Mike Chaney's Tech Corner
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1  Mike's Software / TT Dyno / Re: The ambient correction factors. on: September 17, 2012, 04:05:32 PM
Thanks.  Smiley
2  Mike's Software / TT Dyno / Re: Explanation of terms please. on: September 17, 2012, 04:04:48 PM
Quote from: Mike Chaney on September 17, 2012, 03:38:11 PM
... The torque multiplier is nothing more than engine speed versus vehicle speed.  Tire diameter doesn't come into play here: all you need to know is how fast the vehicle was moving at what RPM and you can get the torque multiplier.  It is not final drive ratio, although if the diameter of your tire was exactly 2 feet (unlikely but probably close), it would be!

Mike
There you have it.  My tire diameter is ~ 24.3".

Quote
The sample rate is, on average, how many samples were present each second in the data log.
The DashDaq log has about 30 lines per second.  But typically only one signal changes per line.  And mph, being an integer  Sad , less frequently than that.  So I wonder where the 17 came from?

Quote
Smoothing is # passes @ window width.  So yours above means it had to do 5 passes averaging a window of 6 samples.  It is adaptive meaning it looks at how much variation exists (how spiky the data is) and adjusts accordingly until the graph is reasonable without spurious spikes along the way.
How does it choose the window width?


Thanks for the reply.
3  Mike's Software / TT Dyno / Request for new feature: Head/tail Wind Correction Factor. on: September 17, 2012, 02:34:45 PM
I try to log on windless days, but often there is still  a wind of a few mph.

Apparently even for my small car a 5mph head wind at 70 mph vehicle speed could take about 5HP (which is 4% to 5%) off the reported power.

Any chance of being able to input a head/tail wind speed which would be applied to the vehicle speed before calculating the aero drag.

I know that doing runs in both directions will more or less compensate for this, but the downside is that neither of the two resulting dyno plots is correct.  They will just show a ~10HP difference which needs to be split.

 
Many thanks.


see this calculator:

http://ecomodder.com/forum/tool-aero-rolling-resistance.php
4  Mike's Software / TT Dyno / Position of the header line in the log? on: September 17, 2012, 02:26:49 PM
Must the header line be the first line in the log?

Or can there be various comments and info above it, as with the DashDaq logs?

I'm just trying to reduce the amount of log massaging I need to do in Excel, before submitting it to TT Dyno.
5  Mike's Software / TT Dyno / Request for a "Speed Correction Factor" on: September 17, 2012, 02:08:07 PM
If you would like a suggestion for future releases that likely isn't too hard to do here is one:  speed correction factor.

The DashDaq has a GPS interface so I tried logging GPS speed to compare to vehicle speed.  The GPS only updated once per second so I had to do a bunch of constant speed runs.  Anyways I came up with a +1.014 correction factor.  Thing is close to what would be needed for my slightly oversize tires.  Anyways I am massaging the log in Excel to correct the speed.  

A Speed Correction Factor would help a lot.

Thanks in advance.
6  Mike's Software / TT Dyno / Explanation of terms please. on: September 17, 2012, 02:05:39 PM
Could you please explain the following items that appear in the information box underneath the dyno plot.  I have some experience with math and statistics, and have some ideas, but prefer not to make assumptions.

If I understood more about the smoothing algorithm I might be able to pre-massage the log to reduce bumps in the plots for very short runs.


Sample rate: 17 samples/sec
Smoothing: 5 @ diameter 6
Torque mult: 14.88

That last one seems to be the overall engine to wheels drive ratio, but I'm not sure how it is being calculated/estimated since the tire diameter is not known to the program.

 Huh?
7  Mike's Software / TT Dyno / Problems with the Barometric Pressure input field on: September 17, 2012, 02:03:05 PM
The Barometric Pressure input behaves strangely when unit of “mb” is chosen.  Any attempt to enter a number like “1000” results in “34.00”.

Very strange.  I have the latest version, V2012.100.

I got around the problem by converting to inches.


Anybody else notice this?

Is there a fix in the works?
8  Mike's Software / TT Dyno / The ambient correction factors. on: September 17, 2012, 01:57:53 PM
I read that there actually quite a few different standards for the dyno correction for atmospheric conditions.

Can I assume that this program corrects data to "the newer SAE J1349 standard of 77°F (25°C) day with 0% humidity and a barometric pressure of 29.234 in-Hg (99 KPa). "

Quote
The most common are the SAE standards. The older J607 standard considers that the engine was run on a 60°F day with 0% humidity and a barometric pressure of 29.92 in-Hg or the newer SAE J1349 standard of 77°F (25°C) day with 0% humidity and a barometric pressure of 29.234 in-Hg (99 KPa). Also the ECE standard is the same as the SAE J1349, but does not use mechanical efficiency in the calculations. The DIN standard which corrects to 68°F (20° C) day with 0% humidity and a barometric pressure of 29.92 in-Hg (101.3 KPa) and the JIS standard corrects 77°F (25° C) day with 0% humidity and a barometric pressure of 29.234 in-Hg (99 KPa), but uses different correction curves than the others (as a substitution for using mechanical efficiency factors). Further, we have the J1995 corrects 77°F (25° C) day with 0% humidity and a barometric pressure of 29.53 in-Hg (100 KPa).


http://www.land-and-sea.com/dyno-tech-talk/corrected-horsepower.htm
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