Propellers selection is always a headache. After sometime flying copters I´ve got many, many (maybe too much) propellers at home. So I decided to make a selection and keep only the "good" ones.
Propellers are the main source of vibrations, so it´s really worth to get the "lowest possible vibrations" from them. I decided to make a calibration of all propellers I had.
Calibration was done as follow:
1.- static callibration: this is known as "balancing". That is, each blade should induce same static moment around the rotation axis. We can correct it by using small masses added until a perfect balancing (thin Scotch tape)
2.- Dinamic callibration. This is more tricky because dynamic unbalance comes from aerodinamic effects derived mainly from diferential "shape" of each blade. This is almost impossible to correct. The idea is to test each propeller and through out the bad ones.
In order to test the Dynamic Callibration, my simple, cheap and quick system (yet a bit dangerous) is to take the motor mounted on a separated arm and keep it by hand while rotating the propeller. You can "feel" in your hand very preciselly the vibs induced by bad propellers (see image attached). Good propellers induce a very small micro-vibration on your hands. Obviously, I was using a good motor without any doubt of missalignement.
The results was very interesant. I mainly have only two types: RC-Time carbon and Flyduino plastic.
I´ve attached an Excel table with all results, but in summary:
- about 50% of the propellers I had were rejected
- 63% of the rejected propellers were CW . This is probably due to there are much less producction of CW tahn CCW
- Not all sizes has same results (obviously this depends of the quality of the mold). For instance 75% of the RCTimer 11x4.5 are good, while only the 36% of the RCTimer10x4.5 are good. Best RCTimer props are 15x5.5 (100% good)
At the end of the table I added the "weighted prize" per unit (Total prize/good propos only) and I´ve compared with the very good T-motor propellers (yet expensive!).
As a global conclussion is that RCTimer props are not so bad considering prize/quality and comparing with the refference price of T-motor (3x times the unit prize average). ... and buy the doble+ of RCTimer props you´d need in order to keep about 50% of them as good.
Comparing two propellers well calibrated (same size, material) from different manufacturers, makes really negligible performance in my experience.
Using well calibrated propellers on the copter (combined with good, calibrated motors) makes a BIG-BIG difference!. It worths the effort.
Hope this helps any of you
Angel