title_body: What are the usual engineering considerations for a UAV current sensor?
upvoted_answer: Is the shunt resistor usually mounted high-side (i.e. at the positive battery terminal), or low-side (at the negative terminal), and why? Does it matter?  
  
  
  There should be no significant difference to the measurement if the shunt resistor is on the high or low side. As the resistor is in series the absolute voltage across, and current through, the resistor remains the same. However, there may be a small advantage to one or the other depending your sensor design - for example, having it on the low side makes the measurement relative to the circuit GND, which may reduce the component count of your amplifier/signal conditioning design.
  
  
  What class of amplifier, in terms of precision, is used for the sensed voltage?  
  
  
  This will depend slightly on your design, and you may find the precision of the ADC to be the limiting factor (e.g. an 8 bit 5V ADC has a resolution of 19.5mV.) That said, the job of the amplifier is to match the range of values from your sensor to the input range of your ADC. While a linear relationship is intuitive and straightforward, it may be more desirable to have a curve to give greater sensitivity around the expected ranges but still report invalid values with slightly reduced precision. You would need to characterise the curve and program it into your flight controller for correct reporting.
  
  
  What range of output voltages does the FC expect?
  
  
  This will depend entirely on the flight controller - but typical ranges for ADCs are 0 to 3.3V or 0 to 5V. Remember that if you want to report a negative reading, you will need to bias your zero value sensor ourput for mid range on the ADC.
  
  
  Is there any smoothing (lowpass filtering) applied to the sensor's output to reduce aliasing from possible high frequency current ripple?
  
  
  Filtering is a good idea to help reduce unwanted values. The response time of the filter needs to be fast enough to capture valid changes while rejecting noise. You can compare the filter response rate to your sample rate - your filter response can be slower if you are checking the voltage every 0.5 seconds instead of every 0.05. Alternatively you may decide to do some filtering in software, sampling several times and averaging, but this takes CPU time away from other tasks.