21

A stable system is one where there's a force that pushes the system back towards it's original state when the system is moved from its balance point. For example, when the driver gets into a car, there's more weight on one side of the car than the other but the car doesn't flip over. The springs on that side of the car compress and push harder on the wheels....


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 ...


9

Gain, as a general term, is a measure of how large or strong something (a voltage, a radio wave, a sound wave, or whatever else) is relative to some baseline value of the thing being measured. A gain is a ratio: If a device takes a voltage on one end and makes it 20x larger (amplifies) it 20-fold, it has a gain of 20. In practice they are represented using ...


7

Inherent stability is a concept from aeronautics – it is the tendency of an aircraft to return to an equilibrium when the controls are released by the pilot. Quadcopters are not inherently stable. Say, you have the quadcopter rolling to the right: (image source) A quadcopter requires active counter manoeuvres to restore it to a stationary hover: (...


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

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

Like most things, it depends on how you treat it. As far as I know, you should never need to worry about a brushless motor wearing out, especially for our purposes where we will likely demolish them before they have a chance to wear out. You do have to watch out for the bearings and magnets, however. With the bearings, like any mechanical component, they ...


5

'Antenna gain' gives you the power transmitted by an antenna in a specific direction, when compared to a theoretical antenna that radiates equally in all directions (this is known as an 'isotropic antenna') In effect, 'Antenna gain' defines how strong a signal a particular antenna can transmit or receive in a specified direction. Antenna Gain is related ...


5

If you're using a flight controller running either the Cleanflight or Betaflight firmware, you can make use of the builtin "Blackbox" logging features. These firmwares rely on the flight controller to have a MicroSD card slot which you can populate or an onboard flash chip to save the flight data to. In order to configure the flight controller to use ...


5

Altering the location of the CG (center of gravity) also changes the CM(center of mass) because the force of gravity acts roughly on the CM. Normally, the motor arms are equally sized so that all motors have equal control authority and all contribute equally to providing thrust while in level flight when the CM is close to the center of the multirotor. ...


4

There are also some external logging devices that are available if you have a free UART on your flight controller. For example the OpenLager project which is a fast serial attached SD card logger, which you can purchase from Racedayquads and others if you search for it. Theres also the SparkFun OpenLog which is basically the same thing, but not quite as ...


4

Aside from fancy material science which can result in propellers that interact with air more cleanly and is highly proprietary, the primary way a propeller could gain more "grip" on the air is by being more aggressively pitched or having more blades. In a propeller spec which can be displayed either as: [diameter in tenths of an inch][pitch in tenths of an ...


4

The simple answer is "more width equals more torque". More torque let's you drive a higher pitch or larger diameter prop effectively. Given the same size prop, it will drive it with more effectiveness. Added torque allows the prop to spin up or slow down faster, which ultimate results in a better flying quad because it can more quickly and accurately ...


4

I personally have never used a Deadcat frame, but I found this forum thread asking a similar question, the answer is: I was more interested in how the dynamics of a dead cat might affect efficiency. But based on what some of the long-range guys have found, it doesn't appear to be an issue. One thing that did come up with the SG+ at its genesis was ...


4

I'm afraid it's not that simple. As you mention, planes can fly with a fairly low thrust to weight ratio. Obviously gliders can fly with no power at all, so there's no critical lower-limit. The other issue is that pitch-speed is important - the prop needs to be producing thrust when the plane is moving, not stationary. Measuring static thrust only tells you ...


3

To simplify this discussion, it's easiest to focus on a single size class for these motors - 22XX-24XX motors on 3.5-6g propellers (5"-6"). It is also incredibly difficult to decouple effects of batteries and propellers in concert with these changes. Generally the wider stator is capable of greater instantaneous torque, and can generate a proportionately ...


3

I've heard that you want to keep your battery weight no heavier than 1/3 your drone weight.


3

TL;DR: Yes, a semi-rigid frame will cause vibrations while flying because it alters the nature of motor and propeller oscillations as the frame parts move around. This will cause a drop in efficency as the flight controller attempts to combat these vibrations and return to stable flight, using slightly more power in the process. Excessive vibrations in ...


3

tl;dr: In terms of radio performance, they're almost identical if you compare similar-gain models, so choose based on dimensions, durability, maintainability and other practical considerations. If you're buying, patch is usually better simply in terms of size and toughness. However, consider DIYing a helical; it's cheaper, a nice project to do, and makes a ...


3

It is my understanding that in general a helical antenna will perform better than a patch antenna. I should really find a source for that though. However a patch antenna is flat or nearly flat and thus easier to pack and transport. The bulkiness of the helical is probably the main drawback. RcModelReviews has some great instructions on building your own ...


3

7" props have a disk area that is almost twice as large as 5" props, so the motors will be heavily overloaded. (7 squared is 49, 5 squared is 25, the other terms in the equation for the area of a circle cancel out) Assuming you use 5x4.5 3-blade props on a 5" quad, you could reduce the load 33% by switching to 2-blade props. You can reduce the load further ...


3

Lower kV motors will spin more slowly but with more torque. Spinning more slowly (with the same prop) will give you less thrust and less power (and thus lower current) at full throttle. However, a well setup quad doesn't spend much time at full power, especially when you're considering your total flight time. The amount of thrust required to fly is still the ...


2

Antenna gain is a measure of how effectively an antenna sends or receives a signal. It is a relative measurement and is usually a comparison to a simple antenna design called a dipole antenna (dBd) or an ideal reference (dBi) - often a manufacurer picks whichever of these numbers happens to be bigger. Gain of below 1 means the performance is worse than this ...


2

Not really. Since brushless DC motors have no brushes to get worn out, they represent a huge leap forward in technology. Brushless motors have significantly higher efficiency and performance, and a lower susceptibility to mechanical wear than their brushed counterparts. They can last 10,000s of hours if used correctly and not overheated etc.


2

I don’t think there are diminishing returns, if the propeller+motor+controller efficiency stays the same regardless of overall weight. Imagine a drone where all the weight is in the battery and the motors have just enough power to hover the drone. Double the battery and you’ll double the capacity but you’ll also double the weight (and required power output ...


2

Other than running high cell count batteries on low-power drones for the lols, there isn't much point in doing this, which will result in the throttle being SUPER twitchy and ultra-responsive to small stick movements without throttle correction. Increasing the battery cell count on a multirotor results in an increase in motor RPM because kV rating of the ...


2

I am going to jump in here with more than comments to other answers and I am going to answer this question in my own unique way. First, I have a similar related question, and I recently posed it to an industry expert. I asked a question about stiffness of Carbon Fiber frames. Sorta like this: "How stiff is stiff enough?" And the answer which I will ...


2

The amount of force generated remains the same, however it is applied in a different direction; you therefore get an effective reduction in force for a given axis. To use the two extremes: If the airflow is straight down, all of the force is used for lift If the airflow is completely horizontal, none of the force is used for lift Aligning the motor at ...


2

The motors would still generate the same amount of thrust, however it would be aimed in a different direction. Think of the thrust as horizontal and vertical vectors. You can work out the ratio of these vectors using trigonometry to work out how much of that thrust is going to be effective in the downwards direction and how much will be horizontal.


1

Propeller tip losses are a function of, or perhaps we could say it is a side effect of the propeller design itself. The designer of a propeller can influence the tip losses, but a user is unlikely to find a practical way to accomplish it for a propeller they already own. So this question is theoretical. The overall size and geometry of a propeller can ...


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