cheaper and simpler single motor simple gearbox method for the semi. I’m sure they have people way smarter and with way more resources than we have to determine the best way to go. I strongly believe the better way is the simpler way, but I could be wrong.
 

JBee

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Well, when I brought it up earlier it was when you claimed high torque low speed motors created a lot of heat. I explained that the only time I knew of where low speed caused excessive heat is in this fan cooled type of motor. I was pointing out that unless you have this type of motor, (which EV’s most likely do not), low speed has virtually no effect on motor temperature. I believe we’ve gone full circle and now you are also claiming speed has virtually no effect on the motor temp.
Sorry I don't think it was me who brought it up. Maybe the OP?

My opinion on the matter is that technically a planetary gear is only necessary if a relatively high reduction ratio is required, which would be too cumbersome for a normal transmission to handle. In the end the final drive ratio can be achieved in various stages of the drivetrain.

From memory the Tesla Semi uses a M3 motor per wheel for drive. A total of 4. Doing a direct drive of a wheel on each side one would assume no differential, so the vehicle would have an electronic differential using the motor speed controllers instead. The top speed required for the semi is less and the tyres are bigger so they spin slower too. That makes the ratio required higher overall.

So if we assume Semi uses a 315/70 22.5 tyre with a 3.2m circumference we get about 730rpm at the wheel at Vmax 140kmh (87mph). We know that the M3 motor does 18,000 rpm. Thats about a ratio of 24.6. Fairly high for a standard gear, who knows, it might be a planetary gear already.
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Sorry I don't think it was me who brought it up. Maybe the OP?
That is the second time I confused you and the OP. I am sincerely sorry and, quite frankly, a little embarrassed.
 

JBee

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No worries. I sometimes have problems with forum names as well, especially if they are some abstract mumbo jumbo with letters and numbers. Thats why I keep mine simple. :)
 


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This system could be a big benefit to the boring company because of the exceptional amount of low end torque. I'm not sure if the wide rpm range would be as applicable but the torque could be put to good use.

The other configuration would be more appropriate for small spaces. If the shaft of one motor is hollow the shaft of the other can go through it (like a dual spindle jet engine) and connect to the power split device on the end.
 
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I forgot how ridiculous we were. I think resent events may be a good sign. Naturally, I would have liked to acquire a fixed dollar amount of Tesla stocks while the value of the stock was low. I guess I should be happy with what-ever.

There are many other applications for this dual motor power split technology. The spindle for milling machines could be designed with this for astonishing low end torque, especially for the size and weight. The tunnel boring machine could conceivably benefit greatly from the torque and speed control.

I do need some money to test this technique of moving matter at a distance with electric and magnetic fields. Carrying propellant is so cumbersome. I still want my flying car, even if it is more suited for space.
 

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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.)
Interestingly, Cyber* trucks may be a fit.

But not for the first principles you assert. Traditional ring gear and pinion carrier ass’y provide power distribution enabling reduction in sprung weight.

Sprung weight becomes most important to performance. Performance in power delivery, traction, balance and quickness.

Sprung weight using carrier ass’y enables suspension geometry to rotate 90° providing for swing arm .v. A-arm as Cybertruck is engineered. Performative improvements are in power delivery, ground contact, speed and handling. Simply it would be able to maneuver, control and improve Cyber* truck’s capabilities off road, recreational and racing stability.
 

Crissa

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  1. Electric motor efficiency range is huge. They already have a gear included.
  2. Tesla already did this, their motors were limited by heat, mostly. They have enough amperage in the battery to avoid voltage dip.
  3. See 1. Again, they have a single, static gear for this. Electric motors are actually easy to have too much torque. Which does you no good if your tires break from the road.
  4. See 1.

-Crissa
 

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Does anybody else think this dual motor power split drive train a good idea? Does anybody else think this would be an excellent opportunity for Tesla?

The benefits it provides:
1) Greater efficiency, the motors can run at their most efficient rpm range.
2) More power, it flattens the power curve so you can have maximum power at all rpm's.
3) More torque, since the power curve is flattened the torque at low rpm's is extremely high.
4) Regeneration is more efficient at all rpm's!
BEV is fast moving. Li dominant, electric motors are in-competition and EV design just emerging. 70% of EV companies evaporate in 5yrs. Exactly how does planetary gear save a single company in 4 years time?

Robotics mfgr, injection casting, additive printing, AI controlled power, computer managed energy and arbitration thru automation at the interface of non-spin generation are pioneering territory.

The problem is finding a layer in which these companies can thrive. Tesla own 2/3rds of the BEV market. 50% are copy competitors. 5% are taking slivers down market(i.e.Vanderhaul, Rivian), 1% cross market(i.e. Arrival, Canoo) and 40% are failing(i.e.TOY, VW). A 3 or 4% are unknowns(i.e. VinGp).

Presenting a Hdwe solution at the nexus of a Software revolution in automotive industry isn’t scaling the scope or disrupting anybody. In a field of equals(power, money,product and energy) as scifi as Planetary gear sounds its moment in time has passed, well served in duty to the automatic transmission. Planetary gear is an unwelcome complexity from the past, effectively eliminated by the electric motor.
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