IMO, it's not "just" software. Car and air ESCs have to deal with different driving characteristics where current peaks are much higher in cars. Well, maybe not compared to helis, but definitely most plane ESCs. Car ESCs need more copper for less I^2*R losses at high burst currents, not to mention the FETs chosen have to be able to handle both the high current peaks and whatever constant currents. And, car ESCs have to be able the extra voltage (above battery voltage) that could be generated during hard braking.
That said, I think it would be easier to add
aircraft software to a
car ESC than the other way around due to hardware design. Of course, if all ESCs were designed with worst-case scenarios in mind, application wouldn't matter since all bases would be covered. But then cost would be higher and/or physical size would increase and people would complain.
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