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Measuring Standard Range Plus Acceleration

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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 (1,803 kg)
  • 77F (25C)
  • asphalt road surface
  • wind 0 mph, 9:09 PM (21:09) CST
accel_010.jpg


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.

Bob Wilson

ps. 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:
ham_small.jpg

Code:
;Title, http://www.gcdataconcepts.com, 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.
 
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Very similar to how I measure the acceleration for my car. I just use the internal accelerometer in my phone and the Physics Toolbox app, but data looks very similar! Very cool.
When I was working on the Gen-3 Prius, brake-pause problem, I found my iPhone MEMS data had other problems including an unexplained drift and data dropouts. However, for maximum acceleration runs, it is good enough.

Bob Wilson
 
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
accel_100.jpg


accel_110.jpg


Bob Wilson
 
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Thanks, Bob!

The timing is not relevant for me. I am curious to know what power is available at what speed and secondarily if your data aligns with Model 3 dyno data.
Thanks, you've given me some ideas which I also picked up from:

I didn't think about using 'slip mode' or turning off traction control. One of the reasons for my testing is the larger battery, performance 'labeled' cars get tested. No one thinks to test my much lighter weight, efficient, Standard Range Plus Model 3. BTW, this was the first time for me using 'Standard' mode instead of 'Chill.'

I have no interest in improving the acceleration and steering performance of my Model 3 for a 'track day.' At age 69, I don't have the reaction times needed for such fun. But of course others might want to 'reduce weight' and do silly things on the track or road. As for traffic lights, the low-speed launch versus required ICE spin-up ... well I do like to reach the speed limit first. <GRINS>

Bob Wilson
 
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@bwilson4web Would you mind sharing how you are calculating the drag power? I would definitely be interested in that.
It came from a discussion in: EPA roll-down coef vs HP at 100 mph - Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com

"HP = v * (A + B*v + C*(v*v)) / 375"
v - speed in mph​

The roll-down coefficients come from the EPA "Test Car Database": Data on Cars used for Testing Fuel Economy | US EPA

Ecomodder is a forum for 'roll your own', efficiency oriented folks. I can't endorse every approach but I do admire their work.

Bob Wilson
 
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