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Homebrew AHRS?
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Tim(at)MyRV10.com
Guest

Posted: Thu Nov 30, 2006 5:39 pm Post subject: Homebrew AHRS?

So you say you haven't had any failures on fixed units, but are

you not counting the one that was reported to you on the flight

home from OSH 2006?  The one that failed was a "fixed" unit.

After replacing it with another brand, there are no longer

any problems with the new one mounted in that location.



Tim Olson

do not archive

Mike(at)Crossbow wrote:

 	  Quote: 	
		   

 <msmith(at)xbow.com>

 

 First, I would like to apologize for hijacking the thread.  That

 wasn't my intention.  In reference to the original topic, what

 Malcolm and others have said is completely correct.  We are

 approached by customers occasionally that complain that they could

 build the unit for far less because the parts are relatively

 inexpensive.  Yes, the parts aren't too expensive but the software is

 very complicated and you will need to rely upon some sort of aiding

 (GPS, Kalman filtering, Airspeed, etc..) to improve performance of an

 AHRS.  MEMS gyro's without this aiding are really not accurate enough

 for aviation in my opinion.  By the time you are done creating

 software and testing a fully functional unit you would have saved a

 significant amount of money by purchasing a completed solution.  Now,

 if you want to create an AHRS for your personal enjoyment...then yes

 it's probably worthwhile.

 

 In regards to OP Tech, we have not seen any failures with the

 NAV420's that we shipped to OP Tech, but a very large percentage of

 the ones that were shipped to OP Tech were already updated with the

 latest hardware/firmware so we wouldn't expect to see much.  The

 early units that were shipped OP Tech have also come back to be

 updated and we haven't been informed of any problems with those

 units.

 

 Crossbow is aware of the delay and inconvenience that we have put our

 NAV425EX customers through and on behalf of Crossbow I would like to

 personally apologize for the amount of time that it took to get this

 fix in place.  We have been updating these units since May of this

 year and are confident that the fixes we have in place remedy all

 noted issues that are stated in the service bulletin.

 

 -------- Michael Smith Application Engineer Inertial Systems Crossbow

 Technology msmith(at)xbow.com

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=77859#77859

 

 

 

 

 

 

 

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aadamson(at)highrf.com
Guest

Posted: Thu Nov 30, 2006 6:05 pm Post subject: Homebrew AHRS?

Oh, shoot, I might as well chime in as well.  What I find as troubling with

Mikes comments is that while it might be true that they haven't had any

*recent* problems (highly suspect), the larger issue is that the people that

I know that *were* working thru fixes and updates finally gave up and moved

to something else.  All the fixes couldn't resolve the problems.  So not

sure if that counts as fixed or failed in Xbows eyes...



Either way, I know of at least 2 and probably more that never were resolved

(and both failed either too or from OSH in one way or another).  Also, in

talking with the guys at OP while I was at OSH, they did say that they had

had units that had showed similar troubles, but they don't have very many

units flying, so I suspect that the percentages are pretty low based upon

that.



I also know of at least one high performance airplane (an EPIC LT), that

could make the 500 fail.  Perhaps this issues has since been resolved as it

was a year ago that I heard of it.  All it took was a 2500 fpm constant rate

climb from sea level to 20K feet and then a negative G pushover to level and

the 500 would show a bank for a few minutes until it was able to settle back

to normal.



I'm not really trying to sling mud here, but there is evidence that the

"everything is peachy" comments are just a little misleading.



My .02,

Alan - back to regular schedule content now.....



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mthomson(at)showmeproduct
Guest

Posted: Thu Nov 30, 2006 7:50 pm Post subject: Homebrew AHRS?

Seems to me that if Crossbow is "hiding" known problems or issues with their

products, specifically the 425 units, they are creating a huge liability for

themselves, especially if they are making statements to the contrary. This

is the kind of thing lawyers have a hay day with, especially if someone

should end up in a hole in the ground flying with an xbow unit. (Doesn't

matter if it was caused by xbow failure, lawyers still will go after them).



So, Mike (at Crossbow), I'm getting concerned about the recent emails

claiming that there has indeed been several issues, with several customers,

with the "fixed" versions of the 425.  Can you state you have not seen any

reports of this prior to the recent emails posted here.  I really want to

get my units upgraded but don't want to waste your or my time if the fixes

are ready.  I sent you a private email about how to get my two units updated

with minimal down time.  I will be more than happy to report to this mail

list with the results of the update - I believe if you guys say it is fixed

and are prepared to update my two units then it must be fixed.  



Perhaps posting the results will help to put this issue to bed.



Malcolm.



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Mike@Crossbow

Joined: 28 Nov 2006
Posts: 8

Posted: Mon Dec 04, 2006 8:43 am Post subject: Re: Homebrew AHRS?

Wow!  I'm out of the office for a couple of days and there are all kinds of messages.  Let's see if I can square these away in one swoop.



Bob- Unfortunately, that was not me that you met.  Most likely that was our CEO (also a Mike) who still runs Crossbow.



Tim - The failure that was reported by a customer leaving Oshkosh was the result of a poor installation.  The customer (a good friend of yours) had a low grade GPS antenna mounted in a poor location that was causing multi-pathing of the GPS signal.  This is not a problem with the NAV425EX but with the installation.  We have seen a few installation problems with these units and have been happy to help our customers walk their way through the process of correcting the matter.  In addition, I think it is important to note that you have a horse in this race as they say.  



Adam- We have had a couple of customers that refused to install their NAV425EX properly and as a result we were unable to rectify their problems to their satisfaction.  I deeply regret that we weren't able to assist them further, but I do feel that we made every effort possible and at the end of the day they decided to go a different direction.  As to the assertion that there are other NAV425EX failures, if there are other customers who are not happy we would like to hear from you.  We can only help the customers that contact us directly.  If I can rant for a bit, I have seen a few customers that would prefer to bash us on a forum than contact us directly for support.  We can only help if we are aware of the problem.



The Epic LT was utilizing a different unit, the FAA Certified AHRS500.  This is the first certified MEMS AHRS and we have sold countless units to various EFIS manufacturers.  The AHRS500 is very cost effective and a variant has recently been used in the Eclipse 500 jet which should give you an idea of what it is capable of.  The problem with the Epic installation was constrained to the autopilot portion.  This was not a "failure" but a poor autopilot response.  MEMS gyro's are inherently noisy and as a result they do need significantly more tuning in order to get smooth responses (no up and down motion).  This tuning was performed in the Eclipse jet for example, but in the case of the Epic it was more cost effective to replace the AHRS with a competitors Fiber Optic Gyro which is inherently quieter but significantly more expensive than it was to spend time on the tuning portion of the problem.  



Malcolm-  Crossbow is not "hiding" any problems and we continue to sell the NAV420 and its variants to several customers.  We have sold a lot of these units (I would love to post a number, but I'm temporarily forbidden for obvious reasons) and continue to sell them to military contractors, EFIS manufacturers and research institutions.  Crossbow has been extremely forthecoming with the problems that we have had with the NAV425EX, to the extent that we have published the exact problems and causes on our website.  I personally can't think of another major company that has been so open about the issues at hand.  http://www.xbow.com/Support/service_letters.htm



Malcom- In regards to your email.  I received your email on Thursday and I apologize for not getting back to you in a timely manner.  I got the flu last week and was out of the office on thurs and friday.  You'll have a response from me this morning.



OK, hopefully that covers everything.  If not, I'm here to answer as many questions as you folks can throw at me.

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_________________
Michael Smith
Application Engineer Inertial Systems
Crossbow Technology
msmith@xbow.com

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