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Registered Member #49
Joined: Thu Feb 09 2006, 04:05AM
Location: Bigass Pile of Penguins
Posts: 362
I started playing with the idea about a year ago; i made some posts at that time about a pretty crappy servo controller that worked through a cellular telephone. I shelved the idea for a semester, and picked it up again this christmas.
I hope CR's PIC GPS code is still in the archive; i do plan to add GPS tracking, but not right away. I guess my goal right now is more of a stabilization/autopilot than a true UAV.
Answer me this: why a horizon sensor for orientation control? I know some commercial systems use the same, but I was planning on using accelerometers alone. I can imagine the errors from turbulence and whatnot, but I kind assumed, hoped, it'd come out alright...? bad assumption?
A lot of my efforts have been devoted to sorting out my transmission protocol. As it stands I don't want to have to learn lots about RF, but I still want to do this my own way, so I've made my system's signals very audio-like, such that I can connect my thingy to any transmitter/reciever pair that xmits voice/music/.5-3kHz. So far I've tested it through a $10 FM audio transmitter for ipods, and used a $5 FM radio as a reciever. I've also used FRS radios, and my trusty cell phone. Its actually really flexible; I can use digital transmissions as well, which is what its doing when I'm using those short range RF modules on the board.
I'm going to take a plane out this week and give my system a test run. Basically I'll be testing that I can actually fly a plane using a joystick instead of the twin sticks on a transmitter. Then I try a simple wings-level controller, and maybe an automated loop or something. Not too ambitious, I guess, but thats where I'm at.
Registered Member #128
Joined: Fri Feb 10 2006, 05:02PM
Location:
Posts: 19
Unfortunately the attitude information derived from rate gyros are too sensitive to drift. Geniuine gyros would probably work- even with a cheap one, you should get positive attitude control for over 30 minutes.
To keep communication electronics simple, I am transporting all telemetry and command input as digital packets over a cell phone. Most phones are equipped with a USB connector that allows internet access. I have a nearly dead cell phone that is still up to the task (the clam shell broke off so it will not send voice, just data.)
The computing power will be divided among two single board computers. One is solely dedicated to navigation (IMU, GPS, and Kalman Filter) and the other is for the autopilot, command and control (IE: communicating over internet.)
For manual flights that are being conducted as of now, it's using a FUTABA radio and servos with 7 cell NiMH and two cheapo ducted fans. So far, the aircraft has not been flown with any of the planned avionics.
Registered Member #49
Joined: Thu Feb 09 2006, 04:05AM
Location: Bigass Pile of Penguins
Posts: 362
Unfortunately the attitude information derived from rate gyros are too sensitive to drift. Geniuine gyros would probably work- even with a cheap one, you should get positive attitude control for over 30 minutes.
huh? i'm talking about using accelerometers to measure the direction of gravity, not gryos as an inertial referrence. i realize turbulence and centripetal acceleration will affect my readings, but i'll be able to use the magnitude of the resulting vector to find when my results are being skewed. considering that an aircraft is not capable of true 3d motion, my software makes some simplifying assumptions to reduce these errors. gyros, even the MEMS kind would all but eliminate error due to centripetal acceleration errors, and not be subject to drift at all.
Registered Member #65
Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155
â€how do you plan on controlling yours?†I was thinking of a simple old laptop motherboard (5†x 8â€) with a modified 802.11 high gain antenna, USB boot key, and GPS. At the client end an old Playstation analog controller wired into the LPT port on another laptop. Personally I am more interested in navigation software then building more robotic systems.
“I can imagine the errors from turbulence and whatnot, but I kind assumed, hoped, it'd come out alright...?†Actually unlike airplanes the helicopters have a built-in stabilization bar, a low stable centre of gravity, and a large spinning thing that tends to prefer to stay horizontal with its axis vertical. So accelerometers work on helicopters having only to adjust for sudden changes in relative position to prevent exceeding the safe operating area. In fact if an uncorrected gyro assisted flight system were used here it would fight the controls to try and remain level.
Airplanes differ somewhat. Some artificial horizons have some pretty robust proven stabilization systems built it... This is needed to provide a true reference for the guidance system. Without this a plane will need constant human or secondary sensory flight path data corrections.
Registered Member #128
Joined: Fri Feb 10 2006, 05:02PM
Location:
Posts: 19
Andrew wrote ...
Unfortunately the attitude information derived from rate gyros are too sensitive to drift. Geniuine gyros would probably work- even with a cheap one, you should get positive attitude control for over 30 minutes.
huh? i'm talking about using accelerometers to measure the direction of gravity, not gryos as an inertial referrence. i realize turbulence and centripetal acceleration will affect my readings, but i'll be able to use the magnitude of the resulting vector to find when my results are being skewed. considering that an aircraft is not capable of true 3d motion, my software makes some simplifying assumptions to reduce these errors. gyros, even the MEMS kind would all but eliminate error due to centripetal acceleration errors, and not be subject to drift at all.
Maybe I misunderstood what you're trying to do. I imagined that a system using the g-vector for attitude control would become confused in (unintentiona) turns and other maneuvers. I think as I understand your idea now, that you're keeping the aircraft straight and level before the rate gyros drift, while constantly reset their values with the g-vector. I guess the trick is to filter readings that are in the close neighborhood of 1g. Is that what you meant?
No wait.. You're not using rate gyros at all. I get it now. I would suppose the hard part is figuring out how to disambiguate the situations when the trajectory of the airplane is changing, but with magnitude is still around 1g (IE, diving/slipping turns, etc.) I have heard that there are situations when using gravity to orient oneself is deceptive (or rather I was warned against it during my IFR training.)
Honestly, with any luck, your idea will work and would prove significantly less expensive to implement. I have this nasty tendency of making things more complicated than they need to be. Let me know if it works! :)
Registered Member #49
Joined: Thu Feb 09 2006, 04:05AM
Location: Bigass Pile of Penguins
Posts: 362
now you're with me. I have the oppsite problem, i tend to simply things too much, well see. Honestly i had always planned to implement gyros too, and do exactly what you described. but then i discovered analog stopped sampling... everything, and gyros are quite pricey.
Registered Member #128
Joined: Fri Feb 10 2006, 05:02PM
Location:
Posts: 19
Andrew wrote ...
now you're with me. I have the oppsite problem, i tend to simply things too much, well see. Honestly i had always planned to implement gyros too, and do exactly what you described. but then i discovered analog stopped sampling... everything, and gyros are quite pricey.
time will tell, good luck to both of us.
Hahah we don't need luck. One of us is going to nail this sucker to be sure. :P
I have a truckload of Firebird Freedom carcasses (read: planes I obliterated while teaching myself to fly RC) that I am going to gut for parts, such as the horizon sensor. I am trying to keep the avionics under $1000.
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Old-school Vs. MEMS Accelerometers
