I finally did the test of hard fixing the APM case to the frame, thus not having two separate masses with vibration dampening materials in between, as before (i.e. : frame/props on one side and APM on the other side).
This is explain by Forrest Frantz in a post I made earlier about moongel use here:
and in more details here:
I have to say that I felt on my bottom when I saw the results : TWICE less vibrations with this method WITHOUT any moongel nor any other vibration dampening techniques. JUST ONE SINGLE mass (APM fixed on frame directly).
Look at this graph that shows ZACC within plus or minus 0,1g which is twice less than the best +-0,2g I had with moongel combined with rubber bobbins and/or silicon gel. It is measured on the exact same aircraft (except moongel was removed and rubber bobbins were replaced by hard pylons). APM is stcked to the plate with NON foam double sided tape (hard double sided tape, as I did not want to drill screw holes in the APM plastic case).
Not only have I less vibration but I will also get better control on the craft since I get rid of the lag effect of dampening materials.
I confirm thus the theory of Forrest Frantz. It works for my frame.
It would be nice if others could confirm this also on their frame.
I publish this UPDATE after the information about 200hz dangerous vibrations came out thanks to the debate initiated of this post: the APM and its integrated sensor's hardware have a limit (due to low processing power limiting sampling frequency - that should be solved with the more powerful PX4 hardware) in such a manner that all frequencies of 200hz (and multiple of) will impact the APM control (accel) and will go through the 20hz software filter, undetected (thus noise id processed instead of valid signal, possibly creating catastrophies). As there is no way to analyze in a log AccelZ graph if you get these 200 Hz frequencies on your arducopter, it is necessary as a precaution to use dampening technique(s) to eliminate these high frequencies (even if the AccelZ log seems to show low vibrations by direct fixing APM on the frame).
Thank you so much for taking the time to do that test.
You are absolutely correct. Will any other test this? The score is now 0 to 2. The underdogs lead.
From personal experience I've learned that when someone has a lot of time invested in something they built, it can be hard to face the reality that all their work and all their inventiveness was all for not. For me, an inventor, I was really hoping to find a solution that improved vibration over doing nothing but tying the APM securely to required mass (the batteries). So much for hope. But at least now I can focus on other more rewarding issues.
Well done Hughes. One of the brave. One of the few. Thanks for doing the test.
P.S. Something I haven't tested yet, since we tie the APM indirectly to the mass of the battery, is if multiple straps of Velcro is adequate to secure the battery to the electronics platform or if the battery needs to be more firmly secured. And if so, how to do that using only a few grams.
P.P.S. Your z beats mine!
thx for the compliment and I return it to you as you feed this forum with excellent scientific information that makes me learn a lot.
In the current test I fixed the battery with velcro straps but it is not fixed enough to the rest of the frame mass.
If I had a 3D printer, I would print a snug plastic cage to slip the battery in. I may try with a tupperware box if I find the right size for it.
For info, my total frame mass without battery is quite heavy and that explains probably the good vibration results : 8 pounds (4kg).
Good to see others have had similar results to myself.
Though admittedly I have just never liked moongel to begin with. Most of these vibration absorbing gels are bloody shams to be honest. I have tried moongel for a number of things - especially camera vibration dampening and I finished with some pretty disheartening results compared to high quality silicon vibration dampeners. NOT the stuff you buy from fox tech and NOT the stuff that comes with a vibration dampening "kit".
All of the "designed for RC" dampening systems are really gimmicky and I would advise you look elsewhere.
In regards to the APM or flight controllers the trick seems to be to get something fixed, but not quite completely rigid - which is why I would advise against hard mounting in most cases honestly.I know for me what worked the best was hard mounting the apm and simply using a tiny sliver of highly compressed wire insulation around the screws. (I have the old non cased apm 2.5) The wire insulation was very compressed though, and if you tried to wiggle the APM around you would certainly not be able to tell the wire insulation was there.
Thanks for the informative post - I really wish we could get a dedicated thread where we just listed vibration dampening techniques and results for both the APM and camera systems.
There is a ton of info out there but it is outdated and spread through hundreds of rcgroups threads each with hundreds of pages.
Oh good to know you are a third person confirming that a fixed APM on the frame gives good vibrations results (I would not say the same for a camera gimbal because the objective of a camera gimbal is different than APM).
What this would mean if more people like you and Forrest Frantz confirm it too on all kinds of frame types, is that the APM wiki about anti vibrations is misleading, i.e. instead of all kinds of techniques to limit vibrations, the simple physics law F=MA (one mass) applies, meaning we should not decouple frame and APM. Quite a mind change for what most droners think about APM vibrations control.
Hi Hugues/ Forrest,
It is a good news to the community that something new has been achieved, congrats :) I did read the two posts quoted by Hugues and that has some good information which did not occur to me.
If I can request you to post a couple of pictures with some illustration on what/ how you have achieved better vibration isolation in the 'true sense' (with the APM board stuck on the plate or battery). Right now I am a bit confused on where do we put it precisely (frame, where in the frame?), among the slew of posts by different people on their implementation.
A picture speaks more than a thousand words, don't get me wrong ;)
here a picture of my setup. APM is directly fixed on to the frame with no anti vibration device whatsoever so that APM follows exactly the movements of the frame (it forms a single mass with the rest of the frame which is key against acceleration=vibrations, because F=MA=>if M is big, A is small, force being constant).
Nice illustration and thank you for the super fast response. Exactly what I wanted to learn..
Is the (Nylon fixed pylon) and balsa plate material the same (or similar) as is used by the 3DR frame plates? Can someone answer this too?
@Hugues, also can you tell me what is there on top of the APM. I see you have screwed a wooden part to something?
I was thinking on sticking the APM to the center of the plate using glue from the glue gun on the sides of the board. It would seem to do the same task as above (F = mA)?
Can somebody confirm this?
I would use mounting tape of some sort like Hughes did.
Glue would work - but it would also probably be a pain in the neck to remove/ generally work with.
My testing seems to agree with this.
Here are two flights within minutes of each other. Only change was to remove the thin layer on compressed moongel that sits between the APM plastic case and carbon fibre plate.
The APM case also has 4 small elastic bands pulling the APM onto the plate for both flights. See attached photo.
MoonGel removed and replaced with 1mm double side foam tape:
I'll run a few more tests over the coming days across some of our other airfames. Also see what the results are on same airframe without the 1mm foam tape in the vibration sandwich. I'll post any results here.