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Old 04-12-2009, 11:46 PM   #7 (permalink)
bwilson4web
Engineering first
 
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Join Date: Mar 2009
Location: Huntsville, AL
Posts: 792

14 i3-REx - '14 BMW i3-REx
Last 3: 45.67 mpg (US)

17 Prime Plus - '17 Toyota Prius Prime Plus
90 day: 58.25 mpg (US)
Thanks: 79
Thanked 196 Times in 126 Posts
Both the Prius and Echo have the speedometer and displays located in the center of the dash, between the driver and front passenger. So the area in front of the steering wheel is available and easily reached. However a ham posted this photo of his instrumentation setup and now I'm designing proper instrumentation mount:


But I wanted to share something I found with the Garvin nuvi. When mounted as a USB drive, there is a file:
GARMIN\GPX\Current.gpx
A text XML file, it includes not only way-points but also a history of your driving. Using an excel hack, I was able to parse the trace and overlay it with a Google Map:

Within the limits of a quick hack, the graph traces exactly the route I drove that day.

I then went to my favorite 'flat tracks' and set way points:
  • Coast 01
  • Coast 02
  • Coast 03
  • ...
This will significantly improve the data capture quality as well as make it easy to characterize the performance of other vehicles. Yes, there is the problem of GPS 'wander' but the same problem exists with manual data capture. The solution is multiple runs and averaging out the error.

One other thing, my Prius does not have a way to adjust the calibration of the speedometer. But the GPS speed and trip duration matches exactly the calculated tire diameter difference. I am seriously thinking of blocking the existing speedometer with electrician's tape and using just the GPS indicated speed. But when I record my mileage, I'll still adjust the distance per the difference between the GPS and tripmeter.

Bob Wilson
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2019 Std. Range Plus Model 3 - 134 MPG3 || 2014 BMW i3-REx - 117 MPGe, 39 MPG
JuiceBox 40 Pro (240 VAC, 40 A), KHONS portable (120-240 VAC, 12-32 A)
Retired engineer, Huntsville, AL (five times AutoPilot saved.)

Last edited by bwilson4web; 04-12-2009 at 11:59 PM..
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