Blogs

Some of you may have heard about SmartPlanes in Sweden. We have been quietly working with survey and mapping from UAV's for about 5 years now and keeping a bit of a low profile. I have just been putting a bit more information on our homepage about the kind of work we do and wanted to share it with you guys here at DiYDrones. I know a lot of you have ambitions of doing something commercial with UAV's in civilian applications and I'd be glad to share our experience.

Our plane was designed to be a portable system for aerial photography that can handle professional use in the field. We use a flying wing made out of covered EPP with vacuum formed polycarbonate fuselage that can be disassembled into 3 pieces for transport. It has an aft mounted electric motor and weighs about 1.1kg with camera and flys for about 35min on a 2500mAH flight pack. Our first version of this plane used a MicroPilot 2028g, now we use paparazzi autopilot. ask me why. It is hand-launch and manual landing. Flight planning is done by defining a single rotated rectangular block with dimensions and one waypoint. The actual navigation path is calculated in the autopilot code.

I think that aerial photography over small areas and single objects is a very good first civilian application for UAV's. We have seen a lot of interest in the technology, but the market is really undeveloped. For most mapping applications though, it is not enough to just take pictures from the air- you have to be able to generate a georeferenced photomosaic that you can use in a geographic information system. This is an area we have put a lot of effort into, within smartplanes and through some partners. We now have some software that allows you to create a good georeferenced mosaic already in the field on a laptop. For the more demanding applications that require true orthophotos and surface height models, we send the data in for processing.

We have found a lot of interest especially in making surface height measurements over small areas, because you can then measure volumes of things like gravel piles, sawdust, peat, rock aggregate, garbage, compost. Whatever people scoop up into big piles, they usually need to measure it and it is expensive to do it with conventional ground survey or aerial photography.

We normally cover an area of about 500x500m in a single flight because aviation regulations in most places require flying within line-of-sight. We can however join several flights into a large block for mapping larger areas. I think the largest block we have done to date had 30 blocks and almost 8000 photos. Very interesting to know it can be done, but at this size, laser scanning becomes more competetive.

Anyway I just want to tell you a little about our work and invite you to have a look at our homepage. Leave a comment here if you have any questions.

Source: http://www.rent-a-drone.de

German company providing drone rentals @ 190 EUR [private use] or @ 420 EUR [commercial use]. Interesting to note, units supposedly easy to control for the novice via video goggles and Tablet PC, remote control or using GPS waypoint navigation. English translation of website via google available here.

For the record, not associated with firm(s) in any way -- posted for informational purposes only.

Natural gas leaked out of a PG&E pipeline in San Bruno, CA, killing an unknown number. Clearly the Buried Natural Gas infrastructure is beginning to age. Only UAV's can reasonably fly low enough in neighborhoods to create a map of NG concentration. I heard on NPR that PG&E flies airplanes to inspect gaslines, but clearly not low or often enough.

Given that Methane sensors are light, cheap and readily available:

It's conceivable that Amateur UAV's could fly a pattern and log Methane levels against a GPS coordinate.

(Does anyone else think this could be a viable task for UAVs? and Why not propose a T3 contest in which mapping methane is the objective?)

I have been tinkering with solar powered RC planes this summer. The photos above shows the latest incarnation.

This model uses the Parkzone Vapor's radio gear and motor ( http://www.parkzone.com/Products/Default.aspx?ProdID=PKZ3380 ), plus five Powerfilm solar cells ( http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_228056_-1 ). The motor/prop are quite well matched to the cells, delivering about 2.5 watts in direct sunlight. Here are some test data:

All up weight is 38g, 18g in solar cells. It has a tiny 20mAh battery (1g) in parallel with the solar cells that acts to smooth out the voltage. Before I flew, I ran the motor using battery power until the voltage dropped too low to run the motor, then I plugged in the solar cells. That way, when I flew, I knew I was really running on solar power alone. I flew it for about 5 minutes or so, but it was a pain to fly because the wings were too torsionally floppy. I am planning the next revision that should address some of this design's shortcomings.

Related Work

There have been many successful solar airplanes. I found the following efforts particularly interesting because they are not military or NASA scale projects, and they are well documented.

Andre Noth's (ETH Zurich) 3.2m span Sky-Sailor, which flew 27 hrs in 2008

www.asl.ethz.ch/research/asl/skysailor

Carl Engel and Adam Woodworth's (MIT) 3.1m Aphelion, which has flown over 7 hrs

http://www.rcgroups.com/forums/showthread.php?t=572000&pp=15

Solar Cell Selection

In many applications, solar cell performance is measured by efficiency. In my experiments with the Powerfilm cells, I got about 70 watts per square meter. Using a fairly standard irradiance value of 1000 watts per square meter puts the cell efficiency at something like 7%. This is not particularly good compared to the state of the art (see e.g. http://en.wikipedia.org/wiki/File:PVeff%28rev100414%29.png).

The Aphelion uses an array of 18 A-300 Sunpower Solar Cells. The total encapsulated array weighs about 350 grams and can deliver 55 watts of power. These cells are reported to be upwards of 20% efficient. BTW, if you dig deep enough into the Aphelion thread referenced above, Carl reveals his secret supplier of these cells:

<quote>

Also, here is the contact info for our solar array supplier, now that he has given permission for it to be posted. One note that he wants to be made clear: he is very busy, and it's a small operation, so there can be a serveral month lead-time on ordering an array. With that, here is his info:

SunCat Solar is the name of the comany, and our contact in Alain Chuzel(pronounced "Allen"). His email address is
ahmchuzel<at>aol<dot>com. (replace the <at> with @and <dot> with . )

He can fabricate pretty much any size or confguration of array, given a good drawing (and enough money )

</quote>

The weight of solar cells accounted for 47% of the total weight of my airplane. Therefore, I would argue that for a solar powered airplanes, an important performance measure of performance is watts per gram. I measured about 0.27 watts per gram for the Powerfilm cells. This compares favorably to the Sunpower cells at 0.16 watts per gram.

Some other attractive things about the Powerfilm cells is that they are reasonably priced, and readily available in small quantities. I have not contacted Suncat Solar to determine the cost/availability of the Sunpower cells.

Scaling Arguments

I think it would be very cool to build a solar powered drone that could stay up all day, and possibly all night. My little airplane has essentially no payload capacity. Presumably, a larger airplane would be required to carry up a GPS, IMU, two way radio, etc.

As the airplane gets bigger, we have more area for solar cells, but the weight gets larger too. So how does the power budget work out with a bigger airplane? Here are some scaling arguments to help answer that question objectively.

Definitions:

Preq: required power

Pavail: available power

Rp: the ratio of available power (Pavail) to required power (Preq)

D: drag

V: flight speed

W: weight

g: acceleration due to gravity

rho: air density

S: wing area

CL: lift coefficient

Kcell: power output of solar cell per area

LOD: lift/drag (or glide ratio)

WOS: wing loading, weight per area

Relationships:

(1) Pavail = K * S (assuming the entire wing is covered with cells)

(2) Preq = D * V

(3) V = sqrt( 2 * W * g/ (rho*S*CL) )

(4) D = W * g / LOD

Combining (2), (3), and (4) gives

(4) Preq = W * g/ LOD * sqrt( 2*W *g/ (rho*S*CL) )

Combining (1) and (4) gives

(5) Rp = K * S ^ (3/2) * LOD * sqrt(rho * CL) / ( (W*g) ^ 3/2 * sqrt(2*g) )

Finally, simplifying (5) gives

(6) Rp = K * (1/WOS) ^ (3/2) * LOD * ( sqrt(rho*CL/ 2) * g^(-3/2) )

There are four terms in (6). The first term depends only on the solar cell. The second term depends only on the wing loading. The third term depends on the aerodynamic efficiency of the airplane, and the fourth term we can treat as a constant. Thus, starting from my little airplane, as we increase the size of the airplane, if we use the same solar cells, maintain the same wing loading, and maintain the same LOD, then we should still have enough power to fly.

The bad news is that as airplanes are scaled up, their weight usually goes up faster than their area, thus their wing loading goes up. Stated another way, bigger airplanes usually have higher wing loading than smaller airplanes given similar structural technologies.

The good news is that as we increase the size of the airplane, we can expect the LOD to improve. The LOD of my airplane is around 7. Doubling or even tripling this value should be possible ( see e.g. http://www.rc-soar.com/tech/perfanal.htm ). The wing loading of my airplane is 540g/m^2. If we double the LOD, we can increase the wing loading (WOS) to 850g/m^2 (i.e a factor of 1.58) and maintain the same power ratio.

Also, as we make the motor and propeller larger, we might expect an improvement in propulsive efficiency, meaning that we fly with a reduced power ratio.

Considering these factors, building a bigger solar airplane is probably harder than building a small solar airplane. Based on the successes referenced above, I must conclude that it is possible, but not easy (or cheap).

Jose Juilo from the ArduCopter team has been doing great work adding the GPS position hold and autopan features to the code. Yesterday you saw the video of the flight; here's the picture that the quad took, a stitch of 8 photos taken with a programmed slow yaw movement linked to shutter triggers.

Full GPS navigation is the next feature ArduCopter will inherit from the ArduPilot Mega code. Expect a public beta within the month....

First bumpy, but successful landing in X-plane with Erlang autopilot from Benjamin Nortier on Vimeo.

There's a long and good profile in the LA Times of the UAV industry in San Diego (General Atomics) and Los Angeles (AeroEnvironment), which now employs an estimated 10,000 people. Read it here.

Classic New York Post: (via Gawker)

"Attack of the Drones

Airborne Eyes Peer at the City

In New York City, someone's always looking down on you.

Low-tech, miniature versions of battlefield drones have come to the boroughs. Only here, they are controlled mostly by hobbyists and photographers, not soldiers shooting insurgents from the sky.

There are only 282 official permits to fly drones nationwide, according to the Federal Aviation Administration. They range from $4.5 million jets that can fly for two days without landing, to hand-launched helicopters that fit in a book bag.

The FAA would not say if any of these permits have been issued in New York City.

But the number of drones patrolling the nation's skies is expected to "explode" if the agency, as expected in December, relaxes restrictions on law enforcement for aircraft weighing 4.4 pounds or less.

Until then, hobbyists are the only people who can launch unmanned aircraft without a permit, as long as devices aren't being used to make money, said an FAA spokesman. They're supposed to fly below 400 feet."

more here....

Waiting for my new copter legs I decided to see how the Jani copter could be adapted. The frame fits very well on the Gaui. I still have parts to add to the top but it works. I tried larger motors and 10" props but I need to raise two of the motors for this to work. So the picture shows the standard 10a esc and Gaui motors

Sonar and IR to follow. I liked the esc calibration of the Gaui so I have implemented this in my ardu copter code. This means the copter will not start if you have never calibrated the esc's and after that will not start if throttle is not in the lowest position.

Next job automatic PID adjustment!

Hi,

I have been following this site for a while now, I guess it is time to post something myself.
Above is a picture of my latest scratch-built quadcopter running an STM32 ARM processor board with home-brew software. This is my second quad, on the first one (you can sort of see it in my profile picture) I used a home-mode, dual Atmega 328 board.
So far, the quad features the following setup:

• Aluminium frame "Home-Depot" style
• Alpha 370 size motors (HobbyPartz)
  
• Salvaged 6dof sensor board from a Walkera XUFO 5 (4?)
• 2-axis magnetometer (I know, 3 axes would make my life a little easier)
• Maxbotix sonar range finder for low-altitude hold
• Mediatek LS20031 GPS
• Modified ADNS2610 optical mouse sensor for low-altitude position-hold
• Custom software, using ChibiOS RT OS (http://chibios.sourceforge.net)
• 72Mhz RC gear (Futaba TX, generic RX)
• XBee telemetry downlink
• Onboard data logging to SD/MMC card
• Oh, yes: taped on keychain-camera for onboard video ;-)
  

Here is picture of the (rather untidy) electronics setup (the Xbee is normally mounted on the inside of the canopy, the mouse sensor and ultrasound sensor are underneath the copter for obvious reasons):

• Quaternion based attitude representation - tried Kalman filters at first, switched to a more DCM-like approach later
• Attitude-hold and aerobatic flight modes (can be switched in flight)
• GPS position hold (activated by channel 6 switch on TX)
  
• OR alternatively at the moment: Optical flow position hold via a downward-facing, modified optical mouse sensor with custom optics (NOTE: both GPS position hold and mouse sensor position hold work, but only on a good day - definitely requires more tweaking/PID tuning)
• Data logging to SD card (not very reliable atm - I do not really use this much since I have telemetry via Xbee)
• "Ground station software" for data logging and displaying the state of the quad in various graphical ways

The software is written pretty much in straight C, making use of ChibiOS' multithreading. The ground software is a collection of Perl/Tk scripts - all my development happens on Linux.
Below is a video of the quad in "mouse sensor" position hold mode in my driveway - apologies for the terrible video, I will try and shoot a better one soon...

If somebody finds any of this useful or interesting, I am glad to share some more details...
Best,
Marko

For those interested ther engine mounts and baseplate were constructed using a rapid prototyper and are made out of ABS plastic which is quite strong.

Cheers,

Tried APC propellers again. Propeller struck ground but didn't bend. Motor broke off mount & propeller struck ESC, damaging something. ESC started smoking. Fortunately we test fly on the golf course instead of a dry field. It's been a long time of occupied storage, but now it's time to trash the APC's.

Finally got operational with the fulltime orientation hold. Next, the helical antenna finally got its show.

It certainly doesn't get as many satellites as the patch. It hasn't had any sudden glitches yet, either. It has a lot more of a random walk & seems to lag more.

The main difference with fulltime orientation hold is the lower D gains possible. That reduces the amount of oscillating. The human controlled cyclic needed such high D gains it always oscillated. The only option for full cyclic was different gains when in full autopilot.

We're not entirely crazy about fulltime orientation hold any more than basic cyclic. Now there's a very narrow limit to angle of attack because our accelerometer only does right side up. It needs a bit of margin to keep from going over 90' & flipping.