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Thread: Track Driving

  1. #1
    Roadster#433, Model S#S37 Cottonwood's Avatar
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    Track Driving

    Last Friday, I took my Tesla out to the local sports car track here in Colorado for some driving lessons and to see what the Tesla could accomplish. Below is a copy of what I sent to many friends last night. After that, I have some technical discussion and questions for this forum.

    ===============
    I took my Tesla out to the High Plains Raceway (HPR), to get some driving lessons from Michael Pettiford.

    It was quite an interesting day. I got my first sports car, the Tesla Roadster, five days ago. Yesterday, I did my first day of track driving in it, and experienced a level of driving that I only knew about from a theoretical point of view. Let me tell you that driving the car on the track is an amazing rush and takes some real skill. I got a great introductory lesson from Mike, but still have a whole lot to learn. There are some videos from Mike and HPR at the end of this e-mail.

    Getting power at HPR worked out well by taking my home High Power Charger (HPC) and connecting it in parallel with an RV owned by a former student of Mike's, Marsha Hubbel. This made it possibe for me to keep driving the car hard 20 minutes of each hour, my track time, and almost keep up with the charging the other 40 minutes. The Tesla was by far the quietest car there and got a lot of attention.

    The day was great and my nephew, Andrew, came with me and took many pictures and videos. I did a quick selection of the pictures and a simple hard cut edit of the video highlights. See the pictures at Picasa Web Albums - Butch - Tesla at HPR and the video at Tesla at High Plains Raceway on Vimeo

    Boy, is this Tesla fun!!!


    For more info and videos of Mike Pettiford and HPR see:

    * High Plains Raceway: High Plains Raceway | Your Colorado Performance Driving and Racing Future
    * Go4It Services: Go 4 It!
    * Mike talks about his driving school: YouTube - GO 4 IT Car Racing
    * 9News Feature on HPR: YouTube - HPR Media Gran Prix - Governor Ritter Drives
    * Accurate In Car View Simulation: YouTube - High Plains Raceway v2.0 - in car view M3 GT

    ===============

    I have several technical issues that I would like to discuss.

    Performance Limits:

    High temperature first on the PEM and then on the motor very quickly limit performance. HPR is, as they tell me, a fast, technical track. It is 2.55 miles long with the fastest cars doing that in 2:05 on Friday; that's 73 MPH, average. I don't know what my fastest lap, but it wasn't close to that. I am guessing it was more like 3 minutes or more. I am guessing that the mix of driving was, 20% coasting, 10% max braking, and 70% max power. The driving was a 20 minute session on the track out of every hour. Typically, the PEM hot warning would come on in 1 to 1.5 laps, then the motor hot warning would come on in several more laps with associated power reductions. As an example, on the highway straight away, with a fresh cool car, I could get 110 MPH, but with reduced power, all I could get was 90 to 95 MPH. As my instructor joked, when the popcorn is done (the car beeps), the Tesla slows down. When the Roadster is cool, it is competitive with most cars on the track, with the power limited, its a different story.

    Obviously, driving 70% of the time at max power is very different than normal street driving, but it would be interesting to discuss how to get better cooling to the PEM for better track performance. The discussion on "Powertrain 1.5" at Tesla Motors - Engineering does not talk much about the PEM cooling. Is the PEM liquid cooled? If so, can we do something as crazy as carry some ice in the trunk and pass the liquid to the PEM through that first.

    Charging:

    As you can see from my pictures, because my MC240 is back ordered, and I also installed a 50 Amp, 14-50, in my garage, I made my HPC into a large, mobile charger. It just fits into the Tesla trunk. With the 14-50 "Y" cable, I was able to share power with an RV very nicely and charged at 40 Amps all day.

    Here are the data that I collected on charge state. I used Ideal Range (EPA) miles as my measure of charge state. See Picasa Web Albums - Butch - Tesla at HPR for these numbers.

    I have two big questions. Why did the charge state change so much between the end of the drive to HPR and plugging in with the RV? Why did the charge rate slow down in the afternoon? I was using a charge current of 40Amps and "Performance" mode for each charge, and the voltage was between 240V and 244V for each charge.

    Energy usage:

    This was pretty much as I expected. See Picasa Web Albums - Butch - Tesla at HPR On the drive to HPR, I wanted to conserve as much energy in the ESS as I could, so I drove out at 50 MPH, minimized regen by coasting down hills, etc. WIth that, I got, 218 W-Hr/mi, not bad. On the way home, I drove the 60 to 70 MPH and drove in a normal highway mode, getting 286 W-Hr/mi, as expected. On the track, with very aggressive track driving, I got 732 W-Hr/mi; again within expectations.


    Has anyone else taken their Roadster out on the track?

  2. #2
    Head Moderator / Administrator doug's Avatar
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    Quote Originally Posted by Cottonwood View Post
    The discussion on "Powertrain 1.5" at Tesla Motors - Engineering does not talk much about the PEM cooling. Is the PEM liquid cooled?
    The PEM in DT1.5 is air cooled. Version 2 (2010MY) is also air cooled. The Model S PEM is expected to be liquid cooled on the same water circuit as its motor. This improved drivetrain is anticipated for some future version of the Roadster, but can't be expected till the Model S makes it to delivery. A water cooled PEM and motor would hopefully take care of the overheating issues.


    Quote Originally Posted by Cottonwood View Post
    Here are the data that I collected on charge state. I used Ideal Range (EPA) miles as my measure of charge state. See Picasa Web Albums - Butch - Tesla at HPR for these numbers.
    What are your units for Charge Rate.

    Quote Originally Posted by Cottonwood View Post
    I have two big questions. Why did the charge state change so much between the end of the drive to HPR and plugging in with the RV? Why did the charge rate slow down in the afternoon?
    Not sure about the answer to the first question, I can guess at the second.
    Did you measure the ambient temperature? As the air got warmer in the afternoon, the cooling system had to work harder to keep the batteries cool. So more power went to the compressor.


    See also these articles:
    Would the Tesla Roadster be a suitable track car? - AutoblogGreen

    Tesla considering a track-ready version of the Roadster - Autoblog


    Additionally, there's this old thread, but it might be more noise than signal.
    Last edited by doug; 2009-05-17 at 09:36 AM. Reason: fixed typos

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    ERIC VFX vfx's Avatar
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    So Andrew rode with you and a full trunk out to the track and Mike was in the passenger seat on every run (include when you went in the marbles?)

  4. #4
    mod squad TEG's Avatar
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    By the way, thank you so much for posting all the details (including pictures and video) of your experience. I bet there are a bunch of other Roadster owners watching this with interest.

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    Quote Originally Posted by Cottonwood View Post
    Has anyone else taken their Roadster out on the track?
    Thanks for the great info on your track day.
    I am taking a performance driving class on July 6th at the local Seattle track, if my Roadster is here in time.

    It looks like great fun.

    Then on July 24-25 we are taking my Roadster Sport down to the Portland drag strip for the Wayland Invitational. The infamous White Zombie and the Killacycle will be there that weekend.

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    Cottonwood,

    Thanks for sharing this - very exciting for those of us who've been wondering if a 'real' track day was possible.

    The fact that you could run your 20 minutes of each hour and more or less keep up on charging (at 40A) is great news...

    Sounds like roughly half of each session was at reduced power. Perhaps a slower course would allow you to get through a full session without reduced power.

    In any case, it does make me hope that water-cooled PEM and motor can be retrofitted later when they figure all of that out. Of course, if water-cooled PEM and motor come after a chassis redesign, a retrofit would be very unlikely.

    Thanks again for sharing.

  7. #7
    Roadster#433, Model S#S37 Cottonwood's Avatar
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    Quote Originally Posted by doug View Post
    The PEM in DT1.5 is air cooled. Version 2 (2010MY) is also air cooled. The Model S PEM is expected to be liquid cooled on the same water circuit as its motor. This improved drivetrain is anticipated for some future version of the Roadster, but can't be expected till the Model S makes it to delivery. A water cooled PEM and motor would hopefully take care of the overheating issues.
    That would help a lot. The motor heat was an issue, but the PEM heat was a much quicker issue. I wonder how hard it would be to put some extra fans on the PEM.


    Quote Originally Posted by doug View Post
    What are your units for Charge Rate.
    Ideal miles/hr. I will updated the picture.


    Quote Originally Posted by doug View Post
    Not sure about the answer to the first question, I can guess at the second.
    Did you measure the ambient temperature? As the air got warmer in the afternoon, the cooling system had to work harder to keep the batteries cool. So more power went to the compressor..
    In further experimentation, it seems that you get more ideal miles for the same charge state in range mode than in standard or performance mode. I will try to gather more data.

    For the charge rate, that would be a LOT of power to the cooling system. 40Amps x 240Volts = 9.6 kW. 1/3 of that is 3.2 kW or over 4 HP. Does the roadster have that much of a heat pump? My guess is that it is a combination of cooling power and a calibration issue versus battery temp and battery voltage.


    Quote Originally Posted by doug View Post
    See also these articles:
    Would the Tesla Roadster be a suitable track car? - AutoblogGreen

    Tesla considering a track-ready version of the Roadster - Autoblog


    Additionally, there's this old thread, but it might be more noise than signal.
    All very interesting. I will have to sift through the old thread. Thanks for the links!

  8. #8
    Roadster#433, Model S#S37 Cottonwood's Avatar
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    Quote Originally Posted by vfx View Post
    So Andrew rode with you and a full trunk out to the track and Mike was in the passenger seat on every run (include when you went in the marbles?)
    Yes, on the drive to and from HPR, Andrew, me, the HPR, many plug adapters, an MC120, two laptops, and two cameras were all in the Tesla.

    On the track it was me, Mike, and almost nothing else. Mike and I are both a little over 200 lbs.

    As for going into the dirt:

    The HPR has a layout that is very safety oriented. There are at least 200 feet of well graded soil on each side of the track. My instructor, Mike, put the driving into multiple safety plan levels

    • Plan A - Hit every turn at the right points with the correct speed
    • Plan B - You are a little off in speed or position and cannot make it though the turn at perfect speed; let up on the brakes or hit the accelerator late to stay on the track and come out of the turn slower.
    • Plan C - You can't stay on the pavement; go off the track in control and with the wheels rolling. The quickest way to roll the car is to go off the track sliding sideways.
    • Plan D - You keep going past the safety graded dirt; don't hit anything solid. The reasons are obvious.
    • Plan E - You can't avoid hitting a solid object; hit the solid object head on. Slamming into the object on the drivers side is bad. If you hit head on, the front of the car will absorb a lot of energy and the airbags will work well.

    In that turn where I went off-road, I got out of my rhythm with the track and was braking too late going into the turn. I remembered that Plan C was the way to go. It worked well.
    Last edited by Cottonwood; 2009-05-17 at 02:30 PM.

  9. #9
    mod squad TEG's Avatar
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    Quote Originally Posted by Cottonwood View Post
    For the charge rate, that would be a LOT of power to the cooling system. 40Amps x 240Volts = 9.6 kW. 1/3 of that is 3.2 kW or over 4 HP. Does the roadster have that much of a heat pump? My guess is that it is a combination of cooling power and a calibration issue versus battery temp and battery voltage.
    It is my understanding that the same AC compressor can be used to chill the ESS coolant as to cool the cabin.

    There is info on Masterflux AC compressors here and here.
    I think it can draw about 1500-2000 watts, so a couple of HP could be gobbled up there.

  10. #10
    Roadster#433, Model S#S37 Cottonwood's Avatar
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    Quote Originally Posted by TEG View Post
    It is my understanding that the same AC compressor can be used to chill the ESS coolant as to cool the cabin.

    There is info on Masterflux AC compressors here and here.
    I think it can draw about 1500-2000 watts, so a couple of HP could be gobbled up there.
    That all sounds reasonable. 1.5-2 kW for cooling and the rest 1.7-1.2 as calibration error could be a plausible breakdown.

    As a side note, you can see the green, cooling fluid circulating to the ESS if you open the trunk. I put my hand on the side in the afternoon and it was obvious that the ESS coolant was cooler than ambient, and much cooler than the evaporator coils of the heat pump up front, so the heat pump was working to help keep the ESS cool during charging and to cool it down from the hard driving on the track.
    Last edited by Cottonwood; 2009-05-17 at 03:14 PM.

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