If the question is to use forced induction on a uav...

The answer is probably, "Hell Yeah!". I have been learning everything there is to know about practical, turbocharged-systems. So over the next few posts, I will hopefully generate a reasonable technical approach to safely turbocharge a 4-stroke Briggs and Stratton Animal engine or a Raptor. It depends on which one I can find and afford here in Central Europe.

We have found a few 1.5# turbos good for 3-4psi of boost. The mad scientist in me says that I think we can find some light super chargers and run them on a small electric motor for less weight. I know that the whole point of a turbocharger is more about recovering wasted energy in the exhaust system. However, I wonder if the weight/power generated ratio would be better served with a high efficiency electric motor. Since they are pretty amazing these days.

As I come up with some numbers for weights, and possible concepts, I will keep everyone in the loop.

Adventures in Composites

The big thing that we learned in this episode is how to manage holes or penetrations. We made a male mold and were trying to decide how to mark and spot where we wanted to make penetrations called for in the fuselage.Marking the fabric was not particularly accurate, but it did work. The real answer that we saw was to make a potrusion where the penetration was.

It is easier to cut off a piece that sticks out past the piece that you want than it is to dig out material where you do not want it. Our design has four or so penetrations into the fuselage. Additional wedges of blue insulation were hacked to fit into the holes. They were not made to perfectly match, but were close. So you could easily see what you wanted to keep and cut.

Another interesting thing that we learned was the relative softness of home-owner classes of epoxy. Be aware of this. Y, is that any feature that looks liou can make a mess of your piece if you heat it too much to melt the wax. You have to pull the piece free form the molds and set them back down once the part is free. Putting it back down to the mold really helped the part retain its shape. As we pulled our parts off, we were concerned that they would not be square when we put the parts back together.

Due to some communications issues, there were some delaminations in areas that would have been better had they not occured. These anomalies were healed by forcing a needle into the void and using a syringe to fill it with epoxy. Epoxy is viscous, be aware that it is tough to dispense through a narrow needle. Voids were filled until it appeared to be full visually, pockets were no longer hollow appearing.

Molds seem to be effected strongly by Murphy's Law. Everything that could have gone wrong with our parts did. Our shape has several bays. Bays are hollows where square sides would be best. The bay that we took the time to box in with plywood came out well. The bays that had no boxing in had delaminations and other issues such as corner delaminations, non-square lay ups and twists where pieces hung on something and were not carefully managed back into place. In a bay, is the only area that we had any mold damage. It was due to pieces of cloth almost wrapping a narrow piece of mold. Had it been boxed in, the pieces would not have been able to wrap the way they did and pin the mold into place. This damage was minimal and was fixed with filling the cracks with glue and for the most part was a non-issue.

Adventures in Composites: Two Bogans and the Art of the Lay... Up

After a year of sitting, our polyester resin had spoiled. So we contacted some people and they said you could do it with just about any medium cure time epoxy. Out into the proper disposal container for petro-chemical waste. Yeah, I went there. Off to the local hardware shop for some epoxy. We bought several batches of 60 min epoxy. Some of the information that our friends told us suggested that we could use isopropyl alcohol to help keep the viscosity of the epoxy down as it is laid up.

Information like this is when it gets exciting. We found out a few things. You can paint the alcohol onto a layer to help flow the epoxy and to reduce the bubbles and flatten wrinkles. I would suggest that pour some alcohol into a cup and paint it on where you need it. Each layup will be different so it is hard to say where you would have issues.

There were some bubble generators in the seam where the semi-mold met the backing. This is probably pretty obvious, but it was due to training air under the resin laden cloth. Our mold also had several regions with nearly perpendicular sections which were hard to wet. In areas like that, I would suggest liberally pre-painting. Be careful not to pool the resin in the bottom since that is not where you want the part to be strong. Another observation was to make sure that when each layer is put down, both people should work in the same direction. Do not work the resin from the nose and the tail. It makes wrinkles and other defects.

It is very important to make sure that each layer has as much of the resin out, or at least even distributed as possible. This means that all of the bubbles, wrinkles and puddles need to be worked toward the edge of the layup. A roller and brushes are the weapons of choice for this work. The handle edges are great for wringing out excess resin from tight radii.

So Much For our Idea

We were thinking that we could roll our Schoolgirl UAVs with some great NEU 1915/1.5Y motors to swing our huge props in a dual-motor configuration. I am sure it would work, but I think we will put it into a pusher configuration.

We kind of knew that the motors were big. I got a pair of these 2.7kW beasts from the guys down at Esprit Model in Palm Bay,FL. They are another great supplier of rc stuff. Esprit Model is good about not advertising that they have hard to find stuff and then them being out of stock. Better to know, than to get an email two weeks later saying that they cleared your payment but that you will not get anything for four weeks.

So I got these beer cans. I mean the motors are as big as beer cans. Not an issue, they look great and have built in fans to help with air flow (heli version). I just think that motors are way too big for our school girls. The kevlar skin that we used is way too dense for the skin application. The carbon fiber equivalent material was great and the other airframe came out pounds lighter. I thought I could pay the piper by just putting down more power. It is not going to work that way. We will have to put it in a pusher configuration.

That is one of the cool things about the school girl. We can run with two under-wing motors, as a puller or a pusher. The changes do not effect the airframe much and really are about moving some power wires in the fuselage. It is really convenient. I hope the balsa kits come out well, it should be a great sport flier.

Ok, I guess it should not bother me

I have been researching the Android 2 as a robotics platform. Several people have weighed in to say that the only big advantage of Google's Android 2 is that it is essentially free to distribute. However, it has other overhead that has to be overcome. It has to be recompiled per processor, so there is more to sourcing cpus and instruments for it.

I did find in my rolodex that Toradex has a Limestone PDA kit that claims to boot Android 1.6. I have to keep looking. One of my mad scientist ideas is the multiple chips flying closely together to distribute computing projects into manageable chunks. I will keep looking for more. I am not an EE so it is important these solutions be mostly plug and play.

The only "robot" stuff, that I have found before are canned apps from canned boards. I guess I was thinking robot not rc kit. Yeah, I use a lot of rc stuff, but I am not looking to directly control the devices at every turn. They should have increasing levels of autonomy. However, I do have to say that I like that some companies have the same idea that I do. The kit I have found that has the most coverage is the Surveyor SRV-1. It looks interesting enough, but PIC sucks. ;) An interesting couple of "rc toys" on Android movies can be found at robots.net.

UGV autopilot

Taking the lessons learned from the UAV stuff, I am trying to trim down the UAV pilot to a UGV pilot. The two have different requirements so I am hoping that it can all be put into the mission planner. I have found playing with the UAV autopilot that the event driven solution works well, but is a bit honery.

So I am working on a bus model. Where the individual managers all call into the bus to pass messages, then the bus manages the message delivery. This should decouple the messaging. I was trying to avoid the inevitable hard coding of observers and subjects in the code. This would make the relationships less fixed and hopefully ini-file-able.

I have some other lessons learned about this.

One other question, does anyone have any opinion of Java on Android 2 rather than c#.NET on Windows 7? They would both target netbooks or computer on modules (COM). Let me know if anyone has any practical/constructive opinions of these platforms. info "at" fatmanflying.com

Motors, motors, motors

Did anyone else ever notice that anything truly important must be said thrice for men to notice? Girls, girls girls, XXX, I have a million examples. Just an aside, but interesting to note. That may be why no one ever reads DANGER, and stays away, Or don't click.

This week I have been fighting the forces of evil all week. I know the buzzlabs.us site is not a work of art. It is a work in progress. Yeah, yeah need more pictures. Let's get one step at a time. I found several distributors of NEU motors whose website said, yeah they are in stock. Seems that they need to update their site? WTF still are not online with inventory status... or are not advertising things correctly. If you don't have it, just say so.

Anyway, there I was thinking I had the NEU motors in hand 1912/3Y jobs. however, it seems that there is no such thing as in stock with these guys. They are supposed to be the best. I have been reading that the heli guys dig the X-Era motors from NC too.

I called Dave at X-Era. He was friendly and very helpful. I will keep up with his 4035 3y 400kv motors. He is actually sizing a motor for us to swing these huge props. I am actually pretty curious what he will come up with. The NEU calculator came up with the 1912 line of motors because of the three bladed props. I will post what he says when I get back his response.

If anyone knows of any 5-6 bladed props that would be good to know too. I heard on the boards that Dario makes them. It is my opinion that I can slow the prop down enough by adding blades to lower our planes and reduce the current draw by adding voltage. I would love to get our current draw to 20A at 9s (33.3V) our batteries would last for a lot longer. I think maybe Bolly Props down in Oz may have them, but three bladed jobs though.

I almost forgot

Prototype two's wing is now almost complete. It will be mated to the fuselage hopefully tonight. I must have really bollocksed up using the pattern that I made on the first plane. It is a different diameter than the first. The second prototype has a more tear drop shaped fuselage that the first aircraft. I think it will make it easier to shore up the system with stringers than the purely round shape.

Before we get to actual code...

Before we hop off into any actual implementation, I would suggest that we sit and think about some basics. The very first thing that should be done is to come up with a basic skeleton of the code that you would like to write. This may impact many decisions down the line. Basically, a UGV and a UAS/UAV are the same from the code's perspective. The UAV/UAS use different actual algorithms for certain processes, but the data flow and data collected are not so different. Some data is read, a decision is made, a servo solution is calculated, servos are moved into position and then the system loops again.

One thing that I did, was to develop an object that was a sensor, ISensor. This will be the part that actually interact with any device. ISensorReading will also act as a fundamental contract for data. I would make sure that this object follows in general an observable pattern. That way it is easy to allow other objects to read its data, or to be notified when new data is available. This will make it easy for filtering algorithms to execute and work on the newest data as soon as it arrives. It will also make it easier to make the data collection to be asynchronously collected and processed.

Then I made an instrumentation manager, IM. The IM will have factories for each kind of sensor and observe instances of each of the instruments. This way if something happens the IM can close an instrument and try to reconnect with a new object. In turn, the IM presents data to other parts of the code as needed. No other parts of the code need to see the sensors or interact with them directly.

On top of the instrumentation system, should be a director layer. This will actually be the layer that does all of the work. It makes a nice break line between the device and the presentation, or intelligence. Separating the systems is an important object-oriented technique that is necessary for keeping the code healthy.

More about the director later... I will see if I can get some pictures in to make it easier to see.

What I am Thinking At the Moment

At the moment, I am trying to decide what is the most interesting way to proceed with this blog. It is important to discuss some of the howto aspects of UAVs and autopilots. I think that it is also important to speak about some of the interesting applications and business difficulties of it as well.

At the moment, there are many stories in the news about blowing up bad guys with thunder bolts from the sky. However, I think that this is not the most interesting thing to be done with the technologies. We are investigating a number of small-scale recycled materials and techniques to apply energy reclamation systems so that the uavs harvest as much of their energy from the environment and recycle as much as they can.

For the record, the soybean epoxies available are just not as good as their petro-chemical equivalents. We are still trying to use them in our skin layups. If we can make use of them, they do come from a renewable resource stream. These adhesives are not recyclable though.

Another big idea, that Buzz Labs is working on is the heat pipe system to pull heat away from the motors and batteries and either use that to generate trickle charges or to be able to cool the batteries to a point that we can keep their chemistries from over heating down to the limit of their endurance. Lithium-polymer (LiPo) batteries do have some physical limitations that make exciting failures possible. Read about the exploding notebook batteries. Buzz's engineers are seeing some success with maintaining battery temperatures even above their rated currents. Battery performance increases are especially good news for the racers and autonomous vehicle systems

We will keep you posted here as we make significant breakthroughs or cool flaming rc parts.

Basic Quantities and Some Trigonometry

So You Want to Build a DIY Autopilot

Accelerations

One of the most important quantities for you to measure are accelerations. If your two or more-axis accelerometer is mounted along the traditional axes of the aircraft it will be the easiest to code for. The three traditional axes are:

• From the nose through the center of gravity on the line of symmetry, the Y-axis, roll
• From the center of gravity out of the fuselage toward the tip of the right wing, the X-axis, pitch
• From the center of gravity away from the earth, the Z-axis, yaw
  
     

Figure of Rigid Aircraft Axes

So, now for some basic Trigonometry, everyone remembers SOH CAH TOA.

In general, the following picture is true for a vehicle moving through space.

Figure of the Direction of the Force of Gravitation on a Body

As you can see from the image, the angle of pitch relative to the surface of the earth is the same angle offset of the weight vector relative to the z-axis in the body frame of reference. If we put our accelerometer so that one of its axes is parallel to the body's z-axis at its center of gravity we are measuring this offset vector. Which is really neat, because it means that we can express the angle of the body in level, non-accelerating motion as ratios of the accelerations

Pitch: 

The angle theta between the actual gravity vector and the measured gravity is related to the pitch of the aircraft (pitch = theta + 90°). If we know theta, we know our pitch! Since we know the magnitude of the earth’s gravity, simple calculus gives us our pitch angle:

accelerometer = cos (theta) * gravity

theta = acos (accelerometer / gravity)

And since pitch = theta + 90°

pitch = asin (accelerometer / gravity)

Woot, we calculated the pitch orientation of our airplane using an accelerometer. Pretty easy, huh?

The real formula that we need to use for the software looks like this:

pitch = atan2(accelerometer / gravity, z / gravity)

Common piezo-electric accelerometers return in units of, g, 32.17 ft/s^2 or 9.81 m/s^2. We also know some more things about the flight that let us calculate the angles relative to the ground. More on this later, it is a bit more than basic trigonometry to describe. These equations assume non-accelerating flight. You can use a magnetometer to get the relative plane in space with less math, but magnetometers generally take more interface programming in my experience.

Roll:

Roll needs a second accelerometer with an axis perpendicular to the first so that we can figure out the resultant vector between them and then the angle. Essentially the vector between the accelerometers becomes the "gravitational" acceleration and the relative readings lets us calculate the angle with an atan2 function. The second accelerometer will have some other things to manage such as the effects of the distance between them on the accelerations measured. Physics fun and none of the boring class.

Yaw:

Yaw is the hardest of the angles to measure. The only answer is to use a magnetometer or a compass. In many ways, yaw can be solved by dead reckoning. Dead reckoning is all that is important for most of the projects in the DIY garage. They will be covered later.

Next we will discuss gyroscopes and the beauty of rates and integral calculus

How I started writing a DIY Autopilot

My intention still is to write my own c# based autopilot. It is not trivial as I found out. Lots and lots of details are needed. The first thing that needs to be done is to determine the instruments that you will need to measure the quantities that you need to know to control flight. Even this seems to be a matter of opinion. For a reference, I found every group that I could that was writing their own version.

From my perspective the quantities that we need to know to control flight are:

• air speed, ft/s or m/s
• altitude, ft or m
• orientation, roll, but pitch is good

These are intrinsic quantities that are really easy to do yourself. Air speed is the model's forward velocity. Altitude is the vehicle's position relative to the surface of the earth. Pitch and roll are the angles of the vehicle relative to the ground. Let me rephrase that, roll is the angle between the right wing and a plane parallel to the ground. Pitch is also known as angle of attack. Pitch is the angle between the plane at the center of the vehicle located on vectors from the center of gravity to the right wing tip and the center of gravity to the tip of the nose and the relative wind.

At the beginning you will need to measure the following quantities:

• air pressure
• acceleration in at least two directions
  

Pressure taps are the easiest ways to measure air pressure in a flying vehicle. Piezo-electric accelerometers are cheap these days and are really accurate. In the next post we will talk about issues with these instruments and the physical quantities that you are actually measuring and how to use those as a basis for a control system.

For all of those inch haters, a quick note about units. You can do this in any unit system. It is unimportant. I will write a quick post on the conversions between the US Customary System and the metric (mks) system. Remember metric is actually several unit systems in one and you have to keep them consistent. Oh, and for those trying to buy nuts and bolts, Japanese manufacturers use odd metric sizes, European use even metric sizes, and the US Customary System/SAE is in units of 1/64th of an inch. So SAE/SAME will have three bolt sizes for every bolt size in the two metric systems. Remember that the thread counts are different though.

In my opinion, if the units are managed consistently then the issue is one of presentation to the user. Part of the display system of my code will show you how to do this with a simple object oriented approach.

Squadron Badge Ideas

Every squadron needs a symbol. Some research into the oldest American squadrons lead me through some interesting history. More filler for my head, I must admit. From two of these, I drew up some low color variants. Let me know which looks best out of each group.

US UAV Squadron

Jolly Roger	Jolly Roger with Triangles	Jolly Roger Round
EU UAV Squadron
Felix Beer	Felix Camera	Felix Bomb

Let me know which you guys like best. email

Tiny 2.11

I need another u.fl connector-based antenna for the ground station XBee Pro modem. I found some at Sparkfun. Per advice, the best plan is to go for the cable and duck route. All of the electronics will be boxed to make them easier to shield from the high current wiring from the batteries to the ESC to the motors.

My current plan is to use:


SMA duck antenna

u.fl to SMA cable

Tiny 2.11 Out of the Box

For those of you following these projects, I have tried to wing an autopilot myself. It actually is getting there, but I thought. Better to get to market with a product before we spend five years debugging stuff that was just a dead end to begin with. I was reading around about each of the other projects on DIY drones. I was considering the Ardurino autopilot, but was a bit concerned of writing ANSI C at a register level. So I went with the Paparazzi autopilot which is well received and more finished to a level where I was willing to get my feet wet.

I got my Tiny 2.11 from Chebuzz in California/UK.

"unpaid recommendation" The guys at Chebuzz are great, I do suggest buying from them. They are better priced for the American market than the other assemblers, have great service and are willing to answer even my bone-headed questions. "unpaid recommendation"

Out of the box, well it came in a normal padded envelope. I was eagerly trying to figure out what each board did. Having returned from vacation, I had forgotten what I had learned. So, here are the parts I received from the "Everything You Need" kit from Chebuzz.

XBee Pro modems
modem0modem1modem2modem3modem4

Main Tiny 2.11 board with pico blade connectors
top
bottom

ESC throttle wire
black and white two pin

The "Fat Man" Is Still Grounded, He Is At the Pub So We Won't Worry Just Yet

Yeah, this kind of sucks. After a year of construction and planning, we find out that there is an international weapons treaty that says that you cannot sell certain weight vehicles internationally that have autonomous guidance systems capable of free flight beyond a certain range. Ok, I get it. Who wants Tom, Dick or Harry building a 150lb (70kg) pop rocket and flying it half way across the planet to make a real mess.

When you think about it, they are just setting rules to make it hard for the forces of evil. I have no interest in being one of the "dark side." My master tells me so. Ok, no more Star Wars references, but I make no promises. If anyone knows more about the "". Or what the real rules are about any of this, please let me know. There is no interest in using this device for any government purpose. I want to pull banners at the beach or to do small scale spraying of crops.

Another question that would be great to hear some explanation of and/or some reasonable listing of what can be discussed between international unmanned vehicle (UAV/UAS/UGV) colleagues. I would hate to blip someone's radar because I was talking about a simple guidance system idea at the pub. Yeah, yeah this is a real problem, I am more likely to be drinking a pint than trying to sink a 40' put on the back nine of Pebble Beach.

I am pretty sure that this is a messy topic and probably best left well-enough alone. However, if there is a chance to get this sorted and get the Fat Man to fly as more than a giant-scale RC plane that would be freaking awesome. Any qualified help is appreciated, I know that the FAA has been pretty draconian in their official guidelines.

Chebuzz Paparazzi Tiny 2.11 Autopilot Setup

I will start posting my adventures in setting up a Chebuzz Paparazzi Autopilot. It does not seem to hard, but there are always hitches to these things. I have the equipment, I will post some pictures tonight or tomorrow.

I bought an "everything you need" kit witht he Xbee Pro 2.4GHz modems. I had some questions from the Chebuzz guys, and I will gladly post their responses to the blog as they come in.

One of the things that I would like to cover here is the construction of some airlock boxes for the Tiny 2.11. That way there is no cable tension on the devices themselves and we will have some nice boxes to mount inside the fuselage. It is not very professional to just stick boards into fuselage, there can be all kinds of issues if they are not properly secured.

What the Heck Are the Real Rules?

I have been canvasing anything that says UAV and not Boeing, Lockheed or General Atomics for several years now. One thing that I have noticed is that few if any sites even mention much less brag about Special Airworthiness Certificates or even Experimental Flight Airworthiness qualifications for their UAS. Knowing that they seem pretty tough to get still, I would think that they would happily brag about the fact theirs received one.

So how are they making money? Is this some sort of strange smoke and mirrors game? If you do not have a certification you are not allowed to fly in the United States' airspace. So how are they doing it? I know way back when in 1998 they flew from New Foundland to Ireland, major props for that. Back then noone really cared or probably knew to care. What about now? As I read it on DIY drones and other places the rules are pretty clear, no commercial and LOS. I get it, it seems like a good idea to film the kids' soccer game with your UAV. It does right up to the part when the LiPo packs overdraw and now you have a really cool shot on goal.

As a matter of fact, it took me a few minutes to come up with that example. Most of mine were far more brutal, but that seemed to be a happy medium. Little Jimmy running away as dad's new rc plane which was an ARF and still took him two weeks to build catches on fire. Mom's new HD camcorder and all comes down in a ball of wicked fire streaking toward the goal. Oh no, Gahd'zee'ra. Always have to have the monster movie reference when a flaming anything streaks across the sky. Mothra could not shoot flames.

Does anyone have any ideas how these companies stay afloat? Is it just a better marketing face than balance sheet? I can say that I am intrigued how you can be much bigger than a room in the garage sized company under the current regime. I guess maybe there is a private property application here, maybe that is enough to keep you afloat. At least in the , what they do not know, will not hurt them ballpark.

Wicked Hard

Having never scratch-built an rc plane with mixed-materials it is pretty tough to get it right. Yeah, I suck, but this is more than that. Over the last two years my co-conspirators and I have tried about every technique to repeatably build airframes. We have come full-circle now and say that a normal composite construction system is probably our best chance to make a good quality product with the least effort.

Try to epoxy carbon fiber and Aluminum together, you will get sticky fingers and big globs of epoxy everywhere. It will eventually fix the pieces, however we find that we cannot get a great bond this way. You can scuff and sand all you want. The epoxy does not do more than touch the surface of either part. Meh. It works and you can do it, do not get me wrong. The difficulty involved is a bit more than I think is necessary. We are running some experiments now with some almost ready to fly (ARF) models. Sacrificing a few models to the Gods seems a good start, and par for the course.

At least they already have all of the places for servos, spars and wire harnesses precut and in a reasonable place. Why reinvent the wheel, we have our own wheels but need to practice a construction technique. It is a well-documented idea in the composites industry. Essentially we make negative molds that allow us to control composite gauge in the best places and create bumpy sheets of composite. These sheets are bonded and reinforced as needed. Finally, they are covered with a material so that they may be painted or have decals applied.

I will include some pictures a bit later when we get closer to a final product. We noticed that alignments are still an issue. Aligning six pieces is really easy compared to aligning and balancing forty pieces. That is really silly in my opinion. We tried a bunch of techniques to make airframes consistently. Maybe next time I will talk about some of our creative failures. None were failures, but some took a lot more work than others or cost a small fortune.

We are trying to be Orville and Wilbur-like not like that other guy. The Wright brothers got off the ground for less than $2000 and their main competitor was funded by the Army and had something like 50x their budget. He even built a special barge to take off from and that never worked either. It is time to get a good rugged system in place so we can go into nearly serial production of the airframes.