I have just purchased 4 new Graupner 10x5 Propellers to replace the existing APC 10x4.5 slow fly props on my TBS Style Quad as I was not happy with the vibration levels.
Thought I would share the results.
Vibration levels for APC Props
Vibration levels for Graupner Props
I had spent a lot of time trying to balance the APC props but could never get much improvement. I just balanced Graupner props very quickly and got the above result
David Ardis
Comments
Leonard
Had the quad out at the weekend and got the pitch and roll P up from 0.14 to 0.18 and as you have said altitude hold is much the same.
The quad still needs some fine tuning but even on a windy day it is very stable any easy to fly.
Thanks for everyones comments
Hi David,
Sorry for the delay. Here are the results of my analysis. The is the standard deviation after subtracting a 5 sample moving average filter from the data to account for real flight accelerations.
Graupner
X Noise: 0.23909
Y Noise: 0.14196
Z Noise: 0.52456
APC
X Noise: 0.46539
Y Noise: 0.31099
Z Noise: 0.53945
So it looks like the Graupner are better in the X and Y but have similar performance in the Z. So your position hold should be better but your altitude hold should be about the same.
Thanks for providing the files and sorry for the delay in my reply!!
Leonard
You can download the the files from the link below.
If you want me to do any other test send me a PM
Graupner Props
APC Props
Hey David,
Could you post the two logs you used here. I would like to run them through my matlab code to put numbers to the pictures you have above.
Thanks!
Hi Oliver and Robert,
Actually one of the more interesting points is how the multicopters are used, if as Oliver said, <10mph.
Then most of the dynamic motion based characteristics aren't as important.
What you want are propellers that will permit stable vibration free hover and appropriate response for necessary maneuvering. And high efficiency is important too.
If you want speed then the situation gets a lot more complex.
But I would say that the veruy large majority of actual uses for these things do not require speed and the majority of high performance options are pretty much hobby fun only so not critical for "pro" uses.
Basically for the significant and professional use, speed is not an issue, optimized hover and precise handling and payload carrying and stable (and vibration free) camera platform capability are what are important.
So basically I think the complexities of high speed prop design for multicopters can be deemphasized.
What we really need are propellers designed for our actual multicopter applications, various sizes and weights of copters with stable camera platform operation in hover and slow speeds.
Also increasing propeller diameter increases efficiency but introduces more asymmetric forces acting around the prop shaft (vibration or tilt). So that is always a trade off.
All that said, except for Paul Pounds, it doesn't seem like anybody has done any serious design of rigid propellers designed to hold a vehicle primarily stationary in a hover and we are just using airplane castoffs.
Yep, that's what the dampers are for. Some head designs now feature a firmer pivot point in the center of the head, allowing even softer dampers to be use. Align has a sleeve with tapered bore which fits between the dampers. Gaui has the "Formula" head, which actually has the feathering shaft retained by a central ball bearing system.
Robert: Right, I see what you're saying, this flexing is allowed on most R/C helis by the feathering shaft being held in o-ring-like mounts, the stiffness of which have a lot to do with the handling character of the aircaft. Some effectively similar but simpler mount could be contrived for fixed pitch multicopter blades but I wonder if it would be worth any decreased vibration and/or increased efficiency. The idea of accomplishing it with the flex being in the blades themselves is pretty spooky unless the prop is designed for that, and then there would maybe be harmonic vibration issues and control mushiness... sort of like automotive suspension via chassis-flex, if you know what I mean.
Oliver, lead/lag is a different thing. Blade flapping really is up and down, and is taken care of by either the teetering hinge at the center of the head, or the flapping hinges at the root of the blade. Flapping and Lead/Lag do get intermingled in some weird ways that I haven't actually understood yet. It makes a difference if the lead/lag hinge is inboard or outboard of the flapping hinge.
In forward flight, the entire rotor disk actually tilts over, this is due to the flapping to relieve disymmetry of lift.
Personally the best i have experienced in 14-15" size are the wood XOAR props because they are very light, rigid and produce two times less vibrations than the APC of the same size.
Robert: That's an interesting point about vibration in fast forward flight, and is of course a well-known factor in trad-helis where a common solution is to hinge the individual blades so they can "lead and lag" in the plane of the rotor disk (my understanding is that the failure to discover that was a big reason why helicopter development stalled for decades in first half of the 20th century). But this "flapping" is not up and down, as a soft blade might do but rather fore-and-aft (as it were) in which direction even soft blades are pretty stiff. It would be interesting to see comparison vibe logs....
I would think that soft prop blades would potentially introduce vibrations just from bending back and forth with load changes while maneuvering, especially on a heavy lift machine. People seem to forget that the rotor blades literally support the entire weight of the aircraft, including big inertial loads induced by asymmetrical commands.
A lot of props used for multis were not designed for loads like that, nor are they optimized for producing static thrust. Gary M. & I have been grumbling about that for a long time, but it seems that nobody in the hobby is set up to really investigate what's what with props, let alone build any, and the available information all seems pretty much anecdotal. I guess there's not a whole lot of incentive (yet) for a manufacturer to get into this, it's probably cost intensive with not much potential return.
For the record I'm flying the biggest really stiff carbon-filled balanced Graupners that will fit on my distinctly pudgy hex and they seem vibration-free (but my idea of fast forward flight with this truck is maybe10 mph, LOL).
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