TOP TEN REASONS FOR DRONE CRASHES FOR PUBLIC SAFETY
And easy solutions to avoid them
It’s possible that you might find this article quite odd. Odd that MAXSUR, a provider of drones and drone services would write an article about drone failures. Well…we’re not most companies, and keeping true to our mission statement of public safety…letting others know why drones fail is aligned with our MAXSUR team beliefs. It’s our hope that if you use a drone in your agency for police, fire, or emergency management...that this article will help you avert disaster and maximize public safety via your drone system.
Over the past five years, the MAXSUR team has successfully repaired 2,295 drone systems (UAS), and because of that, has gained a unique library of knowledge about why drones crash. Just like an auto mechanic, or even a doctor, the drone technicians at MAXSUR prefer to know what led up to a drone crash. Knowing the contributing facts, the techs can more quickly and accurately diagnose, and complete the repair. Over time, the crew has established the top ten reason for drone crashes, and here they are in descending order:
1. DISTANCE MISJUDGEMENT
By far-and-away, improper distance judgement is the leading cause of drone crashes. In those cases, the most evil objects are powerlines and trees. Whether piloting the drone in the legally prescribed manner of VLOS (visual line of sight), or the not-so legal method of FPV, it is incredibly difficult to really tell how far the drone is away from a given object. Even a faint strike with an object will cause drones to immediately lose control, and make the all-hated uncontrolled descent to the ground.
As of late, some of the newer drones with forward-obstacle-avoidance sensors have left pilots complacent. These new sensors are fantastic at avoiding such things as trees, walls, people, cars…basically anything with mass. But smaller objects can be invisible to these sensors. Consequently, complacent pilots are also experiencing crashes, and expensive repair bills.
THE SOLVE – In most situations, the easiest way to prevent these types of crashes is to maintain an operational-floor based on the highest object.
2. LOSS OF ORIENTATION & LACK OF SITUATIONAL AWARENESS
Not knowing how a drone is orientated in reference to controls, is perhaps the leading cause of injuries and property damage as a result of a drone crash. All too often, pilots operating at low altitude and/or near objects will temporarily forget the orientation of the drone. In these cases, the pilot wishing to make the drone go right will move the control stick to the right, but the drone will instead go left and crash into the object.
THE SOLVE – There are two easy and effective ways to prevent these types of crashes. Firstly, for new pilots, the drone should be kept squared to the orientation of the controls. With most drones, this means having the rear of the drone facing the pilot. Secondly…practice, lots of practice. For those of us who didn’t grow up playing video games, it may take awhile for us to fly third-person and to intuitively know the craft orientation.
3. LACK OF, AND FALSE COMPASS CALIBRATION
Not having a proper compass calibration prior to flight is the number one culprit for the most horrific drone incidents, dubbed fly-aways. Untrained drone pilots, are often not aware that one of the key components the drone uses for RTH (Return-Home) navigation, is an electromagnetic compass. The compasses used in drones, although highly accurate, are also highly sensitive. When performing calibrations, even re-bar found in concrete is enough to throw the compass off, and provide a false reading. As a result, when pilots are forced or willingly initiate a RTH function, the drone will fly to an erroneous location.
Beyond local magnetic interference at the time of performing a compass calibration, drone compasses can be off kilter after being exposed to magnetic sources such as vehicle speakers or high power radios.
THE SOLVE – The easiest way to prevent compass calibration issues are to, always perform the calibration over areas other than concrete, and away from other large magnetic material such as vehicles. Additionally, it is highly recommended to calibrate your compass after every change in location, every new set of flights (calibration not required for every flight), and after initiating a RTH function.
4. BATTERY FAILURE
Lithium Polymer batteries, a.k.a. LiPo’s is the battery technology of choice for drone systems. LiPo’s offer the highest power to weight ratio, and yield performance results unlike any other type of battery. Because of their unique attributes, they must be managed unlike any other type of battery. A prime example of their unique nature is that if left on either a completely full or empty charge, it will sustain permanent damage. All too often, pilots in public safety wanting to be prepared leave batteries on 100% charge, after seven days though…damage begins, and the battery will no longer operate at peak performance.
Drone flight batteries continually left on a full charge will start to exhibit swelling, and eventually will provide a false power reading. Unfortunately when the symptoms arise, pilots believing they 100% power…actually only have 10% power, and without notice, the drone goes into auto-land (not RTH). In the worst of cases, drones flying with bad batteries can completely shut-off in midflight.
THE SOLVE – For public safety, the best way to manage the special needs of LiPo batteries, and be ready for flight missions quickly is to setup a battery rotation system. As an example, with a set of seven batteries, one battery can be left on a full charge for three days. After the third day it should be discharged to 50%, and the next battery in rotation should be brought up to 100%. This rotation allows for one battery to always be at full charge, and when a mission call is received…the other flight batteries can be charged en route.
5. MOTOR FAILURE
Whether it’s an inexpensive starter drone, or a multi-thousand dollar professional system, most drones available these days have a quad-rotor configuration. There are technical benefits to quad systems, but the major drawback is that when a motor fails in midflight, there is nothing to mitigate…the drone is coming straight down.
Although motor failure is one of the top reasons for drone crashes, it is almost completely avoidable, and catastrophic motor failure is extremely rare. By that, I mean that drone motors rarely ever are fine one moment, and then not fine the next moment. Failing drone motors almost always fail over time, and increasingly exhibit symptoms leading up to the failure. Symptoms include a change in the magnetic indents which can be felt by hand turning the motors, an observable fluttering movement of the motors, a change in the audible pitch, and some advanced drones will warn pilots via software.
Drone motor failure can be brought on by accumulation of particulates, corrosion from salt spray, worn/unbalanced props, and binding of motors from previous crashes.
THE SOLVE – Always perform pre-flight checks of the motors by hand turning each one, checking motor spin when at idle, checking and replacing worn/unbalanced props. For maintenance, drone motors should be blown-out with moisture free compressed air, and for operation in areas with salt spray…treatments such as CorrisionX should be considered (of course, follow manufacturer guidelines). For insurance, it’s also worth considering a parachute system, or drone systems with larger motor counts.
6. INCORRECT TIME/FUEL CALCULATIONS
A critical mistake when piloting drones is mismanagement of available flight time. This often happens when pilots become hyper-focused on the activity at-hand, and neglects to monitor battery levels. Beyond simple neglect, sometimes pilots on a long range flight can experience a shift in wind, creating a headwind on return trips to the landing point. Headwinds of course require the drone to exert more propulsion which causes a faster battery drain, and can result in the drone automatically landing at an undesired location.
Even with newer, advanced drones that monitor battery levels and return the drone when the level is too low, are not immune to low-battery crashes. Drones equipped with such features cannot account for headwinds, and additional thrust the pilot may add to the equation.
THE SOLVE – Drone pilots should always include a time buffer in flight missions. If at all possible, adding in a protection of 5 minutes can save tremendous heartache and keep the drone available for continued public safety use. If available, pilots should make use of co-pilots that can also help monitor drone battery levels via slaved remote/tablets. Lastly, using a timer on a smartphone, watch…or even a kitchen timer is a great way to remind pilots of the limited flight time available.
New drone pilots are very susceptible to panicking and consequently, making fear-fueled decisions that end in disaster. This is brought on by the pilot putting the drone in circumstances beyond the his or her skill level, and is amplified by the fear of crashing an expensive drone, or causing injury or damage to people or property. An all too common scenario is when pilots lose line-of-sight with the drone, and cannot for whatever reason discern the drones orientation via remote video or telemetry. In such cases, new pilots are apt to crash the drone into ground objects in a panicked effort to regain line-of-sight with the drone.
THE SOLVE – Quite simply the solve to panicking, is training before the event ever even occurs. For brand new pilots, it’s key that they receive instruction from veteran pilots that can guide them on the do’s & don’ts, and that can give them the tools for solving problems. Additionally, routine training is important to maintain skills and to learn about new features that may have come with drone firmware updates. Concerning the cited example of loss of line-of-sight with the drone, a simple solve is to give the drone altitude to where the pilot can regain visual contact.
8. RAPID VERTICAL DESCENT
Just like manned helicopters, multirotor aircraft (drones) do not perform well in rapid vertical descents. A drone in such circumstances is forced to fly into its own prop wash, which creates an unstable flight, and creates extra work for the flight controller (autopilot). Additionally, a rapid descent can trigger false sensor readings that tell the flight controller the drone has already landed, and consequently the motor will stop producing thrust in mid-air.
THE SOLVE – Rapid vertical descents should not be done except for emergencies. For routine descents, the drone should be given some pitch (angle) as its being lowered so that it always avoids running into its own turbulence. If a straight vertical descent is required for whatever reason, then it should be done at a reasonable, but slow pace.
9. LACK OF FIRMWARE UPDATE
Drone manufacturers typically do not publish the full list of reasons why firmware updates are made available. However, having been involved with drones at many levels over the past five years…I’ve come to learn that firmware updates typically includes fixes to bugs that cause crashes. Flying without firmware updates is a game of Russian-roulette, and it unfortunately catches up with pilots in the form of a drone crash. As a classic example but leaving the manufacturer unnamed, a drone would depower in mid-flight if the throttle was held in the lowest setting too long. A simple firmware update solved that problem, but many pilots that didn’t take the short 20 minutes to check, obtain and install the firmware suffered some dire consequences.
THE SOLVE – Fortunately most newer drone systems that are able to connect to the internet via tethered smartphone or tablets, will alert the pilot through the installed app that firmware updates are available. Even so, it is the pilots responsibility to action and install those updates. In public safety, because the drone may be needed on a moment’s notice…it is important to routinely check for firmware updates before the need arises. It’s a great idea to check for firmware updates weekly for aircraft models less than six months old, and monthly for drone models older than six months. Additionally, the pilot should subscribe to the drone manufacturers newsletters, and community forums that include technical topics for the drone models in use.
10. IMPROPER COG (CENTER OF GRAVITY)
If you’re about to take the FAA part 107 test, issues concerning drone COG is something you’ll likely see on the test. Almost all drones have the capability of carrying additional payload. Even the off-the-shelf consumer drones are capable of handling some items like flashlights, or beacons for nighttime flights. No matter the payload type or drone used, there is always a center-of-gravity. Payloads that are not centered and balanced will cause at a minimum extra work for one or more of the drone motors. Over time, this extra work will cause those particular motors to fail and potentially result in a drone crash.
Additionally, incorrect COG can at worst cause the drone to catastrophically lose control during high angle flight maneuvers. Typically, once control is lost during such a circumstance, the inertia is too great for the drone to compensate and recover from.
THE SOLVE – Drone manufactures will typically provide some advisement concerning where the COG of the aircraft is and how to balance additional payloads. However, if that information is not available, drones should be balanced from front-to-rear, and side-to-side. Payload should also be as close as possible to the vertical center of the drone.
Thanks for reading, and again…we hope this article is of assistance to you and your agency. For some additional learning, and perhaps humor at someone else’s expense, please watch the drone crash video compilation below. Granted, the crashes you’ll see in the video are not from public safety operations. Even so, there is plenty to be learned which will aid you in safe drone operations.