Merge pull request #2 from nexor-dynamics/liquid-cooling
Revise README for liquid-cooled BLDC motor research
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# Motor Research
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# Motor Research (Apr 24, 2026)
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## Liquid-Cooled Small BLDC Motor (≈30 mm) — Research Sheet
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## Focus: Internal Channel / Directed Cooling (Concept B)
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---
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# 🧠 1. Objective
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Design a **high power-density, continuous-duty BLDC motor (~30 mm class)** for EDF/prop aircraft using:
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> **Directed internal cooling channels through the stator (not full immersion)**
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Goal:
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- Maximize **continuous power**
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- Maintain **high efficiency at very high RPM (30k–100k)**
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- Avoid fluid drag losses from rotor immersion
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---
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# ⚙️ 2. Core Concept (B)
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### Definition
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A motor where:
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- Coolant flows through **engineered paths inside the stator**
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- Heat is removed **directly from windings and core**
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- Rotor remains **dry (air-filled cavity)**
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---
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## 🧩 2.1 Cooling Architecture Types
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### A. Axial Channels (through stator stack)
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- Holes or ducts aligned with shaft axis
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- Coolant enters one end, exits the other
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### B. Slot-Integrated Cooling
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- Channels embedded near winding slots
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- Coolant flows alongside copper
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### C. Back-Iron Cooling
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- Channels placed in stator back iron
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- Lower impact on copper fill, but less direct
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---
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# 🔥 3. Thermal Model
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### Heat Sources
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- Copper losses:
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\[
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P_{cu} = I^2 R
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\]
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- Core losses:
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- hysteresis
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- eddy currents
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---
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### Cooling Mechanism
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Convective heat transfer:
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\[
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Q = h \cdot A \cdot \Delta T
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\]
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Where:
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- \( h \) = heat transfer coefficient (high for liquid)
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- \( A \) = channel surface area
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- \( \Delta T \) = temp difference
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---
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## 📊 Expected Thermal Performance
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| Coolant Temp | Winding Temp | ΔT | Notes |
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|--------------|-------------|----|------|
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| 30°C | 40–60°C | ~10–30°C | Moderate cooling |
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| 20°C | 35–50°C | ~10–25°C | Strong |
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| 10°C | 25–40°C | ~10–20°C | Very strong |
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| 5°C | 20–35°C | ~10–15°C | Diminishing returns |
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---
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# ⚡ 4. Electromagnetic Tradeoffs (Critical)
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## ❗ 4.1 Reduced Copper Fill
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Channels take space → less copper:
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- ↑ Resistance (R)
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- ↑ Copper losses
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- ↓ Torque per amp
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---
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## ❗ 4.2 Reduced Iron Cross-Section
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Channels remove stator material:
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- ↓ Magnetic flux capacity
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- ↑ Risk of saturation
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- ↓ Maximum torque
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---
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## ⚖️ Tradeoff Summary
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| Parameter | Effect |
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|----------|-------|
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| Cooling | ↑↑ |
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| Resistance | ↑ |
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| Torque density | ↓ |
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| Efficiency (if optimized) | ↑ overall |
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---
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# 🌀 5. Fluid Design Considerations
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## ✔️ Goals
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- Maximize heat extraction
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- Minimize pressure drop
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- Ensure uniform distribution
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---
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## ❗ Constraints
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### 1. Channel Size
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- Too small → high pressure drop
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- Too large → weak stator + lost copper
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---
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### 2. Flow Regime
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- Laminar → predictable, less transfer
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- Turbulent → better cooling, higher loss
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---
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### 3. Pressure Drop
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\[
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\Delta P \propto \frac{L \cdot v^2}{D}
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\]
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Impacts:
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- pump requirements
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- system efficiency
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---
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# 🧲 6. Magnetic Design Constraints
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## Saturation Limit
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Even with perfect cooling:
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- Core saturates at high flux
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- Current increase → diminishing torque
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---
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## Design Implication
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You must balance:
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- channel placement
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- iron thickness
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- slot geometry
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---
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# ⚙️ 7. Mechanical Constraints
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## 7.1 Structural Integrity
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Channels weaken stator:
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- risk of deformation
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- vibration issues at high RPM
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---
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## 7.2 Sealing
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Unlike concept A:
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- sealing is localized (inlet/outlet)
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- not full rotor enclosure
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---
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## 7.3 Weight
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Added:
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- coolant
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- tubing
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- pump
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Must not exceed thrust gains
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---
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# 🚀 8. Performance Expectations
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## Compared to Air-Cooled Motor
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| Metric | Improvement |
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|-------|------------|
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| Continuous current | ~1.8–2.3× |
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| Continuous power | ~2.5–4× |
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| Efficiency | ↑ (if well designed) |
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| Peak temp | ↓ significantly |
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---
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# 🧠 9. Key Design Strategy
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## 🔑 Optimize for:
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- Minimal disruption of magnetic path
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- Maximum contact with windings
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- Controlled coolant flow
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---
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## ❌ Avoid:
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- Large voids in stator
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- Random channel placement
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- Overcomplicated routing
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---
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# 🧪 10. Recommended Cooling Fluids
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| Fluid | Pros | Cons |
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|------|------|------|
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| Dielectric oil | Safe, good cooling | Viscosity |
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| Water-glycol | Excellent heat capacity | Conductive risk |
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| Fluorinated fluids | Ideal electrically | Expensive |
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---
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# ⚡ 11. System-Level Optimization
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## Important Shift:
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> Cooling allows higher current, but optimal design reduces current
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---
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### Best Practices:
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- Lower KV motor
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- Higher voltage supply
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- Thicker windings
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- Maximize slot fill before adding channels
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---
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# 🧩 12. Hybrid Enhancement (Best Approach)
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Combine:
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- Partial channel cooling (B)
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- Directed oil spray (controlled A)
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Avoid:
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- full immersion
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---
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# 📌 13. Final Engineering Insight
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> Concept B does not give “free performance”
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It trades:
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- electromagnetic efficiency
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for
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- thermal headroom
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---
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## 🏁 Conclusion
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For ~30 mm EDF motors:
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✔ Internal channel cooling is **more viable than immersion**
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✔ Enables large continuous power gains
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❗ Must be carefully balanced against magnetic losses
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---
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# 🔍 14. Future Exploration
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- Additive manufacturing stators
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- Micro-channel cooling
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- Slot liner cooling integration
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- Oil jet targeting windings only
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---
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# Motor Research (Jul 20, 2025)
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The research for better motor tech. We will be comparing between different kinds of motors in order to gain a better understanding of them.
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### Priorities
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- **Efficiency**: Current efficiency range (70/87%), goal (90-95%), efficiency is measured in output power (rpm/torque) per watt.
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