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ros-drivers / um7

ROS driver for UM7 inertial measurement device.
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Constant accelerations while stationary #2

Closed NCharabaruk closed 9 years ago

NCharabaruk commented 9 years ago

Hello,

I was checking out the data from package and I found that I am getting constant linear accelerations in the y and x directions despite the fact that the IMU is stationary. They are in the range of 0.12-0.17. Any ideas on why this may be?

Nick

rbirac commented 9 years ago

Hi Nick,

The X and Y axes pick up part of the gravity vector unless the accelerometers are mounted perfectly level.  Also, the accelerations may vary somewhat due to tolerances.  Since both X and Y vary to the sine of angular error to true vertical, and gravity being 9.8 M/sec/sec, the values you are seeing indicate angular errors of one degree or less.   Since the UM7 calculates and corrects the Z axis angle to the X and Y accel values, these offsets will cause errors in pitch and roll axes of about one degree.  For most purposes, this is pretty good.

On my robot, I shimmed the UM7 installation to minimize the X and Y accels when the robot is on a level floor. It is also desirable to have the X axis carefully aligned with the robot’s forward direction so that forward accel by the robot doesn’t affect the Y axis and vice versa.

Alex

Alex

From: Nick Charabaruk Sent: Thursday, June 04, 2015 8:12 AM To: ros-drivers/um7 Subject: [um7] Constant accelerations while stationary (#2)

Hello,

I was checking out the data from package and I found that I am getting constant linear accelerations in the y and x directions despite the fact that the IMU is stationary. They are in the range of 0.12-0.17. Any ideas on why this may be?

Nick

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NCharabaruk commented 9 years ago

I did not think of that. Thanks for your time.