Some Standard Range Plus Model 3 metrics

[bwilson4web]

Hi,

• Standard Range Plus Model 3 (version 19.16.2)
• SOC ~75%, 15 mi (24 km) warm-up
• 3711 (empty weight) + 250 (driver) + 15 (EVSE, patch kit) ~= 3976 lbs (1,807 kg)
• 77F (25C)
• asphalt road surface
• wind 0 mph, 9:09 PM (21:09) CST

The acceleration data will be used to calculate the velocity. Then I'll add the EPA roll-down drag coefficients to calculate the total force on the car and eventually the vehicle HP (kW). This will be for both chill and standard modes.
. . .
Those 'down spikes' are the end of the maximum acceleration runs. I targeted 80 mph as my ending speed because the car sounds an excessive speed alarm at 90 mph. Yes, I could have disabled the speed alarm but earlier GPS measured runs showed 80 mph was adequate to our goals.

I'm using a Gulf Coast Data Concepts, Human Activity Monitor:

Code:
;Title, Gulf Coast Data Concepts, LLC, X16-MPU-ham, ADXL345, MPU-9250
;Version, 1191, Build date, Nov 15 2016, SN:CCDC3016B4874F1
;Start_time, 2019-06-05, 21:09:12.423
;Temperature, -999.00, deg C, Vbat, 4174, mv
;MPU SR, 200,Hz, Accel sens, 4096,counts/g, Gyro sens, 16,counts/dps, Mag SR, 10,Hz, Mag sens, 1666,counts/mT
;Deadband, 50, counts
;DeadbandTimeout, 0,sec
;Time, Ax, Ay, Az, Gx, Gy, Gz, Mx, My, Mz
0.004486,-170,1156,-4192,5,-54,-1
0.018432,96,1210,-3916,-21,-20,-9,-311,-383,-506
0.038421,-396,1242,-4240,-20,-34,0
0.058410,-370,1302,-4166,-25,-13,-8
0.078399,680,1450,-4722,-17,-10,-7,-304,-371,-506
0.098419,-384,1138,-4572,-18,-18,0
0.118408,-584,1142,-4106,-8,1,-7
0.138397,124,978,-3978,7,15,-8
0.158386,250,1096,-4122,16,1,-5
0.178406,-640,1222,-4154,17,-12,3,-296,-387,-514
Time - seconds from start of data file. Use the header to get the 'real time' clock and date.
Ax - side to side acceleration
Ay - front to rear acceleration
Az - top to bottom, gravity, which we use to scale 1 G
Gx - rotation about the door axis
Gy - rotation about the front to rear axis
Gz - rotation around a vertical axis
Mx - magnetic field along door axis
My - magnetic field along front to rear axis
Mz - magnetic field along the vertical axis
MEMS accelerometer data are noisy so I used a 7 element Gaussian filter (0.063, 0.250, 0.375, 0.250, 0.063) to do a weighted average. Unlike a linear average, this preserves the local peaks while significantly reducing the noise.

Each data file has 16,000 data samples covering about 5 minutes which puts a significant load on the OpenSource spreadsheet. Somewhat arbitrary, I used 500 counts, 500/4096 ~= 12.2% G, to trim the non-acceleration elements reducing the samples to 2,185 which was easily handled by the spreadsheet.

Perhaps more details than you were expecting, I was looking for an opportunity to share where the data came from.
. . .
So this is what the velocity looks like:




Remember, my car has a heavy driver, the EVSE, and a tire patch kit.
. . .
There are two parts:
Inertal HP - this is how much is used to move the mass
Drag HP - this is how much energy is lost due to rolling and aerodynamic drag
Since we have the mass, we can calculate the HP that accelerated the car and its contents to a given speed. Then add the drag HP to get the actual HP that was applied at the wheels.
. . .
Both Chill and Standard mode acceleration metrics:

• HP - the inertial power needed to accelerate the car and contents
• drag - the power needed to handle rolling, transmission, and aerodynamic drag
• Total HP - the total power needed at the drive wheels

. . .
I'm using a recording, MEMS, accelerometer to capture the data and CAT (truck stop) weight for the mass. Then I used physics to calculate the speed and HP. I also used the EPA roll-down coefficients to calculate the drag power.

You are welcome to my data in the zip file. It isn't a well documented spreadsheet as I use it for my curiosity. If you have questions, I'll be happy to explain what is going on.

I could clean up the spreadsheet if there is interest in a more 'formal' presentation:

• improved noise filter - I used a 5-element Gaussian filter but could increase it to 7-9 to further reduce the noise. I won't use a linear average because it suppresses the peaks even though it is more commonly used. Still, I could code the spreadsheet to let each method be used.
• standard units - I mix both SAE and metric metrics and calculations which ever is easiest. I could change all of the metrics and calculations to metric and then at the end convert the results to SAE.
• table parameters - in some calculations it was easier to hardcode the functions instead of referencing a well documented table. By using tables, different models and cars can be instrumented and values used to get useful results. Just I'm not in that business ... yet.

Bob Wilson

[bwilson4web]

BACKGROUND

In 2016, I visited the local Toyota dealer to replace our 2003 Prius with a new one with TSS-P, the safety package. Unfortunately of the three Prius models and trims, the fuel efficient ECO version did not have TSS-P. They offered instead an upscale trim which the test drive barely reached 98 MPG . . . not good enough. Their last offer, $28.9k was the same as a used, end-of-lease BMW i3-REx, 72 mi EV, which sealed that deal.

Six months later, after a +700 mi trip to Stillwater OK and back, the BMW had become my primary ride. Then an infantile problem with a motor mount bolt break led to replacing a 2010 Prius with a 2017 Prius Prime Plus, a 25 mi EV range plug-in. At least this one had the TSS-P safety package that was missing six months earlier in the Prius ECO.

February 28, Tesla announced the $35k Model 3 and I ordered one with basic AutoPilot. Then March 26, we drove to Nashville to trade-in our Prius Prime Plus, $18.3k, for a Standard Range Plus Model 3. We're keeping the BMW i3-REx as backup.


Bob Wilson

[bwilson4web]

RANGE VS MPH

Of the different approaches, I decided to run three, 10 mi benchmarks and record the trip meter metrics:

• 25-35 mph - low speed needed to include vehicle overhead
• 45-55 - middle, urban speed needed for around town metrics
• 65-75 mph - high speed to get aerodynamic effects

I plotted these three points and used the Excel trend line for a quadratic equation to plot the kWh consumption as a function of speed:

• Max mi - normally the battery is partially charged so there is 'head room' to absorb regenerative energy. This improves mileage in stop-and-go traffic.
• 90% line - a little optimistic, I now use 85% giving a 203 mi range around town. It is so much I no longer look for 'free' chargers as I can drive all day yet return home with +50 mi and recharge. If free charging is available, I'll use it but it no long drives my shopping choices.

If leaving for a cross country trip, I set the limit to 100% knowing the next day I'll be on the highway and regeneration will play little or no part. But then we drive based upon the "reserve range."

• battery range - a fairly accurate estimate based on recent driving, this becomes the 'no further' indicator
• mi to destination - the navigation unit, sensitive to terrain, gives a fairly accurate miles to go which must remain less than the battery range. If I have the time, I leave with 30-40 miles reserve between the two. At 20 miles, I begin slowing down as best I can. At 10 miles, I start looking at secondary charging options like RV parks, distribution, and J1772 chargers.

Bob Wilson

[bwilson4web]

SUPERCHARGER

One of my first tests was to use a dash cam as a video recorder of SuperCharger sessions:

• > 60kW - it costs $0.26/min to charge
• =< 60 kW - it cost $0.13/min.

There is no advantage to carry extra miles to the next charger but you must reach the charger. By adjusting speed to maintain a minimum reserve miles, you can reach the next SuperCharger with 15-30 miles of reserve charge. This gives the fasted charge rate at a cost of ~$0.16/kWh, or ~$0.04/mi. Below 60 kW, the price goes from $0.13/kWh to much higher at slower rates but sometimes you need the range. Rule of thumb:

• ~16 minutes above 60 kW gives ~50% charge, ~120 miles
• ~70 minutes gives a 100% charge

Our charging protocol is my wife and I do a biology break and I leave her there for refreshments. I park at the SuperCharger and walk the dogs back to where the wife is. A short break and I return to the car and drive back to load the wife and dogs.

With gasoline costing ~$2.50/gal, the Model 3 SuperCharger costs return about 64-94 MPG depending on weather and use of AC or other accessories.

Bob Wilson

[bwilson4web]

BASIC AUTOPILOT

Originally costing $3k with dynamic cruise control, it is now standard with an increase in base price. There is an advanced version called "Navigate on Autopilot" (NoA) but this was offered for $10k on top of the $3k. Actually NoA remains a work in progress with a promised faster processor and improved software in the future.

AutoPilot senses the lane lines or the curb/pavement edge and steers between them. However, it reliably detects and steers within ~40 yards in front. This leads to steering delays which takes getting used to. It has been described as riding with a 'nervous student driver'.

• Bad lane markers at angled intersections can lead auto steering to try and drive into approaching traffic ... not good.
• Going from one lane into two, the car vacillates between the two, again another time to take manual control.
• Going from two lanes into one, the car detects the initial, wider lane and steers to the center, not abrupt but predictable. It won't drive into other traffic.
• Mississippi cross roads have a curved intersection that with a dashed straight line works fine. But if the dashed line is missing, the car tried to split the difference and drive for the opposite ditch.
• Surveys show ~80% use AutoPilot regularly and ~20% don't.

Returning to Huntsville after 10 days of poor sleep and a missing CPAP (sleep apnea treatment,) I suffered five, micro-sleep events along a barren road about an hour after dawn. Autopilot kept the car in its lane with dynamic cruise control maintaining speed and safe distance from other traffic. Once we got to Decatur, I took a biology, coffee, and stretch break before driving home. Basic AutoPilot is the next generation, safety system far more advanced than TSS-P.

Bob Wilson

[bwilson4web]

Source: Munro EV conference trip report