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fix(mc_pos_control): handle rejected velocity filter cutoffs [1.18] by Saibernard · Pull Request #28534 · PX4/PX4-Autopilot · GitHub

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fix(mc_pos_control): handle rejected velocity filter cutoffs [1.18] - #28534

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dakejahl merged 1 commit into
PX4:release/1.18from
Saibernard:backport-1.18-mc-pos-control-filter
Sep 4, 2026
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fix(mc_pos_control): handle rejected velocity filter cutoffs [1.18]#28534
dakejahl merged 1 commit into
PX4:release/1.18from
Saibernard:backport-1.18-mc-pos-control-filter

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Saibernard commented Sep 4, 2026

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Backport of #28451 to release/1.18, the same commit as on main.

A rejected filter cutoff was silently accepted and degraded altitude hold on multicopters.

fix(mc_pos_control): bypass the velocity low pass when the cutoff is …
bc1f459 
…rejected (PX4#28451)

setCutoffFreq refuses a cutoff at or above half the sample rate and
leaves the filter untouched, but all four velocity filter calls ignored
the return. With the filters at their initial alpha of zero this froze
the velocity feedback at zero, and the condition is reachable from a
permitted parameter value, MPC_VEL_LP allows up to 50 Hz while the
position loop commonly runs at 100 Hz or less. In SIH a hover with
MPC_VEL_LP=50 oscillates half a metre in altitude with vertical speed
peaks near 1 m/s, and holds 2.5 m within centimetres with this change.

Follow the pattern VehicleAngularVelocity already uses, check the
return and bypass the low pass stage when the requested cutoff is not
achievable. One deliberate behaviour change comes with that, a runtime
parameter change from a valid to an unachievable cutoff now bypasses
the stage instead of keeping the stale previous configuration.

Assisted-by: Claude:claude-fable-5

Signed-off-by: Saibernard Yogendran <bernie97@seas.upenn.edu>
(cherry picked from commit 71f8b37)
github-actions Bot added kind:bug Something is broken or behaving incorrectly. vehicle:copter Copter-specific behavior. scope:control Rate, attitude, position, allocation, or actuator control. labels Sep 4, 2026

github-actions Bot commented Sep 4, 2026

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🔎 FLASH Analysis

px4_fmu-v5x [Total VM Diff: 48 byte (0 %)] 
    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.0%     +48  +0.0%     +48    .text
    +1.5%     +52  +1.5%     +52    MulticopterPositionControl::parameters_update()
    +3.0%      +8  +3.0%      +8    AlphaFilter<>::setCutoffFreq()
    +4.8%      +4  +4.8%      +4    FlightTask
     +44%      +4   +44%      +4    g_nullstring
    -2.1%      -2  -2.1%      -2    events::send<>()
    -0.6%      -2  -0.6%      -2    matrix::SliceT<>::operator=()
    -0.0%      -4  -0.0%      -4    g_cromfs_image
    -0.0%     -12  -0.0%     -12    [section .text]
  +0.0%     +55  [ = ]       0    .debug_abbrev
  +0.0%     +20  [ = ]       0    .debug_info
  +0.0%     +13  [ = ]       0    .debug_line
   -33.3%      -1  [ = ]       0    [Unmapped]
    +0.0%     +14  [ = ]       0    [section .debug_line]
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  +0.8%      +2  [ = ]       0    .shstrtab
  -0.0%     -14  [ = ]       0    .strtab
   -12.8%     -14  [ = ]       0    AlphaFilter<>::setCutoffFreq()
     +76%     +16  [ = ]       0    __sq_addafter_veneer
   -37.2%     -16  [ = ]       0    __stm32_endtransfer_veneer
  -0.6%     -48  [ = ]       0    [Unmapped]
  +0.0%    +160  +0.0%     +48    TOTAL
px4_fmu-v6x [Total VM Diff: 40 byte (0 %)] 
    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.0%     +40  +0.0%     +40    .text
    +1.5%     +52  +1.5%     +52    MulticopterPositionControl::parameters_update()
    +3.0%      +8  +3.0%      +8    AlphaFilter<>::setCutoffFreq()
    +4.8%      +4  +4.8%      +4    FlightTask
    -2.1%      -2  -2.1%      -2    events::send<>()
    -0.6%      -2  -0.6%      -2    matrix::SliceT<>::operator=()
    -0.0%      -4  -0.0%      -4    g_cromfs_image
    -0.0%     -16  -0.0%     -16    [section .text]
  +0.0%     +55  [ = ]       0    .debug_abbrev
  +0.0%     +20  [ = ]       0    .debug_info
  +0.0%     +21  [ = ]       0    .debug_line
    [NEW]      +7  [ = ]       0    [Unmapped]
    +0.0%     +14  [ = ]       0    [section .debug_line]
  +0.0%     +84  [ = ]       0    .debug_loclists
  +0.9%      +2  [ = ]       0    .shstrtab
  -0.0%     -14  [ = ]       0    .strtab
   -12.8%     -14  [ = ]       0    AlphaFilter<>::setCutoffFreq()
  -0.7%     -40  [ = ]       0    [Unmapped]
  +0.0%    +168  +0.0%     +40    TOTAL

Updated: 2026-09-04T01:36:40

dakejahl merged commit b61b2c9 into PX4:release/1.18 Sep 4, 2026
73 checks passed
Saibernard added a commit to Saibernard/PX4-Autopilot that referenced this pull request Sep 10, 2026
docs(releases): add the v1.18 note for the position controller filter…
d488827 
… fix

PX4#28534 merged onto release/1.18 after the first five entries.

Assisted-by: Claude:claude-fable-5
Signed-off-by: Saibernard Yogendran <bernie97@seas.upenn.edu>
hamishwillee added a commit that referenced this pull request Sep 17, 2026
docs(releases): add v1.18 notes for five backported fixes (#28547)
fe87271 
* docs(releases): add v1.18 notes for five backported fixes

The estimator selector, VTOL mission return, analog battery filter,
home altitude filter and mission end fixes are on release/1.18 now,
this adds their entries to the release notes.

Assisted-by: Claude:claude-fable-5
Signed-off-by: Saibernard Yogendran <bernie97@seas.upenn.edu>

* MOve entries

* docs(releases): add the v1.18 note for the position controller filter fix

#28534 merged onto release/1.18 after the first five entries.

Assisted-by: Claude:claude-fable-5
Signed-off-by: Saibernard Yogendran <bernie97@seas.upenn.edu>

---------

Signed-off-by: Saibernard Yogendran <bernie97@seas.upenn.edu>
Co-authored-by: Hamish Willee <hamishwillee@gmail.com>
dakejahl pushed a commit that referenced this pull request Sep 22, 2026
docs(releases): add v1.18 notes for five backported fixes (#28547) (#…
c1d6212 
…28749)

* docs(releases): add v1.18 notes for five backported fixes

The estimator selector, VTOL mission return, analog battery filter,
home altitude filter and mission end fixes are on release/1.18 now,
this adds their entries to the release notes.

Assisted-by: Claude:claude-fable-5


* MOve entries

* docs(releases): add the v1.18 note for the position controller filter fix

#28534 merged onto release/1.18 after the first five entries.

Assisted-by: Claude:claude-fable-5


---------



(cherry picked from commit fe87271)

Signed-off-by: Saibernard Yogendran <bernie97@seas.upenn.edu>
Co-authored-by: Hamish Willee <hamishwillee@gmail.com>
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kind:bug Something is broken or behaving incorrectly. scope:control Rate, attitude, position, allocation, or actuator control. vehicle:copter Copter-specific behavior.

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