Thermal management and cooling
Summary¶
libdrone's electronics zone generates 6 W of waste heat in hover (ESC, VTX, FC, and buck converter) and up to 14 W at peak. An always-on Gdstime 3010 fan at the rear of the Platform draws air front-to-rear across the ESC and FC stack. In standard open-frame configuration, the fan provides adequate cooling under normal conditions but delivers only ~1.5°C of temperature rise above ambient — insufficient to prevent condensation in the Czech autumn/winter operating envelope. The Thermal Retention Shroud (TRS) addresses this by partially enclosing the electronics zone, raising the microclimate temperature above the dew point using the waste heat already being generated.
Concept¶
The cooling fan¶
The Gdstime 3010 (30 × 30 × 10 mm, 5V ball bearing) is hardwired to the FC 5V pad and runs continuously whenever the FC is powered — no thermostat, no control. The "massively overcool" design philosophy: for a mapping drone that flies methodically rather than aggressively, the thermal margin is more important than marginal current savings from variable-speed control.
The fan is rear-facing and exhausts rearward. In hover, it creates a pressure differential that draws air through the electronics zone front-to-rear. In forward flight, ram air enters through front arm root gaps and is exhausted by the fan.
Power draw: ~70 mA at 5V = 0.35 W. Always on, drawing from the FC BEC.
Heat sources and budget¶
| Component | Waste heat (hover) | Waste heat (peak) |
|---|---|---|
| ESC (4 FETs, ~30A total) | ~3 W | ~8 W |
| VTX (800 mW RF, 40% PA efficiency) | ~2 W | ~5 W |
| FC + Buck converter | ~1 W | ~1 W |
| Total | ~6 W | ~14 W |
Open-frame thermal performance¶
At 6 W waste heat and the fan moving 0.2 m³/min (3.3 L/s) through the open backplane (65% open area), the temperature rise above ambient in the electronics zone is approximately:
ΔT = Q / (ṁ × cp) = 6 / (4.0×10⁻³ × 1005) ≈ 1.5°C
1.5°C above ambient is below the dew point margin in most Czech autumn conditions (worst case: 5°C ambient, 90% RH → dew point ≈ 3.5°C, requires ΔT ≥ 5°C for real protection). The open-frame build is thermally unprotected against condensation.
Thermal Retention Shroud (TRS)¶
The TRS is a single printed PETG part that partially encloses the electronics zone. By restricting airflow to approximately 20% of fan capacity through the cavity (with 80% recirculating), the temperature rise above ambient increases proportionally:
T_cavity = T_amb + Q / ((1 − R) × ṁ × cp) = T_amb + 6 / (0.20 × 4.0×10⁻³ × 1005) ≈ T_amb + 7.5°C
7.5°C above ambient provides real-world protection across the Czech autumn/winter envelope (target: ΔT ≥ 8°C). The TRS uses the waste heat already being generated — no additional electronics, no additional power.
At forward speeds above approximately 40 km/h, ram air pressure dominates and recirculation stops. This is acceptable — condensation risk is greatest in slow hover and on the ground, not at cruise speed.
Reference¶
Fan specification¶
| Parameter | Value |
|---|---|
| Model | Gdstime 3010 (30 × 30 × 10 mm) |
| Voltage | 5V (hardwired to FC 5V pad) |
| Bearing | Ball bearing (adequate for always-on continuous duty) |
| Current | ~70 mA |
| Flow rate | ~0.2 m³/min |
| Mount | Platform rear face slot |
| Control | Always on — no thermostat |
ESC temperature monitoring¶
The Pilotix 75A AM32 ESC reports temperature via DShot telemetry. In Betaflight: set set osd_esc_temp_pos to display in OSD. Normal operating temperature: 40–60°C at sustained hover. Above 80°C: ESC current limiting may activate — land and investigate airflow restriction.
Procedure¶
Verifying adequate cooling after build¶
- Fly a 5-minute hover at 80% of maximum payload (approximately hover-relevant throttle, not full throttle).
- After landing, immediately feel the ESC through the backplane (carefully — it will be warm). Should be warm but not painful to touch (<60°C).
- Check OSD ESC temperature during flight if configured. If consistently above 70°C, verify fan operation (audible, feels airflow from rear) and check that the airflow path is not obstructed.
- If fan is not audible after FC boot: check 5V connection to fan leads. Fan failure is a maintenance-priority item — fly without fan only in cool conditions and at reduced throttle.
Rationale¶
Why ball bearing and not sleeve bearing¶
Ball bearing fans are rated for longer service life under continuous-duty conditions. Sleeve bearing fans are adequate for intermittent use but degrade faster when run continuously, particularly in horizontal orientations where gravity acts perpendicular to the bearing's designed load axis. The 3010 in libdrone runs continuously in a horizontal airframe — ball bearing is the correct choice.
Connections¶
requires: - power-rail-architecture related: - thermal-retention-shroud - conformal-coating - lipo-batteries leads_to: - thermal-retention-shroud