Originally Posted by PeterVRC

jrjr, I would do the motor alone first. I was going to make up a laser system like that one you show, but I will do it via running just the motor in the housing with the android phone balancing setup for that.
That laser setup idea is too rough to use for total fan balancing, you wouldn't see fine enough detail. (but still better than none I guess!)

Well, I have devised a plan of sorts. I already static balanced the fan and next I will do just the motor/housing assembly, maybe with the laser setup and the cellphone both just for comparison..... then assemble it and try the cellphone/clock approach and see how it comes out. Should be pretty close after that I would think. I don't have access to the high end balancing machines so homebrew will have to do. Not sure what to use for weight on the assembled unit or where to place it. Most likely duct tape to sort out the location and some sort of glue for permanent.

Originally Posted by PAPE

Peter, here is a hint...

If you static balance the fan firsts, then when you go to do your dynamic balance, your added weight will mess up the 2 plane balance. I hope you understood that, what I am trying to say is, if your going to dynamic balance beter start with no added weight.

and when you dynamic balance move your weight from the back of the rotor to the front, And on anothere note, I use an iphone 4S to do my balancing and my jig will register 0.10g
I dont know if an android based jig will be the same.

We have three parts: motor, rotor and spinner (and the adapter, that has to run true)

What others have found -.and I agree 100% - is that you first have to dynamically balance your motor. I was not successful with the balancer and now just run it, mounted in the housing, c-clip removed in my hand to feel the vibrations, peel the sticker off, put small stripes of tape on the bell at diffferent places and run it up each time to feel the balance - in the end add thick CA and kicker in the bell between the magnets where it is needed. Not difficult to get it to run nicely, especially the L-2855 series seem to need that.

If you DO NOT dynamically balance the (out-of balance outrunner - inrunners are unsually balanced) then you will never get the assembly dynamically balanced right because an imbalance in the rear (motor) can only be balanced by an appropriate imbalance in front in one dimension (rotation) but then it will wobble in the transverse axis. Also I have found that it is a lot easier to balance the setup once the motor is balanced.

Now for rotor and spinner: Ideally, you would not balace statically either of them separately at all but just both of them together dynamically. Problem is, the spinners are imprecise in their seat on the rotor, and in order to turn the rotor, you need to take off the spinner...
So I think it is still best to NOT statically balance the rotor (for the 10- and 12-bladers which are pretty good, in the case of cheap 5-bladers, e.g., you would need some crude static balancing to get the worst out). Then balance the rotor dynamically, e.g., by the clock method, and then adding the spinner - and only add weight to the spinner if you don't find a spinner position which balances the assembly nicely.

That's what works for me now without any fancy technology. Comments and suggestions welcome. I am quite frustrated that I am not able to use the dynamic balancer for the motor, and also the rotor I prefer to balance with the clock method. I put it on Bob's balancer only at the very end with the spinner on to get the very last bit out if needed.

cheers
Clemens

After checking the 2855-2100 balance, without and with adapter and then with the fan, everything turned out to be well balanced.

Now i need to install it either on the FMS Phantom or the HK Rafale.

hehe, I can see the logic in those processes.....

Today I attempted to balance an L2855....
It has a terrible noise... buzz sort of.... at a few RPM areas. It seems to be the bearings to me. No balancing attempts could reduce that..... so I gave up for now.

I then balanced the shaft/rotor/nut assemly statically - testing the rotor at various spots around the shaft adaptor too. It needed a few 'small chunks of fibre tape'. Enough to be measurable (I should have weighed the clump! DOH)

The I put the shaft adaptor onto the motor - an inrunner (not the lousy L2855!!) and checked it for running true - it looked perfect to me. It was already a nice snug fit on the shaft and testing by hand, and by Phone Accelerometer, the vibration was negligible.

I put the fan on and tested it by Phone Accelerometer.... it was "approx 10m/s/s".... I just rotate it approx 45deg for each test (very easy to do in situ), and within a few moves it passed through 3m/s/s... so after checking it getting larger again past that, I went back to that spot. That proved to be super smooth. Perfect.

I don't know what part the rotation actually 'matches up' to give optimal balance... probably a bit of a few areas. eg possible motor imbalance, or possible shaft adaptor on motor shaft 'error'.

So I grabbed another one and did all the same stuff.
7m/s/s at best, but that is still very smooth anyway. Its worst spot was about 12m/s/s, which was still not terrible by any means. So I would say anything 5m/s/s, or better, is a good result. Not a single 'buzz' etc at any RPM point.

But I can see that 3m/s/s is possible, so I will revisit the first one again tomorrow to pinpoint HOW to get it under 5m/s/s also.
After doing this process I doubt that NOT Static Balancing the rotor/shaft/nut could match the end result they got. The rotor would have been a dominant offset that probably would not have anything else to cancel out enough.

But I would have to do them again with NO balance weights in them, to see what that really did. Plus I wouldn't mind pulling out the weights and weighing them to see what amount it was that they needed. So I guess I will try that when I re-do the first one....

I mounted the Het 2w23 2950kv inrunner into my CS12-70mm.
I also looked at the static balance of the rotor and seemed near perfect without need for much adjustment.
I recieved the 4 grub shaft adaptors with my fans. I had to ream out the centre hole with a round file to provide clearance. I would imagine there would be a brief break in conditioning period for both the motor and the fan.
This is the resultant numbers I got with the first bench test:

Warthog bench tests

Het 2w23 - 4s 3500mAh 35C
cs12-70

72Ap settle at 65amps WOT 15 seconds
987Wp settle at 890watts

Sorry I don't have a method for measuring thrust yet... Would a scale behind the fan work?

PeterVRC , what is a good accelerometer for iphone 5 ? What was the one you used ? Could you post a pic of it ?

I grabbed about 5 Accelerometer apps (Android), 4 free ones. Most were fine enough anyway. All I wanted was the readouts, and leave the point where weight is needed up to me.
So the iPhone should have plenty too.
The one I liked best was "Accelerometer Monitor".

Whalley.... I assume/hope that the shaft adaptor filing was really just to clean out the burrs from the grub screws!! If it was cleaned up and still too small.....never file out a shaft adaptor! hehe
At best you will make it worse than it was.... they need to be DEAD TRUE. Which maybe it wasn't even in the first place, but doing something by hand is unlikely to ever improve anything!

So the first thing to check for is burrs from the grub screw holes. They don't clean them up at all internally, so there can be sharp edges in there. they will actually clean up when you push a shaft through them - IF your shaft fits the real hole diameter ok.
You can use some other shaft to clean it too.... a file is not a great idea, or at least be VERY careful.

If a shaft does not fit at all, because it truly is a bit larger than the shaft adaptor hole, then HEAT UP the shaft adaptor. This is actually a good situation to have! As long as it is only that bit too small.....
Heating it up expands it, so the hole gets 'bigger' temporarily.
Heat it up with a hot air gun preferably... or over a flame (not too close to go black from soot!)... and put it onto the motor shaft. You then have a rock solid fitting result!

The opposite of this is having a LOOSE motor shaft, which you can never truly fix 100%.
So you really want a firm/snug fit... or too tight.... rather than loose/sloppy.

You don't get much choice... you get what they gave you.
If it is a terrible shaft adaptor you really should buy an aftermarket one from ExtremRC or Tamjets.
But also beware as it might be your MOTOR shaft that is the part that is not to specs.... eg a 4mm one that is really 3.85mm etc. So check that with a vernier too.

Originally Posted by PeterVRC

Whalley.... I assume/hope that the shaft adaptor filing was really just to clean out the burrs from the grub screws!! If it was cleaned up and still too small.....never file out a shaft adaptor! hehe
At best you will make it worse than it was.... they need to be DEAD TRUE. Which maybe it wasn't even in the first place, but doing something by hand is unlikely to ever improve anything!

So the first thing to check for is burrs from the grub screw holes. They don't clean them up at all internally, so there can be sharp edges in there. they will actually clean up when you push a shaft through them - IF your shaft fits the real hole diameter ok.
You can use some other shaft to clean it too.... a file is not a great idea, or at least be VERY careful.

If a shaft does not fit at all, because it truly is a bit larger than the shaft adaptor hole, then HEAT UP the shaft adaptor. This is actually a good situation to have! As long as it is only that bit too small.....
Heating it up expands it, so the hole gets 'bigger' temporarily.
Heat it up with a hot air gun preferably... or over a flame (not too close to go black from soot!)... and put it onto the motor shaft. You then have a rock solid fitting result!

The opposite of this is having a LOOSE motor shaft, which you can never truly fix 100%.
So you really want a firm/snug fit... or too tight.... rather than loose/sloppy.

You don't get much choice... you get what they gave you.
If it is a terrible shaft adaptor you really should buy an aftermarket one from ExtremRC or Tamjets.
But also beware as it might be your MOTOR shaft that is the part that is not to specs.... eg a 4mm one that is really 3.85mm etc. So check that with a vernier too.

Lol no, sorry I think I confused you. I didn't file the shaft adaptor itself but the hole it passes through in the mount. My bad for not being clear.
In the meantime I benched the second pair same setup. The fan was pushing a 1000 watts steady @ 76 amps but I couldn't get the spinner to balance. At mid throttle it sounded rough but at wot it was smooth. Without the spinner the fan was dead quiet and smooth for the whole throttle band.
How do I balance this spinner (aluminum one)?

I have never balanced a spinner, but you should be able to just add a drop (drop by drop) of CA inside it...... but to WHERE? LOL. Lucky dip, test, then scrape it off.

This is where the Dynamic Balancers that have a processor and strobe light show their best strength! (eg Bobs balancer, or Vortex) - seeing they can show you WHERE weight is needed. And even how much.

Originally Posted by PeterVRC

I have never balanced a spinner, but you should be able to just add a drop (drop by drop) of CA inside it...... but to WHERE? LOL. Lucky dip, test, then scrape it off.

This is where the Dynamic Balancers that have a processor and strobe light show their best strength! (eg Bobs balancer, or Vortex) - seeing they can show you WHERE weight is needed. And even how much.

I ended up using a cf rod, rubber stoppers and was balancing it on the top of a couple glasses and by adding CA. In the end I discovered that to just simply not over tighten the spinner screw. Just barely snug on the spinner seemed to eliminate all the noise and vibration. A dab of loctite on the screw and it was done.

Is it the aluminum spinner?

Make sure the spinner is seating properly. It took me some time to make it click on the right position.

Originally Posted by Tartago

Is it the aluminum spinner?

Make sure the spinner is seating properly. It took me some time to make it click on the right position.

Did you have to balance any of the parts?

Originally Posted by pencon

PeterVRC , what is a good accelerometer for iphone 5 ? What was the one you used ? Could you post a pic of it ?

Hi,

I also tried some and had the best results with the iPhone-App "iVibrometer".



Peter (Austria, Salzburg)

Pete (australian, not oestereicher!)

How repeatable are you g readings? I use a blob of blu-tac between the phone and fan, and find that it's only repeatable for one session. Once I take the fan off, I use a slightly difference amount of blu-tac next time, hence an absolute number becomes meaningless.

Any chance you can work out what 3ms^-2 comes to in G (units of unbalance)?