Just want to know your opinions of motor/blade choice, more specifically:
-Do you prefer a smaller blade & motor with higher RPM or a larger blade & motor with lower RPM? Why?
-Do you prefer 2, 3 or 4 blade props? Have you tried them both/all? Why?
-Outrunner or inrunner? Why?
My thought (Without testing to back my theory up) is that the higher RPM blades would be more stable, but also louder? How correct or incorrect is that?
I'd like to keep mine as quiet as possible so was thinking of 3/4 blade large prop with a brushless outrunner. I have seen videos of multi's with inrunners and although it seems to work well it sounds noisy as hell. But on the same note I don't want to trade off too much stability or performance for the quiet, I'd like to keep it balanced.
Replies
Using this here are some figures for you to process
12" props 850kV @ 12.6V = 3382.08g thrust 0' asl
12" props 850kV @ 9.6V = 1889.74g thrust 0' asl
10" props 880kV @ 12.6V = 1837.87g thrust 0' asl
10" props 880kV @ 9.6V = 1035.31g thrust 0' asl
8" props 1000kV @ 12.6V = 805.85g thrust 0' asl
8" props 1000kV @ 9.6V = 455.17g thrust 0' asl
8" props 1500kV @ 12.6V = 1888.69g thrust 0' asl
8" props 1500kV @ 9.6V = 1066.78g thrust 0' asl
8" props 2000kV @ 12.6V = 3456.31g thrust 0' asl
8" props 2000kV @ 9.6V = 1952.22g thrust 0' asl
This is thrust only though. As Jani said higher control is had but using slower RPM but thrust for your circumstance must also be matched. The PID settings can be tweaked to stop the bad behaviour but if you do not have the thrust it will not matter. Of course finding motors capable is not as easy as doing the maths though.
Bigger props and smaller RPM's is best way to go. RPM does now bring stability to quads it actually brings unstability. Whole idea on making quad as stable as possible is to control as accurate as possible airflow with accurate propeller speeds. If you go high speed motors you will loose a lot of this accuracy.
On generic ESC there are about 127 steps that can be used to control motor speeds. Math is rather simple. If you have a motor that spins 11500 RPM at 11.1V or motor that spins 25000 RPM difference is huge.
With 11.5k RPM one step is about 90 RPM with 25k RPM one step is about 200. This is just rough numbers but it gives the idea on how it works.
Two blade prop is best and most efficient, 3 blades usually creates more vibration. Ok 3 blade props diameter is always smaller because it has 3 blades. But they are not so efficient as 2 blade. One reason for this is that blades will travel earlier blades turbulence more than 2 blade model does.
Usually you also need to spin those 3 blades a bit faster to get same thrust which again means that you need to have faster motors which again means that your rpm accuracy is not as good as with smaller rpm motors.
Hope that this gives some idea about motor/propeller combinations and yes I have been using 3 blade propellers on our test quads and been doing tests for those.