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The drone was originally shuttled at high altitude, and I don’t know what the obstacles are. But the popularity of multi-rotor has changed everything. Low-altitude applications such as plant protection, shipping, surveying, crossing, entertainment, and photography have become the norm. Then the various obstacles on the ground became abrupt, became valuable, and could be speculated. So large and small drones began to talk about obstacle avoidance whether they were necessary or not. 
Obstacle avoidance diagram / map source network
What is obstacle avoidance ? Simply put, it is to avoid the route or the objects encountered in flight, to avoid damage on both sides, pay attention to both sides. How to avoid obstacles? To solve three problems: 1, what types of obstacles; 2, how to locate obstacles; 3, how to avoid.
Simply put, there are three types of obstacles: big obstacles, small obstacles, and moving obstacles. Big obstacles are insurmountable, such as walls, buildings, mountains, etc., and such obstacles can only be avoided. Small obstacles are obstacles that can be avoided by poles, trees, and the like. The obstacle is the human and animal birds. Some people say that flying a stone, okay, it can be considered. For the latter two obstacles, most manufacturers are vague, because the real obstacle avoidance, know the obstacles to know its location; avoid obstacles and know where to hide. It's not as simple as rumoring, it requires a series of sensors and algorithms.
And is this kind of obstacle avoidance really needed? We can see that the obstacles are all in the entertainment process. The basic problems encountered in industrial operations are small obstacles. Why can't we use the route to avoid it? The tree is a dead person is alive, is it really necessary to avoid obstacles? Some people say that there are birds in the operation process. Why don’t the man machine do obstacle avoidance? The reason is very simple, and the evasive action may encounter new obstacles, leading to new control problems. The aircraft is not a toy. It cannot be caught in an unknown danger to avoid known dangers. It can only improve the aircraft's anti-collision performance. Only entertainment drones are needed, because the aircraft itself is not worth the money, and the damage to people and buildings is greater.
The sensor for obstacle avoidance is the biggest pit in the promotion now! The so-called obstacle-avoidance sensor does not exist because the sensor can only detect and cannot escape. It's like being able to write an article, it's all like a writer. The sensor can only be used with distance sensor, scanning sensor and binocular vision.
Distance sensors refer to ultrasound, radio ranging (promoted as radar), and laser ranging (promoted as lidar). They all actively emit sound waves, electromagnetic waves or lasers to the front material, and measure the echo time difference to determine the distance. Therefore, they are suitable for the detection of large obstacles. For small obstacles and moving obstacles, they can only know whether there is any, and they cannot know the position or even the distance. And there may be problems with uneven materials (vegetation) and non-solid materials (water surface). Therefore, these sensors that should be used for flying height are used to avoid obstacles.
Scanning sensors are equipped with a rotating device on the distance measuring sensor to continuously detect obstacles in all directions by rotation. Commonly, laser scanning and ranging, with plane and three dimensions, his biggest problem is the long life and cost of mechanical components.
Then there is the binocular vision. This kind of equipment that has been in the laboratory for many years has finally come to the table this year, and the effect is to be tested. The distance between each point is calculated by the difference of binocular video, which is the same as the principle of human eye distance. But as long as the image processing is done, this is the most practical device in terms of cost and practicality. Now is the bottleneck of processor performance and algorithms.
Let's talk about obstacle avoidance, there are three ways to deal with obstacles, stop and other instructions, planning obstacles and autonomous obstacles. Stopping is the most basic way to deal with it. You must do this when you encounter big obstacles. Planning for obstacles applies to small obstacles, which is economical and reliable. Autonomous obstacles require the aircraft to evade the algorithm, regenerate the route on the aircraft, and face new problems. I think only the entertainment drone has this need, because the obstacles it faces are much more valuable than the aircraft.
Conclusion: Obstacle avoidance needs to be carried out, but autonomous obstacle avoidance is not necessary. It depends on the flight environment and the value of the aircraft to determine.
With the release of a new round of entertainment drones , obstacle avoidance has once again become a hot spot. Why do drones avoid obstacles, how to avoid obstacles, and what are the techniques and pits? Today is August 18th.
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