highaltitude.log.20090726

[00:01] <Laurenceb> not a lot.. been very busy
[00:01] <Laurenceb> renovation work
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[00:01] <Laurenceb> thinking about an n prize vehicle... :P
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[00:03] <Laurenceb> http://robosavvy.com/site/index.php?option=com_content&task=view&id=183&Itemid=135
[00:04] <Laurenceb> was thinking of that for a flight computer... not sure how FPU speed relates to CPU speed
[00:04] <Laurenceb> - the processor has an fpu
[00:04] <qbert55> why not use a real one
[00:04] <grummund> 23:08 < rjharrison> !msg laurenceb I can't do tomorrw as wife is away. She hadn't told me
[00:05] <Laurenceb> yeah I heard thanks
[00:05] <grummund> ok
[00:06] <qbert55> the autopilot I'm using can and is used on any RC plane / glider
[00:06] <Laurenceb> qbert55: as that board is kind of convenient :P
[00:06] <Laurenceb> link?
[00:06] <SpeedEvil> rjharrison: !msg laurenceb I can't do tomorrw as wife is away. She hadn't told me
[00:06] <SpeedEvil> ah
[00:06] <Laurenceb> ok ok
[00:06] <qbert55> can't give you one for the new version but here is the link for the 1.8
[00:07] <Laurenceb> :P
[00:07] <Laurenceb> I was thinking of that board together with an anlogue devices IMU
[00:08] <Laurenceb> nicely sticks straight onto the SPI interface
[00:08] <qbert55> www.attopilot.com
[00:09] <Laurenceb> oh thermopiles
[00:09] <Laurenceb> ok
[00:10] <qbert55> I'll get back to you guys later, It's 28C and little wind so I'm going flying and supper is calling
[00:10] <Laurenceb> I was thinking of avoiding thermopiles completely by making use of the gps derived acceleration
[00:10] <Laurenceb> - for a rocket
[00:11] <Laurenceb> so you use magnetometer + gps acceleration vector for attitude calculation
[00:11] <qbert55> the new one use full IMU CU later
[00:11] <Laurenceb> neat
[00:11] <Laurenceb> I got the maths working in matlab
[00:12] <Laurenceb> using data from a sparkfun 6DOF IMU
[00:12] <qbert55> MAG + GYROS+GPS
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[00:12] <Laurenceb> but the number of operations is pretty high
[00:12] <Laurenceb> and accel ?
[00:13] <Laurenceb> if your clever you could used ints for most of the work... but its nice to be able to use floats
[00:13] <Laurenceb> that board I linked would handle it easy
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[00:16] <Laurenceb> nooo http://news.bbc.co.uk/1/hi/sci/tech/8168954.stm
[00:17] Nick change: KingJ -> kingj
[00:17] Action: Laurenceb hopes the launch vehicle doesnt blow up
[00:20] Nick change: kingj -> KingJ
[00:20] <Laurenceb> qbert55: http://wiki.ukhas.org.uk/code:4_state_extended_kalman_filter_in_matlab
[00:25] Nick change: KingJ -> kingj
[00:27] <Laurenceb> bbl
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[02:23] <SpeedEvil> http://catless.ncl.ac.uk/Risks/25.49.html lau
[02:23] <SpeedEvil> oh
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[11:46] <SpeedEvil> Laurenceb: http://fatpita.net/?i=378
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[12:00] <SpikeUK> SpeedEvil - nice!
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[22:46] <natrium42> hello sir DanielRichman
[22:47] <DanielRichman> hello sir natrium42
[22:47] <DanielRichman> wassup?
[22:47] <natrium42> reinstalling windows on desktop computer
[22:47] <natrium42> you?
[22:47] <natrium42> getting closer to launch? :)
[22:48] <sbasuita> DanielRichman, yo simon's ubuntu is foobarred; he's recovering xp tomorrow when his cricket gets rained off
[22:49] <DanielRichman> sbasuita, I heard, no idea what he did to it
[22:49] <DanielRichman> natrium42, yes, but don't shoot me! shoot sbasuita and alex
[22:49] <sbasuita> DanielRichman, where is alex?
[22:49] <DanielRichman> god knows
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[23:19] Nick change: KingJ -> kingj
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[23:30] <Laurenceb> hello
[23:31] <SpeedEvil> 
[23:32] <Laurenceb> a diode?
[23:32] <Laurenceb> looks like I underestimated the ISP from cesaroni motors
[23:33] <SpeedEvil> :)
[23:33] <natrium42> *misunderestimated
[23:33] <Laurenceb> 250 looks more likely than 230
[23:33] <Laurenceb> heh
[23:34] <Laurenceb> but I'm not sure about my gps idea....
[23:34] <Laurenceb> the doppler rate will be very high during motor burn, and it might lose the stats its tracking
[23:34] <Laurenceb> if that happens it'll need to re aquire them before apogee
[23:35] <Laurenceb> a typical gps PLL will lose lock at about 5G from what I can see... but hallam appeared to get much better results
[23:36] <Laurenceb> most off the shelf receivers fall back to a FLL - but I'm not sure how tolerant of accel they are
[23:36] <Laurenceb> I think in theory much better
[23:41] <SpeedEvil> yeah
[23:41] <SpeedEvil> push it with accel data, and...
[23:42] <Laurenceb> but I want to use an off the shelf receiver
[23:42] <Laurenceb> and extract pseuorange and doppler
[23:43] <Laurenceb> http://imgur.com/AyfCI.jpg
[23:43] <SpeedEvil> ah
[23:44] <SpeedEvil> I wonder if they stay locked if >nnnn m/s
[23:44] <Laurenceb> apparently so
[23:44] <Laurenceb> but some may have a limit of doppler
[23:44] <Laurenceb> - sanity check
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[23:46] <Laurenceb> it should be possible, but if you drop all the sats when the motor fires, its a bit more tricky
[23:49] <SpeedEvil> For straight velocity range, you've got the +-2Km/s of the sats to help a little
[23:49] <SpeedEvil> which takes you to 4km/s ish
[23:51] <Laurenceb> first stage delta v is 2.3Km/s in this design
[23:51] <Laurenceb> at <20G max accel
[23:51] <Laurenceb> http://www.gmat.unsw.edu.au/gnss2004unsw/SON,%20Seok%20Bo%20P147.pdf
[23:52] <Laurenceb> FLLs are typically used in commercial receivers as they are good at low SNR
[23:52] <Laurenceb> but they also work well at high G .... but its the implimentation and filter bandwidth ect that couldns
[23:52] <Laurenceb> *counts
[23:53] <Laurenceb> my idea was to use GPS velocity to work out when the first stage is about to reach apogee, then ignite a small (~30gram) slow burning charge
[23:54] <Laurenceb> then use the delta V from the gps and the output from the magnetometer to get the attitude right for second stage firing from the launch tube
[23:54] <SpeedEvil> Apogee is opposite side of earth from launch?
[23:54] <SpeedEvil> oh
[23:54] <Laurenceb> no
[23:54] <SpeedEvil> right
[23:54] <SpeedEvil> first apogee
[23:54] <Laurenceb> its a hundered Km or so downrange
[23:55] <SpeedEvil> ranging from the launch site is almost plausible
[23:55] <Laurenceb> oh with a transponder?
[23:56] <Laurenceb> hmm transponder derived doppler + accel output during slow burner firing + magnetometer would allow an attitude quaternion to be derived
[23:56] <Laurenceb> nice idea
[23:57] <Laurenceb> but itd be nicer to use the gps
[23:57] <Laurenceb> it has to fly with a gps anyway for recovery
[23:57] <SpeedEvil> yes
[23:57] <SpeedEvil> I was actually wondering at one point about a laser ranger
[23:58] <SpeedEvil> tracking laser ranger on telescope gives you a position
[23:58] <SpeedEvil> with a reteroreflector on the rocket
[23:59] <Laurenceb> attitude is very important for second stage firing
[23:59] <Laurenceb> actually... you need the position for the transponder technique to work
[00:00] --- Mon Jul 27 2009