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1  Using Arduino / Sensors / Re: Simple angle measurement on: March 03, 2014, 11:17:05 am
Quote
Because he said:-

arg.  Apparently I couldn't read yesterday.

Skyhook, then.

t
2  Using Arduino / Sensors / Re: Simple angle measurement on: March 02, 2014, 02:47:25 pm
Why not just a 2- axis accelerometer?

Otherwise, how about a pendulum and a pot?
You'd have to process the signal, but with a bit
of fussing, I bet it would be pretty accurate.

t
3  Using Arduino / Sensors / Re: Reading data from multiple Melexis MLX90614 IR Sensors I2C on: March 02, 2014, 02:44:27 pm
From looking at the data sheet, yeah, if you reduce all filtering to a minimum  (wonder if that's default?)
you can get a roughly 25hz sample rate.

But whether that's a 40ms read of the thermopile, a 20ms read and 20ms of processing, or a 1ms read and a 39ms process,
I couldn't tell.  I'm sampling at a rate about 3x lower than revs- I figure, about the only mistake you could make, given
the limitations of the device, is to sample at the same place on the tire every rev.

I found that raw IR temps were a lot less useful than I thought they'd be.  They're very environmentally- determined
(higher when the tire is in the sun, for example) and the effect of air cooling on the tire surface is phenominal.
Processed IR temps have been somewhat more useful...

hth

t
4  Using Arduino / Sensors / Re: Reading data from multiple Melexis MLX90614 IR Sensors I2C on: February 28, 2014, 08:26:55 pm
Yeah, unless you're looking for gross events ('the wheel fell off here') some form of
tone ring, hall switch etc is a much better way to look for/at lockup. 

Quote
So each reading I get from the MLX90614 is an average of the tyre temperature over some portion of the tyre,

I'm not sure about that.  The data changes when you read it faster than its published sampling rate.
But whether it's continually averaging what it's seeing, I'm not so sure.  I never did any transient testing beyond
simple stuff on the bench with a soldering iron, and on the track, I never got any data that counterindicated
what I found on the bench, so I moved on to where I am now, which is data analysis.

And yes, what you hope to get are 3 spots across the face of the tire that somehow correlate to what is going
on with the contact patch. 

hth

t
5  Using Arduino / Sensors / Re: Reading data from multiple Melexis MLX90614 IR Sensors I2C on: February 28, 2014, 02:01:02 pm
As to time limiting, no, the sensor's apparently continuously averaging.  The data sheets show a data refresh rate of
something around 2 hz (from memory) but I could read at 10 hz and always got unique numbers from the device.
Given the nature of the data from tire temperatures, they read fast enough to track pretty closely.

As to wheel lockup, no, they don't read fast enough (nor give appropriate data) for determining that.
Look at OEM ABS systems for parts that work pretty well for detecting that- our base cars (e30's) have
that hardware as stock, and it's easy to take that signal and use it for lock- up detection.  Useful for setup,
less so during a race.

hth

t
6  Using Arduino / Sensors / Re: MLX90614 sensor on: February 28, 2014, 01:52:54 pm
Practically speaking, it averages its field of view.

Take your hot soldering iron and slowly move it into the field of view of the device-
and then get closer to it.  It's averaging that hot iron and everything it sees as
the background, and outputting that as one number.

There are several different fields of view available- they seem to do it with lensing.

hth

t
7  Using Arduino / Project Guidance / Re: Data analysis software- or, now that I'm logging, what am I getting? on: October 17, 2013, 12:57:17 am
Yup, looks like Scilab is going to do it.

Of COURSE this is going to take all winter...

heh

Thanks again,

t
8  Using Arduino / Project Guidance / Re: Data analysis software- or, now that I'm logging, what am I getting? on: October 15, 2013, 02:19:16 pm
Phew!  I thought it was just me! 

The spreadsheet route couldn't do more than one lap's worth of data in a timely fashion,
and one of the major things I was hoping to find was lap- to- lap variances in the same
parts of the track.  And trying to paste large quantities of functions?   yech...

Thanks for all the suggestions- I'll go digging now. 

I'd come across Matlab, but not the free version,
and that Python book looks interesting, too.
Lua?  Off I go!

Thanks, all!

t

9  Using Arduino / Project Guidance / Data analysis software- or, now that I'm logging, what am I getting? on: October 15, 2013, 02:25:28 am
This is a horribly broad question, but I'm stuck.
I'm successfully logging a ton (10K+ samples per session)
of temperature data, and it's hard to manage.
Manual observation of the numbers seems to indicate that the data's
all valid, but grinding through it byte- by- byte isn't time effective at all!
For background-
http://forum.arduino.cc//index.php?topic=89926.0

I'm trying to find a PC- based program that will let me window,
average, smooth, build comparison channels, etc for 'large' volumes
of data.  Excel can do it- but it really chokes on bigger chunks, and it
can't do any useful condensation and hiding of 'uninteresting' data.
Statistical analysis is what I'm really interested in- as in, 'What's the correlation
between tire temperature and cornering loads?' for example.

Examples of operations would be correlating temperature data to
lateral load data.  Smoothing load data,  Windowing out (or highlighting)
out- of- range events and data.  Hiding long, 'boring' straights...

I'm not picky- I'm looking for direction as much as specific answers.
I'm a novice coder, so doing this myself would be... painful.  Existing
commercial products all seem to be tied to hardware- and hardware that
doesn't do what I need it to do (thus, the Arduino logger)

Thoughts?

Thanks!

t
10  Using Arduino / Project Guidance / Re: Timers, interrupts and timing? on: August 18, 2013, 12:15:50 am
Seems to me, from working on similar issues with (ridiculously bloating) datalogging projects, that dedicating one processor to just throttle/esc/braking control gives you plenty of responsiveness.  Then offload almost all the other work (display, cell monitoring, etc) to another processor that won't be
life- threatening if it crashes.  This lets you leave your mission critical code short and sweet, and then you can play with lots of other ideas with (relative) impugnity.  One of the best things about this platform is that the hardware is so inexpensive, 3 or 4 processors aren't much of an investment compared to a propulsion battery...

Of course, you'll have a panic handle that unhooks the main battery, so anything short of a battery fire will simply be a quick grab of the handle and a longer coast to the side of the road....  Death by EV is usually a pretty slow, predictable process, so if you have a redundant hardware disconnect, you'll probably be able to avert it.

Just another way to do it,

t
11  Using Arduino / Sensors / Re: Reading data from multiple Melexis MLX90614 IR Sensors I2C on: August 17, 2013, 08:29:44 pm
Follow- up from the dead-
it's working, and the data seems to be valid.

USEFUL, however, is another question- we're finding
all sorts of interesting things about how a tire responds dynamically.

t
12  Using Arduino / Networking, Protocols, and Devices / Re: problems reading gps output on: July 15, 2012, 02:53:23 pm
Hmm- I can't get the sheet to open from USGlobalsat.  But the board I have from them runs at 4800 baud, default- might be worth a quick try just to see...

t
13  Using Arduino / Displays / Re: Questions on using a 4x40 display. on: June 17, 2012, 10:16:16 pm
Ressurecting an old thread, I know, but the LiquidCrystal440 library works seamlessly with an old leftover
'dual 2x40' I dug out of the basement.

t
14  Using Arduino / Networking, Protocols, and Devices / Re: GPS problems- can't get a fix... on: June 09, 2012, 10:08:43 am
Thanks, John- I'll give that a shot. 

t
15  Using Arduino / Networking, Protocols, and Devices / GPS problems- can't get a fix... on: June 09, 2012, 02:11:06 am
so after a bit of rewiring and poking around, I've gotten the Globalsat 406a (http://www.usglobalsat.com/store/download/46/em406a_ug.pdf)
 to talk to the Mega 2650 through an Adafruit shield http://www.adafruit.com/products/98.

It'll read properly parsed empty phrases from the module indoors, and if I take it outside, it gets a bit more data.

But the problem is, it can see 12 satellites, but can't get a fix.  Tried it at work, tried it at home, same results.
I let it chug along for at least 5 minutes, no luck.  Sees 12, no fix.  Moving it, sometimes it even loses the $GPGSV phrase.
If it was a radio, I'd change the antenna, but this one's part of the module.

Using the Adafruit code modified to read through the hardware serial port 1, I get:

Read:
$GPGGA,064518.403,,,,,0,00,,,M,0.0,M,,0000*5F
Read:
$GPGSA,A,1,,,,,,,,,,,,,,,*1E
Read:
$GPGSV,3,1,12,21,52,183,23,29,52,062,30,30,51,303,26,31,44,226,*7B
Read:
$GPGSV,3,2,12,25,33,127,,16,18,304,,05,16,051,,06,13,264,*73
Read:
$GPGSV,3,3,12,18,02,153,,23,02,313,,13,01,342,,03,-1,265,*6C
Read:
$GPRMC,064518.403,V,,,,,,,090612,,,N*48
   Time: 6:45:18
   Date: 6/9/12
   Lat: 0* 0' 0.0"
   Long: 0* 0' 0.0"

but even a simple serial1 to serial0 repeater gives the same results.


I'm GPS- clueless.  Is there something obvious I could be missing?

Thanks,

t
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