Pack Performance and Launch Mode Limits

[jerjozwik]

so uh.. is anyone else using teslalog.com?

over the past 3 days i have been trying to see what kW im getting out of ludicrous only mode. yet everyting the data points around the WoT run seem to be conveniently missing. this has happend 3 times now with this latest attempt was after the car had a good signal for 15 min then drop around acceleration and come back after i settled into my commute. seriously interested to see if anyone else is getting this.

i have had no problem logging all my driving when in sport.

 

[stopcrazypp]

I think the power curve tells us more. Vbox will tell us what the acceleration was, but not if it could have been more.
The power curve shows us what the max power is and that the approach to it is linear with rpm, indicating that torque isn't being held back at the beginning.

Well I'm talking specifically about the acceleration. It's a more accurate way than using a butt-dyno.

 

[n2mb_racing]

so uh.. is anyone else using teslalog.com?

over the past 3 days i have been trying to see what kW im getting out of ludicrous only mode. yet everyting the data points around the WoT run seem to be conveniently missing. this has happend 3 times now with this latest attempt was after the car had a good signal for 15 min then drop around acceleration and come back after i settled into my commute. seriously interested to see if anyone else is getting this.

i have had no problem logging all my driving when in sport.

I use the powertools app. I logged a bunch of runs this weekend. No problems, except for when my cell phone ran out of service in a remote area.

 

[jerjozwik]

I use the powertools app. I logged a bunch of runs this weekend. No problems, except for when my cell phone ran out of service in a remote area.

cool, so its probably just teslalog.com rotting away from inside due to its developer loosing interest. one day ill get a canbus logger...

 

[n2mb_racing]

Power tools doesn't need canbus. It runs over the air.

 

[St Charles]

Only if the small motors can generate enough toque to break the wheels loose.

fiksegts said that he felt the acceleration increase later in the run, but the power curve is linear with speed(rpm), so if any thing the acceleration would be decreasing throughout the run.

I've never seen actual measurements for any of Teslas motors, large or small. Do you have actual measurements for power output on these motors? If not you are looking at meaningless marketing material. I say meaningless because we have all felt the sting of reality vs what is on the Tesla website.

Regardless, these motors specifically put out around 250lb·ft of torque which equates to over 2,250lb·ft at the wheel. As others have already stated, if these motors were to produce maximum torque immediately like you are stating then tires would scream and parts would break. The fact that this doesn't happen means the car is tempering the ramp of power through torque limiting as the car accelerates.

Finally, if you have a Ludicrous equipped vehicle. Pay close attention to how power builds differently between Sport and Ludicrous modes. Not only does power build faster in Ludi but tapers differently as the vehicle approaches maximum output. If you were to measure acceleration between Sport and Ludi, you would see a different shape in the acceleration rather than a 1:1 shift along a single axis.

 

[TIppy]

I've never seen actual measurements for any of Teslas motors, large or small. Do you have actual measurements for power output on these motors? If not you are looking at meaningless marketing material. I say meaningless because we have all felt the sting of reality vs what is on the Tesla website.

Regardless, these motors specifically put out around 250lb·ft of torque which equates to over 2,250lb·ft at the wheel. As others have already stated, if these motors were to produce maximum torque immediately like you are stating then tires would scream and parts would break. The fact that this doesn't happen means the car is tempering the ramp of power through torque limiting as the car accelerates.

Finally, if you have a Ludicrous equipped vehicle. Pay close attention to how power builds differently between Sport and Ludicrous modes. Not only does power build faster in Ludi but tapers differently as the vehicle approaches maximum output. If you were to measure acceleration between Sport and Ludi, you would see a different shape in the acceleration rather than a 1:1 shift along a single axis.

Assuming 5% loss through drivetrain:
250 fl-lbs * 9.73 * 0.95 = 2311 ft-lbs
torque at the wheels.

9.73 is the final drive ratio for the big motor in the rear. I don't know if they use 9.3 in the rear like they do on the small front motor. If they do, the torque at the wheels would be even less.

The wheels are about 1.125 feet in radius, so that's 2311 ft-lbs / 1.125 ft = 2054 lbs of force at the road. The car weighs about 5000 lbs with about a 50:50 distribution, so the rear wheels have about 2500 lbs of downward force on them. The tires have a coefficient of friction of at least 1.0, so it would take greater than 2500 lbs of driving force at the road for them to break loose. Since there is only 2054 lbs of driving force, the wheels will not spin. Due to acceleration, the force on the rear wheels would actually be greater than 2500 lbs while that on the front wheels would be less.

 

[jerjozwik]

Power tools doesn't need canbus. It runs over the air.

requires an iphone.

 

[n2mb_racing]

requires an iphone.

True, yeah. Or an iPad. I use an iPad tethered through my Android phone. I've also used Tm-spy with a bluetooth can bus interface, but I don't know how to parse the data yet...

 

[St Charles]

Assuming 5% loss through drivetrain:
250 fl-lbs * 9.73 * 0.95 = 2311 ft-lbs
torque at the wheels.

9.73 is the final drive ratio for the big motor in the rear. I don't know if they use 9.3 in the rear like they do on the small front motor. If they do, the torque at the wheels would be even less.

The wheels are about 1.125 feet in radius, so that's 2311 ft-lbs / 1.125 ft = 2054 lbs of force at the road. The car weighs about 5000 lbs with about a 50:50 distribution, so the rear wheels have about 2500 lbs of downward force on them. The tires have a coefficient of friction of at least 1.0, so it would take greater than 2500 lbs of driving force at the road for them to break loose. Since there is only 2054 lbs of driving force, the wheels will not spin. Due to acceleration, the force on the rear wheels would actually be greater than 2500 lbs while that on the front wheels would be less.

your weights are per axle. These cars have open differentials, there will be wheelspin.

 

[TIppy]

your weights are per axle. These cars have open differentials, there will be wheelspin.

Both wheels receive the same torque, which is equal to the torque of the wheel with the least traction. So the total torque is 2 times the torque to the wheel with the least traction. In this case, each wheel will receive 1027 lbs of driving force and 1250 lbs of down force. The wheels will not spin.

 

[hostman]

Both wheels receive the same torque, which is equal to the torque of the wheel with the least traction. So the total torque is 2 times the torque to the wheel with the least traction. In this case, each wheel will receive 1027 lbs of driving force and 1250 lbs of down force. The wheels will not spin.

All depends on the surface conditions.

 

[St Charles]

Both wheels receive the same torque, which is equal to the torque of the wheel with the least traction. So the total torque is 2 times the torque to the wheel with the least traction. In this case, each wheel will receive 1027 lbs of driving force and 1250 lbs of down force. The wheels will not spin.

It's not that simple. One wheel will almost always break traction first and all torque will go to that wheel. There will be wheelspin.

 

[TIppy]

It's not that simple. One wheel will almost always break traction first and all torque will go to that wheel. There will be wheelspin.

All the torque doesn't go to the slipping wheel. The torque to slipping wheel is lowered and the same amount of torque goes to the other wheel. The other wheel doesn't spin because the static coefficient of friction is higher than the dynamic friction of the spinning wheel.

In this case neither wheel is receiving anywhere near enough torque to break loose and so they won't.

 

[benjiejr]

The wheels do spin on my measly P85DL. You can see the icon appear many times and see the power fluctuate as they spin in the video I posted further up in this thread:

Pack Performance and Launch Mode Limits

 

[TIppy]

The wheels do spin on my measly P85DL. You can see the icon appear many times and see the power fluctuate as they spin in the video I posted further up in this thread:

Pack Performance and Launch Mode Limits

We're talking about a non-performance model x that has two of the small motors. Your measly P85DL has a much higher power rear motor and inverter.

 

[benjiejr]

We're talking about a non-performance model x that has two of the small motors. Your measly P85DL has a much higher power rear motor and inverter.

Sorry, didn't realize that we were talking about the Model X.

 

[St Charles]

All the torque doesn't go to the slipping wheel. The torque to slipping wheel is lowered and the same amount of torque goes to the other wheel. The other wheel doesn't spin because the static coefficient of friction is higher than the dynamic friction of the spinning wheel.

In this case neither wheel is receiving anywhere near enough torque to break loose and so they won't.

What you are describing is a Traction control system. Tesla uses the brake system in tandem with torque limiting to accomplish what you are describing. Mechanically, there is nothing stopping torque from flowing through the slipping wheel. Mechanical intervention would mean a limited slip differential. If teslas had these then your argument would be valid.

My entire point is that traction control is engaged to prevent wheel slip. The core difference being that traction control can be engaged on command whereas a simple mechanical limited slip is always engaged. Additionally, it is just not reasonable to assume that the motors will provide immediate maximum torque every time the driver commands it. Almost no factory delivered vehicle from any car company does this.

A lot that goes into making a modern car easy to control in everyday driving. More so than most people realize. If you have a PXXD car, play around with sport and ludicrous modes. Pay attention to how these cars build power relative to how much you command through the accelerator. you'll notice that Ludicrous has a lot more throttle response than Sport. Not only is more power available but it builds to that power maximum much quicker. This is very intentional behavior and one of the major selling points of the performance model Tesla. Obviously, sport mode is closer the experience you would get with a 90D/100D and that's what Fiksegts is talking about.

 

[TIppy]

What you are describing is a Traction control system. Tesla uses the brake system in tandem with torque limiting to accomplish what you are describing. Mechanically, there is nothing stopping torque from flowing through the slipping wheel. Mechanical intervention would mean a limited slip differential. If teslas had these then your argument would be valid.

My entire point is that traction control is engaged to prevent wheel slip. The core difference being that traction control can be engaged on command whereas a simple mechanical limited slip is always engaged. Additionally, it is just not reasonable to assume that the motors will provide immediate maximum torque every time the driver commands it. Almost no factory delivered vehicle from any car company does this.

A lot that goes into making a modern car easy to control in everyday driving. More so than most people realize. If you have a PXXD car, play around with sport and ludicrous modes. Pay attention to how these cars build power relative to how much you command through the accelerator. you'll notice that Ludicrous has a lot more throttle response than Sport. Not only is more power available but it builds to that power maximum much quicker. This is very intentional behavior and one of the major selling points of the performance model Tesla. Obviously, sport mode is closer the experience you would get with a 90D/100D and that's what Fiksegts is talking about.

What I'm describing is how an open differential works. It always delivers the same amount of torque to both wheels. If one wheel is in the sand, it controls the amount of torque that goes to both wheels. That's why traction control works. By applying the brake to the wheel in the sand, the torque it can generate goes up thereby increasing the torque to the wheel on the road. You don't have to bring the wheel to a stop. You just have to create enough drag with the brake so that the wheel on the street can move the car out of the sand.

Of course you can always limit the performance of the P cars. But I'm talking about fiksegts' contention that Tesla is intentionally decreasing the performance of the non-P Model X. Looking at the power curve he included in his video, the ratio of power to speed up to max power is the same. This indicates that they are applying max torque the entire time.

Certainly you agree that if the model x had a 5 horsepower motor that only generated 50 ft-lbs of torque at the wheels that it wouldn't spin the tires. So there is a certain amount of torque that will cause the wheels to spin. That is when the tangential force at the road/wheel interface is enough to overcome the friction of the tire. In this case it's about 1250 lbs, which the small motors just can't provide.

 

[TIppy]

Sorry, didn't realize that we were talking about the Model X.

I understand your confusion. fiksegts ( st. charles and me, too ) kind of hijacked this thread. I guess we're just trying to entertain ourselves while we wait for some more feedback from Tesla.