IMU Frame off

dvz

Hello,

According to your website, it seems like the VOXL2 coordinate frame should be FRD. However, on both of our VOXL2s with different SDKs, we get z pointing upwards (IMU telling us -9.81m/s^2).
This holds true for voxl-inspect-imu and the rostopic imu_apps.
Is this a bug? Are we doing something wrong? We are a little confused, as this contradicts your information on your website and in your documentation.
The only topic that seems to be correct is imu_apps_raw. However, there is not documentation on imu_apps_raw at all and it only exists in one of our SDKs.

Thank you.

zauberflote1

@dvz Hi would you be able to confirm which airframe and SDK versions you are using?

dvz

@zauberflote1 We are using our own custom airframe. Our SDKs are 1.6.0 beta and 1.4.5. However, I also just spoke with a colleague who owns a Starling 2, and he confirmed our findings.

Igor

@dvz I have faced a similar issue on the VOXL2 Mini. The X and Y axes match the documentation, but the Z axis has the opposite direction to what is described.

Alex Kushleyev

@Igor and All,

When the IMU is level and at rest, the accelerometer will measure the normal force , which is in the direction opposite to gravity vector. So the normal force will point up (towards the sky) and since the reference frame is FRD (D for Down), the vector that points to the sky will read negative 1g in this frame.

Alex