Now that we have version 2.9 and inertial primary control for the Z axis and soon to have it for X and Y axes as well it is necessary to take vibration dampening and isolation of the flight control board much more seriously.

Primary improvements can certainly be made by balancing the props and motors.

So far it seems that the more rigid the frame the better because frame flex introduces undesirable mechanical delay (hysteresis) in translating motor induced actions to the centrally located flight control board. (Do NOT shock mount the motor Arms).

It may be reasonable to somewhat vibration damp the motor mounts themselves because they are on one end of the mechanism.

However, primary damping gains will be made by vibration isolating and or dampening the flight control board itself.

So far we have undertaken this process simply by trial and error sticking on of Foam or Gel pads or using O-ring suspension of the board to outboard standoffs.

This has achieved (barely) acceptable results, but is certainly by no means optimum.

The crucial fact that we have not properly addressed is that the amount and type of dampening medium needs to be matched to the weight (mass) of the item we are trying to isolate.

In fact we are trying to isolate a flight control board that weighs under an ounce or less than 2 ounces in its case which is a very small mass.

Our current "solutions" are actually designed for much larger masses and are not nearly as effective for the light mass of our flight control board as they ought to be.

I have done some on line research which did fully verify this inadequacy.

Virtually all off the shelf solutions (either pad or stud type) basically require a suspended mass that would weigh at a minimum 5 to 10 times what an APM or PX4 / IO board(s) weigh or more for optimal effectiveness.

This includes all pre-made Sorbothane, Alpha gel, memory foam or other silicone or urethane gel or foam mounts including Lord Micro mounts.

However, Alpha Gel or 30 durometer Sorbothane or Kyosho Zeal Gel double sided tape do appear to be the best possible solutions at this time so long as you use small enough pieces of them.

Simply putting a double sided pad under the entire board as we normally do now is entirely inappropriate for maximum vibration isolation and it is amazing it works at all.

Optimally you would use pads of them smaller than 1/2" square (possibly even 1/4" square) on each corner of the board or APM enclosure box. (smaller for the bare board than the board in the box obviously).

You could also improve isolation somewhat by sandwiching the board / enclosure between pads on both sides in slight compression.

So far we have done a dismal job of approaching this like engineers, but the reality is that with the massive excess quantities of vibration absorbing materials that we are using versus the mass of the APM (or PX4) has produced better results than not using them, but no where near what could be achieved by using the proper weight and size of dampening / isolation material.

The basic solution is to reduce the actual isolation medium to the 4 smallest pads you can get by with on each corner and using the softest commercially available dampening materials you can find.

A further gain can be made by placing the item to be damped in 10 to 20 percent compression between 2 pieces of the dampening material.

Thickness of the dampening material does improve dampening and isolation but is not nearly as important as selecting the right material and the right size of the supports made from it.

I believe that Kyosho Zeal tape is 2/10 of an inch thick and that is probably plenty for our use and the frequency range we are trying to damp.

I would very much like to see 3D Robotics produce a APM (and PX4 / IO board for that matter) case with proper internal shock mounting of the board(s) with dampening data for it.

I actually suspected this result from the start of my investigation and a little thoughtful research has completely confirmed it.

Another significant gain in vibration isolation can be had by using a high flex wire and strain relief approach to all wires connected to the Flight control board (and using the minimum number of wires necessary as well.)

I have used the concept of vibration isolation and dampening somewhat interchangeably in this discussion.

Isolation is simple undamped (spring or rubber band support) which allows the movement of the isolated object largely separate from the containing object.

Dampening is the conversion of vibration into heat energy by a shock absorbing medium (car shock absorber for instance.)

Our ultimate goal here is to provide the most high and medium frequency reduction while still allowing low frequency actual board movement to take place with a minimum of delay.

So realistically our methods embody both Dampening and Isolation.

I have covered a lot of ground here, but this is at least a good start for designing some real world vibration solutions that are bound to work better for us than what we have done so far.

Please try your own experiments and kick in your own thoughts here, that's how we get better and this is just a launching point.

Here is an excellent link to some definitive research and testing that will help:

http://fpvlab.com/forums/showthread.php?4251-Vibration-Dampening-amp-Isolation-Solutions-Guide

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                • It still looks different than yours :(

                  • Ok, now working in spanish :), changing international settings only, works too, perhaps the " . or , " or something little detail like that, Im going to try to change one by one to discover and share but it's only a minimun detail now, your program is international now, thank's

                  • MR60

                    If you ever figure out why it doesn't work in Spanish, let me know so I can fix it.

  • Hi Again Forrest and everyone.

    A few months ago I posted my vibration results for my 7KG quad. They seemed very good at the time but not as good as some of the latest results on here.

    I was trying to keep the whole frame form vibrating for good photographic results. The pixhawk was mounted rigidly.

    Each pair of motor arms were 'floated' on sorbathene bushes (the sort sold for hi-fi vibration feet), also the gimbal was floating on these.

    I had much spectacular video at 55mm zoom without any signs of shake.

    Here is an image with the sorbathane colored pink.

    3702250221?profile=originalThe arm units could be folded or totally removed as I designed 'quick connectors' see below.

    3702139231?profile=original3689665281?profile=original

    Unfortunately, one day when I came home from work, this copter along with others were missing from my workshop. Also gone was a large 3D printer which I designed and a computer containing all the files .

    The good news is that I have now just finished another printer so hope to begin working on the copters again. Its taken about a year to get back to this stage. I still dont have my old equipment but know who took it.

    Im excited to be back in the copter thing and hope to have a copy of the 7kg quad under way soon.

    • T3

      Vince, 

      regarding:

      A few months ago I posted my vibration results for my 7KG quad. They seemed very good at the time but not as good as some of the latest results on here

      you have to keep in mind that you are flying a 7kg copter - not a 1.5kg one with small props. The bigger the props and the longer the arms the more vibrations. So you did a real good job I guess!

    • Nice build, clean and well thought !!!

      How is torsion kept rigid on the 2 frame bars? Torsion forces must be enormous with these powerful motors?

      Manu

      • That question shows good understanding of the problems. High yaw demand can have the 2 opposite corners doing all the lifting and so twist the frame.

        I was concerned about torsion in the main frame. Not the ability of the spiral wrap carbon tubes but the ABS cross pieces and friction connections.

        Occasionally the copter landed with a twisted frame, no matter how hard I tightened the cross pieces but the answer was just a drop of Acetone on each join and - no more slipping .

    • Hi Vince,

      Sorbothane is great stuff, a nearly ideal damping medium.

      I would like to know what durometer Sorbothane you are using.

      90 durometer is the most common, but I have had better luck with softer grades.

      As your copter is heavier, 90 may be better though.

      I also favor the dual damper method you are using with the primary battery and flight controller and camera gimbal containing mass isolated from the motor/prop arms by a damping mechanism.

      The fact that you have also damped the gimbal support should also provide good benefits.

      A multicopter is subject to many modes of vibration as Forrest has said and a separate "dual" system often works very well with the secondary system potentially cancelling out any remaining vibrations.

      (Note to Forrest, this has been my actual in use experience in any case.)

      Really hope you get your stuff back and the thief gets what is coming to him.

      There is nothing worse than having to deal with louts and bullies.

      At least your completely one of a kind stuff ought to be really easy to convincingly identify to the authorities if you go that route.

      Really great Work.

      Best Regards,

      Gary

      • I think I used these but seem to remember there were 2 duo ratings available at the time. I think I used 70 on copter and 50 on gimbal. Either way my design allowed the sorbathane to be compressed and so adjusting the stiffness quite a lot.

        Here is a cross section of the floating arms, the sides could be moved together more to squeeze the sorb.

        At their loosest there was bad oscillation but there was a 'sweet spot' where everything smoothed out.

        3702745951?profile=original3702746377?profile=originalLikewise, the gimbal could be stiffened be tightening the vertical M3 screw.

        3702746350?profile=original

        Early flight test with old gimbal from octa. Trying to induce oscillation.

        https://www.facebook.com/208110089372753/videos/438713529645740/

        More pics here

        https://www.facebook.com/permalink.php?story_fbid=438708532979573&a...

        • Really excellent design Vince,

          The tunability of both sets of dampers should really let you dial it in.

          Ideally, the second set of dampers should be out of phase with the first set letting you tune for near zero vibration on the gimbal mount.

          Actually it could theoretically permit very high attenuation of first and second order vibrations and also mitigate 3rd order ones. (Which are generally pretty small anyway).

          I am going to try and incorporate this methodology in my future designs as well.

          My current "adjustments" are performed by using different diameters and sizes of Silicone O-rings on my suspended Oring mounts and substituting different durometers of shock mounts on the main chassis to frame mounts.

          But that is coarse, not progressive and has very limited tuning ability.

          You have definitely given me something to think about, analog progressive tunability is likely a very important feature of vibration mitigation.

          Proper setting of the adjustable Koni Shocks I used to use on my Formula Vee race car many years ago were often the difference between winning and - not.

          Best Regards,

          Gary

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