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News & Notes

5 Tips to Help You Avoid Drone Accidents

This advice might just save your drone (and your wallet)

March 8, 2016

Any experienced UAS operator will tell you that it’s not a matter of if, but a matter of when something goes wrong. Accidents are often avoidable, provided that the pilot takes the time to perform a preflight check of all components, thoroughly tests their system, flies within their capabilities, and practices. Even with all this, and with all the rules and regulations in the world, you may still experience an “unplanned landing,” the severity of which, you might joke, depends on the number of parts you need to pick up afterwards.

So, what can go wrong, and how do you recover when it does?
If your battery readout says 40% or 50% (this one says 26%, oh my!) it's time to land. Any lower and you could suffer power failure. Though, batteries are getting better about this.
Lauren Sigfusson
1. Don’t underestimate the importance of batteries

Your choice of drone and the components that you utilize in your own builds matter, but do not guarantee the aircraft’s safe performance. One of the most crucial parts of an aircraft is the power source. Practically all consumer and custom-built drones on the market today are powered by lithium-polymer (LiPo) batteries. Anyone who was paying attention to the news this past holiday season probably heard about the issues facing the latest craze in personal mobility: the (exploding) hoverboards. What caused these devices to catch fire has been linked to the poorly manufactured LiPo cells used to power them. When a LiPo battery fails, the results can be catastrophic — like fires hot enough to burn a hole through asphalt.

The first step to making sure your drone doesn’t suffer a similar fate is to use batteries from reputable companies and properly maintain them. Failure to do so can result in poor performance, short flight times, and, eventually, complete failure.

The first sign that something is going wrong with your battery is the gradual reduction in flight time, as well as a loss of power. Depending on the type of drone you have, your flight controller may or may not be set up to deal with low-battery issues through one of its programmable failsafe settings. Many consumer drones on the market today come with visual or audio (or both) warnings to alert the operator that the battery is running low. Some go a step further and automatically engage functions such as Auto-Land or Return to Launch.
If you lose power while flying a multirotor drone, you can use the "falling leaf" approach to get the aircraft to the landing zone in a gentle, controlled manner.
Rick Johnson
In the event you don’t have such failsafe settings at your disposal or choose not to enable them, it is highly recommended that you have a method to determine the current battery charge. Without it, you’d more than likely keep flying until the system shuts down due to lack of power.

Many transmitter and receiver sets are available with a telemetry function that will display the battery voltage on the transmitter screen. You can also use a telemetry transceiver setup to monitor battery voltage. The transceiver displays all critical flight information on a smartphone, tablet, or laptop.

I recommend you don’t discharge your flight packs lower than 3.6V per cell. For example, a 6-cell LiPo battery usually rates a nominal 22.2V when fully charged; the recommended minimum voltage would be 21.6V. I can get 20 minutes of flight time out of one 6-cell LiPo powering a five-pound quad by the time it discharges to 21.6V. Keeping to this minimum voltage rule will ensure the longevity of your batteries.

Regarding battery meters like those on the DJI Inspire or Phantom quads, the LED indicators show a range from 40 to 100 percent charge. When you reach 40 to 50 percent battery life, that’s when you should land. The way these batteries are metered lines up closely with the voltage parameters outlined above.

Knowing this about your batteries will help you avoid having to take emergency actions to land. However, if you should find yourself at a critically low voltage level, there are a few ways to recover, depending on the type of craft you’re flying.

With multirotor helicopters, one of the safest and quickest ways to get your drone safely on the ground is to utilize a “falling leaf” approach. Using this method, you reduce altitude and simultaneously move the drone closer to the landing zone (LZ) by making a number of controlled lateral moves  (see Fig. 1). Like a leaf falling from a tree, you fly the copter closer, reducing the throttle to initiate altitude loss. Before stopping the lateral move, you should increase throttle to maintain a hover and avoid the drone plummeting. Depending on the area where you’re flying and the distance the drone is from the LZ, you may have to do this in steps like a zigzag pattern, or you might be able to pull it off in one gentle descent.
Another way to land your multirotor drone if it malfunctions is by flying to the landing zone and then coming straight down — this could mangle your drone, though.
Rick Johnson
Why not just come straight down? Because a low battery may be incapable of delivering the current needed by the motors to quickly arrest a quick descent and return the copter to a hovering state before landing (see Fig. 2). In fact, the drone may not be able to stop at all, which could result in a hard and potentially damaging landing —  colloquially known as a crash.

Fixed-wing platforms have the advantage of being able to glide, provided that they maintain a minimum airspeed. This makes them a little easier to recover on low battery than a multirotor. Of course, a lot depends on location, distance, and environmental factors, such as wind.

By reducing the throttle and utilizing the wind and control surfaces, you can conserve energy and buy some time before battery failure. The trick is to glide the aircraft down as quickly and safely as possible to an altitude from which you can more easily fly (using power) to the LZ.
Loss of power can be more manageable with a typical fixed-wing plane or drone. Simply glide toward the landing zone using the elevator and throttle sparingly to maintain airspeed.
Rick Johnson
Keep in mind that flying into the wind will allow you to bring the plane down quicker, while reducing the amount of distance needed for the decent and a controlled landing. Decreasing the elevator will increase the speed of the aircraft by forcing it to descend. Once you reach the desired altitude, increase elevator to reduce the rate of descent, attain proper airspeed, and level out the plane for a landing. This can be repeated until you are in a position to land. Utilizing the throttle judiciously will help keep you in the air longer while maneuvering for a landing (see Fig. 3).

Both fixed-wing and multirotor aircraft can also be subject to total power failures. In these cases, there is little you can do to recover unless the aircraft has a parachute that deploys the moment the craft is inverted or when the motors cut out. Try to keep visual contact with your drone so you can recover it. If you’re building your own drone, consider using two LiPo packs in parallel. This allows you to have a backup in case the primary source dies.

Practicing the emergency landing procedures mentioned above before they become necessary will make them a lot easier to pull off if you ever have to perform them.
2. Be prepared if you lose signal or visual line-of-sight with your drone

So you’ve rigged your drone for FPV and are running the signal back to a ground station, monitor, or goggles. Just like the control link to the drone, these video transmitters and receivers have range limits which, when exceeded, can result in video dropouts and the infamous blue screen.

While this may seem like no big deal, it can quickly escalate, depending on how far away you’ve flown the drone and whether or not you know where your drone is relative to you. To say the effect is unsettling doesn’t begin to cover it.

As racing becomes more popular, we’re seeing more video dropouts in unsual places, like in woods where GPS is spotty at best. If you’ve been flying beneath the tree canopy, have lost FPV, don’t have sight of the drone, and lack telemetry to tell you where the drone is, the safest thing to do (if you can maintain your wits) is to gradually reduce speed and hope that when you find your drone, it’s in one piece.

If you’re flying in the open, the best option is to engage the Return to Launch failsafe protocol, if you have one. Being familiar with your aircraft and the controls is paramount as you attempt to keep it at altitude and from flying farther away while scanning the skies for it.

Recovering from a loss of line-of-sight can be very challenging, especially if you have have lost orientation. Experience helps, but sometimes there’s nothing you can do, and you lose the drone. In this eventuality, the following tools may help you find your downed drone:

  1. Check your video. If you recorded the downlinked video, you may be able to trace where the drone was when things went dark. This will give you a place to start your search.
  2. If you were flying with a telemetry transceiver, you more than likely have the last known GPS coordinates on the screen. Write them down and save them, because they will provide you with the starting point for your search-and-rescue operation. Additionally, it is possible that your downed drone is still powered. Before shutting off your telemetry transceiver link, start heading to the last known coordinates. Hopefully, the link will come back, allowing you to get a better fix on the drone.
  3. If you’ve equipped your drone with a buzzer or alarm, you may be able to find it once you get within earshot. Obviously, this depends on the size of the area you have to search.
  4. Some operators equip their drones with PET transmitters or GPS trackers that allow them to track the device on a mobile phone or via the Internet. These are not a bad investment when compared to the cost of losing your copter.
3. To avoid heartache, test your equipment before taking to the air

Things break. They wear out. Thankfully, you can implement practices to identify potential problems before you fly.

Check your propellers before each flight for cracks. If you find one, replace the prop, pronto. If you don’t, the crack could become a split. The blade could shear off and damage the aircraft, not to mention you or bystanders. What’s more, the motor becomes useless and the aircraft is unstable.

Always make sure the propellers are securely mounted to the motors.

Speed controllers and motors that fail could cause your multirotor drone to crash. You may be able to recover a fixed-wing vehicle, but you’re probably going to be picking up some pieces of a quad. Hexacopters and octocopters have redundancy in their motors. However, depending on the type of flight controller you are using, the motors may not be able to handle the imbalance in centrifugal force, causing the drone to rotate and become difficult to maneuver. Multiple motor or speed-controller failures with these types of multirotors may lead to the undesirable process of parts reclamation.

With fixed-wing platforms, the failure of a servo motor on a control surface will disable that surface. Recovering from this requires skills that you can only achieve through practice.

Inspect each of these components for damage before flying to greatly decrease the chances of failure during flight. Make this part of your preflight checklist.

Putting your drone through stress tests before pushing it to the limits in the air can be helpful. A simple way to do this is to find a method of safely strapping the drone to the ground or a table and running it at full throttle while moving the various other controls around. While your drone probably won’t be subject to this type of stress during a normal flight, if anything does go wrong, you won’t lose the whole bird. You can also replace parts that fail or concern you before they come apart in the air.
4. Know that your controller might fail (Do your part to make sure it doesn't!)

All drones require an interface for the operator to control them. This can either be performed via the conventional radio transmitter and receiver link, telemetry link, or a combination of both.

Most modern R/C transmitter and receiver sets have the ability to lock onto each other to avoid interference from other transmitting devices — like other R/C transmitters. Telemetry devices, which link the onboard flight controller with a smartphone, tablet, or laptop, can similarly be configured to only communicate with specific devices. These links have range limits specified by the manufacturer and should be observed when operating the drone.

However, if the communication link between the operator and aircraft is lost, perhaps because of distance, the control device’s battery running out, or some other interference, the only way for the drone to recover is if the onboard flight controller is robust enough to deal with the situation. In this scenario, there is virtually nothing you can do to regain control.

Many midrange and higher-quality drones come with flight controllers that have programmable failsafe settings for this type of failure. Learn what the active setting is, and use the appropriate one for your situation.

Three of the most common failsafe operations initiated by flight controllers that lose radio link communication are:
  1.  Return to Launch
  2.  Land
  3.  Continue Flying if in a preprogrammed mission; if misson ends, Return to Launch

To prevent finding yourself in a situation like this, make sure that the device you are using to control your drone is fully charged before flight,  and know the maximum control-link range. Don’t fly beyond it!

If you are using a telemetry link between your drone and a peripheral device, such as a tablet, keep your radio transmitter handy and powered on so you can take control should the telemetry link fail.

5. Know what causes most crashes

That’s right, the operator! Proper maintenance of your drone is essential, but knowing how to fly and how to react in situations like those we’ve talked about will not only improve your chances of recovery, but will also lead to more enjoyable, less stressful flights. Practice makes perfect. Fly within your limits and gradually push the envelope. Practice emergency maneuvers, such as those needed to quickly and safely land your drone, before you need to perform them in an emergency. Until you become a skilled pilot, fly only in areas and up to distances within which you know you can recover and where your crashing drone poses minimal risk to people or property. Be patient with yourself. Develop your skills. In the end, you’ll be happy you did.

Note: A version of this review appears in the March/April 2016 issue of Drone360.
Featured image: pixabay/fxxu