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An Inertial Measurement Unit (IMU) is an important sensor used in aerial robotics. A typical IMU will contain an accelerometer and a rate gyroscope. Which of the following information does a robot get from an IMU?

  • Position
  • Orientation
  • Linear velocity
  • Angular velocity
  • Linear acceleration
  • Angular acceleration

I don't think it gets its orientation information from IMU. The last time I took the test, I said that all but the first two are true. I failed.

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  • $\begingroup$ Was this question asked on Coursera(University of Pennsylvania) from the subject of Robotics? Dude.... $\endgroup$ – Kirk May 11 '18 at 18:34
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    $\begingroup$ Welcome to Robotics IggyPass. This looks like a homework question, and on stack exchange, questions asking for homework help must include a summary of the work you've done so far to solve/understand the problem, and a description of the difficulty you are having solving/understanding it. Please edit your question to add this information and take a look at How to Ask and tour for more information on how stack exchange works. For advice on how to write a good question, see the Robotics question checklist. $\endgroup$ – Ben Feb 5 at 14:41
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You already know the answer - because as you say it contains an accelerometer and a rate gyro.

An accelerometer measures linear acceleration, a rate gyro measures angular velocity. These are the only quantities the unit will actually measure.

The other properties - whether positions, velocities or accelerations - have to be calculated by the controller. For example integrating an acceleration gives a velocity, and integrating again gives position.

There's an exception - if the device is being held motionless in any position, then the accelerometer is sensing which direction gravity is acting in, so it can be used directly as an orientation sensor. But that only applies if you know the device is being held motionless...

Answer will be Linear Acceleration & Angular Velocity only.

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    $\begingroup$ I had the same misconception at first, but a gyro gives an angular velocity. The accelerometer gives a linear acceleration. $\endgroup$ – Chuck Jun 9 '16 at 12:29
  • $\begingroup$ @Chuck thank you for the correction. Looks like I would have failed the test too! $\endgroup$ – Andy Jun 9 '16 at 12:33
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    $\begingroup$ Also note that the device does not need to be held motionless to accurately measure gravitational acceleration. It just needs to not be accelerating (constant velocity is fine). $\endgroup$ – kamek Jun 9 '16 at 12:53
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    $\begingroup$ Okay I will pass the test again with your advises. I hope I will make it this time. I now know that I can only have acceleration through the accelerometer and the angular velocity thanks to the rate gyro. $\endgroup$ – Revolucion for Monica Jun 9 '16 at 15:49
  • $\begingroup$ This answer fails to take into account that many IMU's contain magnetometers. Furthermore, there does not appear to be an agreed upon set of bounds upon the IMU's capabilities. In other words, by some definitions, an IMU can include some localization software. If this definition is accepted, then the IMU may also output position/orientation/linear velocity. $\endgroup$ – koverman47 Feb 6 at 3:22
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An Inertial Measurement Unit (IMU) is a device that contains three accelerometers that measures a body's specific force vector, and three gyroscopes that measures its inertial angular velocity vector. It often also contains a triad of magnetometers that measures the magnetic field vector around the device. Note that the "accelerometers" do not directly measure the translational acceleration vector, this must be obtained by adding the apparent gravity vector to the measured specific force vector.

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