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Registered Member #128
Joined: Fri Feb 10 2006, 05:02PM
Location:
Posts: 19
I am currently building a UAV for use in medium range (30 to 60 miles from target) aerial photography. Originally, the basic avionics package intended to use GPS for long term and an IMU for short term positional stability. Long term attitude control would be maintained by an optical horizon sensor and short term attitude control will be derived from the IMU. The IMU as proposed would use four, 3-axis accelerometers arranged in a tetrahedral configuration (making for a gyro-free IMU.) The airframe was originally going to be in a twin electric ducted fan "foamy" jet. Now that finals are over, I am resuming work on the project and decided to create a thread, too. :)
After toying around with accelerometers and seeing how miserable the drift skyrockets firsthand, I am downplaying its role in my UAV. Instead, I am going to use 5 medium to low-res (640 x 480 or maybe 320 X 200) web cams (forward and reward looking, starboard and port side, one down looking) and digital signal processing (mainly segmented 2x2 image correlation that narrowed down by optical flow tracking.) The absolute position will be integrated by stitching together maps that it generates on-the-fly, so long-term drift should be substantially less. Attitude and heading information can also be derived from the webcam images, instead of using pyroelectric sensors. Although drift will accumulate for heading measurements, attitude information should be drift-free (though still susceptible to noise.) Its primary goal is to stabilize the GPS readings enough for precision approaches to the target as well as for automated take off and landings.
It sounds a little complex, but I have gained substantial experience with image processing while at tech (astronomy related, but I have a lot of CDS friends.) Currently, I am researching existing DSP/Single Board computers that are up to the task. My first intuition is to network a few inexpensive DSP chips using a SBC/Gumstix-ripoff and try to keep power consumption low.
Against my long-standing tradition of making things too complicated, I abandoned the jet-fighter style airframe and went with a rather plain cruise-missile form instead. I simply got tired of banging my head on where to put all the avionics, payload (4 MP digital camera with 6X zoom) and the sheer act of balancing the COG. I am building the new airframe (also a foamy) tonight and should have something finished by tomorrow with pictures in hand. :P
PS:
If this design ever gets off the ground it will be a miracle. Some less ambitious goals for now would be to derive attitude information from the webcams and achieve straight-and-level flight before attempting to perform image correlation for heading and position.
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
Sounds fun!
As to the horizon sensing... Aren't there some cheap (like $100) commercially available horizon sensing gizmos for planes these days? I remember a few years ago I had a friend that out this little black box with some 'thermal' sensors on the plane that was supposed to keep it flying strait/level if you let go of the sticks... Seemed to work to I remember one time he put it into a dive, let go, and it zipped right back up and was just fine.
Registered Member #128
Joined: Fri Feb 10 2006, 05:02PM
Location:
Posts: 19
... wrote ...
Sounds fun!
As to the horizon sensing... Aren't there some cheap (like $100) commercially available horizon sensing gizmos for planes these days? I remember a few years ago I had a friend that out this little black box with some 'thermal' sensors on the plane that was supposed to keep it flying strait/level if you let go of the sticks... Seemed to work to I remember one time he put it into a dive, let go, and it zipped right back up and was just fine.
Yup, I know which kind of product you are referring to and have seriously considered that. I am not sure if it is a matter of pride or the fact that I want greater control and integration of the flight system. Plus.... DSP-based visual flight control would just be damn coool :P
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
I would recommend you determine the legality of such a device before embarking on your design. For something that will be flown in a local field (i.e. RC aircraft area etc...) it should be fine, but if you are designing something that can travel unmanned for 30-60 miles thats a whole other story. I'm sure the FAA or similar authority will get pretty upset to find unmanned aircraft flying through their airspace. And i'm sure in this day of age with all the terrorism paranoia, anything like this will be called into the authorities and you may find yourself in a whole slew of trouble.
Heck, a few kids in a town near me were arrested and charged under a new terrorism law for simply verbally saying they were going to kill some classmates at school. From the way things are going, they are all looking at some pretty serious time with this new terrorism law that just went into effect.
Registered Member #128
Joined: Fri Feb 10 2006, 05:02PM
Location:
Posts: 19
EastVoltResearch wrote ...
I would recommend you determine the legality of such a device before embarking on your design. For something that will be flown in a local field (i.e. RC aircraft area etc...) it should be fine, but if you are designing something that can travel unmanned for 30-60 miles thats a whole other story. I'm sure the FAA or similar authority will get pretty upset to find unmanned aircraft flying through their airspace. And i'm sure in this day of age with all the terrorism paranoia, anything like this will be called into the authorities and you may find yourself in a whole slew of trouble.
Heck, a few kids in a town near me were arrested and charged under a new terrorism law for simply verbally saying they were going to kill some classmates at school. From the way things are going, they are all looking at some pretty serious time with this new terrorism law that just went into effect.
This was one issue that imediately came to mind. I did a rather superficial check a few months ago; the main legal issue that was uncovered concerned keeping the aircraft under 5 kg. Right now, the proposed design is just under 3.2 kg. As far as I know, they laws governing UAVs are not well established, but I am sure some paranoid guy will try to throw the patriot act. Even as a photographer, I have been run off by locals from time to time (even more so after 9-11.) Now I am combining both hobbies (YIKES!) Hopefully I will get some sort of backing from my academic affiliations just in case.
Now that you mention it, maybe the jet-fighter airframe would have been a better choice (less alarming to anyone who spots it.) Oh well, maybe I'll get a prototype tested in the air field and then consider these issues once it is capable of medium range operation.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
If Josh gets this to work, I'll steal a cruise missile and eat it
The other thing is, technically, Josh's design would in fact be a cruise missile. If he published it (which he has to do to get his omg 1337 respect from us) there would be an open source cruise missile, and I don't know what the US Govt. would think of that. I don't believe Josh's UAV is a threat, but the Govt. even got scared over 128-bit encryption for goodness' sake. If I were a journalist, I would go to town on it
Registered Member #128
Joined: Fri Feb 10 2006, 05:02PM
Location:
Posts: 19
Come on guys, isn't the line between cruise missle and UAV a little blurred these days?
I doubt my aircraft will have the speed, range and payload capacity to be seen as a threat (especially in an economical sense.) Granted, if I do make the flight control software opensource, some one -could- use it in a way that was not intended. In reality though (as the sourceforge "DIY-UAV" programmers put it), somone with malavolent intent could simply buy one instead of making it themselves.
And I may publish results in a jounal somewhere. Many of the individual components (such as automated landing using optical flow) have been published, but first glance tells me none of them have been integrated to this degree.
I think, at this rate, the real miracle would be if I do not get burned at the stake. The airframe is built (redesigned for a single EDF), but I think posting the pics here might cause more trouble than it's worth. I think I will restrict the project discussion more to the avionics and software.
Registered Member #128
Joined: Fri Feb 10 2006, 05:02PM
Location:
Posts: 19
Update:
To avoid attracting the wrong kind of attention from the locals, I scrapped the old cruise-missle like frame for more of a fighter-drone frame. While I was at it, I increased the air frame size to 7.5 ft long with a 88" wingspan. It is designed to easily dismantle into 5 pieces: nose cone, main fuselage, 2 wings and a tail cone. The control surfaces will consist of wing canards, flapperons, elevator (for stability when flaps are deployed) and rudder.
Design also uses four camers instead of 5 now. (got rid of rear-facing) I also shed over a pound of weight simply by removing the paper covering of the foam board.
Here is a pic from two weeks ago. The fuselage is now covered and cured, but I posted the bare picture because it looks cool.
]
lots of work remaining on the airframe.
Nose:
Install wing canards/fairings Install control linkage from servos Install avioinics Install molded tip of the nose cone Install mounting velcro
Fuselage:
Install Servo extensions Finish install of mounting slots for nose and tailcone Install wing interface/fairing Install landing gear/retracts Install shear tape port, starboard, top Install Li:Poly batteries and power management
Tail cone:
Remove paper covering/assemble tailcone. Install intake port Install internal ducting Install exhaust port Install 800W Electric Ducted Fan and speed controller Install horizontal stabs- main spar, sleeve bearing, control surface, servo, control linkages Install vertical stab- main spar, sleeve bearing, control surface, servo, control linkages Install mounting spars Install mounting velcro
Wings:
Install honeycomb lattice Install top covering Install shear (packing) tape on undersurface. Install flapperons/hinges/horn Install control linkages from servos Install mounting velcro
Avionics:
Install GPS module Install Air Speed Sensor Install Altitude Sensor Install magnetic heading sensor Install webcams foward looking, port, starboard, downward looking. Install DSP-Linux board. Install 4 external DSPs (total of 5 DSP modules) Install JR radio for emergency manual control. Install main SBC/Servo control board.
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Josh's evil UAV project.
I remember one time he put it into a dive, let go, and it zipped right back up and was just fine.
The airframe is built (redesigned for a single EDF), but I think posting the pics here might cause more trouble than it's worth. I think I will restrict the project discussion more to the avionics and software.
