highaltitude.log.20070404

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[16:42] <Laurenceb> jcoxon, could I fly a payload on pegasus5?
[16:43] <Laurenceb> it'd be a vlf radio reciever
[17:08] <jcoxon> hey Laurenceb
[17:08] <jcoxon> what sort of weight?
[17:09] <Laurenceb> 100 grams
[17:10] <Laurenceb> there would be an amplifier and mp3 recorder
[17:10] <Laurenceb> it'd need to hang a long way underneath the payload
[17:12] <jcoxon> whats the plan?
[17:12] <jcoxon> to broadcast to it during the flight?
[17:12] <Laurenceb> just to see what it picks up
[17:12] <Laurenceb> use some fft software to look at the recording later
[17:13] <Laurenceb> http://www.vlf.it/
[17:14] <jcoxon> okay
[17:15] <jcoxon> a small box with an off/on switch etc would be great
[17:15] <jcoxon> don't want to have to mess around with it on the launch site
[17:16] <Laurenceb> yes, the mp3 recorder would probably have to be turned on
[17:18] <jcoxon> cool
[17:20] <Laurenceb> I was thinking of getting a javelin stamp...
[17:21] <Laurenceb> but it cant do floating point it seems
[17:22] <jcoxon> oh right
[17:24] <Laurenceb> the only other decent parallax probuct is the propellor chip
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[18:09] <Laurenceb> jcoxon, have you got servos working directly from a gumstix?
[18:09] <Laurenceb> ie straight off one of the io pins
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[18:21] <jcoxon> yup
[18:22] <jcoxon> i can generate a PWM signel
[18:22] <jcoxon> signal*
[18:23] <Laurenceb> what language do you use?
[18:25] <jcoxon> C
[18:25] <jcoxon> i didn't write the driver myself
[18:26] <jcoxon> it creates a device file which you just pass a number to it and it'll move the servo
[18:27] <Laurenceb> so you write to the file?
[18:27] <Laurenceb> and the servo moves
[18:27] <jcoxon> sort of
[18:27] <jcoxon> yeah
[18:27] <Laurenceb> how fast?
[18:27] <jcoxon> never really measured the responsiveness
[18:28] <jcoxon> its software rather then hardware driven
[18:28] <jcoxon> therefore will be slower
[18:30] <jcoxon> why what are you thinking?
[18:31] <Laurenceb> I was thinking the code for the glider
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[18:32] <Laurenceb> could be done in c for a gumstix
[18:32] <jcoxon> would be quick :-p - all 400mhz worth
[18:32] <Laurenceb> you'd need to get serial from the gps and convert to float
[18:32] <jcoxon> or 600mhz with the new gumstix
[18:32] <Laurenceb> wow
[18:33] <jcoxon> the new one is damn nice - 600mhz, usb2 host
[18:33] <Laurenceb> how would you get the serial tho?
[18:33] <jcoxon> well there are 4 serial ports
[18:34] <Laurenceb> but software wise
[18:34] <jcoxon> well you just read a device file
[18:34] <jcoxon> everything in unix is a file
[18:36] <Laurenceb> can you process nmea in c?
[18:36] <jcoxon> sure
[18:36] <jcoxon> there are prettier ways
[18:36] <jcoxon> i personally use perl as it has better string manipulation
[18:36] <Laurenceb> hmm, but how do you transfer to the c?
[18:37] <Laurenceb> or would you just use perl for all the main stuff?
[18:37] <jcoxon> well my set up right now is to take the nmea string use perl to convert it to a nice form and then put it into a file
[18:37] <jcoxon> then take it out of the file
[18:37] <jcoxon> with anyother program
[18:37] <jcoxon> but then i'm not doing time critical stuff
[18:37] <Laurenceb> doesnt that trash the flash?
[18:38] <jcoxon> well in theory yeah
[18:38] <jcoxon> but that'll take ages
[18:38] <Laurenceb> :(
[18:38] <jcoxon> as the filesystem is designed to stop that
[18:38] <jcoxon> it mainly uses a ram disk
[18:39] <jcoxon> and actually doesn't write to the disk for a while
[18:39] <Laurenceb> ah okay
[18:39] <jcoxon> jffsd is designed for embedded systems
[18:39] <Laurenceb> but my flight code is very time critical
[18:39] <Laurenceb> need to process the string as soon as it arrives
[18:39] <jcoxon> well
[18:39] <jcoxon> it could be done very fast
[18:40] <jcoxon> process it in C - pump out the string
[18:40] <jcoxon> probably faster then a microcontroller
[18:40] <jcoxon> however the bottleneck would be the servo part
[18:40] <Laurenceb> oh you could write some variable to the file, say 1
[18:41] <Laurenceb> and the main code would check that to see if a new string had arrived
[18:41] <Laurenceb> if yes, read it in and process, set variable to 0
[18:42] <jcoxon> skip the file part
[18:42] <jcoxon> or maybe not
[18:42] <jcoxon> make use of the multiprocessing capabilities
[18:42] <Laurenceb> doing it all in c would be faster
[18:43] <jcoxon> basically it could be done
[18:43] <jcoxon> how many servos would need to be controlled?
[18:43] <Laurenceb> one or 2
[18:43] <jcoxon> let me check something
[18:43] <jcoxon> there is a hardware pwm
[18:43] <Laurenceb> just one with the existing code and something stable say a parafoil
[18:47] <jcoxon> if you need rapid response then i recommend using a microprocessor
[18:47] <jcoxon> for hte parafoil i think we are going to leave the servo control to a PIC
[18:47] <jcoxon> have a gumstix doing the higher level stuff
[18:48] <Laurenceb> have you programmed any pics yet?
[18:48] <jcoxon> not really
[18:48] <jcoxon> not my department
[18:49] <Laurenceb> thought you were trying it
[18:50] <jcoxon> oh i briefly
[18:50] <jcoxon> i don't like PICs
[18:50] <jcoxon> all this programming them
[18:50] <jcoxon> much prefer something with an OS
[18:52] <jcoxon> something that can be edited on the fly
[18:52] <Laurenceb> I'm looking for something to run future missions on
[18:53] <Laurenceb> my existing system is too unreliable
[18:53] <jcoxon> well if i was looking for a system i'd personally use a new gumstix with a robostix board
[18:54] <jcoxon> have the robostix do all the hard stuff like servo control and sensors
[18:54] <jcoxon> and the gumstix doing the hardwork
[18:54] <jcoxon> then use the usb for a webcam etc
[18:54] <Laurenceb> that would be cool
[18:55] <jcoxon> right have to go
[18:55] <Laurenceb> are the webcams that will run over the usb?
[18:55] <jcoxon> will bbl
[18:55] <Laurenceb> cya
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[22:25] <mc-> hi rocketboy
[22:25] <mc-> hi jcoxon
[22:26] <mc-> I was talking to someone about a project for stablizing a model helicopter
[22:26] <mc-> I thought it should be possible with simple sensors such as accelerometers.
[22:27] <mc-> They can't use thermopiles, as it needs to hover nr ground level
[22:27] <mc-> do you think it's possible? + use GPS to compensate/calibrate.
[22:30] <mc-> cya
[22:30] <mc-> I look at the logs tomorrow, if you have any comments.
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[23:07] <rocketboy> mc - would have thought the best thing for hover neer ground level would have been ultra-sonic sensors (as per car parking sensors and ultrasonic distance measures)
[23:07] <rocketboy> neer = near
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[23:23] <jcoxon> evening rocketboy
[23:24] <jcoxon> they've found nova 5
[23:28] <rocketboy> wow - where?
[23:29] <jcoxon> thats all i know
[23:29] <jcoxon> henry left me a message
[23:30] <rocketboy> ah ok
[23:30] <jcoxon> rob is collecting it tomorrow
[23:32] <jcoxon> so i guess all will be revealed
[23:32] <rocketboy> hopfully they will get some video from it
[23:33] <jcoxon> yeah
[23:33] <jcoxon> oh i found a video from drop test day
[23:33] <jcoxon> of one of the first drops
[23:33] <jcoxon> i'll stick it up tomorrow when i find my camera cable
[23:33] <rocketboy> that reminds me - must see what video was on mine
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[23:40] <rocketboy> I'll send you a couple of clips and photos to add
[23:40] <rocketboy> if thats ok?
[23:40] <jcoxon> yeah
[23:40] <jcoxon> ummm my google accout would be better
[23:40] <jcoxon> the address is on my website
[23:46] <rocketboy> ok
[23:48] <jcoxon> right i better get some sleep
[23:48] <jcoxon> night rocketboy
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[00:00] --- Thu Apr 5 2007