Revise README for liquid-cooled BLDC motor research

Updated README.md to include detailed research on liquid-cooled small BLDC motors, focusing on internal channel cooling concepts and thermal performance expectations.

motor/README.md

@@ -1,11 +1,301 @@
-# Motor Research
+# Motor Research (Apr 24, 2026)
+## Liquid-Cooled Small BLDC Motor (≈30 mm) — Research Sheet  
+## Focus: Internal Channel / Directed Cooling (Concept B)
+
+---
+
+# 🧠 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
+
+---
+
+# ⚙️ 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)**
+
+---
+
+## 🧩 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
+
+---
+
+# 🔥 3. Thermal Model
+
+### Heat Sources
+- Copper losses:  
+  \[
+  P_{cu} = I^2 R
+  \]
+
+- Core losses:
+  - hysteresis
+  - eddy currents
+
+---
+
+### 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
+
+---
+
+## 📊 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 |
+
+---
+
+# ⚡ 4. Electromagnetic Tradeoffs (Critical)
+
+## ❗ 4.1 Reduced Copper Fill
+
+Channels take space → less copper:
+
+- ↑ Resistance (R)
+- ↑ Copper losses
+- ↓ Torque per amp
+
+---
+
+## ❗ 4.2 Reduced Iron Cross-Section
+
+Channels remove stator material:
+
+- ↓ Magnetic flux capacity
+- ↑ Risk of saturation
+- ↓ Maximum torque
+
+---
+
+## ⚖️ Tradeoff Summary
+
+| Parameter | Effect |
+|----------|-------|
+| Cooling | ↑↑ |
+| Resistance | ↑ |
+| Torque density | ↓ |
+| Efficiency (if optimized) | ↑ overall |
+
+---
+
+# 🌀 5. Fluid Design Considerations
+
+## ✔️ Goals
+- Maximize heat extraction
+- Minimize pressure drop
+- Ensure uniform distribution
+
+---
+
+## ❗ Constraints
+
+### 1. Channel Size
+- Too small → high pressure drop
+- Too large → weak stator + lost copper
+
+---
+
+### 2. Flow Regime
+- Laminar → predictable, less transfer
+- Turbulent → better cooling, higher loss
+
+---
+
+### 3. Pressure Drop
+\[
+\Delta P \propto \frac{L \cdot v^2}{D}
+\]
+
+Impacts:
+- pump requirements
+- system efficiency
+
+---
+
+# 🧲 6. Magnetic Design Constraints
+
+## Saturation Limit
+Even with perfect cooling:
+
+- Core saturates at high flux
+- Current increase → diminishing torque
+
+---
+
+## Design Implication
+You must balance:
+- channel placement
+- iron thickness
+- slot geometry
+
+---
+
+# ⚙️ 7. Mechanical Constraints
+
+## 7.1 Structural Integrity
+Channels weaken stator:
+- risk of deformation
+- vibration issues at high RPM
+
+---
+
+## 7.2 Sealing
+Unlike concept A:
+- sealing is localized (inlet/outlet)
+- not full rotor enclosure
+
+---
+
+## 7.3 Weight
+Added:
+- coolant
+- tubing
+- pump
+
+Must not exceed thrust gains
+
+---
+
+# 🚀 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 |
+
+---
+
+# 🧠 9. Key Design Strategy
+
+## 🔑 Optimize for:
+- Minimal disruption of magnetic path
+- Maximum contact with windings
+- Controlled coolant flow
+
+---
+
+## ❌ Avoid:
+- Large voids in stator
+- Random channel placement
+- Overcomplicated routing
+
+---
+
+# 🧪 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 |
+
+---
+
+# ⚡ 11. System-Level Optimization
+
+## Important Shift:
+
+> Cooling allows higher current, but optimal design reduces current
+
+---
+
+### Best Practices:
+- Lower KV motor
+- Higher voltage supply
+- Thicker windings
+- Maximize slot fill before adding channels
+
+---
+
+# 🧩 12. Hybrid Enhancement (Best Approach)
+
+Combine:
+- Partial channel cooling (B)
+- Directed oil spray (controlled A)
+
+Avoid:
+- full immersion
+
+---
+
+# 📌 13. Final Engineering Insight
+
+> Concept B does not give “free performance”
+
+It trades:
+- electromagnetic efficiency  
+for  
+- thermal headroom  
+
+---
+
+## 🏁 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  
+
+---
+
+# 🔍 14. Future Exploration
+
+- Additive manufacturing stators
+- Micro-channel cooling
+- Slot liner cooling integration
+- Oil jet targeting windings only
+
+---
+
+# 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)**   |
+| Feature                  | **BLDC (Brush-less DC Motor)**         | **PMSM (Permanent Magnet Synchronous Motor)**   |
 | ------------------------ | -------------------------------------- | ----------------------------------------------- |
 | **Rotor**                | Permanent magnets                      | Permanent magnets                               |
 | **Stator winding**       | Trapezoidal                            | Sinusoidal                                      |
@@ -20,4 +310,4 @@ The research for better motor tech. We will be comparing between different kinds
 <img src="images/bldc.png" alt="BLDC motor" height=300 />
 
 ## PMSM - Permanent Magnet Synchronous Motor
-<img src="images/pmsm.png" alt="PMSM motor" height=300 />
+<img src="images/pmsm.png" alt="PMSM motor" height=300 />