FlyCorsair

My Feedback: (2)

Considering we are running mechanical parts and anything moving will have a certain amount of vibration...........
The question is how much vibration is acceptable?
I'm asking about the EDF unit.

Glacier Girl

My Feedback: (4)

As in anything that rotates, especially at the speeds an EDF spins, the less the better.

Quorneng

Agreed - the less the better.
Out of balance forces causes things to flex and this requires energy to do, so less vibration actually improves performance.

It is possible to accommodate a degree of out of balance by using flexible mountings (like a washing machine drum!) but its a bit difficult to do this sort of thing on a close fitting ducted fan.

FlyCorsair

My Feedback: (2)

I understand "the less is better". The thing is, how do you know when you have reached that point? Assuming a certain amount of vibration is acceptable, what do you do to achieve that and how do you know when you're there.
Thanks for the replies.

Quorneng

Without some rather sophisticated measuring equipment the answer is experience.
When you come across a really well balanced EDF unit you will know and that then sets the benchmark you try to achieve.

One simple test for smaller EDFs is to run it up holding it in your hands (being careful) and then do the same but holding it lightly against say your building board.
Your hands will tend to dampen any vibration but a hard surface will act as a sounding board.
If there is little difference in the total level of noise then it is likely pretty well balanced.

Glacier Girl

My Feedback: (4)

I would HIGHLY NOT RECOMMEND holding an EDF unit in your hand! There is a thread on RCG about an EDF that let go on a stand, a piece of it went through a pair of safety glasses and cut the gentleman's eye in 3 pieces!!!


And EDF needs to be balanced statically and dynamically. And not just the fan, the spinner and adapter also, and don't forget the motor itself.

Here is a great system for doing the dynamic balance, after static balancing with a cell phone and your PC. Sergey knows his stuff.

http://www.rcgroups.com/forums/showt...+balancing+edf

FlyCorsair

My Feedback: (2)

Thanks for all the help guys!!
One more question............My fan is running very smooth throughout the throttle range, except at low RPM there is some vibration. This is a 70mm Haoye EDF.
2700 Kv motor and 4 cell Battery.
Any suggestions?

Bill G

The last time I accepted a slight harmonic at one specific speed, it cost me a nice front end rebuild of what is now my favorite scratch build jet, after the 3rd flight. The fan exploded, and I assume there was a voltage drop on lockout, which caused the elevator to slam down. It does get old spending 3 hours or more, experimenting with trial tape weight, but I do it now. Interestingly, I've found many problems can be corrected by simply changing the position of the rotor, adapter, and motor rotor, all relative to each other. The have all proven to have some eccentricities in my experiences. I used the method Eflite 15 that is probably the smoothest running fan that I have. Before finding the "happy position" of the adapter and rotor, it was probably one of the roughest sounding fans I've ever heard. They really need to state this in bold in their manuals, and stop stating that they are factory balanced. I've proven this it to not be 100% correct, as there does need to be some trial and error with the positioning of the parts. Microfan gurus have known this trick for ages.



That's pretty scary. I started wearing a pair of really thick lensed safety glasses with the side protectors, when testing fans. Seems it's still not always good enough. I hope that the glasses saved his sight, at least, even though they failed?

FlyCorsair

My Feedback: (2)

Thanks, guys.........................
Still working on it.