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Iterm Relax explained

I term relax aims to inhibit I during fast manoeuvres by preventing it to further accumulate. Simply put I term relax will keep I constant during fast manoeuvres.

I term is relax rely on setpoint or gyro (iterm_relax_type) to detect such manoeuvres and preventing I term to accumulate further. To tune when I term accumulation should be suppressed a cutoff value (iterm_relax_cutoff) can be set. The lower the cutoff value the earlier I term accumulation is suppressed.

  • In setpoint mode this suppression is based on the speed of the change in setpoint.
  • In gyro mode this suppression is based on [TBD].

The following log traces demonstrate how different cutoff value affect I term relax (I value in green and setpoint in red).

Freestyle Tune​

For smooth flying such as freestyle when extremely fast and aggressive turns are rare I term can be relaxed as far as completely inhibit it during manoeuvres. Freestyle tuning might requires lower cutoff values, typically about 10-15.

Ideally I term should be 'locked' as the moves starts and come back on shortly after the sticks stop moving as illustrated in the log trace below.

Racing Tune​

When racing shorter I term accumulation suppression allows the quad to better track aggressive turns and quick blips. Racing tuning might requires higher cutoff values, typically about 20-30. For example, in the above log trace a higher cutoff value allows for better setpoint tracking on quick twitch inputs.

Known Drawbacks​

Bacause I is 'locked' to the pre-existing value before entering a fast maneuver, when it comes back on the old I offset takes a little while to resolve.

Such effect is even more prominent with gyro mode, since the I term locking is slightly delayed compared to setpoint.

How to fix this? Increasing modes​

This can be fixed using the INCREASING modes of the Iterm Relax. The Iterm Relax can be configured in RP, RPY, RP_INC and RPY_INC modes. The two modes that have the _INC in the name only lock the I accumulation from INCREASING, letting it to reduce if the I accumulation is not needed anymore.

By default Betaflight uses the RP mode, so if you want to remove this accumulation you can change it to RP_INC.