Getting back to normal

Well, this is just a post to say that things are getting back to normal after the great fuel disaster of 2016. We put in 2 new tanks and, what do you know, one of them had a hole in it. So now we have that taken care of and seem to be holding fuel.

So with all that sorted, we turned our attention to getting all the avionics back in place. It took quite a while as the companion computer and SSD threw off the layout of the avionics tray, but everything is pretty much in order.

Why yes, that is a 4-port USB 3.0 hub. Your drone doesn't have one of those?

And Patrick got the payload tray pretty much squared away. Now we just have to sort out the mounting/vibration damping part.

I'm still planning to write that tutorial on the companion computer setup, hopefully I'll have time to work on it later this week.

Mugin Updates

Well, it is about time for some more updates on the Mugin. I'll try to go point by point with what has changed since the last post.

The biggest news is that it has flown! We have done a few hours of flight testing including auto flight and everything seems to be working well. With that vibration damped avionics tray seen earlier, there is actually less vibration reaching the IMU on this aircraft than on our electric planes... We have done some early testing on fuel burn and the results have been a little disappointing, but we are re-tuning the fuel injection and may get a little better performance out of it. As it stands, I think we will get ~3-4 hours of flight time. With proper flight planning that shouldn't actually be much of an issue. And, flying longer than that means our 256GB SD cards for the A7ii won't be big enough and we'll have to find another way to store the images.

Waiting to fly

A little photo shoot

Now, some bad-ish news. A pinhole leak somehow found its way through the plane over last weekend. We discovered it on Tuesday when we pulled the canopy off and found the fuselage filled with about half an inch of fuel and all the printed plastic parts melted into goo. Thankfully, no electronics appear to have been damaged as they were all mounted on their elevated platforms. After a couple days of brainstorming, I ordered a pair of the 100oz tanks we use in Mugin 1.0. It isn't the perfect solution but it will get us flying until I come up with something better. I'm thinking maybe a custom aluminum tank...

We didn't get any pictures before this point, we were rushing to get everything out of the fuel

Goo

Stripped bare

The good thing that came of this is that it forced us to strip the aircraft down to the airframe and start anew. That means we were able to go back and rewire and clean some things up that we probably would not have bothered with otherwise.

Pretty wiring

More pretty wiring

A beautifully designed JST power distribution block

So all in all, it wasn't all that bad. I'm just glad we didn't have that fuel leak down in Peru...

Ok, on to other things. The alternator and power system arrived a couple weeks ago. There were some fitment issues and growing pains but it is all installed now and it works flawlessly. It provides clean 7 and 12V supplies to the aircraft that are backed by the alternator, battery backup, and a shore power connection.

That alternator sure does look good... It almost looks like a big brushless motor (which, I suppose, is precisely what it is)

The first motor test with the alternator installed.

Also, we have done some testing with the new IP radios, including range testing. With the 23 dBi antenna and the amplifiers we were able to get a mediocre link at 85 km. We have ordered a 30 dBi dish that should give us the mythical 100 km, or at least get us close. Hopefully we will have that soon so we can get back to range testing. In the picture above, you can see the amplifier mounted fore of the avionics stack. And, I'm also about to get to work on the antenna tracker. Version 1 wasn't robust enough so we go a Yaesu G-5500, which is way overkill but will do the job. I just have to build some control circuitry for it and interface it with the Pixhawk.

Finally, a teaser. I've been working on a companion computer to simplify the electronics inside the aircraft and provide us with some computational horsepower if we every have applications that need it. Using an oDroid XU-4, the core functionality is:

• Forward Pixhawk Mavlink stream over the IP network to the ground station(s)
• Pull images from the Micasense RedEdge and save them to an SSD
• Stream video from the nose camera over the IP network

All of these functions have been bench tested and are working. I expect a couple issues will pop up when I install the system in the aircraft but it shouldn't be too bad. The video is great, with only about 0.5 second lag and great quality (especially considering I've limited the bitrate to 1 Mbps). In addition to these 3 functions, we have a few more that will be forthcoming:

• Data logger function for (non-avionics) sensors
• Payload control
• Forwarding of auxiliary telemetry (motor health, fuel level, etc)
• Saving data from RGB camera (maybe Sony, maybe something else)
• More?

I hope to soon be putting together a tutorial on how to implement those 3 core functions on the XU-4 as there isn't a good one yet. Further companion computer discussion will have to be saved until then. I have waxed on long enough. 

Part 107 and more

Well, it's official, today I passed the 107 test. I did pretty well on it, although I was aiming for over 90 and fell just short. All in all, I thought it was an excellent test that will ensure that yahoos who buy a Phantom on Amazon can't go out and sell their services while endangering the public, or at least not legally. It isn't easy, but that is a good thing as it will absolutely advance the industry and start to build the credibility we deserve.

If you're looking for some insider info, I'll provide a few pointers:

1. Know. Your. Charts. Charts are a HUGE part of the test. My estimate is that they comprised about half the test. I thought I was pretty squared away on sectionals but I still missed 3 or so questions on them. You will need to be able to interpret charts to answer multi-level questions. Further, you will be expected to understand the 107 regulations and determine what is and is not allowed in complex airspace delineated on charts.

2. Know the more obscure parts of 107. Of course you should know that you're limited to daylight operations (or civil twilight with anti-collision lights visible for 3 SM), 87 kts, 400' AGL, 3 SM visibility, 500' vertical and 2000' horizontal cloud separation, etc. But you will also be asked about the non-operational aspects of the rule, too. Be sure you know accident reporting requirements, registration rules, rules about your airman certificate (once you have it), etc. You will have multiple questions on these non-operational aspects of 107.

3. Understand performance. This material isn't inherently more difficult than the rest, but it is easy to get confused, especially if you aren't already familiar with the physics behind how an airplane flies. Know how CG affects performance. Know how loading, including dynamic loads (i.e. turns) affect performance. And know the difference between pressure and density altitude as well as their effects of performance.

Well, that is it for my 107 advice. Now for a couple quick updates on the Mugin. The biggest thing is that I've been working on getting wiring installed and mounting up all the electronics. The wiring isn't looking quite as clean as I was hoping but it isn't bad. Once it is all said and done I think I can make it look pretty nice.

White 3D-printed blocks are epoxied to the fuselage structure and small carbon plates are permanently mounted to those blocks. Vibration isolators then attach the avionics stack. It is hard to see here but the Pixhawk is mounted bottom center, the Piksi is bottom left, Dragonlink bottom right, and Powerbox is on top. Microhard radio will be mounted beside the Powerbox once I get a functional case printed.

The avionics stack will hold everything you see above plus the Microhard radio. The radio amplifier, PMU, and backup battery will be mounted just behind the nose gear. I'm planning to rail mount them so they're adjustable for CG.

Also, I fully assembled the plane to show off and got some pics of it with v1.

The fleet looks nice, doesn't it?

Well, thats it for now. Look for another update in a few more days once some more electronics are in (and hopefully servo linkages for the flaps are here).

Mugin Updates

Here is the latest on the Mugin and a few other updates. First of all, I got the fancy fuel-injected motor mounted to the bench, ran it, and then got it mounted on the plane. That is one big step toward a maiden. Also, it is insanely powerful, as compared to the Saito FG-57, so this plane will have much better climb performance, payload capacity, and ability to fly at high altitude.

Servos are all in and wired up. I still need to make the wiring harness for the fuselage but I'm taking it slow until I get all the electronics mounted in their final locations. And, speaking of, I just finished the custom vibration-damped avionics stack. Hopefully it does its job and doesn't end up amplifying vibration...

All the parts are in except for the alternator and radio amplifiers. Hopfully those will be in soon so we have everything we need. In the meantime, I'm going to finish up getting the electronics we have mounted and wired in. Also, I got around to powering up our Micasense RedEdge today. It is an impressive little camera and it took me no time to get it triggering off the Pixhawk. It is really configurable, which is nice. It means that on the Drak we can simply pull out the QX-1, unplug the trigger from the servo wire, plug the RedEdge into said servo wire, and we're ready to roll.

The other major thing I'm working on is an accuracy comparison of DroneDeploy, Photoscan, and Pix4D. I'm using the campus imagery from 2 years ago, which isn't the best dataset, but it is at least a real-world example. I have a CAD file for the entire campus so I'll be measuring points in it and comparing to their position in the imagery and elevation in the DEM.

There's bound to be some kind of mischief I can get into having all this information...

Well, that's it for now, I'll update in a week or so, hopefully with a nearly-ready-to-fly plane.

The latest from the Skunk Works

Well, it has been quite a while since the last time I posted on here, huh? It looks like the last time I was posting about endurance quads. Well, I still hate quads but we do have some updates since then.

First of all,  the more mundane stuff. We have a fully functional Ritewing Drak. I built one earlier this year for a client and since then the lab has picked one up. It is a really excellent platform that carries more payload, faster, longer than a Z3. It is basically better in every way. The only downside is that it is significantly bigger (1.5 vs 1.2 m wingspan). Here is a picture:

This isn't actually ours, this is the one I built for a client and currently resides in Canada. But you get the idea.

Ok, now on to the really exciting stuff. We are gearing up for another campaign in Peru but, this time, it won't be with any anemic little electric plane. We are building V2.0 of the 3m Mugin and it is shaping up to be pretty incredible. A lot is different from the first, including the airframe. The newest version of the Mugin airframe has a lot of improvements including, but not limited to:

• Carbon fiber fuselage frame (formerly wood)
• Thicker fiberglass fuselage skin
• Fiberglass wing and tail skin (formerly wood)
• Improved fuel tank (so we might not be throwing this one away immediately)
• Beefier main landing gear (unfortunately still the same crappy nose gear)
• Flaps! (split flaps, at that)
• H-tail providing redundant elevator and rudder

And then there are the improvements I'm making to the guts. Again, including but not limited to:

• DA70 motor modified by HFE International for fuel injection
• Sullivan UAV 300W alternator and power module
• Microhard pDDL broadband data links (for telemetry and video)
• TriadRF RF amplifiers (to boost that pDDL and get us 100km range with the help of...)
• Actively tracked 23 dB parabolic grid antenna on the ground
• All around better avionics mounting, layout, wiring, etc and a variety of custom 3D-printed mounts for different bits and pieces

So, it is shaping up to be pretty exciting. I've put some picture below to show off the goods and I'll post again sometime soon(er than last time).

Thats one helluva antenna

V2, with V1's fuselage in the background

Mmmm, redundancy

Love me some EFI

Enduroquad Success

2 EnduroQuads ready to take flight. Both carry 20 Ahr of 4S. Ours, on the left, has a Tarot 2-axis GoPro gimbal as payload and the one on the right has a 6600 mAhr 4S standing in for a Sony a5100.

Well, as I mentioned in my Vibration Consideration post, I have been working on new iterations of an endurance quadcopter. Today I cleared the final hurdle in declaring it ready for use: I flew it in Auto. As I mentioned before, I have seen this quad (and others) descend in forward flight while in Loiter or Alt Hold, so I was a little worried about how auto would go. The only thing to do, though, was to give it a shot. So, I gave it a plan to fly a grid over Davis Field and let it rip. It was basically flawless. After it finished and began loitering at the final WP, I restarted the mission, and let it go again. Then I put it in RTL and let it autoland. Finally I restarted the mission, took off in Loiter, switched to Auto, let it run, and then did an RTL and autoland again. All in all, it was really nice with no significant altitude loss at a 6 m/s cruise.

Screenshot showing 3 auto flights using the same flight plan. Note the excellent agreement between all flights (orange, green, and pink)

Here are my more detailed notes:

• Upping rate_yaw_P to a the healthy value of 0.28 (from a default of 0.2 and above the "maximum" value of 0.25) fixed the issue I had with the nose wandering around. I'll say, this behemoth needs some huge PID values to make it fly well.
• I did observe altitude drop at the end of transects which is well known to the APM community. This seems to be a physical barometric pressure issue and there doesn't really seem to be a workable fix for it. I have never seen it present a problem, though, as it has always been a controlled loss of about 1-2m altitude which is then regained.
• Copter 3.2.1 doesn't like to land on a slope. In both autolandings I had to switch to Stabilize with the throttle down as the landing detector didn't kick in with the slope there. The changelog indicates that this may have been fixed in 3.3 (they added "improved landing on slopes"). I will find out when I test the bigger EnduroQuad which has 3.3. I will also likely upgrade this one to 3.3
• Takeoff in Loiter is quite nice. The devs have done a considerable amount of work with this in recent releases and I now find it to be a less dramatic way to get out of ground effect than punching the throttle in Stabilize.

So, that is pretty much it. My plan for the rest of the week is to get a few more hours of time on our quad and get a few Auto flights in on the bigger quad to convince myself that they are both 100% mission capable. Then it will be on to all sorts of fun projects like using TIR imagery to census lions, tigers, and bears at the NC Zoo and deer at Pilot Mountain. We are also planning to use it to identify energy leaks on some buildings around campus.

Good to be productive

I have been hating on mutlirotors quite a bit lately, and for good reason. Our planes are easy; they work every single time we need them to and they do exactly what we need. They are easy to set up, easy to use, and they get results. Multirotors, on the other hand, tend to be a huge pain to get operational as they are super sensitive to vibration (see my earlier post on this topic) and when they fail they tend to fall out of the sky. I basically have felt like I was spinning my wheels for the past few weeks with the multirotors.

The past couple days, though, I made a lot of progress. First I figured out the vibration and altitude hold problem I had been having. That got alt hold and loiter working quite well.

Today I maidened a second endurance quad with larger motors for carrying a Sony a5100 and gimbal. After a little tuning it flew really incredibly. I think I have as much confidence in it's stabilize performance as any other copter I've flown. It hovers at just under half throttle, it has tons of power, and it flies like its on rails.

I also did some testing with the Swift Navigation Piksi RTK GPS system, which will go on the heavy lift endurance quad. The first thing I noticed is that it is insanely simple to use. For basic positioning you simply connect both Piksis to telemetry radios, power them up, and connect to one over USB or serial. Then you wait 10-20 minutes for it to get an RTK lock and at that point you get centimeter accurate relative position precision. I wanted to verify that advertised accuracy so I measured the distance between the antennas and compared it with the distance reported by the software. I was amazed, the RTK distance varied within +/- 2 cm of the measured distance. I haven't installed it on an aircraft yet but I'll report back in when I do.

With all that good news, I did have a couple problems today. First, Enduroquad 1 had a very odd issue in flight. The controls were all delayed by about a second and changed in a stepwise manner, making it quite hard to get back on the ground safely. I would give input, it would come into effect after about 0.5-1 seconds, stay at that input for about a second, then update to whatever input I was giving at that point. I gave up on troubleshooting it in the field but when I got back to the shop I determined that the Dragonlink was at fault. I had upgraded to a new transmitter and it turns out it has a new firmware version. Even though I fixed it, this does seem to be a significant safety issue to me, as firmware versions should either be compatible or not. There should never be a case where the RC system only partially works. I might report it as a big to Dragonlink but I doubt they would do anything about it...

The other issue I'm having is that both quads are losing 1-3 m of altitude during fast forward flight in loiter or alt hold. I had observed this behavior before and thought it was an air pressure issue. So I used my lessons learned finding vibration and did the same for this. Here is what I found:

Here we have pitch in yellow, target altitude in green, barometric altitude in pink, and calculated altitude in red. When you see sustained positive or negative pitch that means the copter is in forward flight. As speed builds, you see a lot of noise in the barometer and a gradually increasing calculated altitude as the barometric variations slowly cause deviation from the accelerometer readings. Then when the copter stops you see that altitude plummet, as the copter has actually descended but doesn't know it until forward flight stops. Then you get the gradual return to target altitude. The noisiness of the barometer signal makes me pretty confident that this problem will be solved but putting a cover over the pixhawk to hopefully prevent airflow around it and only allow real pressure changes. We will see how that works out tomorrow...