# Tag Info

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 ...

19

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 ...

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

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)/dt;...

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

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 = ...

9

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

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

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 ...

8

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

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

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 ...

6

Something you can do WRONG to very easily unstabilize a quadcopter is to put the wrong propeller on the wrong motor. There are both pushers and pullers, and depending on the configuration you choose, you need the right type. Its possible you had two of them swapped. When they broke, you got the new ones on properly. This page really helped me. This one has ...

6

Using a so-called optical flow sensor is the best way to help with holding the horizontal (i.e. in X-Y plane) position. I don't see any reason why you couldn't do the same for vertical control, although a sonar is probably easier and cheaper to use for this (likewise, if you are indoors, you could use 2 sonars for the horizontal position as well) People ...

6

It looks like your proportional gain is too high. You seem to be constantly increasing RPM on one motor while locking in the other one to make the system rotate. This isn't a good control strategy as eventually those are going to both saturate and you will lose control. Also as time increases your ability to command the system decreases. So you need a ...

6

Yes, they are dangerous. I've cut myself multiple times. Once through the nail. The small toy helicopters are apparently some cause for increased eye injury, although studies suggest the injuries are usually not severe. Larger helicopters though seem to have caused fatal injuries in the past.

6

Ironic answer: you do not need any channel, but your quadcopter will just hover stationary :) Practical answer: The throttle controls translation on the vertical axis. This allows you to gain or loose altitude. Depending on how the quadcopter is programmed you may control the vertical acceleration or the vertical speed (aka autolevel mode). The rudder ...

6

A quadcopter contains (among other things) two separate and independent algorithms: an attitude estimation algorithm, and a control algorithm. The attitude estimation algorithm computes information about the orientation of the quadcopter: the roll, pitch and yaw angles. The control algorithm is responsible for driving the motors so that the orientation of ...

6

In a normal quadcopter configuration, if you tilt you will be pointing some of the lift force to the side. The only way to hover at a tilt, then, would be to somehow apply a counter force. A standard quadcopter can't do that itself, so it would need be an external force (tether, wind, etc). Your other options are to use a nonstandard configuration such as ...

5

A Vicon motion capture system system is used in the TED Talk that you referenced. It is similar to a Kinect in that gives the 3D coordinates of any object being tracked within its field of view. Like the Kinect it uses IR, but uses IR reflective balls attached to the quadrotor and the presenters pointer to identify and track objects. Not to mention it is a ...

5

For the smallest (and cheapest) of multicopters, DC brushed motors are well in use: http://www.rcgroups.com/forums/showthread.php?t=2009496 They are coreless motors1 and have very little inertia, can accelerate very quickly and are perfectly suited for high frquency PWM (we drive them with up to 32kHz). You can achieve more than 3:1 power:weight ratio on a ...

5

In a helicopter (which has 2 rotors, one main rotor and one tail rotor) the angle of attack of the main rotor controls the altitude, pitch, and roll. The yaw is controlled by the counter-torque rotor (tail rotor) which counter acts the reaction torque exerted by the rotation of main rotor which acts on the body of the helicopter. Cyclic Control for Pitch ...

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