highaltitude.log.20070402

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[11:27] <jcoxon> Laurenceb_, sorry to hear that you lost the glider
[11:29] <Laurenceb_> found it now
[11:29] <Laurenceb_> someone rang a couple of minutes ago
[11:31] <jcoxon> oh wow
[11:31] <jcoxon> excellent
[11:31] <jcoxon> where was it?
[11:31] <Laurenceb_> but it was very close to the cutdown position, looks like it went into some sort of dive
[11:31] <Laurenceb_> st-Neots
[11:33] <Laurenceb_> it was more nose heavy than in the test flights, we swapped ou the lithium battery for a duracell one, 10 grams heavier, that made the c of g approx 1cm further forward
[11:33] <Laurenceb_> ou=out
[11:34] <jcoxon> right
[11:34] <jcoxon> well at least you've got it back
[11:34] <Laurenceb_> jcoxon, are you in that area ?
[11:34] <jcoxon> not right now
[11:34] <Laurenceb_> know anyone who is?
[11:35] <jcoxon> nope, sorry
[11:37] <Laurenceb_> hmm I'll have to see, rocketboy can always oick it up, but its a way to go
[11:37] <Laurenceb_> oick=pick
[11:42] <jcoxon> bbl
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[15:07] <mc-> hi Laurenceb,
[15:07] <mc-> what did you use for a cutdown yesterday?
[15:13] <Laurenceb_> hi there
[15:14] <Laurenceb_> 10 ohm resistor
[15:14] <Laurenceb_> I'm not 100% sure where it landed, the guy described it over the phone, I think I've found it on google maps
[15:15] <Laurenceb_> the glider was probably tooo nose heavy, we swapped the battery and it was 10 grams heavier->1cm further forward c of g
[15:15] <mc-> how did you activate the cutdown? By GPS?
[15:16] <Laurenceb_> cutdown went if altitude>2km or time >15minutes
[15:16] <Laurenceb_> looks like it hit the time limit at 1886 meters
[15:17] <mc-> just wondering if the cutdown caused it to start in a dive, and it never recovered?
[15:17] <Laurenceb_> on your payload you had carefully left a gap in the tape for the antenna
[15:18] <Laurenceb_> dont think thats needed as duck tape is transparent to gps
[15:18] <Laurenceb_> hmmm, it should have recovered from the initial drop- tail first
[15:18] <mc-> rocketboy put the duct tape around my payload..
[15:18] <mc-> did you do a range test of my payload?
[15:19] <Laurenceb_> yes, I've covered payloads with duck tape and the gps is uneffected
[15:19] <Laurenceb_> range test-what do you mean?
[15:19] <mc-> to check my payload was transmitting at long distance?
[15:20] <mc-> you didn't launch my payload did you?
[15:20] <Laurenceb_> we tested the payload with the radio at the other end of the ears parking area for approx 30 minutes, up to and past cutdown
[15:20] <Laurenceb_> no did'nt launch yours
[15:20] <mc-> ok
[15:21] <Laurenceb_> looking at the data and what appears to be the landing spot, it seems to have descended at 15m/s
[15:21] <Laurenceb_> which is very fast, it glides at approx 10m/s
[15:22] <mc-> 15m/s sounds fast...I've got a lidl kite, that is triangular, could that be converted to a glider?
[15:22] <Laurenceb_> can only explain this by a spiral dive
[15:22] <Laurenceb_> yes you could use it as a frame for a rogallo, but I'd go for something rigid
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[15:23] <mc-> is the glider in 1 piece?
[15:23] <mc-> Can the guy send it to you? rather than drive to his house?
[15:23] <Laurenceb_> the wings were cracked in half
[15:23] <Laurenceb_> and one half is missing
[15:24] <mc-> my kite has spars on the leading edge, plus 2 spars across. So it might be quite rigid? or not?
[15:24] <Laurenceb_> that sounds nice and rigid, but if the payload hangs underneath things can go wrong
[15:25] <Laurenceb_> eg if it goes into a dive it wont recover
[15:25] <mc-> unless the payload can be held secure
[15:26] <mc-> 3 or 4 wires might be enough?
[15:26] <Laurenceb_> using the wind integration technique on the glider it end up very close to the verge where it was found
[15:26] <Laurenceb_> yes I've tried a rogallo with 3 and 4 wires
[15:26] <mc-> lucky it landed on a verge
[15:26] <Laurenceb_> yes
[15:27] <Laurenceb_> http://video.google.co.uk/videoplay?docid=-7947087481519535776&q=rogallo
[15:28] <Laurenceb_> at 15m/s there will be approx 700 grams of lift from wings
[15:28] <mc-> I saw that, impressive
[15:28] <Laurenceb_> > approx 2 g acceleration
[15:28] <mc-> it can't be more than 1g can it?
[15:29] <Laurenceb_> yes that test had only wires to suspend the payload/bluetack
[15:29] <Laurenceb_> in a spiral dive you can get centripetal acceleration
[15:29] <mc-> i see
[15:30] <Laurenceb_> there's a formula for the acceleration
[15:30] <Laurenceb_> got to go sorry, I'll be back this eventing
[15:30] <Laurenceb_> -evening
[15:30] <mc-> was it your cutdown design? Did you have a single GPS on the glider?
[15:30] <mc-> cya
[15:31] <Laurenceb_> yes my design, and single sirf2
[15:31] <mc-> sirf2 are the best..
[15:31] <Laurenceb_> yes very good, lock on the ground floor of a 3 story building with active ant
[15:32] <Laurenceb_> well, once it had got a lock outside that is
[15:33] <Laurenceb_> gliders with gps only are vulnerable to spiral dives due to the low sampling rate and lag time
[15:34] <Laurenceb_> thermopiles will stop spiral dives and normal dives, so you dont have to be so careful with the trim
[15:34] <Laurenceb_> we messed up the trim with a new battery
[15:34] <Laurenceb_> anyway cya
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[22:00] <Laurenceb_> hi all
[22:01] <Laurenceb_> rocketboy, did you get my email?
[22:01] Nick change: Laurenceb_ -> Laurenceb
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[22:10] <rocketboy> hi laurence - yes OK
[22:11] <Laurenceb> I'm 90% sure it spiral dived
[22:12] <Laurenceb> just cooking some food bbs
[22:12] <rocketboy> ok
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[22:37] <rocketboy> cu guys
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[22:41] <Laurenceb> _defy, do you know a lot about gliders?
[22:51] <_defy> define 'a lot' :P
[22:55] <Laurenceb> well, I was wondering if you could offer some advice
[22:56] <Laurenceb> on how to avoid spiral dives
[22:56] <Laurenceb> it looks like the glider went into a spiral dive
[22:56] <_defy> are you trying to make a glider that will glider its self straight with no input?
[22:56] <_defy> glide*
[22:57] <Laurenceb> well, we were :)
[22:57] <_defy> what did you use ?
[22:57] <Laurenceb> its on the wiki
[22:58] <Laurenceb> cheap ebay plane, it had a polyhedral wing
[22:58] <Laurenceb> think you call that polyhedral?
[22:59] <_defy> got a url with a photo?
[22:59] <_defy> the best way to really avoid that I guess it to make sure you get a nice stable glider design..something thats probably already proven.
[23:00] <Laurenceb> http://wiki.ukhas.org.uk/projects:mihab:glider
[23:00] <Laurenceb> hmm yes good point
[23:01] <Laurenceb> ebay artf glider time perhaps
[23:01] <Laurenceb> but thermopiles are certainly the way to go
[23:01] <_defy> are those props the only way for you to change direction?
[23:02] <_defy> I'd say go for something a little more sterdy, and also larger
[23:02] <Laurenceb> rogallos and parawings are stabilized by the c of g
[23:02] <_defy> and unless you're going to add something like thermopiles to keep it level, you probably want to avoid windy days
[23:02] <Laurenceb> well the props were removed we launched it yesterday
[23:03] <Laurenceb> it was rather windy
[23:03] <_defy> what kind of control does it have? just aelerons?
[23:03] <Laurenceb> rudder
[23:04] <_defy> have you flown this plane with normal RC gear?
[23:04] <_defy> so see how it flys in normal conditions?
[23:04] <Laurenceb> only before it had the props removed
[23:04] <_defy> how did it fly?
[23:05] <Laurenceb> it had lots of glide flights off a hill
[23:05] <Laurenceb> worked very well
[23:05] <_defy> and it the weight now, pretty much the same as it was when you were flying it RC?
[23:05] <Laurenceb> you can see the flight records
[23:05] <Laurenceb> well it ended up a bit more nose heavy
[23:06] <Laurenceb> we swapped the battery, that might be the problem at least partly
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[23:09] <Laurenceb> hello all again lol
[23:09] <_defy> do you have a way of taking over manual control? I find that the be the easiest way...to get it up in the air manually via an RC transmitter, then once its at a decent altitude, switch the auto pilot on
[23:09] <Laurenceb> well its smashed in a car park now, thats where it came down
[23:09] <Laurenceb> but on the next glider that will be the plan
[23:09] <Laurenceb> is your test plane motorised?
[23:10] <_defy> nah, but I'm thinking about throwing a 400 canned motor onto it to get some longer tracks
[23:10] <_defy> plus a motor assures that I'm always going forward...you and sometimes glider backwards, or completely still..which throws off the gps's heading measurement..
[23:11] <Laurenceb> wind compensation solves that
[23:11] <_defy> so I was thinking either a motor to make sure its always going forward or I'll add a little compass sensor
[23:11] <Laurenceb> if you record wind on the way up, it solves that pretty much
[23:11] <_defy> well wind direction sensors would be a little bulky on a model glider
[23:12] <_defy> and its gusts that i'd really worry about, which you cant predict
[23:12] <Laurenceb> just record the wind on the way up
[23:12] <Laurenceb> thats how my glider worked
[23:12] <_defy> thats not really a proper fix for the problem, I'd rather fix the problem perminantly
[23:13] <Laurenceb> compasses only work well when level
[23:13] <_defy> nah there are plenty of dual axis compasses out there
[23:13] <_defy> cheap too
[23:14] <Laurenceb> dual axis?
[23:14] <_defy> plus I'll always know my bank angle
[23:14] <_defy> so I'll be able to compensate
[23:14] <_defy> but I'm thinking an easier solution is to just throw a motor onto it
[23:14] <_defy> for now anyway
[23:15] <Laurenceb> so you get bank angle +heading from the compass?
[23:15] <_defy> http://www.parallax.com/detail.asp?product_id=29123
[23:16] <_defy> nah just heading
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[23:16] <Laurenceb> if its banking or pitching the heading can go way off
[23:17] <Laurenceb> brb
[23:17] <_defy> other people have used these and have had no issues so...
[23:17] <_defy> plug the compass is only really ever needed if the gps's heading gets screwy
[23:17] <_defy> so there are 2 values to work off of
[23:18] <_defy> and if banking affects the compasses reading, it probably does it in a calculatable fassion, so as long as i know my angle i should be able to compensate...obviously if it starts flying upsidedown my readings will be all other the place, but if its doing that then its pretty much all over anyway
[23:31] <Laurenceb> if you have the 2 adc readings, you can find the magnetic field vector
[23:31] <Laurenceb> but you dont know your angle around the mag field vector
[23:32] <_defy> I'll know my angle by the thermopiles
[23:32] <Laurenceb> but, with thermopiles your basically finding the vertical vector
[23:32] <Laurenceb> and 2 non normal vectors define you orientation
[23:32] <_defy> *shrug*, it obviously works or people wouldn't be using it so..
[23:32] <Laurenceb> well... I'd check the maths
[23:33] <_defy> I really try not to get cought up too much in the math, trial and error is the way to go. if i try to make it too smart it'll all end badly, thats for sure.
[23:33] <Laurenceb> I think a glider with 4 thermopiles and gps will work well enough
[23:34] <Laurenceb> but maths and simulation works well IMHO :)
[23:35] <_defy> mostly, but there would be some occasions where head wind might be too strong
[23:36] <_defy> what sims do you use? your own?
[23:37] <Laurenceb> if the glider goes faster than the difference between average and peak wind speed, wind compensation works
[23:37] <Laurenceb> yes, very basic code I wrote, its on the wiki
[23:37] <_defy> that might work where you fly
[23:37] <Laurenceb> simulates yaw behaviour
[23:38] <_defy> but i fly on new zealands western coast, there is no 'average'...winds can go from 10k to 35k in seconds
[23:38] <_defy> and then disapear completely
[23:38] <_defy> +p
[23:39] <Laurenceb> I see
[23:39] <Laurenceb> I need a good flight computer
[23:39] <_defy> plus i dont want to limit the design to only being able to fly in certain conditions
[23:39] <Laurenceb> this avr compiler is crud
[23:40] <_defy> I'd love to be able to launch the thing in the middle of a storm, although that might be a bit much
[23:40] <Laurenceb> what do you use to compile your avr code?
[23:41] <_defy> avr-gcc
[23:41] <Laurenceb> I've necer understood all the makefiles ect
[23:41] <Laurenceb> *never
[23:41] <_defy> they're just like any other makefiles really
[23:41] <_defy> dave from gumstix has some good templates to work from as well
[23:42] <Laurenceb> ....well, whats a makefile
[23:42] <_defy> it holds all your variables etc for gcc, tells gcc what to do
[23:42] <Laurenceb> instructions to the compiler?
[23:43] <_defy> yeah, Dave's Simple-Servo-2 and RCInput projects are agreat start
[23:43] <_defy> most of my avr code is based off either of those
[23:43] <Laurenceb> oh servos yum
[23:43] <Laurenceb> that was what mucked up my code
[23:43] <Laurenceb> I'll take a look
[23:44] <_defy> Simple-Servo2 basically drives servos, and RCInput takes a clock ouput from an RC receiver and reads the pwm...8 channels over 1 wire.
[23:44] <Laurenceb> groovy
[23:45] <_defy> Dave said I'd have issues trying to combine the two pieces of software to read pwm off the interupt and output owm for the servers...I know its possible, i just dont know if it is with his code.
[23:45] <_defy> So instead of combining all the code, I got lazy and spread it over 2 avr chips (2 robostix)
[23:45] <Laurenceb> sorry dont get that, is this a 1 wire rc reciever interface?
[23:45] <_defy> and they just chat via serial
[23:45] <Laurenceb> I see
[23:45] <_defy> yea, I had to find the clock output on one of the chips inside of the rc receiver, and connect that to 1 of the interupts on the avr
[23:46] <Laurenceb> I dont have that much money lol
[23:46] <_defy> and through that, it can pickup all 8 channels
[23:46] <Laurenceb> just a poor student
[23:46] <_defy> yea I was lucky in that the last time i ordered a robostix from gumstix, they sent me an extra one by mistake
[23:46] <Laurenceb> lol :)
[23:46] <Laurenceb> I'd better be off bed
[23:46] <_defy> its a great little avr platform though, especially for only $35 usd or whatever they are
[23:47] <_defy> hehe, sweet :)
[23:47] <Laurenceb> yes not that pricy
[23:47] <Laurenceb> cya
[23:47] <_defy> cya
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