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Crafty — Chasing a Temperature Warning to a New Board

The flight logs are clean

CheckResult
Hover current7.6–8.4 A, against 7.5–7.8 A on 13 and 16 Sep
Stalled motors0.1–0.2 s at crash moments, against ~0.8 s on 16 Sep
Motor 4RPM per command 0.97–1.01, vibration 3–13
Motor 34–6 % less RPM per command than the others, up from 2–3 %
Battery internal resistance16–21 mΩ, against 15 mΩ on 13 Sep
Pack start voltage3.72–4.04 V, against 4.15–4.26 V on 13 Sep

The short flights come from under-charged packs. Blackbox records no temperature, so the logs can only rule causes out.

Bench temperatures

USB only, no battery:

ConditionCore temperature
No airflow, VTX 200 mW42 → 70–79 °C
No airflow, VTX 25 mW41 → 72 °C, then flat
Small fan on the boardsteady 39 °C
Motors disconnected, no airflow48 → 70 °C, unchanged
Air65, no airflow (control)36 → 60 °C at 3 min, still rising

It plateaus, a little airflow holds it at 39 °C, the motors are not involved and VTX power makes no difference. Crafty runs about 10 °C above the Air65 while doing more work: an 8 kHz gyro loop at 49 % CPU against 3.2 kHz at 39 %.

The 39–41 °C USB readings used as a baseline on 13 and 16 September were taken with a fan blowing on the board. That was not known until late in the session and led to a premature conclusion that the board was damaged. Bench temperatures are only comparable when airflow is stated.
A saved vtx_power does not stick on the bench: with no receiver, AUX6 defaults to 1500, which maps to 200 mW. Testing low power needs the radio on with the switch down.

Outcome

The warning persisted in flight at low VTX power and the fault was never isolated. For the new board:

  1. Flash BETAFPV’s custom firmware, not stock Betaflight — see the gyro firmware notes.
  2. Restore from the 2026-09-17_195000_crafty_prereplace backup.
  3. Reconnect the motors, which were disconnected during testing.
  4. Take one bench reading with no fan as a real baseline.
  5. If the new board also reaches 70 °C in flight, the old one was fine and the alarm is simply conservative for an AIO with little airflow. Raise osd_core_temp_alarm.