When selecting a current detection resistor in a drone flight control system, it is important to consider its resistance value, power rating, packaging size, and temperature characteristics of the resistor material. The table below summarizes common resistor selection schemes for different application scenarios, which you can quickly refer to.
| Application scenario (peak current) | Recommended resistance value | Recommended power amplifier circuit gain (Rx) | Applicable packaging reference |
|---|---|---|---|
| Fixed wing (within 40A) | 1 m Ω | 2W 820 k Ω | 2512 |
| Fixed wing (within 80A) | 0.5 m Ω | 4W 820 k Ω | 2512 or larger |
| Traverse machine (within 160A) | 0.5 m Ω | 4W 470 k Ω | 2512 or larger |
| Modular design (100A) | 0.3 m Ω | -100 times (100k Ω/1k Ω) | R5930 |
The suggestions in the table are a starting point, and to make the most suitable choice, you need to understand these core principles:
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Power calculation is fundamental: the rated power of a resistor must be greater than the power it consumes in the actual circuit. You can use the formula P=I ² × R for verification.
For example, in the scenario of a time traveling machine, when a current of 160A passes through a 0.5m Ω resistor, the power is 160 ㎡× 0.005=2.56W. Choosing a 4W resistor can provide sufficient safety margin to avoid damage to the resistor due to overheating.
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Matching the ADC range of the flight control: The ADC (Analog to Digital Converter) of the flight control usually has a full range of 3.3V. In order to achieve the best measurement accuracy, it is necessary to configure the operational amplifier gain so that the output voltage corresponding to the maximum current is close to 3.3V.
Calculation formula: Operational amplifier gain ≈ 3.3V/(maximum current x sampling resistor resistance).
For example, in the fixed wing 40A scheme, the gain=3.3V/(40A × 0.001 Ω)=82.5 times, so an 820k Ω resistor is selected for matching.
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Pay attention to the type and packaging of resistors
Alloy resistor: Due to its low temperature coefficient (TCR), it can ensure stable resistance at different temperatures, making it the preferred choice for current detection.
Package size: Typically, packages with a size of 2512 or larger (such as 3720) can withstand higher power (2W4W or more) and are more suitable for high current drone applications.
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Calibration in flight control software: After the hardware is connected, you need to set the correct ammeter scale and offset in flight control software such as Betaflight and INAV. The proportional value is determined by both your sampling resistor and the gain of the operational amplifier.
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Consider heat dissipation issues: When conducting high current continuous testing, ensure that the PCB layout has a good heat dissipation design. If necessary, copper plating or adding heat dissipation vias can be used to help the resistors dissipate heat.
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Pay attention to layout and welding: The sampling resistor should be placed on the main circuit powered by the battery. For milliohm level resistors, the inherent resistance of PCB wiring will introduce errors, so it is important to follow the layout recommendations in the data manual.
I hope this information can help you choose the appropriate current detection resistor for drone flight control. If you could share more specific application requirements, such as unmanned aerial vehicles, expected maximum current, and packaging space, perhaps I could provide more accurate advice.