Battery Performance

Drone Batteries – What to Know

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Drone batteries lose performance over time; see graph of performance.

Drone Batteries Lose Performance Over Time

Our research indicates that aerial drone batteries need to be replaced every two to four years. This article will explain our reasoning, which may serve as guidance for your operations. For reference, we fly DJI Mavic and Phantom drones, but other drones that use Lithium Polymer technology will have similar performance characteristics.

Do You Trust Everything You Read on the Internet?

So, I go online and the first page or so of Google Search hits tell me that my DJI drone battery will last up to 30 minutes, can take 200 to 400 charge cycles, and last around two years. Well, that hasn’t quite been our experience, so we’re going to present some information that may more accurately reflect the performance you can expect.

Data From Our Flight Logs Paints a Different Picture

First of all, our flight operations are almost all commercial, primarily supporting the real estate sales and housing development markets. So, our drone batteries are often required to support flights at altitudes of 400 feet and speeds of 32 mph. This is a bit more demanding than flying at low altitudes and slow speeds. Thus, we shouldn’t expect our batteries to last 30 minutes. So, what should we expect?

We keep log sheets for all of our drone flights, where four years of data shows us:

1.  Our average flight times are 18 minutes.

2.  Our average battery usage ranges from 96% at beginning to 26% at end (70% diff.).

3.  For an average battery usage of 70%, we get about 3.9% per minute. (This is the same as 0.26 minutes per %, just invert.)

This information alone is probably worth your time to read to this point. However, it gets more interesting when the data is examined.

Graphing the Data Reveals Insight into When Your Batteries Need Replacement

The above graph shows that over time your batteries lose their ability to hold a charge. (Our measure of performance is flight time divided by percent battery usage). Microsoft Excel’s trend line tells us the battery’s capacity is around 0.28 minutes per percent (min/%) for a new Phantom 4 Intelligent Flight Battery. At four years, the battery’s capacity has decreased to around 0.23 min/%. This decay appears linearly related to time (not frequency of use) and for the Phantom 4 battery it indicates a 20% loss at four years.

Note the graph shows a 14-month period of no data – but the slope continued linearly indicating it’s the battery chemistry, not usage, that was driving the decay of capacity.

Key takeaway: Your typical 70% flight on day one will last about 20 minutes, and four years later will last about 16 minutes. (There are a number of factors that also contribute to battery performance including deep discharge cycles, damage from crashes, temperatures, etc.)

Mavic 2 batteries had similar graphs and similar flight times, with one important difference. The slope of their decay line was about twice that of the Phantom 4 batteries. The data analysis showed Mavic 2 batteries decay to 80% capacity at around their two-year point.

How does this Information Compare to Performance Specs on the Internet?

We believe this information is complementary to DJI’s performance spec. If you pop your drone up ten feet and let it idle, a new battery may last 30 minutes. But in more demanding situations (read real-world usage), we believe our data more closely represents your experience.

Our commercial flights have been spread across a number of batteries, so each one has a limited number of discharge cycles (less than 100). If you’re usage is significantly higher, then your drone batteries may lose their ability to hold a full charge at the 300-500 cycle mark, whenever that may occur. According to DJI, that may occur at its two-year mark.

Conclusions

Battery performance depends on its chemistry, which decays over time. We have shown that our Phantom 4 batteries decayed to their 80% capacity point at four years.

Data also shows our Mavic 2 batteries were at their 80% capacity point at two years. We suspect DJI traded off capacity for performance, probably by recalibrating their battery chemistry.

In addition, an aging battery gives off gases, which causes its case to swell. When your battery swells to the point that it requires effort to insert/remove from your drone, this also indicates it’s time to replace. In our experience, our Phantom 4 batteries were sufficiently swollen to warrant replacement at 4 years. Coincidentally, at their 80% point.

Altimeter Error’s Effect on 3D Mapping

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Aerial Drone Altimeter Error

Aerial Drone Altimeter Error

One of the specifications you won’t find for your aerial drone is its altitude accuracy. In fact, if you call the manufacturer’s support team, they probably won’t provide you with that spec. So, what do you tell a client when their mapping accuracy requirement is critical?

At FAD-Photo, we have calculated what you can expect in terms of altitude accuracy and can show you how this altitude error affects 3D mapping.

Your drone’s altimeter takes its readings from an internal barometer, does the conversions, and writes them to the photo tags, which are used by the mapping service. Mapping service providers will tell you that their numerical processing is accurate, but subject to the altitude information provided by the drone. But what if the drone’s altitude data is drifting over the duration of the mapping session?

The map processing service assumes the drone flies its mapping session in a perfectly flat plane. If the drone’s altitude readings shift during flight, then its plane shifts. This in turn shifts the ground plane causing terrain elevations to shift.

How does an Altimeter Work?

This blog is an update to our April 2020 blog Aerial Drone Altimeter Accuracy Specification. We analyzed nine months of data to refine our opinion on altimeter accuracy.

As one goes up in altitude, the air pressure goes down. The relationship between air pressure and altitude is quite predictable. So, using the formula below the altitude is easily converted from the drone’s internal air pressure sensor (a miniature barometer):

A = -(RT/gM)*ln(Po/P)

Where A is the drone’s altitude (height difference between the measurement altitude and the starting altitude), R is the gas constant, T is temperature of the air, g is the acceleration due to gravity, M is the molar mass of air, Po is the atmospheric pressure at the starting altitude, and P is the atmospheric pressure at the drone’s measurement altitude.

This formula is coded into the drone’s software so the barometer’s pressure reading can be converted to altitude. The constants R, g and M do not change, but the variables Po and P do change and are used in the calculation. The temperature T is assumed to be constant, but in reality, it’s affected by the temperature of the drone’s barometer and thus contributes to altitude error.

Over the course of a flight session, not only does the drone’s internal barometer sense pressure but it also senses the temperature effects of ambient air and heat dissipation of the internal components.

What Does the Data Tell us?

Our Flight Logs provided the record of end-of-flight altitudes for flights longer than 10 minutes. The resulting graph appears above.

The data indicate that altitude error is positive during the cooler months and negative during the warmer months. We know that average seasonal temperatures follow a sinusoidal curve, starting about 46 days after the autumn equinox (or 55 days before 1/1). Also, temperature variations are dependent on region, weather patterns, and time of day. In our case, this data was taken in central Virginia.

Developing a Trend Line

Using MS Excel’s Solver add-in, we derived the sine wave “trend line”, which follows this formula:

Altitude Error (trend line) = 2.44 + 4.74*sin((Date + 70.2)/365)

The resulting curve represents the altitude error in feet that may be expected throughout the year. The average offset is 2.44 ft plus a sinusoidal component with a peak value of 4.74 ft. The date offset of 70.2 days was expected to be closer to 55 days but is at least in the ballpark. As we collect more data, these numbers should become more accurate.

Statistical Data Calculated from the Trend Line

Other statistical data were calculated from the trend line minus the landing altitude data. We calculated a Standard Deviation of 4.60 ft and a Margin of Error of 1.14 ft (for a confidence interval of 95%). We then stacked these errors, so the expected altitude error at end of flight (EOF) is:

Altitude Error (EOF) = 2.44 +/-4.74 +/-4.60 +/-1.14 ft

Which ranges from 12.93 to -8.04 ft throughout the year

Since the drone altitude at takeoff is zero, we know this error has to build up over the course of a flight. Approximating this buildup as linear, the midpoint error is about half of the EOF altitude error:

Altitude Error (midpoint): ranges from 6.47 to -4.02 ft throughout the year

This means that for a 20-minute mapping session, the altitude error specification is around +/-6.5 ft. That is, the error can start off at zero and end at 13 ft, about a mean of 6.5 ft. The graph shows that the worst-case error can be slightly higher, but in most cases is somewhat less.

Conclusions

We take our maximum calculated error of +/-6.5 ft and round up to +/-7 ft, which we use as our altitude specification. Altitude inaccuracies affect topography mapping because our mapping service takes altimeter readings from the photo tags and cannot compensate for these errors.

For topography maps, contour lines at 10-ft intervals approach the useful limits of this technology. We can generate 5-ft contours (or less), but the overall mapping information becomes less and less useful. However, contour lines on this order may still be useful for assessing localized areas, such as slopes and structures.

Altitude error will be reduced for shorter duration mapping sessions and (as seen on the graph) near the sine wave crossings in late May and late September.

So, why won’t your drone manufacturer tell you its altimeter specification? Well, it’s complicated . . .

Angry Birds That Attack Aerial Drones

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Falcon attacking a Mavic 2

Falcon Attacking a Mavic 2

Birds of prey are fascinating to watch until they set their sights on your aerial drone. Attacks on drones have been widely reported but probably haven’t been a concern to you, as a drone pilot, unless you’ve fallen victim to one.

We recently had our own bad experience with a bird taking down our drone while we were on a commercial photo shoot. We were taking photos using autopilot, where the drone stopped, took a picture, and then continued to its next position. Apparently, a bird took offense at our slow-moving drone and attacked. Fortunately, the 200-ft fall was broken by vegetation! After replacing a broken propeller, we were able to continue our job.

Why Would a Bird Attack a Small Aerial Drone?

Three reasons come to mind:

  1. They feel threatened by the drone’s intrusion into their territory.
  2. They think the drone might be a source of food.
  3. They feel their nest is threatened. Be especially careful during mating and nesting season.

Large birds of prey, such as eagles and hawks, can be hazardous to your drone especially if they’re much larger. I can’t imagine an attack that’s not hazardous to the bird as they have the spinning propellers to avoid. But if they manage to latch onto your drone’s vulnerable underbody, its next stop is going to be on the ground.

This article on bird attacks at the COPTRZ web site provides additional detail.

Avoid Bird Attacks!

We didn’t have a problem with bird attacks until we automated our photo runs, which stop for several seconds to snap each picture. Taking your photos at lower altitudes will present your drone as a threat and an ideal target. However, photography at 250 feet or higher is less threatening and takes away a lot of their advantage. High-resolution photos can be cropped to simulate a zoom-in effect without sacrificing very much picture quality.

Flying significantly faster than most birds (and prey) will also present your drone as a more challenging target. All of our video runs are done on autopilot with altitudes above 200 feet and speeds above 20 mph.

Aerial mapping has its risks as well, but our mapping runs are almost always at 400 feet altitude and speeds above 15 mph. We program our drones to take pictures while maintaining cruise speed because the risk of blur is so low. Most birds at that altitude aren’t going to pay your drone much attention.

Documenting Bird Attacks

Several interesting bird attack videos are posted to this site, Dronelife. The threat is real!

We’re now enabling video in our photo runs, between the photos, to possibly capture our own adventures with angry birds. Should our drone be recovered, at least we’ll have some consolation along with evidence that can be presented with our insurance company claim.

Flying over People and Flying at Night

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Soccer

Flying Over People

The FAA published its final rule on April 21, 2021 regarding aerial drones flying over people and flying at night. It’s posted to the FAA’s website at:  Operations Over People General Overview.

This blog summarizes their new rule, but there are significant details left out for brevity. If you intend to fly over people or at night, then you’ll want to read the details. In addition, the FAA has published further details in their Circular 107-2A.

FAA’s Summary of their New Rule

Cited directly from the FAA, “This rule amends part 107 by permitting routine operations of small unmanned aircraft over people, moving vehicles, and at night under certain conditions. It also changes the recurrent training framework, expands the list of persons who may request the presentation of a remote pilot certificate, and makes other minor changes.”

Mike’s take on Aerial Drone Operations over People

The FAA established four categories of drone operations over people. Category 1 has the lowest requirements through Category 4, which has the strictest requirements.

Category 1 aerial drones must weigh 0.55 lbs or less and are permitted to transit over people as long as rotating parts are covered so as to prevent lacerations (read propeller guards).  However, sustained flight over people is not allowed. Only a one-time transit over an assembled gathering is permitted.

Category 2 aerial drones must meet the requirements of Part 107.120 and be listed on an FAA-accepted Declaration of Compliance. However, sustained flight over people is not allowed. Only a one-time transit over an assembled gathering is permitted. Rotating parts must be covered so as to prevent lacerations.

Section 120 (which is new) states the aerial drone “Will not cause injury to a human being that is equivalent to or greater than the severity of injury caused by a transfer of 11 foot-pounds of kinetic energy upon impact from a rigid object.” (See example below.)

Category 3 aerial drones must meet the requirements of Part 107.130 and be listed on an FAA-accepted Declaration of Compliance. However, sustained flight over people is not allowed. Only a one-time transit over an assembled gathering is permitted, but exposure levels are a little more relaxed than Category 2. Operations over a restricted-access gathering of people is permitted as long as everyone has been notified that a small aerial drone may be flying over them. Rotating parts must be covered so as to prevent lacerations.

Section 130 (which is new) states the aerial drone “Will not cause injury to a human being that is equivalent to or greater than the severity of injury caused by a transfer of 25 foot-pounds of kinetic energy upon impact from a rigid object.” (See example below.)

Category 4 aerial drones and operators must meet a higher degree of certification. The FAA states “Eligible Category 4 small unmanned aircraft must have an airworthiness certificate issued by the FAA under Part 21 and must be operated in accordance with the operating limitations specified in the FAA-approved Flight Manual or as otherwise specified by the Administrator. The airworthiness certificate allows small unmanned aircraft operations for compensation and hire.” The requirements are a good read and recommended for pilots who wish to qualify for Category 4 operations.

How does the FAA calculate Kinetic Energy?

The FAA’s Circular 107-2A page 8-15 provides this formula for calculating the kinetic energy in foot-pounds:

KE = 0.0155 x drone weight (in lbs) x (velocity in mph)²

For example, a DJI Mavic 2 drone weighs about 2 lbs and its terminal velocity is about 45 mph. (Source: MavicPilots forum.) Using these numbers, the KE of a Mavic 2 in terminal velocity (free fall) is calculated to be 63 ft-lbs. Therefore, velocity would have to be reduced to less than 19 mph to comply with Category 2 operations – that is 11 foot-pounds. This number means that you will have to fly low and slow.

Night Operations

This new rule also allows routine operations of small aerial drones at night under two conditions:

  1. The remote pilot in command must complete an updated initial knowledge test or online recurrent training.
  2. The aerial drone must have lighted anti-collision lighting visible for at least three (3) statute miles that has a flash rate sufficient to avoid a collision.

Remote Identification of Aerial Drones, Part 2

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Remote Identification

Coming Soon to Law Enforcement Near You

The aerial drone community is more abuzz than usual with the new FAA rule on UAS Remote Identification. The final rule was published in the Federal Register on March 10 and becomes effective on April 21, 2021. This article updates our July 20, 2020 blog on Remote ID.

Compliance deadlines: September 16, 2022 for manufacturers and September 16, 2023 for operators.

Purpose:

The purpose of Remote identification is to require aerial drones to broadcast their identification and location information. This will help the FAA, law enforcement, and other federal agencies to find the control station when a drone appears to be flying in an unsafe manner or when it enters a location where it’s not allowed to fly.

The FAA’s overview is published at: UAS Remote Identification Overview

The full rule is published at: Federal Register :: Remote Identification of Unmanned Aircraft

How Do I Meet The New Requirements?

There are three ways for drone pilots to meet the new requirements:

(1) Your drone is classified as a Standard Remote ID Drone. That is, your drone was produced with built-in Remote ID broadcast capability, which includes identification and control station location. See the section below to find out if your drone is already compliant.

(2) Your drone has been fitted with a Remote ID broadcast module, which broadcasts identification and take-off location. Many present aerial drone systems fall into this category.

(3) Your drone won’t need to comply with this new rule. The FAA will only allow the drone to be lawfully operated at FAA-recognized identification areas, which are sponsored by community-based organizations or educational institutions.

What’s All This Broadcast Business?

Remote ID broadcast messages will include:

  • A unique identifier for the drone
  • The drone’s lat/lon, altitude, and velocity
  • The control station’s (or take-off location’s) lat/lon and altitude
  • Time mark
  • Emergency status (standard drones only, see (1) above)

FAA Registration

Presently, small aerial drones are registered at the FAA’s web site “Drone Zone.” This date, I don’t see a section for Remote ID Registration, but expect this will be the place for it.

Many Aerial Drones Are Already Compliant With Remote ID

In anticipation of the FAA’s new rule, some drone manufacturers have already programmed Remote ID into their software. At FAD-Photo, our Mavic 2 Pro and Phantom 4 Pro V2 drones are compliant (or nearly compliant). DJI’s control program, Go 4, has fields to enter Remote ID information, but there’s a question as to whether they’re fully compliant. If not, then we expect the remedy will be a software update.

 Check to see if your drone is on the compliant list at Drone U’s web site.

Additional Information

Read what drone manufacturer DJI has to say about Remote Identification at this DroneLife link.

Conclusion

Now that Remote Identification is the law of the land (well, the USA at least) it’s time to start thinking about our compliance deadline of September 16, 2023.

Aerial Drone Flight Logs

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Aerial Drone Flight Log

Aerial Drone Flight Logs

Flight logs for your aerial drone will help you keep track of your flights, including weather, operating conditions, drone performance, and any incidents that may have legal implications. Flight logs are not mandated by the FAA, but they are recommended as a good practice to:  (1) Track your flying hours; (2) Track your drone’s flight time and flight characteristics; and (3) Document your drone’s repairs and maintenance.

What does the FAA have to say?

FAA Advisory Circular 107-2 (June 2016, canceled on 2/1/2021). Paragraph 7.3.5 states the FAA recommends recordkeeping with these words:

Small UAS owners and operators may find recordkeeping to be beneficial. This could be done by documenting any repair, modification, overhaul, or replacement of a system component resulting from normal flight operations, and recording the time-in-service for that component at the time of the maintenance procedure.

The key word is “recommended” as there is no requirement in 14 CFR Part 107 for remote pilots to keep flight logs.

What does your Insurance Company have to say?

The insurance companies that we have done business with have no requirement for pilots to keep flight logs. However, you may want to read your policy or check with your agent to be certain.

Tips for Flight Logs

FAD-Photo keeps flight logs for all of our drone flights. (We also keep copies of all flight programs, photos and videos for at least three years.) We offer these tips for developing your own flight log. Your template can be created on a word processor, with these suggested text boxes:

  • Date and time of lift-off
  • Flight time
  • Cumulative flying time
  • Battery ID, charge level at start and finish
  • Location, client, and purpose of flight
  • Flight control app
  • Max altitude, distance, and speed
  • Weather conditions
  • Flight notes, such as drone issues, photos taken, videos, flight control file names, etc.

Conclusion

Flight logs provide evidence of the number of your flight hours, number of flights, and the ability to review past flight information. Flight logs are particularly useful if you want to repeat a drone session for a client. If it’s been a while, the log will help you to locate the flight program. For example, if you need to record project progress or recapture an event, such as for insurance claims or change of seasons.

Seasonal Variations in Aerial Mapping

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Summer Map, 10-acre site

Summer Contour Map, 10-acre site

Seasonal variations are an important consideration for mapping your property or structure. For summer mapping, that is the late spring to early fall, the landscape is alive with all the vibrant colors that make for great mapping photography. Although the winter months are less colorful, there are significant advantages to these maps as well.

Summer Mapping

Summer mapping is ideal for showcasing properties and structures, especially for real estate sales. Overhead maps capture the properties with beautiful colors, not to mention stunning detail. (Think of Google Maps, but with super high resolution sufficient to see small objects, such as people and animals.)

All of our map products include geoposition and altitude information, so features such as a structure’s location and height can be measured. Our map products are referenced to sea level, in units of either feet or meters. Position and altitude information are available by just clicking the desired point.

The drawback to summer mapping is that vegetation and leaves hide the landscape that lies below.

Winter Mapping

Winter mapping is ideal for topographical charting of land features otherwise masked by vegetation and leaves. Our mapping software can “see” through naked trees and capture much more of the land features otherwise obscured in summer.

Developers of properties use our topographical products to design projects and estimate their costs. The three most common map products that aid in their decision making include:

  1. Contour Maps. We develop contour lines at the interval specified by our client. They can be at any interval, such as 50 feet, 25 feet, 10 feet, etc., and any unit, such as feet or meters. We have advanced post-processing techniques that we use to overlay contour maps onto our color maps. Examples of our composite maps are shown in these summer and winter pictures.
  2. 3D Object Maps. When opened in an object viewer, these maps provide the client with a look at the property from any angle (both above and below) the image. These full-color images provide height and perspective information of landscape and structures.
  3. Point Cloud Maps. These maps provide 3D views of the map image. They appear as a cloud of points, but each point has position, altitude and color information. The real power of these maps is their ability to see landscape underneath the trees and give the project engineer detailed information on features such as mounds, river banks, small structures, etc. Any particular map section can be selected and viewed. The selection can be rotated and zoomed to view the landscape features better than an in-person survey.

For more information on precision 3D mapping, please read our June 12, 2020 blog.

Mapping Challenges

Winter Map, 10-acre site

Winter Contour Map, same 10-acre site

Our aerial drones take overhead photos shooting straight down and in rectangular patterns. At a flight altitude of 400 feet, the ground resolution is typically 1.25 inches per pixel and the resulting map size is approximately 4 megapixels per acre. OK, this is some serious resolution!

However, there are certain areas that don’t resolve well in aerial maps. Water features and non-distinct land features may be difficult to resolve because discernable points cannot be identified or they’re in motion. These challenges are minimized with high overlap photography. That is, overlapping the photos at 90%. (This means taking 18 photos per acre.) Even at high overlap settings, there still may be features that don’t resolve well, such as bodies of water.

Why? Map making software identifies overlapping pixels to determine their exact position in space. At a 90% overlap setting, a single pixel may have as many as 100 look angles, where each angle helps to establish that pixel’s exact position. Errors in calculating these angles lead to errors in the map’s presentation.

Map processing generally goes well at 90% overlap, but can degrade at lower overlap settings, wind conditions, water features, and non-distinct land features. Winter mapping is usually more challenging because land features can be drab and non-distinct.

Which Season is Right for You?

We wrote this blog to take out some of the mystery of good map making techniques. At FAD-Photo, we have developed many photo maps and know how to set up your 3D map products regardless of season.

Aerial Drone Preflight Checks

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Checklist

Checklist

Preflight checks of your aerial drone are always a good idea, especially when you’re flying for a client. You may have seen a requirement from your insurance company to follow a written Standard Operating Procedure. That entails a checklist, which helps you to ensure your drone is ready for flight and to carry out its intended mission.

What does the FAA have to say?

The FAA’s position comes from the standpoint of safety of operation. Here’s the relevant sections:

14 CFR Section 107.15  Condition for safe operation:

(a) No person may operate a civil small unmanned aircraft system unless it is in a condition for safe operation. Prior to each flight, the remote pilot in command must check the small unmanned aircraft system to determine whether it is in a condition for safe operation.

(b) No person may continue flight of the small unmanned aircraft when he or she knows or has reason to know that the small unmanned aircraft system is no longer in a condition for safe operation.

FAA Advisory Circular 107-2 (June 2016, active to this date)

Para 5.9. Preflight Familiarization, Inspection, and Actions for Aircraft Operation. At 296 words, I’d rather provide you with a link than repeat it in this blog.

Para 7.3. Preflight Inspection. Ditto, 337 words, so please refer to the link.

Both paragraphs are well worth the five minutes to read.

What does your Insurance Company have to say?

Several insurance companies require aerial drone pilots to follow a Standard Operating Procedure (SOP). Although your drone manufacturer may not provide one, they’re fairly easy to develop, especially using the information in the FAA Advisory Circular.

Tips for Preflight Checks

Develop your own checklist.  We suggest including the following:

Software and firmware are up to date

SD card is installed

Camera lens is clean

Propellers are in good condition

Fresh batteries in your drone, controller, and cell phone/tablet

Develop a mission profile for your client and review prior to flight

Check the weather forecast, note the conditions prior to flight

Take off and hover at 5 feet; check propellers and flight controls

Add to this list as you see fit and go through it every time you fly. Pretty soon, your preflight checks will become second nature.

Flying Your Drone Indoors – What Could Possibly Go Wrong?

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Flying Indoors

Who Is Your Insurance Company?

Flying your aerial drone inside a covered structure requires safety equipment, special settings, and a high degree of skill. This subject has been explored by a number of other bloggers, so we’ll summarize their recommendations and present a few of our own.

The FAA Does Not Have Jurisdiction over Indoor Flying

Part 107 doesn’t mention flying indoors because these areas are not considered navigable air space. However, there are a number of applications for indoor flying, including real estate photography, conventions, games, and drone competitions. Such applications require special considerations by the pilot. We’ll cover several in this article.

Insurance

When flying indoors, there’s significant risk that your drone will get damaged, harm people, and/or damage property. Therefore, check with your insurance company to see if indoor flight injuries and damages are covered.

Many drone pilots use Verify, now Thimble, a popular pay by the hour insurance company, which specifically excludes coverage for indoor flying. Our own insurance company, Global Aerospace, excludes coverage for competitions, but otherwise appears to cover indoor operations (per my agent). This gets confusing, since Thimble contracts with Global Aerospace. So, read your policy carefully to ensure you’re covered for flying indoors.

Tips for Flying Indoors

  1. Always use propeller guards to reduce injury and damage.
  2. Turn off GPS positioning. Interference or loss of signal can lead to unintended drone movements. For certain DJI drones, this means turning off P mode, and using ATTI mode instead.
  3. Related to 2, don’t use automated flight settings such as tracking or waypoints.
  4. Turn off obstacle avoidance. Although vision systems are excellent for outdoor flying, they can lead to stubborn flight control indoors and possible human error through over-reaction.
  5. Use beginner mode, if your flight controller supports it. Flight control stick sensitivities are decreased.
  6. Avoid ceilings, walls, and other flat surfaces. Prop wash causes unpredictable flight behavior.
  7. Turn off automatic Return to Home. If possible, set loss of signal action to hover in place.

For additional information, please refer to:

Drone U

Pilot Institute

Dronegenuity

Alternatives to Flying Indoors

Indoor photography can often be done just as effectively with a camera mounted onto a pole, rather than using an aerial drone. For example, mount your camera onto a glide stabilizer and walk your camera through the desired area. (We use our Samsung S20+ cell phone on a DJI Osmo for these shots.) Reduce camera shake with your video processor’s image stabilization filter.

This same technique can be used outdoors as well. A client once asked us to survey an asphalt road, suggesting that we fly just below the tree canopy. They were happy to learn of a much simpler method to mount a camera in front of and above their truck to capture their footage.

However, the cell phone/Osmo solution doesn’t work in high winds. For example, I once tried this technique from the open cockpit of a biplane but the 80 mph wind overpowered the Osmo. That approach was an epic failure, but salvaged by holding the cell phone and stabilizing the video in post processing.

When there’s no other solution than flying indoors, then we advise extreme caution, following these tips, and checking your insurance coverage.

DJI Phantom 4 Pro Yaw Drift

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Phantom 4 Pro Yaw Drift

Compensate P4P Yaw Drift

What causes the Phantom 4 Pro to drift in yaw (heading) during programmed flights, such as Orbit Mode? This appears to be a common thread in a number of blogs and is a problem we’ve also encountered. As you know, I like to take on the hard problems, think them through and develop solutions. In this blog, I’ll offer ways to measure the offset and a method of compensation.

As I stated above, this is a common problem, but no one that I know of has determined the cause. Please comment if you have a better explanation and I’ll update this blog.

Are other aerial drones similarly affected? Please comment, I’d love to hear from you.

We See Yaw Drift in All of Our Programmed Flights

The yaw drift that we’ve encountered with our Phantom 4 Pro V2 is much more significant than crabbing (please see our April 28, 2019 blog on crabbing). Our data files indicated that the crabbing effect is around ±1.5 degrees, and is largely compensated by the drone’s flight controller. However, our measured yaw offset runs as high as 30 degrees, sometimes more.

Of note, from our data files we plotted the GPS position, which showed the drone stayed on its programmed circular path and its heading was tangent to the circle.

Measuring Yaw Offset

We program almost all of our aerial drone photography sessions, so when the drone’s camera offsets then it’s pretty obvious in the recorded video. A simple method to measure yaw drift is to record a Point of Interest video. That is, to run a circle around a point with the camera pointed at the center. A large radius allows the drone to be operated at maximum speed (we used 1000 feet radius and 21 mph in our test runs), where the drift was quite noticeable.

For example, print out a Google Map of the test site; then graph the video’s centerline of sight at 15-second intervals. You can measure the yaw offset with a ruler for distance, and a protractor for angle. E.g. measure the distance/angle from the centerline to the center point.

Graphical Data Results

Our data set included ten video runs, taken on different days so we had variations in drone speed, wind speed, and wind direction. In almost every case, the yaw drift was affected by both the drone speed and wind speed. One key measurement was the combined speed of the drone, where we found correlation between the maximum yaw drift and the combined air speed of the drone (that is, heading into the wind).

Our graphical analysis suggests that yaw drift can be minimized when both the wind speed and drone speed are less than 10 mph.

Conditions

  1. Drone: a 2-year old DJI Phantom 4 Pro V2 with an iPad 9.7-inch tablet. Yaw effects were similar for both DJI Go 4 and Litchi apps.
  2. Yaw drift appeared to be the same before and after INS and compass calibrations.
  3. We tried to force the drone’s yaw drift by hovering 5 feet above ground and blowing the drone with a fan. We blew the drone so hard that the camera’s gimbal was pushed into its stops, but it returned to linear after the wind was reduced. The drone’s airframe did tilt into the wind to maintain position, as we would expect, but it didn’t change its yaw (heading).
  4. We measured yaw drift in circular “Point of Interest” runs, where the drone’s camera was pointed toward the center and the drone airframe was flying sideways into the wind. CCW runs resulted in less yaw drift, so only one run was CW.

Conclusions

In flight, it appears that the drone’s flight controller is adjusting heading as the drone tilts into the headwind. So, if there’s a large headwind, the drone tilts more to maintain its GPS speed and it also yaws to the left. Since the drone’s legs don’t appear in the video, we conclude that the flight controller must be changing the drone’s airframe, not the camera.

Minimizing the Effects of Yaw Offset

  1. Fly your drone at a speed of less than 10 mph and when the wind is less than 10 mph.
  2. The yaw offset can be compensated by changing your programmed center point into the wind.
  3. Fly a larger diameter radius so the desired field of view is around 80% of the frame, then crop down to the desired field of view in post-processing.

Use an Alternative to Orbit Mode

Program your drone with waypoints, enable curves, and place a Point of Interest in the center. With a little practice you can capture a beautiful “orbit” that doesn’t suffer the effects of yaw drift. This has become our preferred method of flying circular patterns.