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I am asking this question to see if mid-air collisions of drones can be prevented using simple analog sensors. Can an ultrasonic sensor mounted on a drone pick up another drone strongly enough to sense and avoid it?

I know that the sensor is range limited so the aircraft cannot be flying towards each other very fast, but to even do any sense and avoiding, can this sensor work? Or does the drone not provide enough of a return?

Also, could the range of sensor be increased if both drones emitted ultrasonic energy to be picked up on the sensor more strongly at a distance?

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    $\begingroup$ by "ultrasonic sensor" do you mean an ultrasonic proximity sensor, or an ultrasonic microphone? $\endgroup$ – niels nielsen Mar 3 '18 at 0:55
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    $\begingroup$ Bats should be proof enough that it works, right? So why ask here? $\endgroup$ – Peter Kämpf Mar 3 '18 at 7:28
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    $\begingroup$ I think its going to have a very hard time hearing it through the sound of it's own blades hitting the air. That plus the vortexes created by the movement of the air would make sound detection very very tricky at best. $\endgroup$ – Jay Carr Mar 5 '18 at 22:30
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    $\begingroup$ @PeterKämpf Bats aren't beating the air with their wings 1000 times per second. Plus, a bats ears and mouth are ahead of the wings, so they have clean air to hear through. This is more equivalent to a hummingbird trying to use sonar when its ears are placed between its wings. $\endgroup$ – Jay Carr Mar 5 '18 at 22:31
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    $\begingroup$ @JayCarr, propeller/rotor noise is still not ultra-sonic, so it can be filtered out just fine and there is nothing saying the sensor is mounted in the middle—it can still be mounted ahead of the wings or rotor on the drone. $\endgroup$ – Jan Hudec Mar 5 '18 at 22:58
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The range of the ultrasonic sensors ends up at somewhere 5 meters (here is the pre-configured search). However a simple sensor would only measure the distance, by the signal travel time. It does not provide the angular co-ordinates or exact location. Same problem as with the simple radar.

May make more sense to fit the drones with transponders so that they could actively broadcast they own location, speed, orientation and intentions to other members of the flock.

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  • $\begingroup$ So he would need two sensors to pick up the angle then. $\endgroup$ – jjack Mar 5 '18 at 20:21
  • $\begingroup$ Three at least, to get azimuth and elevation. Plus some brains to calculate relative velocity and decide what to do about it. That is: a little more than just sensors. $\endgroup$ – Rob Vermeulen Mar 5 '18 at 20:57
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    $\begingroup$ This question doesn't really address the issue of noise distrubances caused by the operation of the drone carrying the sensor... The microphone may be able to pick up the sound under normal operations, but at 50kph in flight? I dunno... You at least need to address it. $\endgroup$ – Jay Carr Mar 5 '18 at 22:33
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There's a video of a ultrasonic-collision-avoiding drone. So, in principle, this should work. Also, note the reflector surface used by the guy in the second half of the video - it's not incredibly big (but, indeed, approximately orthogonal to the propagation direction of the finder beam). So, let's count this as "it could work, in principle" - especially, if you put more power into the outgoing sound waves, to pick up the weaker return signal of a drone.

But, as consumer drones already reach speeds up to 72km/h, it looks a bit unlikely that this is will become the go-to technology for avoiding a possible head-on collision. In this scenario, two drones will move in on each other at 2x72km/h, which is 40m/s. By using the numbers of @h22's answer, we get 1/8th of a second between earliest detection and impact. In this time you need to come up with a solution, and you need enough thrust to divert your course far enough to avoid the oncoming traffic.

I'd expect the physical reaction time of the drone - the time until max. diversion thrust is applied - as well as the amount of thrust, to be the limiting factors.

And your generic solution ("it's an obstacle, just fly upwards to avoid") may not work, as your counterpart may have the same idea, resulting in the same collision just a meter higher from ground.

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