highaltitude.log.20080410

[00:00] <natrium42> already?
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[08:17] <mc-> bonjour Ed
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[19:51] <Laurenceb> jcoxon: got the radio working?
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[20:07] <fnoble> hello
[20:10] <Laurenceb> hi fnoble
[20:14] <jcoxon> Laurenceb, i haven't really done anymore
[20:14] <jcoxon> had a crazy day
[20:14] <fnoble> jcoxon: did you ever test the gps?
[20:15] <Laurenceb> jcoxon: can you post me that gps and nds card btw?
[20:15] <jcoxon> fnoble, again i haven't done much more on the gps
[20:15] <jcoxon> it wasn't working immediately
[20:15] <jcoxon> Laurenceb, i have a horrible feeling that i have sent it
[20:15] <fnoble> ok cool
[20:15] <Laurenceb> :-(
[20:16] <Laurenceb> where to?
[20:16] <Laurenceb> my uni address or home one?
[20:17] <jcoxon> hmmmm
[20:17] <jcoxon> let me have a search
[20:17] <Laurenceb> k
[20:18] <jcoxon> haha
[20:18] <jcoxon> found it
[20:18] <jcoxon> obviously i didn't put it in the post
[20:18] <jcoxon> to oxford?, i've got the address
[20:19] <Laurenceb> cool :P
[20:19] <Laurenceb> well, unless the post is insanely slow
[20:19] <Laurenceb> you could post it here, I'll email you if you havent got my home address
[20:20] <jcoxon> okay
[20:20] <jcoxon> i'll get it in the post tomorrow
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[20:28] <jcoxon> fnoble, i've managed to gather a long list of things to do
[20:28] <jcoxon> and have exams in 2 weeks so might take me some time to clear the backlog
[20:29] <Laurenceb> good luck
[20:29] <jcoxon> might be position for a launch in may
[20:29] <jcoxon> Laurenceb, thanks, they are practical exams which make it slightly harder to revise for
[20:29] <fnoble> well dont worry, there is no time limit for atlas
[20:30] <fnoble> was just curious, not pestering, honset :)
[20:30] <fnoble> *honest
[20:30] <jcoxon> :-)
[20:44] <Laurenceb> jcoxon: on your parafoil, did you just use brake lines?
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[20:44] <Laurenceb> I'm thinking of making one at some point
[20:44] <Hiena> Good evening!
[20:44] <Laurenceb> hello
[20:46] <jcoxon> Laurenceb, yes
[20:46] <jcoxon> thats how we steer
[20:46] <Laurenceb> how well does it work?
[20:47] <Laurenceb> have you tried anything else?
[20:47] <jcoxon> it works well
[20:47] <jcoxon> thats how pretty much everyone does it i think
[20:47] <jcoxon> check out the X38
[20:48] <Laurenceb> I've been playing around with a few C of G shift designs
[20:48] <Laurenceb> but its a bit hard as you need to keep to payload stable and stop the chute tangling during ascent
[20:49] <Laurenceb> you use a "beam" above the payload right?
[20:49] <jcoxon> yeah that as well
[20:50] <Laurenceb> well that will be brilliant at stopping tangles
[20:50] <Laurenceb> maybe I could have a line off either end of that, going down to the payload, then use C of G shift with a winch servo
[20:51] <jcoxon> should work
[20:51] <edmoore> why parafoils now?
[20:51] <Laurenceb> the problem is that the paload can swing fore and aft, but that wont couple to the rate gyro very much... so it might work ok
[20:52] <Laurenceb> dunno, easier to transport, possibly better performance
[20:52] <edmoore> it is fairly couples, you will have problems with that method
[20:52] <edmoore> but you can overcome them with some cunningness
[20:52] <edmoore> hmm.... seem to remember saying that :p
[20:52] <Laurenceb> hmm the axes are orthogonal
[20:52] <Laurenceb> but its not really what you want
[20:53] <edmoore> watching house, ping if there's something interesting to say
[20:53] <Laurenceb> you've got enough problems without the thing swinging all over the place :P
[20:53] <edmoore> ergo, i do not expect to be pinged
[20:53] <Laurenceb> lol
[20:53] <natrium42> edmoore, edmoore edmoore edmoore
[20:53] <edmoore> yes
[20:53] <natrium42> just wanted to say hi
[20:53] <natrium42> :)
[20:53] <Laurenceb> hahah
[20:53] <edmoore> :p
[21:02] <edmoore> ok, episode over
[21:02] <edmoore> so to ignore some of the rolling affecting heading readings, you can get the stabilisation loops to hold a bank angle rather than a heading rate
[21:03] <edmoore> they are couples by the obvious state sums, but you don't have to deal with some much rubbishy feedback
[21:04] <edmoore> model the foil and you will derive, according to my sums, that the 2nd derivative of bank angle is:
[21:06] <edmoore> -2*dampingratio*naturalfreq*1stderivativeofangle - (naturalfreq^2)*(bankangle-servocharacteristic(as_a_function_of_servo_position))
[21:06] <edmoore> if you find natural freq and damping ratio, you have yourself your pid gains
[21:07] <edmoore> and a stable flight
[21:07] <edmoore> try deriving that stability from heading rate and you get all sorts of extra gremlins
[21:09] <edmoore> For ease I'll be deriving damping and nat-freq from flight data
[21:09] <edmoore> ok, new episode of house... bbl
[21:10] <Laurenceb> erm yes
[21:11] <Laurenceb> thats sort of the technique I was using with the rogallo test flights
[21:12] <Laurenceb> what do you mean by natural frequency?
[21:14] <jcoxon> Laurenceb, edmoore is in house mode
[21:14] <Laurenceb> lol
[21:14] <jcoxon> he'll be back during the advert break
[21:15] <Laurenceb> I dont even know what that is
[21:15] <Laurenceb> something about houses?
[21:16] <jcoxon> House is about a doctor call Greg House
[21:16] <jcoxon> he is an antisocial incredible doctor
[21:16] <jcoxon> this a medical drama
[21:17] <Laurenceb> ah
[21:18] <jcoxon> bbia
[21:18] <jcoxon> b
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[21:21] <hyperb_> every episode he solves some mysterious one-of-a-kind medical predicament
[21:22] <Laurenceb> I'm trying to understnad what ed's terms mean
[21:27] <Laurenceb> actually I think I see it, servocharacteristic is equilibrium back angle as a function of servo position?
[21:28] <Laurenceb> doh
[21:29] <Laurenceb> its just damped shm
[21:29] Action: Laurenceb bangs head on table
[21:30] <Laurenceb> yes, parafoils are quite simple beasts... until you start thinking about how it handles in turbulence ect
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[21:30] <Laurenceb> still, a bit nice than rogallos
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[21:33] <edmoore> Laurenceb: correct, just a damped mass spring system
[21:33] <edmoore> ain't it pretty!
[21:33] <edmoore> all the state equations fall out as that
[21:33] <Laurenceb> I'm going rusty
[21:33] <Laurenceb> didnt spot it
[21:34] <edmoore> you're used to crazy quantum stuff
[21:34] <Laurenceb> I was trying the same thing with rogallos, but they are quite nonlinear
[21:34] <edmoore> :)
[21:35] <Laurenceb> http://wiki.ukhas.org.uk/_media/projects:ukhas_glider_project:rogallocomparison2.png?cache=cache
[21:35] <Laurenceb> I shold retry that, none of the fits are very good
[21:35] <Laurenceb> but you can see its ot shm
[21:36] <Laurenceb> a lot of whats going on is phase lags in the system
[21:36] <edmoore> exactly
[21:36] <Laurenceb> then its obviously hitting turbulent air, giving the small higher frequency disturbances
[21:37] <edmoore> you're operating around that area, which makes sense if you think of the bode plot of it
[21:37] <edmoore> that could be all sorts
[21:37] <edmoore> it would be interesting to see an FT of that
[21:37] <Laurenceb> I turned the D and I terms off there
[21:38] <edmoore> could be twisting resonance in the guy-lines or something
[21:38] <Laurenceb> hmm I will dig out the data and do some better analysis
[21:38] <edmoore> right, back to house
[21:56] <Laurenceb> if you assume a linea relationship between servo position and drag coefficient, servocharacteristic isnt linear, even for small angles :(
[21:56] <Laurenceb> due to the v^2 drag relation
[22:05] <edmoore> I don't assume that
[22:05] <edmoore> bbl house
[22:05] <Laurenceb> I know
[22:05] <Laurenceb> I was just thinking about a nice mathematic model of a parafoil
[22:06] <Laurenceb> but why bother when you can build one
[22:06] <edmoore> exactly
[22:06] <edmoore> however, self yuning isn't out of the question
[22:06] <edmoore> tuning*
[22:06] <Laurenceb> when you move to more complex models, they become further from reality
[22:06] <edmoore> lots of time, slow response, stable
[22:07] <Laurenceb> unless they are very good models
[22:07] <edmoore> oh there are 700 papers on modelling parafoils
[22:07] <Laurenceb> lol
[22:07] <edmoore> with vast matrices
[22:07] <Laurenceb> ha
[22:07] <edmoore> i like my damped shm
[22:09] <Laurenceb> http://news.bbc.co.uk/1/hi/technology/7341031.stm
[22:11] <natrium42> grrr @ spiritofknoxville
[22:11] <edmoore> why?
[22:11] <natrium42> they like keeping us in suspense
[22:11] <natrium42> no updates about the balloon
[22:11] <natrium42> :P
[22:12] <jcoxon> now this is really odd
[22:12] <jcoxon> pretty much all the AT commands work apartfrom AT#WSCRIPT and AT#RSCRIPT
[22:26] <jcoxon> very weird
[22:26] <jcoxon> as it works on the same wiring with a gm862-gps
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[22:35] <natrium42> jcoxon, what's the url to the canon firmware again?
[22:36] <natrium42> nvm, found it
[22:36] <jcoxon> oooooo, i just tapped into the second serial port
[22:36] <jcoxon> debug info
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[22:45] <Laurenceb> jcoxon: can you do the gps reflashing trick?
[22:45] <jcoxon> nah i didn't make much progress
[22:45] <jcoxon> it requires a windows 'puter which is a tad annoying
[22:45] <jcoxon> i'll have another go this weekend
[22:45] <Laurenceb> do you think you can?
[22:46] <jcoxon> no idea
[22:46] <Laurenceb> it'll be interesting
[23:23] <akawaka> natrium42: got an sd400 from a friend with a broken lcd
[23:23] <akawaka> might try to port the chdk firmware to it
[23:30] <natrium42> akawaka, cool
[23:30] <natrium42> let me know how it goes
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[00:00] --- Fri Apr 11 2008