FoxhallGH
Well-Known Member
I take all that on-board, but I had no expectations that my CF prop's would be more stable than the stock DJI ... My flight test at the time was all about 'duration' ... I was however viewing the Mavic against a cross-hatched fence, that allowed me to very easily see the sideways movement of the craft while it hovered. In addition, I was able to compare video from the two runs, where I could see more sideways movement (the vertical movement was damped out by the gimbal) in the recorded video when the Mavic was flying with stock DJI prop's ...Can you be confident your observations aren't skewed by your expectations?? Absent actual measurements the reliance on observation is questionable particularly given that any improvement would be subtle at best.
In any case supposing your claim of increased responsiveness might proved true what advantage does it provide? Does the benefit justify a 10% reduction in efficiency?
If we consider other attributes you claim as favouring their use they aren't quieter, there is no evidence of increased stability (this is unlikely given higher thrust/rpm = higher motor torque loading with reduced ability of the propulsion system to respond as quickly to commanded speed changes resulting in delayed response and less precision in applying small adjustments to thrust). The increased brittleness at low temps consideration is probably irrelevant and to the extent it might come into play would likely favour the stock props. Nylon performs very well at low temps (certainly those within the range the Mavic could be flown) however we don't know what aftermarket props are composed of, particularly the FAUX CF ones.
MOSFETS could be said to be like a tube to the extent they are voltage drive and applied to a linear amplifier the circuit topology and operation is similar in many respects. That is where the similarity ends and it can't be said they might be preferable to bipolar transistors in audio although they often are but that is principally due to the overall design and circuit complexity. The fact remains, all MOSFETS regardless of efficiency experience conduction losses which generate waste heat proportionate to the current delivered to the load. Lower motor RPM for a given thrust = higher current, an inescapable fact and the observation I was making. I did not suggest you should expect ESC failure however higher operating temperature is a given with reduced reliability and efficiency.
Any consideration of efficiency and performance needs to be applied to the whole propulsion system, not just the rotors. What happens when you fit a wheel tyre combination to a vehicle with a larger rolling diameter? Your engine runs slower for a given speed, no question. Do you save fuel? Not usually.... What happens when you are climbing a steep grade? You often need to change down a gear as you are now operating outside the design parameters of the engine and driveline. The vehicle definitely won't be more responsive, this comes from operating the motor over a wider RPM range and at higher revs generally where more output power is available.
So - no - I was not recording that as part of my test - but still, I believe it to be an accurate observation. I may do a test just to look at that aspect of the prop's separately.
In regard to justifying ... Well - I have flown over Gull's without disturbing them, and I can see that if you were wanting to do close-up inspections of a structure - then there may be advantages in trading off that 10% flight duration ... ??? There have been recent posts on this forum regarding the way stock DJI prop's go brittle at low temp's and how CF prop's are stronger when flying in below-zero temps.
As soon as you mention 'Gear's in comparing prop's to wheels, you get into the realm of why a constant speed (variable pitch) prop' is so superior to a fixed pitch ... I think we are in violent agreement on these points! I agree that the prop's and the Mavic are one system, and my flight tests actually showed that the best duration was with DJI [quiet] prop's on my Mavic Pro Platinum. But just like my tool-box, I have one screwdriver I like to use sometimes, and another exactly the same Posi-head, that I like to use in others.