|Jul 04, 2012, 05:46 AM|
Thats very difficult to answer, the diameter of the outlet has more impact with this fan from my experience.
I have the F16 and Vampire flying with one, a few guys at my field are running the vampire as well, one has a 64mm version in a hawk, and one has the 70mm 4s version in a starmax F15 that has bifuricated inlets and outlets!
The F15 is the quietest of the lot without doubt, I will get video of it this weekend, in fact will be getting new vid of all the jets now I can edit again.
The F15 has almost no roar from either end, and no fan noise, its too quiet, he loves it, I keep looking round the sky wondering where the hell it is!
I never expected it to be so quiet with the bifuricated outlet, so I dont think anyone can answer you definitively.
|Jul 04, 2012, 06:23 AM|
Australia, VIC, Melbourne
Joined Nov 2006
Well I got the ERC alloy fan all running.....
The big issue was the ERC adaptor shaft. Too much freeplay on the motor shaft - which I could feel assembling it, but once all locked down (screws) it spun up fine. It seemed. But I had only run it up to about 50% RPM in hand, to visually check.
So now I went through all my 3.17mm shaft adaptors (1x ERC, 8x CS) and even though the CS ones were all snug fits, or tighter, every shaft adaptor would move to notable off centre spin at the tip - and thus vibration - at full RPM. Up to about 50% or a bit more they were all fine. Which is why the ERC one looked to be ok the other day.....
Rev down... perfect again... rev up past 50% or so... off centre again....
I have never even tested that aspect before, seeing all fans have come out great (4mm) anyway.
But this 'off centre' rotation at high RPM is not the true issue. I think that occurs just due to 3.17mm motor shaft 'flex', because it isn't strong enough to fend off the 'micron' imbalance of an adaptor shaft, which totals great G's at high RPM!
Sure, if it was a PERFECT adaptor shaft then even that high RPM distortion would not occur - but it is also not as fatal an issue as it might seem, as it turns out.
The ERC adaptor (old design version), which uses 4 grub screws, is never going to hold a true position really. The slop, that allows the adaptor to move/rock on the shaft, is pretty certainly going to come into play sooner or later - when it sooner or later moves/rocks any fraction on the shaft.
Requiring a super tight grip by 4 grub screws is never going to be a very good solution.
Of course that was not Mark's aim either... this was just a poor tolerance adaptor.
ALL the adaptors have that off-centre tip spin, but that is because of the motor shaft flex... NOT the adaptor being drilled off centre etc.
This is confimed when the rotor is put on and it all spins right up to full RPM without a micron of flex, or off centre spin. Because if the adaptor had an issue it would remain an issue even with a rotor on - UNLESS you fluked putting an off balance rotor EXACTLY opposong the adaptors amount of issue. And the grand total permutations, and thus odds, of fluking that are HUGE.... so it is not the case.
What is happening is that the adaptor is not perfect, but only by a micron, and the stability that having a rotor on gives (a notable rotating mass), then easily swamps out the adaptor issue.
Of course some people probably have had adaptor shafts (CS) that were poor tolerances beyond this 'acceptable micron level', so those will never be perfectly workable.
So anyway, now I have a stock CS 3.17mm adaptor shaft, with the ERC supplied (modded?) rotor and ERC nut - but I left the washer off as I don't like ANY of those, except Tam's design which covers all needs to be a perfect solution - and it runs as perfect as any I have had.
Hand held testing to full RPM (!! but using a glove - I figured alloy can be trusted?) it is extremely low, if any, measurable vibration. My measurement said "What vibration? As good as zero to me". So that was a very good end result.
THEN... throw on that same original ERC spinner..... and it remained the same! Which then means it most likely has no mass offset - or so small it is undetectable - or extremely small and it just offset a micron imbalance in the prior system very well anyway.
I think that taking it off last time, and the 'very large' vibration dropping right down then, must be tied in with the mass of it adding to the prior systems ERC shaft offset.... and probably a bit of fluke of how ithe spinner was on (though that seemed perfect). I am not sure of a solid answer to it.
But whatever the reason, or reasons, on the better CS shaft balanced system it did what it was supposed to do. NOTHING. LOL.
I will still go and 'phone app balance' it, to see what balancing to "the very best" means. But I could happily use it just as it is.
It does have less (err, none) 'plastic housing reverberations', so I expect it would sound tons better than a stock CS housing in a plane too.
And to note again:
Mark did right away, the other day, offer to take back the shaft adaptor and motor to check and replace as required. So that was good, but I chose to keep it all and pin-point the issue myself if I could, because of shipping delays etc. And as it turns out it was worth doing that, to save time and shipping costs.
I am amazed that I have still not had a single 'bad' CS10 stock adaptor of 4mm, and now 3.17mm. I wouldn't be able to say if they are PERFECT (and I am sure they are not), because I have no reference myself, but they have certainly been ADEQUATE to get a great end result anyway.
Maybe it could all be even a bit better......
|Jul 04, 2012, 09:34 AM|
You're not the only one who struggles with "perfectly" balancing fans. All my motors, that are being used at the moment, have 3.17mm (1/8") shafts. I just balanced one yesterday. A HET 2W-30 in an E-FLite housing and RCLander rotor. Don't ask why. I was able to get it to balance perfectly and high rpm's, but there would be an unacceptable amount of resonance at about 15-20% throttle. By moving the spinner incremental bits, I could all but eliminate the low throttle resonance, but then there'd be a slight vibration at full throttle, which was unacceptable. By ever so slightly moving the spinner, I was able to smooth out the full throttle vibration to nothing, but the low rpm resonance came back, but not as much.
Of all the fans I've put together, I don't think I have a single one that spins absolutely true (a little spinner wobble), but they are balanced and might resonate a little at low to mid throttle, but produce no vibration at full throttle.
You're not alone....
|Jul 04, 2012, 11:49 AM|
Yep, many of my fans do the same thing. Just a little vibe for a very short range of power in about the 15% power level, then very smooth all the way up after that.
Very acceptable IMO for a $15 fan. The alternative is spending and additional 400% just on the fan to get rid of that, not me. I`d rather have 4 more fans.
|Jul 04, 2012, 12:18 PM|
|Jul 04, 2012, 01:15 PM|
I doing some TJ70 stator testing comparing data between standard 4 stators and 7 stators.
Here both videos run with the same batteries and same motor.
Only different is the shroud one shroud had 4 stators and other are 7 stator.
I'll graph the chart later to see what the different at certain RPM, thrust and watts.
TJ70 7 stators video.
TJ70 4 stators video.
|Jul 04, 2012, 01:35 PM|
glad you got it sorted out peter
the reason you have imbalance at diff rpms is because the cg is off front to back on the rotor. this is very difficult if not impossible to get rid of manually or by feel. hopefully the rpm where the vibs are showing up are in the lower range of operation that way it will not be much of a problem. if the vib is in the 50% to 100% throttle range then you should continue to try and remove it or at least shift the imbalance to a lower rpm or it will cause premature motor failure.
|Jul 04, 2012, 01:54 PM|
Looks like the 4 stator was a little lighter load, but the 7 stator was a little quieter and had a little more power. It will be intresting to see how the graphs compare.
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