# Tag Info

41

For quadcopter designs, you generally want to have around a 2:1 thrust-to-weight ratio. That is, at 100% throttle, you want your combined propeller thrust to be capable of lifting two times the weight of the craft. You then need to determine the amount of power the motors need to generate that thrust (usually given on the datasheet). When you have that ...

31

Choosing the correct prop/motor combination can be challenging. Even worse, the vast majority of RC motors will have vague or non-existant specifications. This makes it very hard to do "real" math. Instead you will have to rely on prop thrust ratings or use a known combination that other people have tested. Propellers: Manueverability of a quad is ...

21

At least in part quadrotors offer a nice balance between the complexity of the dynamics and power requirements. With traditional single rotor helicopters, control is a function of the orientation of the rotor which means you must change its orientation to change direction of the craft. This makes for very complex mechanical linkages comparatively speaking ...

19

Is an underwater quadrotor possible? Absolutely. Whether it's practical in that configuration is a different matter. In air, viscosity and buoyancy are negligible; in water, they are not. An aerial quadrotor will expend energy fighting gravity, while an underwater quadrotor can simply rely on positively bouyant materials to keep it from sinking. You ...

18

The answer to the larger question here is that when running the initial test of any vehicle that has the capability to harm itself, it should be sufficiently restrained until you are satisfied that it can be kept under control. In the case of a quadcopter, this would involve tying a bit of string to the corners, leaving enough slack so that it can rise 6-12 ...

18

Most motors on quadcopters are outrunners. In outrunner motors, the rotating part is on the outside, and not the inside (as opposed to the inrunner motors). Because of this layout this type of motors can generate much more torque. High torque is required for quadcopters, since you balance by changing the revolutions of the motor. The higher your torque the ...

17

As Rocketmagnet suggests, what frequency you "need" will depend on a lot of things. The more responsive your rotors are, the more sensitive your craft will be to random spikes in motor commands. These random spikes may be caused by noisy sensor readings caused by physical imperfections, which means you would need to lower your controller gains, which in turn ...

16

You almost definitely want to have the battery rigidly mounted to the center of the airframe. Mounting a battery underneath each motor (though I have never seen this) will increase the multicopter's moments of inertia, which will make it more "stable" in that it will more sluggishly lose its balance and thus give a controller more time to react. This, ...

13

I'm guessing that your question is based on whether the mathematical model of a quadrotor would work in a water environment, and not the hardware. Quite obviously the electronics and mechanical systems would need changing to work in the water: the electronics would short and the rotors would spin too fast. The rest of my answer is based on the work Design ...

11

Just to add to user65's good answer. Rapid rotation about a horizontal axis will come from a large difference between the thrust produced by opposite motors. The larger the difference, the greater the rotation rate. So motors that can produce much more thrust than is needed to simply hold the 'copter in the air will help to achieve fast rotations. Rapid ...

11

The brushless motors are way more powerful for their weight than available brushed motors, and they last longer. Power to weight ratio is king, in an aircraft.

11

In controls this is known as disturbance rejection. In order to sustain your motion in the presence of high winds you need the controller to be as responsive as possible, and an accelerometer would help. A fast loop rate will also help. You also have to deal with the nonlinearities of thrust, drag, weight, and lift. Depending on the design of your ...

11

The glaring issue I see at the moment is that you are forcing polarity on the I and D terms. In general, you are using a lot of sign checks, sign assignments, and conditional programming. None of that belongs in a PID controller. The entire controller should look like: pError = Input - Output; iError = iError + pError*dt; dError = (pError - previousError);...

10

You need 4 degrees of freedom to control yaw, pitch, roll and thrust. Four props is therefore the minimum number of actuators required. Tricoptors require a servo to tilt one or more rotors which is more mechanically complicated. There is no restriction to only 4 props, hexa+ coptors are also very common. Generally you want an even number of props unless ...

10

For testing simple algorithms, you might be able to get by with a 2D simulator. There are a few out there that I am aware of: Stage: http://playerstage.sourceforge.net/index.php?src=stage STDR: http://stdr-simulator-ros-pkg.github.io/ Stage is an older, but useful, simulator which has integration with ROS (http: //wiki.ros.org/stage_ros) which will allow ...

10

The barometer carried on the pixhawk has an altitude resolution of 10 cm. If that isn't enough, you could write a kalman filter that uses the accelerometer data in the prediction step and the ultrasonic sensor and/or the barometer in the correction step. But I don't see this solving your problem. An accurate measurement of altitude at 20hz should be plenty ...

9

Yes, in general this idea is perfectly plausible. However the method is going to be specific to your setup. I.e. the operating system you are using on your control computer and the onboard controller that you are employing. In our lab we use an Ardupilot Mega as our onboard controller for some of our quadrotors. To solve this problem I used the Linux ...

9

Let's look at how a quadrotor flies, then apply that to a trirotor. Let's assume that we want to remain in a stationary hover position. To do that, you need to balance all the forces: thrust from the propellers vs. gravity, and the torques of each motor. Each motor produces both thrust and torque according to the equations: $$T = K_T\rho n^2 D^4$$  Q = ...

8

Center, you want the moment of inertia to be as small as possible.

8

You're trying to implement more PIDs than you have degrees of freedom. In a quadcopter, you have only 4: $(Z, \phi, \theta, \psi)$ i.e. (Altitude, Roll, Pitch, and Yaw). via (http://www.draganfly.com/uav-helicopter/draganflyer-x4/features/stability.php) Interestingly, from a PID perspective you definitely do have desired values for $\phi$ and $\theta$: ...

8

You could probably calculate this value, but the sensible thing to do would be to just measure it directly. Just turn it upside-down and put it on a kitchen scale as shown in this video.

8

This is video is from an Edx course on Autonomous Quadcopters...It is 10 minutes and goes over the "Flying Principle" of quadrotors. But basically what you are missing is the reactions. The famous Newtown's third law says (paraphrasing) "for every action there is an equal and opposite reaction". So by spinning the clockwise blades faster, a counter-...

8

It all depends on the video quality that you require. The short answer is to use a 3G or 4G transmitter, assuming that you are in an area with mobile coverage, to either a local device (Mobile phone) or a cloud based service. Other options exist, including the use of XBee networks. XBee networks (depending on the series used and protocol, and whether you ...

7

If your goal is to experiment, then use the cheapest option possible -- it will give you the freedom to make more mistakes. Carbon fiber would be great if your design is in a fairly final state, but are you 100% assured that you correctly determined all the thicknesses, mounting holes, wiring guides, etc? Are you good enough working with carbon fiber to ...

7

The following diagram (1) illustrates a method by which a Lancaster navigator determined airplane height above the water of a lake. Such a method is useful if the ground lacks features needed for other forms of Visual Servoing. A program I saw about mission Chastise showed one spotlight shining green and the other red, to avoid confusion about which way to ...

7

Even very small errors can bother the balancing. Small errors such as: Weight of the quadcopter is unbalanced. One motor is rotating faster/slower than others due to manufacturing or your power-source. Air resistance and wind. Unbalanced propellers due to manufacturing. Strong magnetic forces. You simple can not send the same motor speed to all motors ...

7

Similar answer to this post: Choosing motor for a tricopter This depends on what you want to do with your copter. Hovering: 100-150 Watt/kg ScaleFlight: 200-300 Watt/kg Some chilling acrobatic flight: 350-400 Watt/kg 3D acrobatics 500+ Watt/kg Hardcore 3D 1000 Watt/kg Just take your motors and your flight style and you got some values for the max weight ...

7

Gyro is needed to stabilize angular acceleration. Knowing only your attitude, drone doesn't know how fast on which axis is rotating, knows only where is gravity vector. Gyro gives you feedback on angular acceleration and that's what gives your drone stability. Also, you can use only gyro in your drone, it will stabilize movement, but won't get back to ...

7

A couple things, the first is that the controller does not really care what the "real" values are. Everything is relative, if the controller sees that it is sinking it will increase the thrust until it is not sinking. If it is tilting too far to the left it will decrease the right thrust and increase the left thrust. (Here is a good resource if you want to ...

7

These are markers for a visual Motion Capture system. Buy some markers here Most MoCap systems work by setting up multiple cameras with strong IR-Flashes and IR-Cameras and the surface of the balls are optimized to reflect the specific wavelength. The cameras then almost only see the markers and can use triangulation to compute their position. As at least ...

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