I used to have a DIY quad-rotor drone without GPS modules, which had to identify its own flight status and relative displacement through internal IMU (just a combination of gyroscope and accelerometer sensor). In this article, based on my own experience, I will analyze the drone hovering technology.
I. What would happen without hovering?
Many people choose to DIY a multi-rotor drone in earlier years. Normally they won’t equip a complete drone due to limited budget. For example, they would give up the GoPro, 3-stabilization or even the GPS modules.
Below is the classic NAZA GPS Module:
In this case, “Teetering” happens frequently and you will be in a flurry operating the remote controller.
The “teetering” looks like this:
Without GPS signal, the drone can realize Attitude Mode through its own IMU and hovers at preset position through manual operations. But the hovering effects vary from person to person.
I call this stage without hovering concept as Wild Era.
I was amazed at the DJI Phantom 3S by its Auto-Hover during my first flight.
Thanks to the GPS technology, I can now try aerial photography flexibly without worrying about the aircraft’s teetering.
The photo below shows the Phantom 3S’s bottom without downward vision system:
At this stage, the Auto-Hover height was measured by barometers (as the flight height changes can influence the barometric pressure) and the horizontal position was determined by the GPS module.
The GPS module can also provide height information. But most drones used the barometers at that time because the low-cost GPS’s data refresh rate was too low, which might cause drone crashes due to data delay.
When the drone rises or descends due to outside influence, the control unit will adjust the motor power for motion compensation in opposite direction; when the drone yaws due to the wind, the control unit will start the side mode—all of these reactions are fast. Most professional drones can overcome reasonable outside influence (professional multi-rotor drones can resist force 4 wind). In this way, you can see the drone hovering there stably.
III. Precision Hover
Parrot took the lead in introducing the Optical Flow visual positioning system. The drone equipped with this technology has greatly strengthened the GPS self-stabilization.
Relevant reading: Bebop 2 review
The subsequent Phantom 3 Advanced and Phantom 3 Pro were also equipped with the downward vision system, making it possible for indoor hovering (GPS-free environment).
The Binocular Stereo Vision technology of DJI Phantom 4 and Mavic Pro elevated Precision Hover to a new level. Besides, the downward and forward facing vision sensors further enhanced the hovering stability.
The downward facing vision sensors can establish 3-dimensional depth information. And the forward facing vision sensors can help observe the environment and calculate the current location information. In this way, the Precision Hover is realized.
Drag the drone away from its hovering place in the underground garage, and it will automatically return to its hovering place after you release it.
Hovering is important for aerial photography.
You can only take photos or record videos flexibly and freely when the drone hovers stably in the air.
For example, in case of insufficient light at night, you have to extend the exposure time which demands for stability. Hence, stable hovering is crucial for aerial photography.
If the aircraft cannot hover stably, the photo shot at night would be like this:
In addition, hovering can also bring psychological comfort for new drone pilots because stable hovering can free them from anxiety and confusion.
The newly added functions of Terrain Detection and Tripod Mode have paved ways for new drone pilots.
The Table below shows mainstream drones’ hovering technology-related hardware information:
In a nutshell, precision hover can only be achieved by the combination of GPS, forward and downward facing vision sensors and other relevant sensors.
Now you have known the hovering principles, go to take some stunning shots!