# Tag Info

12

"LSB RMS" means the root-mean-squared value of the total noise in least significant bits of the digital channel. Roughly, that's the standard deviation of the noise times the weight of one step of the digital value. "$\mu g/\sqrt{Hz}$" means the power spectral density in micro-g's ($1\mu g \simeq 0.000098 m/s^2$). If the power spectral density is flat, ...

6

The main difference between accelerometer and gyroscope vs magnetometer is that first two give only relative information - you may calculate heading relative to your starting position, but you won't have any idea how this heading relates to world directions. What's more, as both gyroscope and accelerometer give you only accelerations values, calculation of ...

4

Mags are used in almost all UAVs. It will be useful and it will be a unique source of information. Adding a some shielding between the mag and your computers and power lines will greatly reduced the noise. Noise can be further reduced by twisting all of the wires that carry significant current (wires to motors and ESCs). Be aware that the measurement will ...

4

This is a complete re-working of the answer I had originally provided. If you're curious, you can check the edit history and see what was posted earlier. In comments to this question, OP stated that they might be able to get throttle and steering angles for the robot, but they probably wouldn't be accurate. That's okay; it's better than nothing. OP also ...

4

First, let's look at if your findings seem reasonable given the datasheet specifications for the sensor. For this, I'll assume that Wikipedia is generally correct and that the strength of Earth's magnetic field is on the stronger end of the range given (0.25 to 0.60 gauss), so I'll use 0.6 gauss. Then I'll also assume that +Y is oriented to magnetic North ...

4

Apparently a magnetometer is useless in indoor environments like man made buildings. I cite from this paper Multi-Magnetometer Based Perturbation Mitigation for Indoor Orientation Estimation Nevertheless, the success of these sensors for orientation estimation is conditioned by their capacity to sense Earth’s magnetic field in environments full of ...

4

The complementary filter you mentioned comprises of both a low-pass filter (which filters out, or attenuates, short term accelerometer fluctuations), as well as a high pass filter (which tries to negate the effect of drift on the gyroscope). A time constant $\tau$ with respect to first order filters describes at what point (the cut-off frequency $f_{c}$) ...

3

Calibration procedures for magnetometers exist, to compensate for soft iron (nearby ferromagnetic objects) and hard iron (nearby magnetic fields) offsets, which skew the measurements. However, these procedures usually map a static disturbance correction and apply it to all new measurements. On the contrary, your environment changes from one end of the tube ...

2

We always need a reference for calibration to which we calibrate our sensor. For example in case of 3D accelerometer we use gravity as a reference which is assumed vertically downwards at a place. For magnetometer calibration we use Earth's magnetic field as a reference. But we dont know the direction of resultant magnetic field vector at the place ...

2

OK so I managed to solve this by doing a couple of things. Connect external magnetometer to the same I2C bus as the FreeIMU. The FreeIMU is 5V and the external magnetometer is 3.3V so I had to use a level shifter to place both devices on the I2C bus. Change this line "accgyro->setI2CBypassEnabled(1);" to "accgyro->setI2CBypassEnabled(0);" to enable the ...

2

I doubt you need to add anything to the state vector regarding the magnetometer calibration. The magnetometer measurement should just be treated at another signal that triggers a measurement/correction update. Adding the magnetometer makes yaw ( how much you've turned) observable. Without the mag you will just be integrating gyro measurements. "Three-axis ...

2

A magnometer lets the drone control its geographical heading. It's really the accelerometer that tells direction (not the gyroscope) and, in this case, the direction is down-wards. This provides feedback to manipulate the drone's pitch-and-roll positions. A magnometer tells another direction - feedback used to manipulate the angular yaw position. At its ...

2

The point of a complementary filter is combine the low-pass parts of some measurements (e.g. accelerometer) with the high-pass parts of other measurements (e.g. gyro). If the accelerometer perfectly reflected the direction of gravity you wouldn't need the gyroscope part. So practical applications that successfully use complementary filters with an ...

1

There are several questions here, so I'll try to address them all. First, using the integrated gyro output. Integrating the gyro output, which provides angular velocity, gives you an orientation estimate. A lot of people that use the term "Euler Angles" generally actually mean Tait-Bryan angles. Proper Euler angles only use two axes, like an X-Z-X rotation,...

1

A magnetometer measures the local magnetic field. When assuming that the Earth is the only magnetic source, then this magnetic field should be constant in world coordinates. But the magnetometer measures the magnetic field in local body fixed coordinates. The world and body coordinates should be related via the unit quaternion. So the magnetometer measures a ...

1

Usually the magnetometer is used to find the yaw. It acts as a digital compass in this case. To calculate roll and pitch you need an accelerometer. But there are some techniques that can be used to calculate the roll and pitch using the magnetometer. For that you need to place a magnet close to the mobile phone and observe the sensor values. Using these ...

1

As mentioned in the previous answer, many small, low-cost underwater (and aerial) vehicles use a magnetic compass. You need a good procedure for both hard-iron and soft-iron calibration of your magnetometer. Constantly having to calibrate them sucks, but they're way less expensive than a FOG. With good calibration, you should be able to achieve adequate ...

1

id recommend estimating position, velocity, and bias in the yaw reading from the imu. You'd assume the yaw bias is a first order system driven by zero mean Gaussian noise. You can also estimate biases in your accel readings if you expect significant drift during operation.

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Typically, and unsurprisingly, proprietary information (to include part numbers, schematics, etc.) is closely guarded by companies. As such, I am not sure how much information you can expect to receive without significant effort on your part. For starters, you can be sure that Apple will not release its specifications or parts list. Take a look at the ...

1

A GPS unit doesn't give you heading, although it is possible to estimate the heading based on successive GPS readings. Unless you're looking to set and forget the heading, which you shouldn't be doing anyways because of wind and other disturbances, you should be using some form of a controller to do course correction along the path. Say you don't correct ...

1

The habitual way to do this is to have an attitude and position loop for the quadrotor, as in next picture. Attitude loop manages the quadrotor to achieve the desired angles (pitch, yaw, and roll). Position circuit on the other hand, calculates which are those desired angles depending on the path you want to follow or the point you want to reach. One GPS ...

1

As other people have said, in a steady-state condition, a gyroscope+accelerometer sensor suite can successfully estimate the roll and pitch values of the UAV, but not its yaw angle. However, there have been early successful fixed-wing UAV autopilots which managed to solve the yaw value through differentiation of the GPS signal. One such example is the ...

1

I don't think it would make a difference what the orientation is. I would recommend maybe using hall effect sensors instead of a 3 axis magnetometer if ALL else fails. That would be a last resort though because they are probably not going to give you the kind of accuracy and precision you are looking for.

1

Everything looks fine to me. Imagine if you kept driving in clockwise circles. Would you want your heading to be 18064? Would that mean anything to you? Which direction are you facing? No, instead whenever you would go below 0 it puts you up to 359, because counter clockwise of North is North-Northwest. Similarly, clockwise of North is North-Northeast, ...

1

There are a lot of possible ways to solve your problem. First, let's get you off the wrong track: this isn't a simple, line following problem. For it to be a line following robot, you need to lay track lines under your lawn for every place that you want to mow. Imagine a grid like a potato masher instead of the one your drew. The problem seems to be: ...

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I'll try to go through your question as best as I can: I was wondering, whether one could calculate the rotation of the sensor relative to the vehicle by application of the accelerometer and gyrometer? Without any more information than an accelerometer and a gyro, no, you cannot, because gyros measure velocity and accelerometers measure acceleration, ...

1

Yes, in theory, from the gyro information. The accelerometers will give you orientation information, but won't help you interpret where the axis has been translated to. Keep in mind though, that data from the gyros are time based and you will only have accurate information for the moments that you actually sample the data. I believe it will be difficult to ...

1

You may want to take a look at FreeIMU library that does 'data fusion' that combine raw data from multiple sensors and present user with a much reliable, stable and easy-to-use data in a roll, pitch and yaw (direction as you require) format. FreeIMU http://www.varesano.net/projects/hardware/FreeIMU This version from the original author use MPU60X0 chip. ...

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