# 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)**   |
| ------------------------ | -------------------------------------- | ----------------------------------------------- |
| **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
<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 />