Let the motor test drive DSHOT motors below the configured idle

[Raffi1202]

Problem

In the Outputs tab motor test, a DSHOT motor does not spin when its slider is set below "Motors IDLE power" but above the point where the motor would normally start (reporter's example: idle 15 %, slider 10 %). With MULTISHOT the same slider position spins the motor; only DSHOT is affected. Reported in #9634 on a SpeedyBee F405 V3 running INAV 7.0.0.

Cause

src/main/flight/mixer.c:551 (maintenance-10.x): for non-reversible DSHOT, writeMotors() passes throttleIdleValue as the stop threshold to handleOutputScaling(), which sends DSHOT_DISARM_COMMAND for any input below that threshold (mixer.c:426). While disarmed, motor[i] is motor_disarmed[i] (mixer.c:652), written directly by MSP_SET_MOTOR (src/main/fc/fc_msp.c:2522). The analog non-reversible branch forwards motor[i] unchanged (mixer.c:589), so only DSHOT turns a below-idle test value into a stop command.

Change

One line in writeMotors(): the DSHOT stop threshold is throttleIdleValue only while armed; while disarmed it is motorZeroCommand + 1, so a disarmed value above mincommand is scaled to a DSHOT throttle. handleOutputScaling() still clamps the result to DSHOT_MIN_THROTTLE..DSHOT_MAX_THROTTLE, so the DSHOT command range 1-47 cannot be produced, and motorZeroCommand still yields the stop command. Armed behaviour (failsafe, turtle mode, motor stop) is unchanged.

Test

Not run on hardware or SITL (writeMotors() is compiled out for SITL). Cause verified by reading mixer.c:426/551/589/652 and fc_msp.c:2522 on maintenance-10.x. Not built: there is no fork CI run for fix/motor-test-below-idle, and the upstream firmware build for 3ee1df0 (https://github.com/iNavFlight/inav/actions/runs/34513097267) is waiting for maintainer approval with 0 jobs. Qodo review of 3ee1df0 reported no issues.

Flash / RAM

Not measured yet. The upstream firmware CI has not been released for this PR, so no size report exists.

Docs

No documentation change needed: docs/Controls.md and docs/Settings.md describe throttle_idle as the minimum throttle while armed, which is unchanged; no firmware doc describes the disarmed motor-test output.

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PR Summary by Qodo

Allow DSHOT motor tests below configured idle

🐞 Bug fix 🕐 10-20 Minutes

AI Description

• Allows disarmed DSHOT motor tests to spin below configured idle.
• Uses the mixer stop value while preserving armed output behavior.
• Keeps explicit stops and DSHOT command-range protection unchanged.

Diagram

graph TD
  A["Motor Test"] --> B["Disarmed Values"] --> C["writeMotors"] --> D{"Armed?"}
  D -->|Yes| E["Idle Threshold"] --> G["DSHOT Output"]
  D -->|No| F["Stop Threshold"] --> G

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High-Level Assessment

The arming-state-dependent threshold is the narrowest appropriate fix. It corrects disarmed bench testing without changing failsafe, turtle mode, or transition behavior while armed; using the mixer stop threshold unconditionally would broaden risk unnecessarily. Targeted output-scaling tests would still be valuable when suitable test infrastructure becomes available.

Files changed (1) +5 / -1

Bug fix (1) +5 / -1

mixer.cUse mixer stop threshold for disarmed DSHOT output +5/-1

Use mixer stop threshold for disarmed DSHOT output

• Changes non-reversible DSHOT scaling to use the configured idle threshold only while armed. While disarmed, only motorZeroCommand is treated as stopped, allowing motor-test values above mincommand but below idle to produce valid DSHOT throttle output.

src/main/flight/mixer.c

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Code Review by Qodo

🐞 Bugs (0) 📘 Rule violations (0) 📎 Requirement gaps (0)

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