Blog 4: How Do Drones Communicate?

Some drone pilots may not realize that they can change frequencies on their controller to get better communication with the drone.  Most often the 2.4 GHz frequency is used because it has better range than the 5.8.  Drones generally can be controlled effectively using low frequencies because they can penetrate denser objects.  But the 2.4 is more commonly used by WiFi from buildings, and you may experience WiFi interference. The 2.4 GHz band of frequencies is unlicensed and allows gadget makers to create devices that operate within this band.  Some newer drones have a third frequency to choose from.  Military surveillance drones typically communicate via satellites.  A new Parrot Anafi can use 4G cellular to communicate with a drone.  Also drones can communicate with themselves as, for example, using collision avoidance sensors to tell the drone to stop or actually fly around objects.  The DJI systems will give the user approximately four miles of range. 

If you go to settings and choose the “HD” option, you can see how busy the frequency is, with jumping lines on various channels.  When you switch to the 5.8, you may be surprised at how quiet that frequency is.  Yet if you are along an unpopulated stretch of coast, you can fly farther with the 2.4, especially over unobstructed water that does not have barriers like on land.

Sometimes there may be so much WiFi interference that you may not be able to do a mission.  For example, once doing a commercial real estate property in Irvine, CA, there was so much WiFi from surrounding medical facilities that my Phantom 4 Pro would lose signal just doing 400-foot quadrant photos.  So I switched to an Autel Evo 2 Pro with better range.  Newer DJI drones have the OcuSync or Lightbridge which is a little more reliable.  The WiFi signal breaks up more often due to interference from all of the other WiFi devices.  My Parrot Anafi also can switch frequencies, but does not do well with strong WiFi interference, and has limited range.

Communication with the drone may be improved with inexpensive parabolic reflectors placed around the antennas.  But these must be pointed at the drone, and are not good when omnidirectional communication is better for, say, orbits or automated flights.

Sometimes the drone may lose communication with the controller/pilot.  If on a programmed automated flight, the drone can continue successfully with the flight even though there is no visual picture on the screen.  Global Positioning Technology helps the controller give the drone instructions on which route to take.  Just make sure the programmed flight takes account of height of trees; so an on-site visual inspection is important.  Once my drone went into a tree during autonomous LITCHI flight, and it cost me $350 for a tree service, which retrieved it unharmed.

If going out of range on a flight and a pilot gets a warning that visual communication is weak, it may be best to immediately fly up in altitude to get a better signal away from ground clutter.  If you find the drone trapped in a grove of trees with no way out, it is tempting to fly up and out; but this may put the drone in higher branches that you cannot see — so better fly down and at least land it.  If signal is completely lost, the drone generally reverts to return to home by itself, using GPS.  If a flyaway occurs, then the drone may go until battery runs out and it lands by itself.  The flight path may be traced on the map to find where the drone went.  (It is a good idea to label your drone with your phone number, if found, hopefully not by security personnel threatening legal action.)

Drones can be piloted in two different ways, either line of sight by visually observing the drone, or by First Person View (FPV). In an FPV system the video image from an onboard camera is transmitted by radio to a personal video display on the ground in the form of a screen or video goggles.  Line of sight naturally is the best way of piloting a drone, because you can have more situational awareness of what is around the drone.  If you are doing a reveal shot for real estate, it is best to go directly to the area to maneuver away from any power lines that you would not see in the video image.  Three-mile collision-avoidance lights on the drone not only help protect aircraft, but also help visual communication with the drone pilot.

A new FAA drone traffic management system will use cellular data plans, ADS-B receivers, and other technology to broadcast ID and location, to allow lots of drones to operate autonomously, safely, and beyond Visual Line of Sight in the area. This will not depend on hand-held remote controllers.

Electromagnetic interference when flying a drone can come from cellphone towers, high-voltage power lines, areas with high concentrations of WiFi networks, or buildings and large metal structures, or even garage-door openers.  It may be a good idea to do a compass calibration depending on if you are in wide-open spaces or near your car, metal storage shed, or even rebar under concrete. 

A cell tower may be emitting any number of other frequencies at a very high power that could interfere with the control and/or video transmission on a drone.  A drone has not been coordinated with the finer points of intermodulation to fly super close to a cell tower.  If flying tower inspections, it only takes one frequency at high power to cause a drone to lose control and result in a flyaway or crash.  DJI came out with the Zenmuse camera with a magnification up to 180x to allow for inspection of a tower from a real distance.

Just as you hear static on your radio when driving under high-voltage power lines, that high amount of electricity may reduce transmission of signal and even disrupt voltage output of an Electronic Speed Controller that sends precise instruction to the motors.  To see how this must all work together, here are terms used when controllers communicate with drones:

Yaw is the anticlockwise and counterclockwise rotation of the drone that allows you to command the drone into making patterns or circles in the air. The left rotation of yaw occurs when propellers 1 and 4 are moving at average speed while 2 and 3 are moving at high speed. If the drone rotates in the right direction, propellers 1 and 4 must move at high speed while 2 and 3 moves at low speed.

Pitch refers to forward and backward tilting of the drone. For the forward pitch movement to occur, propellers 2 and 1 must move at average speed while 1 and 4 moves at high speed. On the other hand, if you want the drone to move backward, propellers 1 and 4 must be at a low rate while 2 and 3 be at average speed.

Throttle is the control of the power being fed to the drone. It is that power that makes the drone move slower or faster. For the power to be adequate, all the propellers must be moving at the same speed.

Roll is the right or left movement of the drone in the air. For this to occur, propellers 1 and 3 must be moving at average speed while 2 and 4 are at high speed. On the other hand, if you want your drone to roll to the right side, propellers 1 and 3 must be running at high speed while 2 and 4 run at a low speed.  

The left stick controls the throttle and yaw. To increase the motor speed and increase the drone’s altitude, push the left stick up. And push it down to slow the drone and lower the altitude. To yaw to the left, push the stick left. And to yaw to the right, move the stick to the right.  The right stick controls roll and pitch. To move the drone forward, push the stick forward and to reverse the drone, push the stick backward. To roll the drone to the left, push the stick left, and to roll it to the right, push the stick to the right.  New pilots may want to label the controller.

Communication problems may be solved by resetting the remote controller or updating to a newer software.  Also reinstalling the app will fix connection issues.  Battery level of the controller and drone may affect connection, and batteries should be fully charged.  Try not to run the drone out to low level charge.  My most serious crash was from battery failure, when the drone fell to the pavement, almost hitting someone.