IMUF 250

IMUF 250

IMPORTANT NOTES

This imuf needs far less filtering than before, as such set your imuf_lowpass_roll/pitch/yaw to 150-200+ hz. This seems to give users the best experience with this version of the imuf.

Changleog:

• Covariance math improvement.
• Non-dynamic BiQuad gyro LPF.
• Refactored sharpness, sharpness=0 is OFF

Notes:

• Pilots are welcome to use any IMUF versions liked best. New IMUF releases are not requirements.
• If you've heard of test-versions 9001 and 9002, this is equivalent to 9002. To make it 9001, simply turn off sharpness.

Compatibility

• IMUF 250 binary for Helio/Strix hardware is compatible only with 0.3.X exclusively. Do not use for older 0.1.0 or 0.2.0.
• Pilots are still welcome to use any IMUF version based on their personal preferences, but only 225 and above make use of the sharpness feature which require newer EmuFlight (0.2.32+, 0.3.0+).

The Windows® based tool is still required for flashing. Keep the "Original Helio Firmware" UN-checked, or you are really going to have a bad time. If for some reason you flash wrongly, just plug usb, and wait 5 full minutes for the DFU to connect.

Imperative:

• Compatible only with 0.2.32+, 0.3.0+
• Save your diff all and dump all prior to flashing IMUF.
• Flashing may possibly cause invalid data in your settings, especially very-large LPF values that could cause fly-away. This is seldom; however, be sure to validate your LPF and other values. The CLI command defaults may not reset them properly, so set them manually if you see a problem.
• The best option is to [re]flash EmuFlight 0.3.X firmware (with full-chip erase) after flashing the IMUF binary.
• If your LPF values are in a normal range, then there is no issue to fix.

Thanks to

• Paweł Spychalski for improved covariance math.
• Andrey Semjonovs for extensive code testing and differentiation.

Additional Information

• Sharpness math in IMUF250 is not applied same as previous versions, where:

src/filter/filter.c:83:	  sharpness = (float)filterConfig.sharpness / 250.0f;
src/filter/kalman.c:16:      filter->s = sharpness * 0.01f;

• and where calculations in kalman_process (src/filter/kalman.c) are:

[...]
  if (kalmanState->s != 0.0f) {               //if sharpness non-zero
    float average = fabsf(target + kalmanState->lastX) * 0.5f;
    if (average > 10.0f) {
        float error = fabsf(target - kalmanState->lastX);
        float ratio = error / average;
        kalmanState->e = kalmanState->s * powf(ratio, 3.0f);  //"ratio" power 3 and multiply by a gain (sharpness)
    }
    //prediction update
    kalmanState->p = kalmanState->p + (kalmanState->q + kalmanState->e);
  } else {          //if sharpness zero (off)
    if (kalmanState->lastX != 0.0f) {
        kalmanState->e = fabsf(1.0f - (target / kalmanState->lastX));
    }
    //prediction update
    kalmanState->p = kalmanState->p + (kalmanState->q * kalmanState->e);
  }
[...]