Simulink IMU's accelerometer is different with MPU6050 acclerometer

I am using Simulink IMU box to simulate my dynamic model, but its accelerometer values seem to have opposite sign. If we lay MPU6050 on flat desk and sensor's Z axis upward, MPU6050 senses [0, 0, 9.81] because of inertial force. but Simulink IMU (ENU frame) outputs [0, 0, -9.81]. Do I just multiply by -1?

Answer 1

[Sanskar]

Hi!

What I understand from your question is that you are expecting positive value for Z-axis upward, but simulink IMU output returns it in negative.

In Simulink, the IMU block follows the right-hand rule convention for the coordinate frames. According to the convention, the Z-axis points upward, which is opposite to the gravity vector direction.

So, if you are expecting a positive value for the accelerometer readings along the Z-axis when the sensor is placed on a flat desk , and Simulink IMU is giving you a negative value, you can indeed multiply the output by -1 to obtain the expected positive value.

Hope it helps!

Sanskar

Answer 2

[Brian Fanous]

I'm not sure which IMU block you mean, but the ones in the Navigation Toolbox and Sensor Fusion and Tracking Toolbox, when in the ENU convention, have the Z-axis pointing up. So gravity will exert a negative acceleration.

You likely cannot only negate the z-axis because then you won't end up with a right-handed coordinate system. You might also need to swap the X and Y axes.

This example Estimating Orientation Using Inertial Sensor Fusion and MPU-9250

shows how to swap and negate the MPU-9250s axes to match the NED convention. The process is similar for the ENU convention.