Phantom 4 – Max Motor Speed Reached

You’d never know it from the high of 85deg today, but the leaves have finally started to change for the season here in North Alabama, so I took my Phantom 4 up this afternoon to get a few shots of the Fall colors.

South Hartselle Fall Afternoon

South Hartselle Fall Afternoon

I’ve been getting more comfortable flying the Phantom, so after I got a few shots I decided to go a little higher than I’ve ever gone before. The legal limit is 400ft AGL, but I’ve never been much higher than 200. Starting from about 120ft, I climbed gently for a few seconds, then gave it max throttle to see what she could do. The drone shot straight up into the air, crossing 200ft in seconds. After a few seconds, my flight display showed a warning “Max Motor Speed Reached”, so I let off the throttle and the warning went away quickly…but immediately my heart started to sink, as the video feed from the drone showed that it was falling from the sky.

I could still see it above me (this was a more or less straight up and down flight), and I could hear the motors changing speeds up and down rapidly. I experimentally gave it some throttle and could hear the motors speed up and see the fall slow down on the video feed, so I could tell I still had some control. Over the next several seconds, I continued to feather the throttle, giving it just enough to keep the sink rate slow but not daring to hold constant throttle against the fall. Somewhere above 100ft, it stopped losing altitude and hovered in place. I landed gently and found no damage upon inspection; neither the motors nor the battery were even particularly hot.

A propellor is just a wing that gets its lift from moving fast in a circle instead of fast in a straight line. Just like any other wing, a propellor can stall. When a wing stalls, there isn’t enough lift being developed to keep it in the air anymore. I am not an aeronautical engineer, so my analysis could be wrong here, but I assume a quadcopter can stall because I do know that helicopter blades can stall: see and

Just as an intellectual exercise, I decided to perform a little investigation. According to Wikipedia, a helicopter blade stall can be caused by any of the following factors:

  • High gross weight
  • High airspeed
  • Low rotor RPM
  • High density altitude
  • Steep or abrupt turns
  • Turbulent ambient air

We can rule out some causes easily. High gross weight: I haven’t added anything to the craft, it is as it came from the factory. Low rotor RPM: according to the warning message, I was in the opposite case. Steep or abrupt turns: I was climbing straight up.

Density altitude had actually been my first thought when I realized the propeller may have stalled. Today was a pretty hot day after all, I figured. It’s not actually the most likely cause, but let’s work it out anyway. Because the air gets thinner as you climb, a wing has to go faster to develop the same lift at higher altitudes than at lower ones. Temperature and pressure affect this too (as in high and low pressure systems, from the weather report), since air expands (gets less dense) as it gets hotter, and a low pressure system literally means less dense air. Density altitude is a formula that tells you how high the aircraft “feels” that it is, taking into account temperature and pressure.

I live pretty close to an airport and have an app that gives weather and altimeter for other nearby airports as well, so I gathered or interpolated the following information, based on the available information for the closest airports:

Altitude: 692ft MSL
Altimeter: 30.14 inHg
Temp: 81deg F
Dewpoint: 50deg F

MSL means “mean sea level”, so the measurement above means that ground level where I am is 692ft above sea level. AGL means “above ground level”, meaning the actual distance above the ground. The numbers above are all approximate, b/c 1. I’m not the NTSB, and 2. the stakes are pretty low here. For instance, I used the reported altitude of the nearby airport even though I was actually launching from higher ground, maybe 20 feet higher.

According to the flight log kept by the DJI app, the highest altitude I reached was 282ft AGL, so that puts me at 692ft + 282ft = 974ft MSL. Plug all those numbers into a density altitude formula and I get 2515ft, so at the point where the drone started falling, it’s as if I was flying at 2515 feet above sea level, though I was actually only 280 feet above the ground.

(I want to point out here, for those who may have missed it, that density altitude is a measure of performance of an aircraft, not an actual height above the ground. My max height above the ground on this flight was 280 feet. Flying a remote aircraft at 2515 feet anywhere, much less near an airport, would have been both dangerous and illegal in my circumstances.)

I couldn’t find any official numbers on this, but I found one reference online that the service ceiling of a Phantom 4 is 19,685 ft. More importantly, I found many people in online forums reporting that they use their Phantom 4 in places like Colorado, at density altitudes around 8000 to 12000 feet. So it should be safe to say that I didn’t exceed the capabilities of the drone flying at a density altitude of 2515.

Wind this afternoon was calm. I was going straight up and down so I should have been in the same air column the whole time. That doesn’t necessarily rule out turbulence, but I think it makes it less probable.

That leaves high airspeed, and that is my best guess: I accelerated so quickly that I reached a vertical climb speed that stalled the propellors. The motors tried to compensate by running all the way up to full speed. Stalled, the craft lost altitude until the combination of the craft’s flight controller and my own feathered inputs got it back under control. That’s my theory at least.

Edit: After a good night’s sleep, one other possible cause occurred to me: altimeter error. Every time you take off, the Phantom 4 counts your current position as altitude zero and displays your altitude then as an offset from that. One thing I failed to mention above is that the log for this flight showed an altimeter reading of -26ft at landing, though it started at zero and I launched and landed from the same spot. I originally chalked that up to the device failing to track altitude change during the time that it was falling, but I didn’t look into a mechanism for how that could happen. I researched it this morning and it turns out that the Phantom 4 uses a barometric pressure altimeter. I did do something just before the flight that may have affected the accuracy of an altimeter: I took the Phantom from inside (about 72deg F) to outside (about 81deg F). Air density decreases as temperature increases, so if the device was just hovering in mid-air, not actually moving, but warmed up to ambient outside air temperature, it may have “thought” it was gaining altitude and tried to compensate.

I’m not sure if that really tells me anything, though. Presumably the unit had done some warming to ambient temperature before it self-calibrated upon being turned on, so I could cherry-pick any intermediate temperature that worked and say that accounts for a 26ft drop. Further, though I was paying more attention to keeping the drone out of free fall than I was the altimeter, I am fairly certain that the actual drop was greater than 26 ft. Regardless, reading the DJI forums, it sounds like the general consensus is that the barometer in a Phantom 4 does experience temperature-driven inaccuracy in its height readout, but the effect is small, and it’s common for the height to drift by several feet during a flight. I still have a feeling that the -26ft landing height is telling me something about what happened to the drone at the apogee of its flight, but I don’t know what.

Hartselle Depot Days at Dawn 2016 – Drone Video

I helped my wife set up a crafts booth to benefit my daughter’s dance class at the yearly Depot Days festival in Hartselle, AL this morning. Just after sunrise I snuck up the hill for a minute to get this video of the vendors starting to set up for the festival day to come.

We also got over to the annual fly-in at Moontown in the afternoon. I have a little video from there too, which will be part of a Moontown-specific video I’m going to do later, but today was mostly a bust there: cloudy and drizzling with a ceiling touching the tops of the surrounding mountains all day, and nobody flew in or out while we were there. Pretty though.

Screen Shot 2016-09-17 at 6.26.14 PM

Getting Started with Flight Training – My Plan

I’ve just posted the first video in a series I’m doing on my journey toward a private pilot certificate (aka a pilot license).

A short trip in an old Cessna last year and the purchase of a drone several months ago reawakened an old desire to learn to fly. At first, I just started flying in X-Plane, a flight simulator, which is what I had done before when the bug hit, but this time a confluence of events led me to start seriously considering the real thing.

So back in the spring I started taking a video ground school and studying everything I could get my hands on, and spent some time looking at various options for how to start flight training.

This video is the first in a series where I’ll document the approach I’ve decided on for getting from zero flight hours to a private pilot certificate. This video series is an experiment. My idea is to document what I learn along the way, not so much about how to fly (the industry and the Internet have that well covered already), but about my journey from here to there, told as it happens rather than in hindsight.

This is an exciting project: I’m putting this major life goal out there for the world to see before I have the accomplishment well in hand, and that’s something I’ve never been very comfortable with. I prefer not to talk about things I’m working on, or working toward, or “gonna do someday”, because we all know the guy who’s always going to do something. So publishing this series is my way of affirming that all the other thousand things that can and do prevent someone from earning a pilot certificate will not in fact prevent me from earning a pilot certificate.

First Flight as Remote Pilot in Command

I flew my first official drone flight under my new Remote Pilot certificate today, to get some footage for a video.

Hartselle from the Air 2016

I only got my drone, Geary, a few months before the text of FAA Part 107 was released. The rule for hobby flight under Part 107 and for the rules that preceded it is that you must notify any airport within a 5 mile radius of your flight. However, all my flights prior to getting my certificate were no higher than treetop level, so I interpreted that rule to have something like this appended: “unless you’re flying so low that nobody wants to hear from you about your piddly drone flight and the only possible traffic conflict with a manned aircraft is from one that is already in the process of crashing into you.”

Today, I planned on going up to about 100 or 150 feet above ground level (AGL) to get some nice shots of the town, which is above the treetops around here. As a remote pilot certificate holder, that 5-mile notification rule is relaxed for me: I don’t have to notify anybody, so long as I’m not in controlled airspace (meaning, not near a larger airport) and am staying out of airport traffic patterns. I planned to fly at my parent’s house, which is near the middle of town and about 2mi NNW of the local small airport. Though I never saw a plane fly as low as 100ft over that house the entire time I was growing up there, I do occasionally see them pass over at maybe 1000 feet, possibly on their way to join the left downwind for runway 36. Two miles out is too far to be only 150 feet off the ground on landing, and I’d only be up for about 5 minutes, but it only takes moments to cause a problem in the wrong place at the wrong time, and it seemed the neighborly (and safe) thing to do to stop by the FBO at the airport and let them know I’d be flying a drone a few miles north later in the day. There is a phone number for them in the chart supplement, but I live nearby, so I just drove over.

This is a tiny FBO, the kind of place that only has one person on duty at a time, so the lady I talked to at the front desk was also the management on duty and manning the Unicom, and I’m pretty sure I’ve seen her out there mowing the lawn before too. She was very nice and had no objection to my flight, but she also had a deer-in-the-headlights look that told me receiving a notification of an upcoming drone flight was a new experience for her. Though I know there have been other drones operating within 5 miles of that airport (I’ve seen the footage), it is entirely possible that I’m the first person to try to notify them.

One example of how new these rules are, and how airport operators definitely should not be relied upon to know them yet, is that when I told her that I had a handheld radio I could use to monitor for incoming traffic (for those manned aircraft that bother to call their approaches), she suggested that I respond to anyone who calls to let them know there’s a drone up. This is definitely not the FAA policy — they are pretty clear that you’re to monitor, not transmit, if you’re monitoring CTAF on the ground during remote flight operations. She did also offer to warn anybody on approach to watch out for the drone herself, and per my understanding that would be the correct procedure since the FBO is licensed to transmit, while I am not. My plan for the foreseeable future is not to communicate with manned aircraft, but rather to get the heck on the ground if I see a plane coming my way, or hear a transmission that implies one will be soon.

By the way, the flight went off without a hitch and I got some nice panoramic shots of town for my video.

Convincing Google Inbox to let you login

If you’ve ever gotten stuck unable to login to Inbox because it can’t be convinced to choose the correct Google account (e.g., looking at the screen that says “Using Google Apps for Work? Your admin must activate Inbox for work.” even though you also have a separate personal account you’re using with Inbox), this post lists the ways I’ve found for dealing with that.

Continue reading

Upgrading Ancient WordPress Versions

You notice time slipping by faster as you get older, but I didn’t realize until today just how _much_ time had passed since I migrated this site to WordPress. The server has been off more than it’s been on for the past few years (to the point where one might question the truthfulness of calling it a “server”), but I’d like to make an effort to keep it up most of the time the way it used to be, so I decided I’d better upgrade WordPress. Turns out I’d be going from WordPress 1.5.2 to 4.0 – a jump of about 10 years.

Long story short, WordPress 4.0 can’t automatically upgrade a 1.5 database to 4.0 (not surprising), and it accomplishes that failure with log messages in /var/log/apache2/error_log about incorrect SELECT statements rather than with a nice “You’re too old. Fail.” message. What ended up working was to download a sequence of older versions of WordPress and let it do its automatic upgrade several times. So I downloaded 2.0, upgraded, downloaded 3.0, upgraded, then downloaded 4.1. The fact that this post (hopefully) appears will be my proof that it worked.

Siri Spring

A few weeks ago I asked Siri to “Remind me to clean the grill for the Spring.” This morning it reminded me — it had apparently figured out what I meant and just picked up a day in early spring to set the reminder for. That’s cool.


I’ve had a Nest for just under a month now. It’s too early to see whether it’ll really help with the energy bills, or if the only real benefit is having a working HAL 9000 hanging on the wall.

This morning I was thinking through possible next steps for that kind of technology, that maybe Siri 9.0 will figure out that I’m driving home for lunch today (which I only occasionally do) and automatically tell the Nest to crank up the heat, and it occurred to me that there’s no real reason to wait that long. The Nest app could request location change notifications from the OS, figure out that I’m getting closer to my house at a time that doesn’t match the Nest schedule, and raise an iOS notification asking if I want to go ahead and bump the nest out of “away” mode.

Anybody from Nest listening?

Making “Date Modified” Stable in Windows Server 2012

We recently replaced one of our servers with one running Windows 2012. There’s a folder on that server that I maintain by hand with this procedure: sort by Date Modified descending, then select and delete all files older than a target date. That worked well in Server 2003 and 2008, but in 2012 it’s a disaster: new files are constantly being written into that folder, and the user’s selection in Windows Explorer in no longer stable in those conditions in 2012: the cursor and scroll position are constantly jumping around so you can’t select exactly the start/stop file you want and, worse, your selection is constantly being canceled for you. Thanks, Microsoft.

The workaround I found for this is to use the Search box. Instead of doing a Date Descending sort in Explorer, type something like this into the search box:


That will get a list that, by definition, is stable (no new files are being created in the past right now 😉 ). That works as long as you trust the search results to actually be correct, something that I wouldn’t give 2003/XP credit for, but which 7 and above seem to have gotten correct.

Google Image Search

Ok, so I know this has been around for a little while now, but today was the first time I had a real opportunity to use Google’s image search. I was up way too late last night reading theories about Looper and one of the random “other story” links on a website I hit had a picture of a monster that really, seriously creeped me out. I mean, grown-adult-with-kids-but-still-might-get-nightmares creeped out. So off to Google image search to learn about this new enemy – and it worked great. It turns out it’s a death spirit (Shinigami) named Ryuk from a live action version of the anime “Death Note”. Just a bit of knowledge, and I’m considerably less creeped out now. (And Death Note is now at the top of my Netflix queue).

Worx SD Semi-Automatic Driver

At the end of my last post, I mentioned a shower-door repair. That repair took all of 5 minutes, mostly because it turned out to be a really easy repair, but one thing that sped things up a bit (and made me look like a mashup of James Bond, MacGyver and Chris Farley) was a Worx SD that my father-in-law got me for Christmas. It’s a good example of the kind of tool I’d never have bought for myself but really like now that I have it. I usually like my screwdrivers to be human-powered, but there’s just an undeniable cool factor in changing bits by sliding back the action of this handgun-shaped driver and revolving a new bit into place.

Siri and Reminders

I’ve always been one to organize and get things done by making lists — shopping lists, TODO lists, and so on — but I’ve generally not been good at following through on lists of things that fall into the “not right now, but not never” category. Lists like that have a long lifetime and a low priority and tend to get scattered, forgotten, etc. I’ve tried several TODO apps and services in the past few years, but the one that has actually stuck has been Apple Reminders+Siri, especially since I recently switched to an iPhone. I’ve always got a computer, iPad or iPhone with me, and while Siri isn’t as good at recognizing my voice or meaning as Google, it’s got two critical advantages:

* It’s good enough.
* It’s exactly one button-hold away at all times.

So now no matter where I am, whenever I think of something, I can hold down that Siri button and say something like:

* Add a ball peen hammer to the shopping list.
* Add The Wealth of Nations to the reading list.
* Remind me to change the car’s oil when I leave work.
* Remind me to help Ian build his pinewood derby car next Saturday.

Siri almost always understands what I mean, and the experience is vastly different than tap-tap-tapping to find an app, then typing on a tiny keyboard. Different enough that with Siri my lists actually get made and used, unlike every other similar tool I’ve never used.

YMMV – I think I read somewhere that the word “list” is important in those instructions to get Siri to do the right thing, something that came naturally to me but may take an adjustment for some.

That ball peen hammer example is a good one: I don’t have a ball peen hammer b/c:

* I only need one once in a blue moon.
* When I need one, you can always work around it by other means – it’s not worth a trip to the store.
* When I’m at a store that might have one, the memory of having needed a ball peen hammer is too distant to come to mind.

With Reminders+Siri, the evidence is that I’ll end up with a ball peen hammer in the next week or two, whenever I happen to be at a store.

Reminders itself is pretty primitive. There’s a few things I’d like to do for longer-running lists/projects, like archiving reminders without deleting, or grouping related TODOs. There are workarounds, though, and these gripes are tiny compared to the one major benefit: it’s well-integrated enough that I actually use the tool to get things done.

Siri isn’t perfect either; again, Google is often better at understanding what I mean. Siri has a tendency to do things like look for nearby restaurants b/c I said a sentence that happened to have the word “steak” in it. If Google (or any other app) could hook into that home button and replace Siri, somebody might make a better Siri for iOS hardware (imagine one of the more fully-featured TODO apps coupled with Google voice recognition!) Apple’s walled-garden approach seems unlikely to see that happen. However, even if they did open up a configuration option and plugin API for what happens when you hold the hardware button, I have little hope that anything better than Siri would actually emerge. I had Android phones for years, and tried a number of “Siri-like” apps, both before and after Siri itself made the scene. Nobody else I’ve tried has gotten it even close to right – they all do unacceptable things like take decaseconds to start listening, or do web searches in a tiny, framed, feature-limited embedded browser instead of switching to the phone’s actual browser app.

Got to go. Siri is reminding me to “Fix the shower door before my wife’s brain melts”.

Anybody know where to buy a good ball peen hammer?

Anybody Home?

One day in 2009, I took my server down for a little routine maintenance…and never turned it on again. Spending time with my young children and helping make this startup a success has just been far more important.

I’ve found myself occasionally rising above the surface for a breath of air lately…and let’s face it, I was also itching to get my hands on a bash command line again :-) So, as part of my multi-pronged effort to return to both the real and virtual worlds, I got WordPress set back up on this server today, and this is my test post to verify whether it’s all working.

See you in 2015!

Comment Bankruptcy

I’ve had a pretty busy year and I haven’t done much writing, and I entirely stopped cleaning out the comment spam. It all gets blocked before it hits a post, but I have to manually comb through it all to throw away the spam and approve the occasional “real” comment. I had to clear some space on this disk today but didn’ thave time to work through 8873 proposed comments (8872 of which are sure to be spam), so I declared Comment Bankruptcy and deleted them all.

delete from wp_comments where comment_approved = "0";

So if you tried to post a comment on a post and it never showed up, that’s why.

Star Trek

It suddenly occurred to me tonight that my son was born exactly as many years after TNG went off the air as I was born after TOS went off the air.

Indiana Jones

I watched Temple of Doom and Last Crusade tonight, for the first time since I was a teenager. A few weeks ago I saw Back to the Future for the first time in as many years as well. It’s funny how many things I notice these days that I never would have 15 years ago. Like the fact that the movie playing in the theater downtown in BTtF was a porno in pre-trip 1985 and a Christian speaker post-trip. Or Julian Glover’s comment as Walter Donovan in Last Crusade that the precious valuables paid for right to travel within Hatay were “donated by some of the finest families in all of Germany,” which almost certainly means they were looted from Jewish families. Forget college, though: that’s 10 years of The History Channel talking.

Clipboard Prioperception

Prioperception is your brain’s ability to know where parts of your body are.  Even without seeing or feeling your hand, you generally know where it is, you can navigate through doorways without running into them with your shoulder, and you don’t typically fall down when you try to sit in a seat b/c you know generally where your hind-end is.

I’ve read somewhere that the concept of having five senses is pretty outdated given our current understanding of the brain, and that there are probably more like 25.  Sure, there are the obvious external senses, but we also have psuedo-external senses like prioperception, and lots of internal senses that aren’t nearly as obvious but that nontheless control things like cravings and hunger (e.g., blood sugar).

One of the possible outcomes of human-computer interface advancement is to provide humans with totally new senses.  I think I’ve developed at least one new sense already, though, after 15 years of using Windows: I know when there’s something in my clipboard.  Now, of course if I cut something and then immediately paste it, I know, intellectually, that the text I just cut is in the clipboard, but this is more than that.  Even if I copy the text, then get distracted and do something else for 15 minutes, I’ll still find myself with a feeling that there is something in my clipboard.  I might not even remember what it is, but I’m almost never wrong: if I open a blank notepad and paste, I’ll find something that I had copied or cut and had not pasted.  Of course, technically, the item often remains in the clipboard even after that point, but after pasting it where it’s supposed to go, the feeling goes away.  Just like I may know that there’s something in my hand, even if I’ve forgotten having picked it up or even what it is (something that happens often when I’m cleaning the house), I just “know” that there’s something in my clipboard that I haven’t pasted yet.  I’ve even had the feeling persist after getting up from the computer and coming back, after totally losing my context.

Computer Interfaces

On the holodeck, on the Enterprise or Voyager, when somebody says, “Computer, delete Medical Consultant program and all related files”, the medical consultant program and his lab disappear from the holodeck.  The computer never says, “The file cannot be deleted because it is in use by the Holodeck.”

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