What is Obstacle Avoidance and how do you use it effectively on your drone?

DJI Air 3S Collision Avoidance Sensors — (Image credit: DJI)

There’s a pretty good chance you’ve heard of a drone feature called Obstacle Avoidance. And, as the name suggests, it aims to sense and avoid obstacles to stop drones from crashing into objects and people. It sounds like witchcraft, and it is in some ways, but it’s far from perfect despite its impressive performance.

This is a feature that is only seen in the best drones, which are typically more advanced models. These are mostly DJI drones and a handful of Autel models. The most popular current DJI models offering Obstacle Avoidance are the DJI Mavic 4 Pro, DJI Air 3S, DJI Air 3, DJI Mini 4 Pro and the DJI Mavic 3 Series. Some newer and more advanced models also feature LiDAR, but this is used for obstacle sensing in low-light situations.

One thing to bear in mind is that collision avoidance can never be fully relied upon because, as effective as it is, and it is incredibly useful, errors can occur, and the vision sensors don’t always detect obstacles. Also, you have to make sure the system is set to the correct setting for the type of flight you’re making.

What is Obstacle Avoidance?

DJI Fly app screengrab to show Obstacle Avoidance in action. — Obstacle Avoidance warnings in the DJI Fly app. (Image credit: James Abbott)

Since it’s mostly DJI drones that feature collision avoidance, we’ll focus on the DJI Advanced Pilot Assistance System (APAS). When this is activated, the drone can be set to behave in different ways when an obstacle is detected. DJI drones with an omnidirectional binocular vision system typically provide 360-degree detection.

Obstacle Avoidance systems usually feature six vision sensors (two at the front, rear and bottom) and a downward infrared time-of-flight (ToF) sensor. These work from as little as 20 inches / 50 cm to as much as 98 ft / 30 m. Most of these sensors have a maximum range of 59 ft / 18 m. This is more than adequate for the majority of situations.

The binocular vision sensors look like small camera lenses positioned around the drone. When activated, the pilot will be alerted to obstacles in the DJI Fly app by default with visual warnings, obstacle distances from the drone are visible in the camera view window and an audio alert is made.

How do you use Obstacle Avoidance?

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Obtacle Avoidance settings in the DJI Fly app — Obtacle Avoidance Brake option in the DJI Fly app.(Image credit: James Abbott)

Using Obstacle Avoidance is incredibly easy and is switched on by default on compatible DJI drones. It’s activated, adjusted and switched off within the DJI Fly app, whether using a standard controller or a smart controller. Click on the three horizontal dots in the top right corner of the app to open the menu and navigate to the Safety tab.

By default, Obstacle Avoidance will be set to Brake, which means the drone will stop and hover when an obstacle is detected. The other option is Bypass, which can be set to either Normal or Nifty. In Normal mode, the drone will bypass the obstacle at a safe distance from the obstacle. In Nifty mode, the drone will make more subtle automatic adjustments to flight with a greater risk of collisions.

You can also switch Obstacle Avoidance off, and this is necessary when it stops the drone or makes it adjust flight in an undesirable way when capturing video footage during flight in complex environments.

Why is Obstacle Avoidance useful?

With everything covered so far, you’ll be building a clear picture of why Obstacle Avoidance is useful. But as previously mentioned, while it’s a great feature to have, it’s not one that you can rely on all of the time. Obstacle Avoidance should only be used as a failsafe after your judgment when flying close to obstacles.

Obstacle Avoidance, when set to Brake, for example, could save your drone in a situation where you’ve accidentally misjudged a flight maneuver. This is the most obvious advantage of the feature, but Obstacle Avoidance also brings with it two additional key advantages.

The addition of Obstacle Avoidance on a DJI drone typically means the drone will have more advanced subject tracking functionality since this relies upon autonomous flight. What’s more, Return to Home is greatly improved and made safer because the drone can utilize the Obstacle Avoidance system. Again, it’s not perfect, but it’s better to have it than not.

What are the pitfalls of Obstacle Avoidance?

We’ve already mentioned that Obstacle Avoidance sensors don’t always identify obstacles, and light can be a reason for this. Too much or too little light can be problematic, such as night flying or flying directly in front of the sun, which can affect the sensors.

Another issue is that Obstacle Avoidance can make the drone fly less smoothly, which is hugely problematic when capturing video in complex environments. In these situations, you will often find that it’s both more effective and safer to switch obstacle avoidance off.

In the example video above, Obstacle Avoidance had to be switched off because the drone was being flown close to the ground, below and alongside trees. This was an Obstacle Avoidance nightmare where the smoothness of flight would have been impossible, even if the mode was set to Nifty.

Switching Obstacle Avoidance in complex environments like this is a calculated risk, but simple flight, care and attention to the environment go a long way. For most other situations, it makes sense to have Obstacle Avoidance switched on, and it will, for the most part, help to keep your drone safe from collisions.

How does LiDAR work with vision sensing?

The forward-facing LiDAR of more advanced DJI drones, including the DJI Mavic 4 Pro and the DJI Air 3S, emits and receives lasers to identify obstacles ahead. Since the LiDAR is forward-facing, it can only sense in this single direction, unlike the standard vision sensing system. If and when an obstacle is identified, the drone will bypass obstacles or brake depending on the situation.

LiDAR is mainly used during low-light and night flights, and the drone will automatically switch between the two systems depending on the conditions. It will also, in some situations, use both systems at the same time. The LiDAR system can work with distances between 20 inches / 50 cm and 82 ft / 25 m. Objects with a diameter greater than 2.5 cm and a reflectivity greater than 40% can be identified, although LiDAR can’t identify wires, glass or snow.

DJI drones with advanced Collision Avoidance

James is an award-winning freelance landscape and portrait photographer, as well as a highly experienced photography journalist working with some of the best photography magazines and websites with a worldwide audience. He’s also the author of The Digital Darkroom: The Definitive Guide to Photo Editing. www.jamesaphoto.co.uk

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