Hi all,
I’ve spent 3 years running continuous load bench testing for heavy-lift industrial multirotor BLDC motors, and recently collected dozens of ULog logs from all-day mapping/thermal inspection flights. A confusing recurring issue appears across multiple custom airframes:
After 2–3 hours of cyclic hover + low-speed cruise, motor temperature rises continuously, and we see clear thrust attenuation at identical throttle output in logs. The vibration spectrum also shifts to higher frequency as winding temperature climbs.
Current test findings to share:
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Hardware side: Motors with standard N35 magnets lose ~8–12% peak torque above 105°C; high-temp N52H magnets only drop ~3–5% torque under the same thermal load. Winding resistance difference between three phases expands 15–25% when hot, which amplifies torque ripple in logs.
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PX4 log observation: When single motor phase resistance imbalance increases, the flight stack automatically raises motor output to compensate, creating a vicious cycle of extra heating. Tighter D gains further amplify this compensation load.
My core questions for the community:
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When you spot consistent thrust decay and rising motor temp in long-duration mission logs, what’s your standard troubleshooting sequence to rule out BLDC hardware flaws before adjusting PID / ESC timing parameters?
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Are there any PX4 hidden parameters or filter settings that can partially offset thermal-induced motor imbalance without sacrificing attitude stability?
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For fleets running 6+ hours daily back-to-back missions, what motor thermal thresholds do you set as hard limits via failsafe triggers?
Would love to compare real-world log analysis workflows with other custom UAV builders.