Micro Motor Community

Nano QX's falling out of the sky


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.


If you have 3 that are still flying fine and you suspect the FC (not likely), you can always swap it out with a known good one, for troubleshooting purposes.
You might want to swap out your props, or at the very least, check them for balance.
Make sure that you have good isolation (double-sided tape) between the FC and the frame and that the FC is sitting level on the frame (important for SAFE mode flying)
Check your power leads - they tend to break inside the insulation. If they feel rubbery or spongy when you slightly tug at it - it’s broken and needs replacing (can cause intermittent performance)

And lastly (most likely), replace the motors. Most stock motors have a 10 hr run time before they expire.
Aftermarket and high performance motors last about 1/2 as much. This is not taking into consideration all those prop landings that can push the .6mm shaft into the endcap, ending it’s life even quicker.


I agree with above comment. Do you have the original power plugs still on them? The stock JST1.25 plug is only rated for 30 mating cycles. A PH-2 power lead upgrade is well worth the time and money. I would start here if you haven’t already.

Thousands of hours on brushed motors is NOT the norm. The slower -11 and -14 speed motors do last longer than the hotter motors though. Always good to have a few spares so you don’t get grounded.


I did the new props on one of the birds and that helped quite bit. As far as checking them for balance they are so tiny I can’t imagine being able to do that.

I have plenty of the the fat double sticky foam pads and always do that to decouple the bird and the FC.

Yep, keep those handy, but haven’t had to replace too many to them.

Have a set of -11s on order, be here on Thursday. :slight_smile:
I guess I baby my birds more, I have 100s of hours on a couple of them. Plus I always fly in grass that is cut 2.5" to 3.5" in length.


Some are original. some are replaced. I will look into the PH-2 power lead upgrade.

Boy did I blow a few decimal places, getting old. :frowning: I was running a battery experiment and I used the same bird for repeatability. It was 8 batteries, 50 times, average 5-7 minutes per flight. That number should be 40 hours, not thousands. I forgot to divide by 60. :frowning_face:

I have three brand new birds, I don’t even want to slow down to fix them.


I am the least scientific person on this forum, so take this with a grain of salt!

I bought a dromida vista that flew fine for a few days and then started flying like trash. Dromida ended up saying there were issues with the FCs so they sent me one from a second batch; which also failed to operate properly after a few days, props would spin but wouldn’t even lift off the ground at full throttle… I also used to have a few RTF birds from latrax, all the same model. and all of them showed an interesting side effect after ripping them for many hours of LOS flying/crashing… their issue was they would fly turbulently vs flying smooth, even with a fresh set of motors. Eventually I chalked it down to cheap components on the FC, seeing as all of them were acting wonky with fresh props, and all fresh parts. (Gears, shafts, props, bearings; all brand spanking new for all 3 latrax, and even for the dromida vista! All a fairly giant waste of my money now that I look back on it… all units and accessories were bought at full retail to support my local hobby shop and my new found FC addiction… ) but yeah they all started off flying okay, but they all eventually “faded away”…

Long story short I feel like big brand companies like latrax, horizon hobby, dromida ALL offer junky stock FCs that inevitably eventually ended up flying like garbage. Not saying this is happening to you but I wanted to share my story and perspective of stock FC boards. It’s kind of like a scam IMO; sell them junky boards so they think it’s the parts that must be replaced…


Never fear, this is not about science, it is about solving problems and seeing if somebody else has experienced the same problem. No sense in re-inventing wheels. :slight_smile:

The reason I gave up on helicopters, tooo many moving parts. Four is enough for me.

The birds exhibiting the problems are three to four years old, have replaced many a frame and props, but no motors, except when I bought the -11s from MMW. But having lost that bird I also lost a valuable benchmark.

The ones flying have been setting about as spares and are essentially new. I’m just trying to understand why the old ones are dying. Searching for answers.

My new -11s arrive today and I will continue my tale of discovery.


You will find out it is motors. The original motors have a weaker field strength and lower quality magnets.

I did a brief study of 5 birds by measuring the relative field strength and pretty much could predict which way they were going to drift. Could not get 100% right, so I gave up.

Motors and props are the key. We only have four moving parts, but at the end of those are some very thin props. Feel the leading and trailing edges for nick, dings, etc. If you can feel anything you can be sure that prop is not lifting as much as the other three. Remember that little hummer is spinning very fast and towards the end of the prop the rotational velocity is higher, so any ding is magnified. Every time you run into something, the ground mostly for me, with props spinning you are damaging the leading edge. That causes less lift on that one prop and it throws the FC off. The FC is programmed for new blades, new motors. Yes the tri-axis sensor can compensate for some of it, but it can’t take it all out. If it tried to we would not be flying the bird, it would.

The -11s and fresh props will make a world of difference. Been there, done that 4 times now.