Zbip57
lvl.4
Canada
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Here are a couple more diagrams. I rounded it up to an even 250 grams to make the math easier for y'all. Also, let's assume this drone is perfectly symmetrical with the Centre of Gravity located dead centre. Since it's symmetrical these diagrams could be depicting the drone viewed from the side, so you see the front and rear rotors and the drone pitching forward or back. Or, the diagrams could just as easily be showing the drone viewed from the front or back, so you're seeing the left and right rotors with the drone rolling left or right. The math is exactly the same either way.
In a level hover, with no wind, the rotors only need to provide equal lift (125 grams) on each side to counteract the 250 gram weight of gravity. Because the rotors are spaced at equal distance from the Centre of Gravity, and are exerting equal lift, no torque is being applied around the Centre of Gravity. This drone will therefor not change attitude (pitch or roll). The total upward force matches the total downward force, so the drone will neither climb or descend.
An increase in lift at one end, while decreasing the lift at the other end, say 150 grams and 100 grams, still totals 250 grams to counteract gravity. But the differential in lift will create a torque applied around the Centre of Gravity, causing the drone to change attitude (pitch or roll).
Let's say the drone pitches or rolls to an angle of 45° as shown in the second diagram. [I realize the Mini's autopilot prevents reaching such an extreme angle, but the math is simpler at 45°.]
In order to maintain a constant 45° angle, the forces have to balance. Gravity is still pulling straight down on the 250gram weight of the drone. But the props are now canted at 45°. In order to balance the force of Gravity, the props still need to generate a combined total of 250 grams upward thrust. And, to prevent the drone pitching or rolling further, they still need to generate the same amount of thrust at each end to maintain Zero Torque around the CofG.
Because the props are canted at 45° the motors now need to speed up to generate 177 grams of thrust at each end, splitting that into 125 grams of upward lift and 125 grams of horizontal thrust. Upward thrust now again equals the downward pull of gravity, so the drone will not sink. But we have a combined total of 250 grams of horizontal thrust, forcing the drone to accelerate horizontally in that direction.
The drone will continue to accelerate in that direction until a total of 250 grams of drag counteracts the horizontal thrust. At that point the drone reaches and holds a steady speed, and altitude (height).
Because the drone is symmetrical, the aerodynamic drag should be distributed equally across its body. But some of you seem to believe the drag is not evenly distributed, i.e there is more drag on the trailing higher end of the drone compared to the leading lower end of the drone, requiring the rear motors to speed up to counteract the torque that's trying to flatten the drone back to horizontal. Why is that?
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