25

With aircraft, there are 6 degrees of freedom (DoF) we want to control (roll-pitch-yaw, and x-y-z), but for hovering vehicles (i.e. rotorcraft) we can get away with controlling two degrees of freedom (x-y) by combining the 4 other degrees (roll-pitch-yaw + z). There are many ways of controlling those four DoF, typically: helicopters, which use variable ...


18

Thrust is proportional to the change in momentum of the air passing through the prop - i.e. how much the prop speeds it up. The power required to do this is proportional to the kinetic energy of the air, which is proportional to speed squared. That 'squared' is the problem. A smaller prop acts on less air, so it has to speed it up more to generate the ...


17

Yaw authority and ease of mixing is generally the answer - since yaw response isn't necessarily the most linear, being able to have N number of motors contribute to yaw in one direction with the same number in reverse is the simplest motor output mixer configuration. Tricopters do work and are relatively common among odd-numbered multicopters, but once you'...


17

An explanation for why this is can be found in this Aviation.SE answer: Why aren't large, low-speed propellers widely used?, which I'll paraphrase here. The thrust a propeller generates is a function of its velocity and geometry. It makes sense that a propeller spinning faster will also generate more thrust. For a smaller propeller to generate the same ...


17

One practical advantage is increased ground clearance, reducing the likelihood of a prop strike on landing or take-off. Aerodynamically, a pusher1 design can be less efficient because the propeller is spinning through the wake of the fuselage - this results in 'lumpy' air, causing vibrations. I don't have exact figures, but I've heard anecdotally that this ...


14

Expanding on @Kralc's answer: Here's a study (unfortunately behind a paywall) that I'm going to copy key parts of below: The hexacopter was mounted on a load cell test stand, and data were collected in the University of Michigan’s 5 × 7 ft wind tunnel over different freestream flow speeds, motor thrust percentages, and hexacopter angles of attack. To ...


13

You know those rubber wristbands that are given out at lots of events? You can wrap one of those around the motor bell to get better purchase on it, and then torque down the prop nut. There are also specialised tools to hold motor bells, such as the one pictured below which can be found here, on Thingiverse.


13

To clarify, the 48kHz is NOT running on the gyroscope or the FC firmware. What 48kHz is referring to is the PWM Frequency in the ESC, namely the frequency at which the power MOSFETs on the speed controller switch on and off in order to provide power to the brushless motors and therefore thrust to the craft. The reason in whoops and small/light craft 3" and ...


12

Overview The most efficient propeller is single bladed, has infinitely narrow chord, has infinitely thin airfoil, has an infinitely long blade, spins infinitely slowly, and requires infinite torque. So at the risk of stating the obvious, propeller design is a study of the tradeoffs and compromises required to make something practical. Here's a list of some ...


12

Background Stiffness, oscillation, and vibration damping are separate concepts but all somewhat relevant to the question. Each affects flight dynamics, and each is (somewhat) a function of material choice. For example, titanium is very stiff, and it rings like a bell. CF is very stiff, but it rings like mud. Aluminum is in between. Stiffness Stiffness ...


11

The way the PID controller works is whenever the actual rate of rotation of the quadcopter does not equal the setpoint, or desired rate of rotation (which you set by moving the sticks), it sends a signal to the motors to compensate and bring the rate closer to the setpoint. This signal is a sum of four terms: The P, I, D and FF. Since it's a sum, you can ...


11

As far I know the only difference is on the whoops. They fly much better on props out. On 2,5-5 inch quads, it doesn't matter. Props in: our camera is dirty, you can stack easier on the tree. Props out: Your flight controller is dirty and then you damage your prop it's a higher risk that pice of the prop damage your flight controller or battery (it is a much ...


11

This is a very interesting question, and one that is always my favourite to answer. Firstly, rotary aircraft commonly need an even number of propellers (though not always) or another way to counteract the inertia of the props. Think, for example, why helicopters have a propeller at the end of their tail boom; they need to counteract the rotational forces of ...


11

It depends on what kind of stability you're after. Nicolas Petit wrote a paper on this several years ago, the graphics below are taken from Pages 4 and 5. The summary is that a higher CG is better for x-y position stability, a lower CG is better for speed stability. Background Before we begin, let's assume we're only talking about a drone flying purely ...


10

30,000 foot view of feedforward as a general concept Feedforward: I hand you a closed box and you anticipate that it will be heavy, bracing yourself in preparation. Your control of the box is rapid and precise. Feedforward failure: I hand you a box and it's much heavier than you anticipated. Your control of the box is sloppy until you recalibrate and ...


9

In order to access the 32kHz gyro sampling mode, the gyroscopes in question (e.g. ICM 20689) would be switched to an experimental mode where there is higher gyro data jitter, and that sampling at the lower 8kHz frequency made use of lower overall latency lowpass filtering built into the gyro. Often to get usable gyro data from the 32kHz sampling rate, more ...


9

In theory, you can't accelerate and decelerate the props as quickly. If the motor accelerates, the props lower angular velocity keeps it from accelerating too quickly. Same for deceleration: if the motor decelerates, the prop's momentum makes it want to stay fast. It is only when the prop's position exceeds the motor's position, that the centrifugal force ...


8

The primary reason that I fly props out is to use the props to push the quad away from trees/gates etc when flying forward. There is a theory that because the leading edges of the rear props are on the outside that it might compensate for the dirty air coming from the front props in forward flight as well, but I've never noticed any difference in flight on ...


7

I have found that the simplest and probably one of the safest ways is to use a compressor (alternatively a compressed air can will probably work), to lightly blow away the dirt. This works especially well if you just want to get rid of grass straws or similar. If you want to more thoroughly clean something Joshua Bardwell has a video on how to clean a motor,...


7

Assuming that you've spec'ed a good propeller-motor match and the heat isn't generated by a tiny motor being forced to drive a giant propeller, the heat generation is likely due to a physical issue with the drone, mistaken filter settings, or a tight PID tune. First of all, it's a good idea to determine whether your motors are actually hot enough to matter. ...


7

When looking for a battery, there are a number of factors to consider: the voltage (or S rating), the capacity, the C rating, the type of connector, and the weight: Voltage You will often see batteries having an ‘S’ rating on them, for example 6S or 4S. This is the number of cells, which directly impacts the voltage output of the battery. Just to be clear, I ...


7

So long as your additions are very lightweight compared to the drone - like stickers or paint - this should not have a significant effect the balance of your drone. However, you want to make sure that you do not cover any ventilation holes or heat transfer surfaces as this might affect the lifespan of those parts. In the case of metallic additions (shiny ...


6

I would personally recommend using isopropyl alcohol or mostly any other type of alcohol and using it with a cloth to gently clean the drones shell and propellers off any marks/stains. This shouldn’t damage the drone. As well as this, a microfibre cloth could also work well.


6

So this method will vary based on whether they are brushed or brushless motors. For brushed: Spin the propeller with your fingers - is anything actively resisting the motion? If yes, remove the prop and check for something not immediately visible, like a hair or carpet fibres caught around the motor shaft. Remove anything you find and try the prop again. ...


6

Airmode and idle up both seek to increase a control authority and stability during ultra-low throttle moves. In normal flight, when the pilot commands the multirotor to pitch or roll (cyclic), the flight controller responds by increasing thrust on one side of the craft and decreasing thrust on the other side by the same amount proportional to the cyclic ...


6

Comment number 7 at this link is an excellent source (and fairly trustworthy as it was written by Joshua Bardwell). The main reason specified for the efficiency is that for a given amount of thrust, a larger propeller (on a motor with an appropriate KV) will draw less current than a smaller propeller on a higher KV motor, so there is less sag. Another ...


6

Surprisingly, that flexible coupling is actually a good thing. If you look at helicopters, this is called a lead-lag hinge, and it allows the propeller to match flight loads when flying around. What happens is the blade advances in the hinge as it retreats in the airflow, and retreats in the hinge as it advances in the airflow. (Watch a fully-actuated ...


6

The advantage of running at higher voltage is that you can use thinner wires and lower current (i.e. cheaper) ESCs, as power lost to resistance is proportional to current (squared) and not voltage. Another reason can be to reach higher prop RPM when you can't find motors with sufficiently high kV, or merely want to continue using the motors you already have....


6

Rounded leading edges are better for subsonic aerofoils. Props and wings have to work at a range of angles of attack. The airflow has to split to pass either side of the aerofoil, and a rounded leading edge allows the separation point to move smoothly. Sharp leading edges cause a lot of drag at extreme angles of attack when air has to flow across the sharp ...


6

Without disassembling the motor, and figuring out how the ESC is designed, there is no other way then simply testing it. From my experience, the motors spinning clockwise has usually been the ones that can be wired without crossing any wires and without having to reverse the direction. But that could just be a coincidence, so you should definitely not trust ...


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