Questions about fusion library

[a8Chcx]

Hi,

I am using Sensor fusion revision 5 to do my testing. I have the following questions:

1) How to decide ACC offset?

2) How to decide GYRO offset in fusion library? Can  I use ACC, MAG and etc. to decide the stationary status to cancel GYRO offset?

3) I tried the gaming mode. After running for several minutes, the direction is shifting. Is it normal and how to correct?

4) My application is moving slowly, like 30 degrees per seconds. Could you tell me what is the better settings for this, like 245 DPS for GYRO is better? How about other settings, like threshold, and etc...?

5) MAG Offset is decided by calibration?

Regards,

Christie

[michaelestanley]

Christie,

Can you tell me what hardware configuration you are using?  If it is a Freescale Freedom board and sensor shield, you should not have to make any adjustments.  There are no settings for accelerometer offset, as the filter treats these as noise.  Gyro offset is automatically computed by the filter.  For gaming, you want the full +/- 2000 degrees/sec range.  Smaller ranges will clip and lead to bad results.

As to your last question, the mag offset does not apply to gaming mode, which uses only accel and gyro.  In the 9-axis mode, we have hard iron offsets computed by magnetic calibration and additional (moving) offsets are treated as noise terms.

Mike

[a8Chcx]

Hi Mike,

When I am using FRDM K64F and FRDM-FXS-MULTI2-B for my testing.

1) In gaming mode, I can see there is shifting in YAW if keep moving a short time, like 1 minute.

That is why I think if it will be better if I am using smaller dps...

Then, I am using my own proto board(K64F MCU+ST LSM9DS1) for this testing.

1) If I am using the same configure as FRDM K64F and FRDM-FXS-MULTI2-B, I can get almost the same kind of performance.

2) But, if I change to 245 dps, I saw zero offset of GYRO is much bigger and the performance becomes worse. I want to know why and how to change these settings?

Thanks,

Christie

[a8Chcx]

Hi Mike,

I am testing FRDM K64F and FRDM-FXS-MULTI2-B. When I put it in Gaming and without any movement, I can see YAW is decreasing 0.1 degree per second. Is there any way to tell it not moving because there is no real movement? Can I set the certain threshold to restrict it?

Thanks,

Christie

[michaelestanley]

Chistie,

You do NOT want the smaller gyro range for gaming.  If you do that, actual movements will exceed the range of the sensor.   That just ends up clamping the fusion's ability to track changes.  Any movement beyond the selected range will then manifest as continued change in the fusion output, even after you stop moving the board.

0.1 degrees/second for a stationary sensor board in gaming mode matches what I see on my own board.  If your sensor is motionless, I'm guessing you probably have the Z-axis aligned with gravity, so there is zero information coming in to manage yaw.  Consider the use case, in gaming mode the sensor should be moving.  And when it is, you can leverage the accelerometer to compute orientation because the axes of the sensor are continuously moving relative to the global frame.

If you are concerned about stability with no movement, then you need to use the 9-axis algorithm, which tosses the magnetic  vector into the mix.

Regards,

Mike

[a8Chcx]

Hi Mike,

Is it possible to set some threshold for ACC/GYRO/MAG to detect as motion? So, below these threshold, just set GYRO DPS to 0, no movement. Or it will cause other problem?

Thanks,

Christie

[michaelestanley]

Our general strategy with the fusion library is to limit the number of heuristic IF-THEN types of rules, and stick closer to base physics.  Generally, you find that everything will be a tradeoff.  Sure, you could roll in a rule like you propose, but then the next person will be unhappy because their low motion has to overcome that same threshold.