Brushed PWM rate and hidden thrust


#21

One thing I have seen with further research on this topic, is that in the past (from what I can tell) and on the motor graveyard threads, is that reducing the pwm rate under 16k, and especially under 8k significantly reduces the life of the motors. I guess it allows more current to pass through the brushes at one time instead of smaller bursts causing much more significant oxidation.

Just my findings though


#22

Now that is an equally valuable contribution and point of interest! Some decreased life expectancy with increased current and thrust is to be expected but I would not have guessed it to be significant. Guess a test could be engineered to quantify this behaviour too.


#23

Hey all.

Awesome research @woodsturning, many thanks.

I shared these links before in a discussion around PWM rates, it seems quite relevant to link them here too.

One thing that caught my attention was the mention of inductance in the windings causing excess heat, as I was trying to figure out why my Scisky motors where getting hot on “break in” (@32k PWM).

http://electronics.stackexchange.com/questions/80153/calculate-dc-motor-frequency


#24

I settled on a PWM of 14k for both my 6mm and 8.5mm Scisky builds. I have no concrete numbers, but subjectively, I feel this is where my “sweet-spot” is, at least for me.
This reminds me of the “Three Little Bears” fable - This one is too cold - this one is too hot - this one is just right. :slight_smile:


#25

im at 23k a happy medium between 32 and 16.
its the loudest squeal i could take.
why so much noise at lower levels?
is the loud noise im getting on lower spin up at 16k alright?


#26

The upper limit of perfect human hearing, only available to babies and very young kids, is 20000Hz. Only pwm rates under around 16000 should be audible to adult humans, are you human? Lol
Btw I’m an audio engineer :wink:


#27

for some reason both my 8.5mm sci-sky builds are loud runners then.
I do have super human abilities and senses due to a minor glitch in the matrix.


#28

Just to add my observations here. I have not had a chance to test this on my Scisky but fully intend to.
My Eachine QX95 came with an EVO F3 FC configured with pwm rate of just 1K in cleanflight. It had a LOT of thrust which I attributed to the motors they used in it.


#29

I have suspected this :stuck_out_tongue:


#30

that or a forgot to add a whole digit.
running 2300 is a bit loud.
ba-ha!

now at 15k and happy


#31

I’d like to see if you crank it all the way up to 32k if it goes from ALOT of thrust to an anemic under performer. I doubt they use anything special for motors and I don’t know about you guys but I have never been able to get decent performance out of cheap hubsan style replacements. Almost gave up on brushed micros because of them. In fact I’m planning a 2s build to give them all a noble death. Maybe the answer is in lower pwm rate.


#32

It’s all about how light you can build your quadcopter. I’ve been focusing on building as bare bones as possible in order to get the lightest weight. Look at the performance of my latest build using a Scisky running Betaflight 3.0.1 and Syma X5C 7mm motors that cost $4 a set. This is what I’m using to learn acro FPV and have been throwing in freestyle moves as well. Next time I’m at the field I’m going to play around with PWM rates to see if there is any improvement to this build.


#33

Yeah I get the weight thing. Maybe I’m just too picky. I have scrapped hubsan 8.5mm bulids at 50 grams all up weight including battery. That’s decently light right? And just yesterday put some 7mm motors back in the tool box cause it was underwhelming at 38g including the battery!


#34

I’ve tried and gave up on two 8mm and and one 7mm build on “generic” motors over thrust so I’m desperately grasping for something that may save the usefulness of those components for me. I have however been very happy with my 0820-15 build at 55 grams all up so I keep trying brushed builds. I’ve just chalked it up to brushed builds needing quality motors only. Now I’m attempting 2s through generic 1s motors - hopefully finishing up this weekend in search of thrust.

Anyway, I was just curious if you set that qx 95 up to 32k - let me know if it gets sluggish. That would help me to explain my disappointment and give me some more hope for brushed!


#35

Brushed FPV is fun if you can flow. But if you need to do big changes in speed/altitude it sucks. The reaction time is slow. Racing brushed quads, I’m frequently crashing into the ground. I try to shed 6", and drop a foot or more.

Flying my friends 2S brushed quad felt much more like my brushless quads.

Caveat: my brushed experience is largely BF2.7 or earlier. I’ve learned quite a bit since then. I expect I could tune better now and video is so much easier/lighter now.


#36

Well stated. I guess I have high expectations before I am satisfied with a build so I just have to respect that and not lose time and create frustration by cutting corners. I am definately hooked on the appeal of this smallest of size / weight quads for the carefree aspect it brings to bombing around. I have gained a lot of perspective in this thread - very appreciative of the community.


#37

The key point I forgot with brushed 2S is that it still sounds like a 1S brushed: pretty quiet. My brushless quads are all too loud/dangerous for around the house inside or out. I’m hoping my 1103 build will be suitable for the front yard but still fly like a brushless quad.


#38

@NotFastEnuf If you’ve got the building light part down, then the next thing to focus on is your motors. For 7mm motors, buy Syma X5C motors ($4 a set) and for 8.5mm buy Shengkai motors ($8 a set) from Aliexpress. These are geared quads and the motors made for them are very fast when used direct drive. Since finding out about these motors, I have been having an absolute blast with my brushed micros and it’s so affordable I buy at least 5 sets at a time so I always have spares.

@Denovich I’m in research mode now for the smallest and lightest micro brushed quadcopter with the highest thrust to weight ratio I can build because I want to fly acro freestyle FPV.

This guy’s quad with 1103 motors seems to perform quite well. So are 1105b motors much more noisy than 1103?


#39

Brushless make noise but even an esc type can make them sound buttery smooth,ontop of that props make noise,i think tris make less noise than your standard 2 blades.so even props make or join in with the noise making process.

Noise on powerfull quads is hard to eliminate but its all part of the buzz!
:slight_smile:


#40

@jayodas Great advice on motors! Thanks. & I basically have the same goal about acro brushed fpv. The learning curve for this goal is a steep hill to climb. I’ve gotten close with cl0820-15 1s build - it will do it but with no extra power to correct dumb thumb mistakes. I still have to do some test changes to pwm rate as a result of this thread. The cl0720-12’s that i just put back in the box were getting 24g thrust but my nqx flight board was completely unstable and anemic in the air. Flew like one motor was bad dropping an arm so I’m not sure was happening there. So as this search continues, that frame and fpv gear is now going to the dm007 2s build. The alternative to that is keep going lighter. 20g motors, 3g fc +jst, 4g lightest fpv, 14g decent battery -> seems like 45 g should be possible with a light frame but not below. I have not gotten there yet myself but I’ve tried 50g and don’t think it’s going to be enough for me even at 45.