What is confusing the issue is to claim that the Ti instructs Brushless motor differently to a separate ESC unit. It does NOT.
You can hook up a Wattmeter to ANY Brushless motor including DJI motors here and see the AMP rate significantly increase, with a depreciating voltage as throttle is increased. The AMP rate is actually an average over time due to ON / OFF nature of the applied power, nearest equivalent being AC ... or sinewave as some prefer. The voltage displayed reduces which is the result of voltage drop as speed / load increases.
IF you can keep the voltage constant ... which is impossible ... then you would see a constant rpm if amps remain constant ... which means the pulsing or sinewave as called does not vary.
KV is NOT a hang over from brushed in any form ... it is a valid measure of the RPM per Volt of any motor and that certainly includes Brushless. The problem is that KV is a theoretical value that cannot be attained in use as load prevents reaching such rpm per volt.
Load .. this is only constant if no changes to any input or external influences. Change any factor and the voltage then drops if load increases while it demands more amps to retain the rpm. It can only do this to an extent before that load is greater than the compensation can accommodate. This is what you see on a Wattmeter and if you have a Tacho. It is why myself and millions of RC users around the world trial different props etc. to arrive at best compromise of power in ... thrust out.
DJI motors are in no way at all different to any other Brushless Motor ... if they were - then explain how they work on my 450 Quad ?
Nigel
You are seemingly proceeding with the assumption that the phantom 3 and later ESC implementation is essentially the same as that commonly employed in most RC electric models- it isn't. While (as you have pointed out) the motors are essentially the same as any other standard BLDC motor the drive system is significantly different (more advanced) than the typical ESC employed in most RC models.
Your common ESC employs a commutation method where a trapezoidal drive pattern is derived using motor back EMF to time the phase switching, This has been the standard method of RC model ESC architecture since day dot- it is simple to implement with low cost and weight as advantages- the trade off is increased motor noise and reduced efficiency. Trapezoidal commutation switches current in the motor phases in six discrete steps. This is inherently inaccurate, having a rotor position margin of error of +/- 30 degrees. These inaccuracies add a torque ripple to the system, which negatively impacts efficiency and torque output of the motor.
The motor drive SOC in phantom 3 and later AC employs a drive algorithm TI calls Instaspin in its marketing blurb- more commonly known as Field Orientation Control (FOC). FOC provides tight control of motor torque and speed independently through the use of true sinusoidal commutation. The benefits are increased smoothness, greatly increased efficiency, higher torque and more accurate speed control. DJI calls the tech pure sine-wave drive, an accurate description.
It is the advantages realised by FOC implementation that have given us longer flight times and allowed the use of higher pitch props at lower RPM in recent DJI models. To give you a number FOC vs standard ESC implementation can give up to 23% higher efficiency (80% vs 57%) in the midrange RPM, clearly a huge advantage when running a fixed pitch prop across a wide speed range as we do with our phantoms.
As you probably know KV is the voltage that might be measured between phases on a BLDC motor driven as an alternator. Spin a 3000kv motor at 3000 rpm and you should see 1V AC. It is essentially the back EMF value. It remains very handy in determining battery voltage for a particular model as trapezoidal drive ESC are really doing nothing more than chopping the supply and max motor RPM is simply a function of KV and battery voltage. I say it is less important now as it is certainly less relevant with FOC drive schemes. The fact that FOC gives higher efficiencies over a broader operating RPM range makes it less critical to find that magic sweet spot where efficiency and thrust align. You are not alone, I too have invested considerable time in matching motors to ESC and batteries while fiddling with headsoeeds and pitch with CP heli’s.
If we go back to your original suggestion that running a phantom 3 or later DJI AC without props might somehow allow the motor KV rating to be reached I took that as being over revving. While that perhaps might be an issue with a trapezoidal drive scheme in a common ESC it is very unlikely with a FOC implementation where max rpm can be set and accurately controlled.
