Replies to This Discussion

DistributorPermalink Reply by Martint BuildYourOwnDrone.co.uk on January 7, 2012 at 8:49am

Hi Cuddy,

 

Now that's a list :)

 

The Ardupilot will work with the flying wings.

 

The Ardupilot will work with just about every airframe, there is tuning needed to match with each airframe, it will not work miracales but if you could fly it the AP should be able too.

 

I would say stick with the stock GPS unless you have the skills needed to put the other in play, it works very well and is not costly.

 

I would say to stay with the setup which works, RTL is a feature and is a working set up, dependeing on the time frames there are two ArduPilot mega's out at the moment, one easy to get and the new one (2.5) which will take you a good 4-8 weeks.

 

Regards

 

Martin

www.buildyourowndrone.co.uk

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Permalink Reply by Cuddy on January 7, 2012 at 10:43am

Thanks for that Martin! Very helpful :)

A quick question about the stock GPS - do you know how it obeys the CoCom limits? The problem we find with the majority of gps's is that above 18km they refuse to work which isn't very good when we go almost twice as high!

Cheers

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Permalink Reply by tuckerobie on January 7, 2012 at 3:00pm

From what I have seen the stock GPS will not function at that alt... There are a few of us working on the same basic project and are using the same Lassen GPS.

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Permalink Reply by Cuddy on January 8, 2012 at 7:26am

Thanks all, 

Will the Lassen work almost plug and play with ArduPilot? Is it supported in the code or does it need modifying manually?

Cheers

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Permalink Reply by Ken on January 7, 2012 at 3:05pm

The units sold in the DIY store will not work at the altitudes you are looking at. They chose the "or" option (too high or too fast = lockout).

Stick with the Lassen. Few people use NMEA parser in ArduPilot so you may encounter "undocumented features."

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Permalink Reply by Art Whaley on January 13, 2012 at 2:18pm

Ken has the answer there.  We're using the Lassen Trimble LP, which does work at that altitude.  You have to go into the Lassen configuration utility and change it from the proprietary binary Lassen protocol to output NMEA sentences and make sure it's outputting the sentences you need.  Then you'd configure ardupilot to use a standard NMEA gps and you're all set.   

Ken, can you point me to more info about 'undocumented features' with the NMEA parser?  I haven't plugged the gps into the ardupilot yet... and I'm interested to know what troubles to expect?  

Also, I'd read somewhere back before I knew enough to ask the question...  will Ardupilot work at that altitude?   Will all the variables and functions that reference the gps altitude work with numbers that big (100,000 feetish) and what will APM 2.0 do when the barometric pressure sensor is outside it's range of function?  Will the plane just assume it's holding altitude and do nothing, will it use the gps altitude number as a backup, or will it assume there's an error and just unbolt the wing or something.  ;)

I'm glad there are more of us working on high altitude projects!  Others to share info with is great!  We may need a wiki... and if the code requires modification maybe we need to all work together and get a fork going for an ArduHAB program!

Art

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Permalink Reply by Cuddy on January 14, 2012 at 5:40am

Hi Art & Monroe -

I agree, there seems to be enough of us to set up our wiki and work together on solving all these problems! Personally - I think the APM2 will provide almost a solution however the code will need tweaking in numerous places.

With regards to the GPS - I have flown a lassen before on my HAB payload and worked brilliantly, however, what I've read recently on these forums has swayed me against using the lassen for the gps for APM2.

So, I'm currently thinking about 2 options:

1) Use a lassen for the main telemetry system (running off a separate ATMega328) that will be on a custom breadboard I make. Then once below 18km, the stock gps that comes with APM2 should be able to kick in and navigate - from looking at previous data, there's no hope of getting stable flight above 18km anyway due to lack of "air".

2) Use a ublox 6 - and connect that up to the APM2 (and my custom ATMega328 for dealing with telemetry and other stuff).

Having thought about this - I am more swayed to go with option 1 and use a ublox instead of lassen simple because the lassen's antenna is a ceramic one (has to point up) and therefore as the glider is 'tumbling' back to earth it's likely to lose lock. The uBlox can use a helical antenna therefore it should be fine with the 'tumbling'.

I certainly think we should progress with some sort of community wiki.. perhaps getting a section on the UKHAS wiki?

Cheers

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Permalink Reply by Daniel Nugent on January 16, 2012 at 10:17am

I had the same idea 6 months ago and now im trying to figure out the bugs. I was going to use ardupilot but i figured out one problem. you would know that air density at those altitudes is extremely low. making surface control hard. it can be overcome but you would need to tweek the code. i was going to do that but then decided to make my own code. Because im not sure how ardupilot works with no motor and if it alllows you to control speed with gravity/dives. problems i encountered when i started to design. check out my forum on a similar glider!

http://www.rcuniverse.com/forum/m_10910937/anchors_10911552/mpage_1...

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Permalink Reply by Cuddy on January 16, 2012 at 11:52am

Yes, the air density is extremely low at the altitudes and therefore I plan to just let it free fall until it can maintain stable flight - looking at past data this appears to be around ~13/14km in altitude (this of course varies with airframe). 

I've done the reverse - started with trying to code my own autopilot system just based on rudder control however building a neutrally stable glider is very hard; so I've opted for arudpilot. I was worried about the control with no motor however it has been done using an APM - see the balloomerang project as part of the iHAB project. (Seemed to work very well in test flights).

But - I really want to hear from people on these forums who know exactly how the APM/APM2 works and can chime in with appropriate suggestions etc! There must be people out there who are reading this! :P

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Permalink Reply by Larry Grater on January 18, 2012 at 7:32am

I've gone in a slightly different direction with GPS and am integrating Venus GPS. This one supports NMEA, altitude and update rate + data logging. I also bought the 3.3v logic converter (all spark fun). I'll post progress.

I did find a handy plugin for xplane that allows standard hil setup for this mission. Initial conditions can be set to check non-simulated parts of the code. i'm away from my pc now and cant post the link. The airspeed calc falls apart but I dont yet know if this is an issue w planner or apm code. Help needed. Xplane data dump looks good, planner airspeed conversion is working. Need to debug planner or start with prints at the entry point into apm?

I think we have this thread + one that's more focused on the CONOPS and airframe! Great stuff.

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Permalink Reply by Larry Grater on January 18, 2012 at 8:01am

I had another comment after rereading one of Cuddy's posts. Some GPS recievers are pretty tolerant to angle and rate excursions, even with antenna patterns like from the ceramic patch. I've seen good performance with Mediatek during aerobatics. I think this is fairly easy to test. I'm tempted to spin down, get data, spin down invedted, get data. Airframe is still down for mods for high altitude but i'm tempted to test on my 3-d a/f since the venus gps has a logger.

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Permalink Reply by Cuddy on January 18, 2012 at 11:19am

Sounds a good idea - lots of good work going on from all different angles!

I've spoke with people about the idea of a wiki and we should be able to set up a subsection on the UKHAS wiki www.ukhas.org.uk where we can detail bits and pieces to help each other out. 

It's a big task but I certainly think we can do it!

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