research/motor/README.md

Motor Research (Apr 24, 2026)

Liquid-Cooled Small BLDC Motor (≈30 mm) — Research Sheet

Focus: Internal Channel / Directed Cooling (Concept B)

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🧠 1. Objective

Design a high power-density, continuous-duty BLDC motor (~30 mm class) for EDF/prop aircraft using:

Directed internal cooling channels through the stator (not full immersion)

Goal:

• Maximize continuous power
• Maintain high efficiency at very high RPM (30k–100k)
• Avoid fluid drag losses from rotor immersion

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⚙️ 2. Core Concept (B)

Definition

A motor where:

• Coolant flows through engineered paths inside the stator
• Heat is removed directly from windings and core
• Rotor remains dry (air-filled cavity)

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🧩 2.1 Cooling Architecture Types

A. Axial Channels (through stator stack)

• Holes or ducts aligned with shaft axis
• Coolant enters one end, exits the other

B. Slot-Integrated Cooling

• Channels embedded near winding slots
• Coolant flows alongside copper

C. Back-Iron Cooling

• Channels placed in stator back iron
• Lower impact on copper fill, but less direct

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🔥 3. Thermal Model

Heat Sources

• Copper losses:
  [ P_{cu} = I^2 R ]

• Core losses:

  • hysteresis
  • eddy currents

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Cooling Mechanism

Convective heat transfer: [ Q = h \cdot A \cdot \Delta T ]

Where:

• ( h ) = heat transfer coefficient (high for liquid)
• ( A ) = channel surface area
• ( \Delta T ) = temp difference

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📊 Expected Thermal Performance

Coolant Temp	Winding Temp	ΔT	Notes
30°C	40–60°C	~10–30°C	Moderate cooling
20°C	35–50°C	~10–25°C	Strong
10°C	25–40°C	~10–20°C	Very strong
5°C	20–35°C	~10–15°C	Diminishing returns

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⚡ 4. Electromagnetic Tradeoffs (Critical)

❗ 4.1 Reduced Copper Fill

Channels take space → less copper:

• ↑ Resistance (R)
• ↑ Copper losses
• ↓ Torque per amp

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❗ 4.2 Reduced Iron Cross-Section

Channels remove stator material:

• ↓ Magnetic flux capacity
• ↑ Risk of saturation
• ↓ Maximum torque

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⚖️ Tradeoff Summary

Parameter	Effect
Cooling	↑↑
Resistance	↑
Torque density	↓
Efficiency (if optimized)	↑ overall

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🌀 5. Fluid Design Considerations

✔️ Goals

• Maximize heat extraction
• Minimize pressure drop
• Ensure uniform distribution

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❗ Constraints

1. Channel Size

• Too small → high pressure drop
• Too large → weak stator + lost copper

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2. Flow Regime

• Laminar → predictable, less transfer
• Turbulent → better cooling, higher loss

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3. Pressure Drop

[ \Delta P \propto \frac{L \cdot v^2}{D} ]

Impacts:

• pump requirements
• system efficiency

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🧲 6. Magnetic Design Constraints

Saturation Limit

Even with perfect cooling:

• Core saturates at high flux
• Current increase → diminishing torque

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Design Implication

You must balance:

• channel placement
• iron thickness
• slot geometry

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⚙️ 7. Mechanical Constraints

7.1 Structural Integrity

Channels weaken stator:

• risk of deformation
• vibration issues at high RPM

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7.2 Sealing

Unlike concept A:

• sealing is localized (inlet/outlet)
• not full rotor enclosure

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7.3 Weight

Added:

• coolant
• tubing
• pump

Must not exceed thrust gains

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🚀 8. Performance Expectations

Compared to Air-Cooled Motor

Metric	Improvement
Continuous current	~1.8–2.3×
Continuous power	~2.5–4×
Efficiency	↑ (if well designed)
Peak temp	↓ significantly

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🧠 9. Key Design Strategy

🔑 Optimize for:

• Minimal disruption of magnetic path
• Maximum contact with windings
• Controlled coolant flow

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❌ Avoid:

• Large voids in stator
• Random channel placement
• Overcomplicated routing

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🧪 10. Recommended Cooling Fluids

Fluid	Pros	Cons
Dielectric oil	Safe, good cooling	Viscosity
Water-glycol	Excellent heat capacity	Conductive risk
Fluorinated fluids	Ideal electrically	Expensive

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⚡ 11. System-Level Optimization

Important Shift:

Cooling allows higher current, but optimal design reduces current

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Best Practices:

• Lower KV motor
• Higher voltage supply
• Thicker windings
• Maximize slot fill before adding channels

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🧩 12. Hybrid Enhancement (Best Approach)

Combine:

• Partial channel cooling (B)
• Directed oil spray (controlled A)

Avoid:

• full immersion

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📌 13. Final Engineering Insight

Concept B does not give “free performance”

It trades:

• electromagnetic efficiency
  for
• thermal headroom

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🏁 Conclusion

For ~30 mm EDF motors:

✔ Internal channel cooling is more viable than immersion
✔ Enables large continuous power gains
❗ Must be carefully balanced against magnetic losses

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🔍 14. Future Exploration

• Additive manufacturing stators
• Micro-channel cooling
• Slot liner cooling integration
• Oil jet targeting windings only

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Motor Research (Jul 20, 2025)

The research for better motor tech. We will be comparing between different kinds of motors in order to gain a better understanding of them.

Priorities

• Efficiency: Current efficiency range (70/87%), goal (90-95%), efficiency is measured in output power (rpm/torque) per watt.
• Reliability: Withstand a long duration of high throttle and extreme conditions of weather.

BLDC vs PMSM

Feature	BLDC (Brush-less DC Motor)	PMSM (Permanent Magnet Synchronous Motor)
Rotor	Permanent magnets	Permanent magnets
Stator winding	Trapezoidal	Sinusoidal
Back-EMF waveform	Trapezoidal	Sinusoidal
Control	Typically 6-step (commutation)	Field-Oriented Control (FOC) / sinusoidal
Torque ripple	Higher (due to 6-step commutation)	Lower (smooth sinusoidal control)
Efficiency (general)	Slightly lower	Slightly higher
Cost and complexity	Lower cost, simpler control	Higher cost, more complex control
Applications	Fans, RC planes, e-bikes, hobby motors	EVs, drones, industrial drives, high-end motors

BLDC - Brush-less DC motor

PMSM - Permanent Magnet Synchronous Motor