This is a short recap of a conversation that @Benedikt and I have been having for the last few days.
Me: I have 5 nQXs that have quit flying. They wander around close to the ground and fly erratically at best.
First, ALL of these birds flew fine at one time, they have suddenly started dying off.
Still have 3 more that are fine.
Some of my nQX birds are running the PWM for the motors at 4KHz. They don’t fly hardly at all, The ones that fly run at 12KHZ. Do you have any knowledge of this particular aspect?
These waveforms are from a current probe on the main power lead to the bird.
Ch1 Vert = .5A per division. Horz is on the bottom of the screen.
DX8 Transmitter, bird in direct flight mode 50% throttle
Benedikt: I have played with the motor PWM on programmable FCs, and found the difference in performance not significant, but measurable.
Lower frequencies (e.g. 4KHz) produces marginally more output at full throttle, but the control frequency is audible, and that annoys me a lot, especially when flying indoors.
16Khz and above, I cant hear anymore, so I usually set it to 16KHz.
Me: I had enough bad birds that as I took them apart trouble shooting I discovered they made two different controller boards for the nQX, one 4KHz, one 12KHz. Pictures attached.
Also as I dug into the problem, PWM was a red herring, as you pointed out. It is all motor related I am convinced. One had a motor that would stop spinning even in direct flight mode, so I swapped it out with a motor I had pulled earlier when I bought a set of motors from you a two or three years back and that cured it. Need to do a full swap of motors to be consistent.
Me: Have you ever measured the static external magnetic field on your -11 motors? How about over time or temperature? Do you even have an instrument that can do that?
The reason I ask is that I am so,so convinced that what has happened is that I am experiencing a decay in the field strength due to time and heat.
These are all old birds that I ran the props off them. I have 1000+ hours on some of them.
Remember these are all Blade motors I am talking about and I assume they are using a lower quality magnetic materials than you.
Benedikt: No, I haven’t measured that. As you say, I don’t even have instruments for that.
But I know that the quality of the magnets is very important for the motor performance, and we make great efforts to source the strongest and most consistent magnets we can.
I also know that heat changes the strength of a magnet. That’s one of the main reasons why you don’t want electric motors to get hot.
Me: I 'm looking for a cheap way to measure the static field strength to see if it can be used to predict motor degradation/lifetime. Working on a couple of approaches.
Back to real time… I started this “conversation” in hopes that some of you might have wandered down this path before and have input to enlighten me.
I had some -11 MMW motors, but “parked” that bird in a tall tree a couple years back. I have another set coming to install in one of my sick birds to see if it cures the problem.