The Why's and How's of Wind Offset

Re: The Why's and How's of Wind Offset

Postby Russ » Sun Jan 04, 2009 6:26 pm

Todays ride, rock steady temperature 47F (depending or where you check, all showed steady).
Voltage varied from 2.90 at start, zeroed wind offset, 2.80v at end wind offset still 0.
I do think I will replace the 123 battery at some point with a pair of the 1.5v lithium's in series
for more umph or I may look into down regulating some rechargeable batteries in series.

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Re: The Why's and How's of Wind Offset

Postby Russ » Tue Jan 06, 2009 10:58 pm

Ok, I have another correction to entry for the 2.5 hour ride.....
where I said:"When I post processed
setting ground wind to zero, the wind offset in the wind analysis screen went to +5.0."
I was taking another look and the sign should have been minus. Guess that was confusing.
Also the setting ground wind to zero, which made the offset go to -5 made a 17.8 watt change in power.

Anyway I have been thinking about what is best to do and think that when the temperature is changing it would be good to zero the wind offset correction every several degrees of change for max accuracy? I know the post correction to the cool down ride corrected a maximized error (steady 5 offset whole ride) and the 2+ hour ride would not have had near that amount of wattage error. Also the post ride processing totally fixed the cool down ride.

Any thoughts?

Thanks,
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Re: The Why's and How's of Wind Offset

Postby JONLEMANS » Wed Jan 21, 2009 7:33 am

my wind offset will not work. When I try to calibrate it it is always at 0. when I download my rides there is no wind offset chart. Any suggestions?
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Re: The Why's and How's of Wind Offset

Postby coachboyd » Wed Jan 21, 2009 9:05 am

so when you ride, you never see any wind speed? That sounds like an issue with the wind sensor. I would recommend emailing John Hamann and talking to him about it.
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Re: The Why's and How's of Wind Offset

Postby iodaniell » Wed Jan 21, 2009 2:47 pm

It could also be that the wind scaling number in your profile is set to a number that makes your wind port less sensitive to changes in pressure. I believe a setting of greater than 1 (x > 1) may set you up for this type of observation.
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Re: The Why's and How's of Wind Offset

Postby rruff » Sat Jan 31, 2009 8:00 pm

Russ wrote:Yesterday's longer ride was interesting. Over about 2.5 hours, from 1500-1730 the temperature was about 50 from 1500-1600 then dropped steadily to 43 at 1730.
I run the external battery mount (new for Christmas with my new gen3) with a 123 battery.
I stopped and zeroed or checked wind offset several times and back home at the end.
First stop offset about -0.7 after about 10 minutes of riding, forgot the voltage.
Second stop at about 1530 voltage 2.85 and offset +1.0, zeroed.
Third stop at 1605 voltage 2.84 and offset 0. Temp just starting to drop
Home at 1730 voltage 2.59 and offset +5.0 Temp now 43F
The last 11 minutes was a separate cool down ride after doing the trip reset, it was roughly a
loop with nearly calm conditions (most of the last hour was near calm). When I post processed
setting ground wind to zero, the wind offset in the wind analysis screen went to +5.0.

All this to continue my above post, same questions.

Thanks,
Russ


Hi Russ... don't know if you've gotten any answers yet, but this is interesting to me. The variation of the wind offset with temperature is my main beef with the Gen2 (which I still have; haven't upgraded yet) but this was supposed to be fixed in the Gen3 models. Can anyone else share their experiences? I wonder if it is temperature, voltage, or a combination of the two? At any rate I see a marked change that seems to be in the opposite direction of yours. If it gets colder the offset goes negative... if it gets warmer the offset gets positive. So maybe your *was* calibrated at the factory, and they screwed it up and over compensated.

BTW, I think the offset you see on the unit is in Pa (N/m^2), not mph or kph.

Your cr123 battery has plenty of juice... that isn't the issue. The voltage of the battery simply varies with temperature.

Do you stabilize the unit at riding temperature before you do the first offset? That is essential if it is cold outside. The temperature always varies a few degrees during the ride and it is off again... but it is a lot worse if you cal at 70 and then go out into 40 degree weather.

Regarding your "net wind" being off in post processing, have you checked this when your offset is zeroed? If you do and are still getting non-zero values in out-back rides, then your wind scaling value is wrong. Adjust it by the square of the speed ratios (wind and bike) to bring it into line, and/or redo your calibration rides.
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Re: The Why's and How's of Wind Offset

Postby Velocomp » Sun Feb 01, 2009 12:03 am

Two days ago we discovered a bug in our cold temperature compensation algorithm that affects some, but not all, Gen III units. The bug causes the kinds of problems described in this thread.

Yesterday we got preliminary firmware that fixes the problem. We've tested it and it works very well.

We will be posting soon a new fw release that, among other things, will fix this problem for all Gen III units.
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Re: The Why's and How's of Wind Offset

Postby rruff » Sun Feb 01, 2009 3:06 am

That's great! I was wondering if firmware could be used to "tune" the calibration...
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Re: The Why's and How's of Wind Offset

Postby bjrmd » Mon Feb 02, 2009 12:44 pm

I was wondering if it was just me, but my Gen 2 is a bit more stable with wind offset than my Gen 3. Looking forward to a possible fix.
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Re: The Why's and How's of Wind Offset

Postby lorduintah » Mon Feb 02, 2009 6:09 pm

That's great - maybe now I can understand how a zeroed offset becomes 16 - with unit that was driven from my place to where I park to ride mounted on the bike (i.e. IN the cold). It is about a 3 mile drive and at 40 mph should really get the internals of the iBike to ambient.

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Re: The Why's and How's of Wind Offset

Postby Russ » Mon Feb 02, 2009 8:03 pm

rruf asked:
"Regarding your "net wind" being off in post processing, have you checked this when your offset is zeroed? "

And answer is yes, in fact for those runs I left it outside for especially ample time periods.
And I think my last ride data (above) where temperature was stable for whole ride but voltage
dropped steadily demonstrated that offset stayed stable for stable temp but dropping voltage.

This is great news about the firmware update coming. I did one, should have been satisfactory
out and back but since I usually ride late in the day and the temp almost always starts dropping
it has been problematic.

Thanks for the feedback and
velocomp, thanks for the continuting great support!

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Re: The Why's and How's of Wind Offset

Postby Velocomp » Fri Feb 06, 2009 12:57 pm

We have new firmware 3.06 available for Gen III users ONLY, using firmware 3.00 to 3.04, who are having wind offset problems.

This firmware upgrade requires that you follow a simple, but very exact procedure.

If the procedure is followed properly your wind offset issues should disappear.

If you follow the procedure improperly you will need to return your iBike to the factory for recalibration.

Here is the procedure:

1. Make sure your iBike's temperature reads 70 degrees F or higher. THIS IS VERY IMPORTANT!!!!!
2. Go to the user setup screen for wind offset and zero the offset.
3. Exit the setup screens.
4. Attach the iBike to the PC using the USB/Serial adapter and upgrade the firmware to v3.06.

If you would like to upgrade your Gen III and you agree to follow these instructions exactly then please send us an email and we will provide the new firmware.

If your unit is NOT experiencing wind offset problems there is no reason to perform this upgrade.
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Re: The Why's and How's of Wind Offset

Postby pjboyle » Fri Feb 06, 2009 7:13 pm

John,
Can you describe what the wind offset problem that this fw release addresses? Anomalies I am observing have been:

1) Rides consistently having a post analysis with a significant avg. ground wind (positive 2-4 mph). Forcing this to zero in iB3 dumps a lot of watts and requires fairly large wind offset.

2) Under some circumstances (I believe it may be in warmer weather ie 60+ F) after leaving the unit outside to temperature-equilibrate pre-ride, upon going into setup and looking at wind offset, it is 0.0 and rock steady, without the amount of drift I am accustomed to seeing. It just stay at 0.0 without variation. Pressing the button at this time has no effect.

I am thinking I am a 3.06 candidate.
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Re: The Why's and How's of Wind Offset

Postby rruff » Sat Feb 07, 2009 2:00 am

The issue I think we are talking about is the wind offset changing with temperature and voltage. This is easy enough to check in the house. Zero the offset at room temperature, then stick it in the frig for awhile and see what happens to the offset.

Positive wind can be caused by various things. For one it could be real... though probably not if it happens a lot. Or the wind scaling could be too high... do a series of out-back rides in the same part of the road when the winds are light, reset the wind offset each time, and check the results when you get home. Adjust the wind scaling factor by the square of the speed ratios (bike/wind) if it is consistently off.
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Re: The Why's and How's of Wind Offset

Postby rruff » Mon Feb 09, 2009 1:15 pm

Now that the Gen3 wind offset fix is out, how is it working for people?

An easy test is to do the offset cal at room temp, then stick it in the frig for awhile and see what the temp and offset reads, then take it out and put it next to a window in the sun and see what that does. A hair dryer works too, but make sure you don't overdo it.
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Re: The Why's and How's of Wind Offset

Postby rruff » Mon Feb 09, 2009 9:03 pm

Well I just got my new Gen3 today, so here is mine:

0 offset at 71F
-3.0 offset at 105F
+2.5 offset at 38F

That is around 1/3rd the magnitude and the opposite sign of what my Gen2 is... a big improvement. Any chance that we could tweak these to get even better stability?
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Re: The Why's and How's of Wind Offset

Postby racerfern » Mon Feb 09, 2009 9:39 pm

Hey! Congratulations on your Gen3. I hope you enjoy it as much as I do mine.

Those are some pretty extreme temperature changes. It seems that within most normal riding days with a change of 20 degrees or so, the change should be negligible.
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Re: The Why's and How's of Wind Offset

Postby Velocomp » Mon Feb 09, 2009 11:02 pm

Boy, I'd sure like other power meter manufacturers publish the effects of temperature variation on their calibrations!

Rruff, your unit is behaving extremely well. You have a VERY minor variation over a HUGE temperature range.

Remember: a 5 mph wind is little more than something that would move a candle flame. For a zero calibration, these are the kinds of small forces we're talking about here.

Enjoy!
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Re: The Why's and How's of Wind Offset

Postby rruff » Tue Feb 10, 2009 3:58 pm

Just looked at a 60mi ride and a wind offset of 2.0 Pa is ~1mph in ground wind, and ~4W in avg power. That isn't bad... but of course it would be nice if it was less... there are other errors that are more difficult to contend with. It would be really nice to just zero it while in the house and have it be good rather than needing to stabilize it at the riding temperature first.
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Re: The Why's and How's of Wind Offset

Postby lorduintah » Wed Feb 11, 2009 1:23 pm

I just checked my iBike Pro - similar temps - range of +/- 7mph for me on the offsets - zero is not very stable at 72F. +/-3 over an hour. I would prefer it be ROCK SOLID at a const. temp.

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Re: The Why's and How's of Wind Offset

Postby rruff » Wed Feb 11, 2009 2:38 pm

That sounds strange. I never noticed much variance unless the temp changed, even on the Gen2. Just check mine and it is reading 0.3 after I zeroed it yesterday.

Do you have the Gen3? Have you installed the new 3.06 firmware?
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Re: The Why's and How's of Wind Offset

Postby mds » Wed Feb 11, 2009 4:42 pm

I continue to see wind offset drift on my iSport, software version 3.03. For example after a typical 3.5 hour ride, wind offset typically reads 3 or 4 and the wind speed display reads 5 or 6mph in a wind sheltered area. Sometimes I think I can see the effects at higher speeds on the flats, with displayed power reading a bit too low or high. Unfortunately my model is not software upgradeable.
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Re: The Why's and How's of Wind Offset

Postby lorduintah » Wed Feb 11, 2009 7:35 pm

Yes - Gen III and 3.06 installed per directions. Temperature and everything else.

A 5 degree 73 down to 68 F resulted in a offset change of 3.5. This could be instability of "zero" of it is still temp sensitive - and I am letting the temp stabilize.
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Re: The Why's and How's of Wind Offset

Postby Velocomp » Tue Jun 09, 2009 8:55 am

MDS:

If your iSport has fw 303 and you're experiencing temperature drifts please send it to us for a free firmware upgrade that will fix your problem. Alternatively, if you know someone with a USB adapter they can do the firmware upgrade for you.
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Re: The Why's and How's of Wind Offset

Postby dusand » Tue Mar 23, 2010 11:40 am

Hi everybody. I've been reading these posts with interest as my wind offsets calibrations involved blocking the front port of the iBike with my hand! Can one take the iBike from the mount and shield it inside jersey unzipped partially while zeroing the wind offset? I have a Gen III IBike Pro.
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Re: The Why's and How's of Wind Offset

Postby lorduintah » Tue Mar 23, 2010 12:50 pm

Hand over the port should work - unless you are actually pressing against the case - you could build up pressure on the sensor and throw it off.

Others use a baggie or sandwich bag over the iBike mounted - this cuts off the port effectively. There is also some belief that - at least some iBikes - have leaks in the lcd window that can also contribute to wind offset by being another source of air pressure fluctuations - one reason the baggie may work better than the hand over the port. You can improve this by using tape over the edges of the lcd window to improve the seal.

The case for putting the iBike under your jacket can work - unless you get interrupts for a wireless fail.

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Re: The Why's and How's of Wind Offset

Postby dusand » Tue Mar 23, 2010 1:11 pm

Hi Tom,

thanks for your post. A sandwich bag sounds like a good idea. I did notice condensation on the back of lcd window after one particularly wet ride and wasn't sure if this was due to drop in temperature or simply moisture getting into the unit. What do you do with the auto wind feature just after the unit wakes up? I guess the iBike is already bagged before pressing the centre button...
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Re: The Why's and How's of Wind Offset

Postby lorduintah » Tue Mar 23, 2010 3:38 pm

You will lose some of the power information because you are not correcting for wind - but you get the rest of it. So assuming you don't live in a tropical rainforest, you only have to do this a few times a year.

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Re: The Why's and How's of Wind Offset

Postby dusand » Tue Mar 23, 2010 4:06 pm

Sorry Tom, I didn't quite get that...what do I need to do to correct for wind? I was planning to keep the iBike in the sandwich bag just before the ride, wake the unit up by pressing the centre button and wait for auto wind to finish calibrating while in the bag. Maybe I missed something...
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Re: The Why's and How's of Wind Offset

Postby lorduintah » Wed Mar 24, 2010 8:13 am

That is what you should do in adverse weather. You will not be getting any wind data to influence you watts, but you also won't submerge your iBike in a drowning pool.

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