Tracking the new roadster - heat soak solved?

[ecarfan]

Thanks @gregd I has missed that. Good to know!

 

[AirKuhl]

The roadster is a ROADSTER, not a track car.
By loose definition it is a car to be driven in a spirited fashion on a long winding road on a sunday afternoon, while enjoying the sport of driving, preferably with the top down.

Even with the carbon ceramic brakes and vector torque steering will likely have considerable understeer, by virtue of its weight.
The same closed body style that gives it its low drag coefficient to reach 250 mph also prohibits any sort of air cooling.
The same thick dense wiring that conducts the needed amperage for incredible performance, also retains electrothermal heat.
The same spoiler that stabilizes the car at 200 mph provides insufficient down force for track performance (hence the 2 wings available for the new ZR1)
The Jetson style steering wheel is incompatible for a technical track.
Currently the roadster has no dashboard to convey critical car information front and center to the track driver who must always be looking at the drive line through the corners.
Many drag strips require roll bars for cars capable of sub 10 second runs.

Hmm, I do a lot of track days and I have a different view.

This is a halo sports car, so even if 99% of owners don't track it, if it embarrasses itself like the Model S did on the Lightning Lap, where it failed to complete a single timed lap without hitting limp home mode, it will fail in its mission to "smack down" gas powered cars.

Understeer or oversteer is not tied directly to weight, it's about weight distribution, suspension settings and tire grip. Modern wide sport tires are more than capable of handling a 4,000 lb car, so the rest is up to Tesla chassis engineers. Note that understeer is often deliberately engineered into a car's suspension settings by the factory for safety for the average street driver, and must be tuned back out for decent track use. Some cars like Porsches tacitly acknowledge this by making track oriented camber rates fairly easy to dial in.

Great aerodynamics can be built into a car or tacked on. A Ferrari 488 doesn't need wings, a Corvette does. There are plenty of great track cars without huge wings that can break 200 mph and also corner on rails.

I agree that the steering wheel isn't practical in any car with a steering ratio that's safe for public use. Like any other concept car, I expect details like this to change by production time.

There is little data of interest for a track day driver while actually driving. All I ever cared about is the tachometer and that's only because all my track cars had manual transmissions. Telemetry data, tire pressure and temps, and stuff like that was interesting between runs, not during.

Teslas do fine at drag strips, this is more about actual track days at places like Laguna Seca or VIR, where streetable electric cars are basically useless so far. I really hope the new roadster changes this.

 

[Prim3]

As a track guy and an EV guy, I'm super excited about this.

I pray (Once a week), they get the heat soak issue down, I'm sure they will get it down for 0-100 sprints all day long, but the track is an entirely different animal. I'm very hopeful they will make cooling changes as well as some others from the steering wheel to the possibility of using more carbon to reduce the weight. Now with new and hopefully more cost-effective ways of building carbon chassis (Ie. Lamborghini's new method used on the hurrican), we may one day see Tesla incorporate this into their flagship model.

I'm curious to see if Rimac has any collaboration with this project?

*First post, glad to be here!

 

[kevinof]

0-60 in 1.9 secs and top speed 250mph does not compute in an electric car.... unless it's got gears. This would in turn make for longer range, less heat and a sustained top end speed. Will be interesting to see what they bring out.

As a track guy and an EV guy, I'm super excited about this.

I pray (Once a week), they get the heat soak issue down, I'm sure they will get it down for 0-100 sprints all day long, but the track is an entirely different animal....
]

 

[ecarfan]

0-60 in 1.9 secs and top speed 250mph does not compute in an electric car.... unless it's got gears

Some on TMC in this forum have noted that the new Roadster front motor is very likely geared differently than the rear motors and optimized for high speed cruising, like the S/X front motor is. So that could explain the ability of the new Roadster to accelerate incredibly fast and also be able to attain a very high top speed.

 

[CarlK]

Let's say in a two gear system the first gear goes up to 155 mph and second gear goes to 250 mph. In the Model S/X we drive with only one first gear. What's the problem then with driving with only one second gear? You might say low speed torque but how how we put 60% more torque to the system? Problem solved. Just a simple straightforward brutal force solution.

 

[ecarfan]

In the Model S/X we drive with only one first gear.

In the Dual Motor S/X cars, since the front motor is geared differently than the rear, there are in effect two gears in the car. That is in part why the Dual Motor cars have greater range than the RWD cars with the same battery pack size.

 

[CarlK]

In the Dual Motor S/X cars, since the front motor is geared differently than the rear, there are in effect two gears in the car. That is in part why the Dual Motor cars have greater range than the RWD cars with the same battery pack size.

The Roadster can do the same although I have a hard time to understand that logic. How can you make it to work like two gears when you need to turn front and rear wheels at the same time? Either way the Roadster will also have low gear ratio and lots of torque to those motors. That's how you can achieve 60% higher top speed without having to have a trasmission.

 

[ecarfan]

The Roadster can do the same although I have a hard time to understand that logic. How can you make it to work like two gears when you need to turn front and rear wheels at the same time? Either way the Roadster will also have low gear ratio and lots of torque to those motors. That's how you can achieve 60% higher top speed without having to have a trasmission.

Yes, that is my point: the new Roadster will do the same as the S/X: the front motor will be geared differently than the rear motor (or motors, in the case of the Roadster).

So there is one gear ratio for the rear wheels, and a second and different gear ratio for the front wheels. Two gears, but on different axels.

The front wheel gear ratio is higher and works more efficiently at higher speeds.

We are saying the same thing, in different ways.

 

[CarlK]

Yes there is no disagreement. Those two are independent to each other. The front and rear can have different gear ratio like S/X but both can also have lower gear ratio with higher torque to provide high top speed and also low end acceleration. This is much better than adding the transmission and a second gear.

 

[kevinof]

Ok but even the S/X have heating problems with sustained high speed - you can't drive the X at 130mph+ for long, never mind 250. The heat buildup and the battery heat will still be major issues at these speeds and that's why I'm convinced there will be a gearbox to bring down the revs and the heat.

Doesn't have to be a 7/8 speed job - just a couple of gears to drop the rpm down as the speed get high. There is going to be plenty of torque at the transmission to maintain performance even with a couple of gears.

Yes, that is my point: the new Roadster will do the same as the S/X: the front motor will be geared differently than the rear motor (or motors, in the case of the Roadster).

So there is one gear ratio for the rear wheels, and a second and different gear ratio for the front wheels. Two gears, but on different axels.

The front wheel gear ratio is higher and works more efficiently at higher speeds.

We are saying the same thing, in different ways.

 

[Cosmacelf]

A few weeks ago one of the EV magazines (Insideevs.com or Electrek.co) had a short article about a new high performance EV that uses direct contact cooling with a non-conductive engineering fluid. Ie. The cells themselves were immersed in a non conductive liquid bath for the ultimate in heat extraction. I’ve searched, but can’t find that article anymore. So I did some more searches and found other information about different approaches to high performance battery cooling.

Here’s a 3M video about battery cooling applications:

And here’s an interesting white paper about different battery cooling approaches: What is the Best Electric Vehicle Battery Cooling System? – AVID Technology

The overall point being that you can’t assume that Tesla’s current cooling technology in the Model S/X is the best. It is highly likely that they have been working on other approaches in the past 4+ years!

 

[CarlK]

Ok but even the S/X have heating problems with sustained high speed - you can't drive the X at 130mph+ for long, never mind 250. The heat buildup and the battery heat will still be major issues at these speeds and that's why I'm convinced there will be a gearbox to bring down the revs and the heat. .

That's not true. S/X do not have problem cruising at 130+ mph. The only time there is heating problem is driving on race track where you need to constantly cycling between maximum power and maximum regen/brake. That the Roadster has 250 mph top speed is also a good indication it will not have an issue with autobahn speed cruising.

Doesn't have to be a 7/8 speed job - just a couple of gears to drop the rpm down as the speed get high.

Even just another gear is best to be avoided. Tesla has learned the lesson from the original Roadster. No transmission could handle that huge torque even when it was nothing compares to new Roadster's 10,000 Nm torque. What's wrong with just using one gear with lower gear ratio when you got enough torque to spare?

There is going to be plenty of torque at the transmission to maintain performance even with a couple of gears.

You finally got my point. Just make it one gear instead of two and trans. Problem solved. Better yet you will not introduce new problems with it.

 

[kevinof]

I've driven a 100D on the autobahn at 140+ and after about 10 mins it starts to complain about the heat. You then (usually) get a reduced power message. My point is - spinning a tranny with just one gear at these speeds does produce a lot of heat and that has to be dissipated somehow. Spinning it up to 250+ is a whole other problem.

So no, I don't think the roadster will do it in one gear - be very surprised if it does. Guess we'll have to wait until 2020 to find out.

That's not true. S/X do not have problem cruising at 130+ mph. The only time there is heating problem is driving on race track where you need to constantly cycling between maximum power and maximum regen/brake. That the Roadster has 250 mph top speed is also a good indication it will not have an issue with autobahn speed cruising...

 

[ItsNotAboutTheMoney]

Even just another gear is best to be avoided. Tesla has learned the lesson from the original Roadster. No transmission could handle that huge torque even when it was nothing compares to new Roadster's 10,000 Nm torque. What's wrong with just using one gear with lower gear ratio when you got enough torque to spare?

Because higher efficiency reduces power demand, which makes things easier for the battery and motor.
That would make it very useful in other products at lower price points.
Not as big a deal for cars, but a big deal for pick-ups and SUVs.

 

[strider]

I do not believe there will be a transmission in the conventional sense with multiple cogs/gears that change the final dive ratio. The reason is that they would need *3* transmissions as there are 3 motors, not 1 like in an ICE. The weight penalty would be enormous not to mention the challenge of keeping them all perfectly synchronized. Elon has said they can torque vector the rears which means they independently drive each wheel.

I believe it is still true that the power of the large rear P motors in the S/X are battery limited. The system can't flow enough power to use the motor's full potential. That was the drama around the P85Ds when they launched with Tesla quoting HP numbers for the motors when the batteries couldn't supply them with enough current to make those numbers. Maybe that's been resolved w/ the P100DLs. I haven't been following that closely. All that to say with a larger pack (as the v4 Roadster has) they may be able to get away with shorter gearing than S/X to get the top end they need. It's also possible that the top speed was a byproduct of the motors overdriving the tires with a taller ratio so they realized they could shorten the ratio while still being traction limited and get a higher top speed for free. Kind of like the long range was a byproduct of needing a huge pack to get the discharge rate they needed for acceleration.

 

[animorph]

They can certainly make the gearing tall enough to reach only 18,000 RPM at 250 MPH. Then they just need to make sure they still have enough torque at 0 RPM to spin the tires. The 200 kWh battery should help out there.

Motor cooling seems like a straight forward proposition. And they have a patent for that as well, right?

And the 200 kWh battery should also spread the thermal load around to more individual cells. Double the current 100 kWh battery cooling capacity if they used the current individual cells.

There will have to be some good-sized radiators to dissipate all that heat without raising temps too high.

Definitely not an ICE killer if they can't run hard for at least 20 min on a track. I don't think they'll let that slip, though it could be a pricey option.

 

[CarlK]

Definitely not an ICE killer if they can't run hard for at least 20 min on a track. I don't think they'll let that slip, though it could be a pricey option.

Yes. When Elon mentioned hard core smack down to gas powered cars I'm pretty sure he has taken this into consideration too.

 

[gregd]

Note that at least part of the motor cooling troubles with Models S & X are inherent in their use of AC Induction motors. The new Roadster is probably using something like the Model 3's PM-based motors, which I believe are easier to cool.