How to make Gimbal Motor in BLDC Motor classification？
Here’s a structured approach to designing/building one:
Step 1: Motor Topology Selection
| Feature | Requirement | Why? |
|---|---|---|
| Rotor Type | Outrunner (external rotor) | Higher torque density, natural heat dissipation, and space for high poles. |
| Pole Count | 14–22 poles | Enables finer control, smoother rotation, and reduced torque ripple. |
| Stator Design | Skewed slots (10–15°) | Cancels cogging torque harmonics by disrupting magnetic symmetry. |
Step 2: Electromagnetic Design
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Windings
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Sinusoidal windings (not trapezoidal): Distributed windings with overlapping phases.
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High slot fill factor (>70%): Tightly wound copper to maximize torque efficiency.
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Low KV rating: 50–150 RPM/V (achieved via more turns of thinner wire).
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Magnets
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High-grade NdFeB magnets (N42SH or higher): Delivers strong, consistent magnetic flux.
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Halbach array segments (optional): Focuses magnetic flux toward the stator, reducing stray fields.
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Step 3: Materials & Construction
| Component | Specification | Purpose |
|---|---|---|
| Stator Core | Thin silicon steel laminations (0.2–0.35mm) | Reduces eddy currents & hysteresis loss. |
| Rotor Can | Titanium alloy or carbon fiber | Minimizes weight and inertia. |
| Bearings | Precision ceramic bearings (ABEC-7+) | Eliminates mechanical jitter. |
| Air Gap | <0.5 mm | Maximizes magnetic coupling. |
Step 4: Control System Integration
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FOC (Field-Oriented Control):
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Implement sensorless FOC using BEMF zero-crossing detection or high-frequency injection.
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Use PI controllers for torque/current loops (not speed loops).
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Anti-Cogging Algorithms:
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Pre-programmed torque compensation tables to cancel residual cogging.
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Low-Speed Optimization:
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PWM frequency >20 kHz to avoid audible noise.
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Step 5: Mechanical Optimization
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Rotor Balance:
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Dynamic balancing to <0.1 g·mm (e.g., laser balancing).
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Hollow Shaft:
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Allows routing of camera cables through the motor center.
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Thermal Management:
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Copper-filled PCB stator bases for heat dissipation.
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Step 6: Validation & Testing
| Test | Target Metric | Tool/Method |
|---|---|---|
| Cogging Torque | <0.02 Nm | Torque sensor + oscilloscope |
| Torque Ripple | <2% of rated torque | Dynamometer + FFT analysis |
| Start/Stop Smoothness | No jerk at 0.1 RPM | High-resolution encoder feedback |
| Vibration | <0.01 m/s² RMS (10–500 Hz) | MEMS accelerometer |
Key Trade-Offs & Pitfalls
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Efficiency Sacrifice: Gimbal motors operate at 60–80% efficiency (vs. 90%+ in standard BLDCs) due to sinusoidal windings and low KV.
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Manufacturing Complexity: Skewed stators and high-pole counts require CNC winding machines.
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Don’t Modify Standard BLDCs: Off-the-shelf BLDCs lack skewed slots/high poles – redesign from scratch is essential.
Example: DIY Approach vs. Industrial
| Aspect | DIY/Prototype | Industrial (e.g., DJI) |
|---|---|---|
| Magnets | N38SH (off-the-shelf arcs) | Custom Halbach arrays |
| Windings | Hand-wound (distributed) | Automated needle winding |
| Control | Open-source FOC (e.g., SimpleFOC) | ASIC-based FOC with anti-jitter AI |
| Balancing | Trial-and-error with clay | Laser vibrometry + auto-correction |
Why Standard BLDCs Can’t Be "Converted"
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Low Pole Count: 4–12 poles cause high torque ripple.
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Non-Skewed Stators: Inherent cogging torque.
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High KV: Unsuitable for low-speed precision.
Final Output Specifications
A true gimbal motor should achieve:
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Cogging Torque: <0.5% of rated torque
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Torque Control Resolution: <1% error at 0.1 RPM
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Acoustic Noise: <20 dBA at 100 RPM
By adhering to these principles, you create a BLDC motor that belongs to the "Gimbal-Optimized" subclass – defined not by basic construction (e.g., inrunner/outrunner) but by motion-quality metrics. This is why it demands its own niche in BLDC taxonomy.
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