[TB3] Curious IMU values?

TurtleBot
1

Hello,

I am working on turtlebot Buger and Waffle, but I get curious values from IMU.
Linear acceleration on z axis in not equal to ~9.8 m/s². And when the robot is static, I have non zeros values on x and y axis.
I have those strange values on both Burger and Waffle robots. Curiously IMU on Waffle was working fine last week.

Some idea ?

Matt

header:
seq: 592
stamp:
secs: 1515485911
nsecs: 742161933
frame_id: imu_link
orientation:
x: 0.0163628198206
y: -0.00983170140535
z: 0.324311375618
w: 0.945753157139
orientation_covariance: [0.0024999999441206455, 0.0, 0.0, 0.0, 0.0024999999441206455, 0.0, 0.0, 0.0, 0.0024999999441206455]
angular_velocity:
x: 0.0
y: 0.0
z: 0.0
angular_velocity_covariance: [0.019999999552965164, 0.0, 0.0, 0.0, 0.019999999552965164, 0.0, 0.0, 0.0, 0.019999999552965164]
linear_acceleration:
x: 526.0
y: 420.0
z: 17362.0
linear_acceleration_covariance: [0.03999999910593033, 0.0, 0.0, 0.0, 0.03999999910593033, 0.0, 0.0, 0.0, 0.03999999910593033]

2

It seems that linear acceleration units are mm/s². So ~400 and ~500 would represent noise
I have compared opencr IMU and Myahrs IMU, results are below.

So, I suppose that x and y linear acceleration are fine except on z axis. It is a calibration problem ?

Screenshot from 2018-01-09 13-00-15

3

Not quite… There was a bit more to it than that. The original OpenCR code doesn’t convert from the raw values. That was fixed in this PR.

That fix and others are present on the features-from-openrobotics branch on the OpenCR repo. If you checkout those changes and flash the image, then your IMU values will be correct.

4

Ok, thank you for those explanation and also for your contribution

Matt

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