hallmark007
Core User of DJI
Flight distance : 11959747 ft
Ireland
Offline
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asaw Posted at 2018-4-27 09:21
OK, on flying without a compass. The problem here is to stabilize orientation - the pitch, roll, and yaw angle velocities - at first and then the position in space (latitude, longitude, height, and heading). To fully stabilize pitch and roll it is enough to know the accelerations along two axes determining the horizontal plane and corresponding angular velocities. To stabilize yaw the angular velocity along the vertical axis is needed. The IMU provides accelerations and angular velocities along all three axes, so there is more than enough information to stabilize the angles. This is what “gyros” in RC helicopters do. But as everyone knows flying an RC helicopter is much harder than flying any of the DJI drones. Because simpler “gyros” in helicopters only stabilize angular velocities, more advanced ones also stabilize pitch and roll relative to the horizontal plane. But they don’t stabilize the aircraft position in space: if there is a gust of wind it can easily blow the helicopter away and the pilot must always be ready to compensate for that. DJI drones add GPS and various other sensors (ultrasonic/infrared/vision/etc) to fix aircraft relative to the ground as precisely as possible. Vision sensors, for example, yield velocities which is enough information to stop the AC from arbitrarily moving in space. Note that these are not the absolute values of latitude and longitude but rather some values proportional to their derivatives. And still, these are just enough to adequately stabilize the aircraft’s position in the absence of GPS data (when flying indoors for example). It is basically the same thing with the compass. You only need a compass to know the “absolute value” of heading. But in order to adequately stabilize yaw, you only need to know the yaw rate, which is given by the IMU (and which should equal the first derivative of heading). If your compass malfunctions you still have two IMUs that give you the corresponding angular velocity. In fact, yaw angle in RC helicopters is the most stable one. So this is how you fly without a compass. If you want to automatically navigate without a compass using GPS you do it in the same manner as you navigate without a compass in your car: you choose an arbitrary direction and then compensate for errors. You don’t need to know your heading beforehand.
Again I’m talking about how it is now, not what you think is a better option, there are many around here that have really credible ideas about what could or should be done to these drones to make them safer and better and yes this should be debated and discussed and I have plenty of ideas as to how all this can be improved, but this is not what you or OP bought into, and that’s what’s being discussed here, I have said how these aircraft work I expected that you would have a different position on that, and that’s what I wanted to hear not how it should be done but how it is done at present. |
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