This is my 1st post here so please bear with me if I'm posting in the wrong board etc!
I'm heavily involved in High Altitude Ballooning which is sending payloads up into near space using a weather balloon with various tech equipment on. A project that I'm exploring currently is the possibility of an autonomous glider that will fly the payload back to a predesignated location once the balloon has burst - for easy retrieval.
I am aware of similar projects and have looked at the posts on this forum and others. I'm currently working with a great guy over at flyingwings.co.uk who is custom building me a flying wing that will be able to house all the payload equipment etc. This is in addition to a glider that I'm building myself out of styrofoam.
For stabilisation/autopilot I'm looking to use ArduPilot. I have a couple of questions though:
Will the pilot work with a flying wing?
Will the pilot work with any old plane (that I'm making!) i.e. not inherently stable?
Currently I have a lassen iQ gps module that I use, will this integrate easily with ArduPilot?
Finally (phew) - if I was to go with a separate stabilisation unit so the glider/flying wing fly stable, would that eliminate the need for the IMU 'oil pan' expansion board? As all I would require is a 'return to home' feature.
Sorry about all the questions, I'm very new to aeronautics stuff.
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.
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!
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.
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."
Will the Lassen work almost plug and play with ArduPilot? Is it supported in the code or does it need modifying manually?
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!
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?
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!
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
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!