Over the weekend I did my first Balloon assisted flight.  Helium balloon carried my glider up to 13,000ft, at that point i issued a remote cutdown command to release the balloon from the plane.  

 

http://twitter.com/#!/W0OTM/status/130798913224577024/photo/1

 

We ha some issues...First know that shortly after launch the XMTR was turned off, to initiate RTL mode.  So, for the majority of the flight (20min) it was in RTL mode while suspended from the balloon.

 

After finding the wreckage, I began to filter though the logs.  (the APM survived the crash)  Here is what i found.

 

The pressure sensor began sending erroneous readings as 1137m (4,000ft) or so.  Here is a sample of the logs.

 

GPS: 71299000, 1, 11, 41.1029510, -92.4485240, 0.0000, 1137.9200, 1294.2400, 2.2300, 338.1000

GPS: 71299000, 1, 11, 41.1029510, -92.4485240, 0.0000, 950.5000, 1294.2400, 2.2300, 338.1000

GPS: 71299250, 1, 11, 41.1029590, -92.4485240, 0.0000, 821.7400, 1296.0200, 1.9200, 18.2300

GPS: 71299250, 1, 11, 41.1029590, -92.4485240, 0.0000, 650.5400, 1296.0200, 1.9200, 18.2300

GPS: 71299250, 1, 11, 41.1029590, -92.4485240, 0.0000, 452.5100, 1296.0200, 1.9200, 18.2300

GPS: 71299500, 1, 11, 41.1029590, -92.4485170, 0.0000, 238.2400, 1297.8101, 2.3700, 38.0600

GPS: 71299500, 1, 11, 41.1029590, -92.4485170, 0.0000, 15.0300, 1297.8101, 2.3700, 38.0600

GPS: 71299750, 1, 11, 41.1029660, -92.4485170, 0.0000, -137.8500, 1299.6100, 2.8800, 55.0100

GPS: 71299750, 1, 11, 41.1029660, -92.4485170, 0.0000, -316.5000, 1299.6100, 2.8800, 55.0100

GPS: 71299750, 1, 11, 41.1029660, -92.4485170, 0.0000, -439.2400, 1299.6100, 2.8800, 55.0100

GPS: 71300000, 1, 11, 41.1029700, -92.4485090, 0.0000, -523.8900, 1301.4301, 3.1900, 61.0800

GPS: 71300000, 1, 11, 41.1029700, -92.4485090, 0.0000, -582.4400, 1301.4301, 3.1900, 61.0800

GPS: 71300250, 1, 11, 41.1029700, -92.4485020, 0.0000, -623.2000, 1303.2400, 3.6500, 58.7000

 

Also, the IMU axis sensors stopped sending values at 7000ft.  Also note the HUGE difference in the MIXALT and the GPSALT.

 

GPS: 71460500, 1, 10, 41.1069680, -92.4342270, 0.0000, 140.1700, 2359.3101, 15.8400, 99.1400

ATT: -17273, -7770, 1014

GPS: 71460500, 1, 10, 41.1069680, -92.4342270, 0.0000, 140.7600, 2359.3101, 15.8400, 99.1400

ATT: -16141, -8484, 35974

GPS: 71460750, 1, 10, 41.1069640, -92.4341740, 0.0000, 141.4400, 2360.8999, 15.1800, 100.5000

ATT: -11298, -8952, 31063

GPS: 71460750, 1, 10, 41.1069640, -92.4341740, 0.0000, 141.8600, 2360.8999, 15.1800, 100.5000

ATT: 0, 0, 0

GPS: 71460750, 1, 10, 41.1069640, -92.4341740, 0.0000, 142.5400, 2360.8999, 15.1800, 100.5000

ATT: 0, 0, 0

GPS: 71461000, 1, 11, 41.1069560, -92.4341280, 0.0000, 143.3000, 2362.7300, 14.6200, 101.7700

ATT: 0, 0, 0

 

What would have caused these 2 failures? 

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Hi Marshall,

 

I'm with Ric & Andrew here, I dont think it's to do with the temp, more the lack of pressure at that hight, I would say to do some testing on the unit in very low pressure environments. Is the data sheet information showing a min and max pressure for operation?

 

Martin.

Hello to 

Ottumwa, IA

 

Barometer problems could be due to temperature extremes and wind.  It's recommended to cover it with a piece of foam.

Temps weren't even below zero at that altitude.

No data on pressure tolerances in the data sheet...

Hello Marshall,

Have you moved this forward with any data sheet information or real world controlled testing? I'm not a betting man, however I would place a few $'s on this being a lack of pressure problem.

 

I would like to know how you are coming along with this, and I'm sure a few other people reading this thread would too :)

 

Regards

 

Martin.

I will be sending the APM up to 100K ft in a traditional HAB (High Altitude Balloon) payload.  Will have the APM powered up so I can monitor sensor performance throughout the ascent.   

 

According the data sheets, temp should NOT be an issue...

 

more to come later. 

Sort of on the subject of the pressure sensor (which drives the non GPS altitude), the data sheet says that the hole in the top should not be exposed to light (during reading) as it can "influence the accuracy of the measurement". I thought that was interesting for those that mount their APM board facing the sky.

http://www.sparkfun.com/datasheets/Components/General/BST-BMP085-DS...

page 25.

 

cosmic rays ;) just kidding

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