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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  • MR60

    Testing will soon be complete on a new vibration dampening system that weighs only 30ish grams and results in vibration levels 10x better that what was rated excellent before while still maintaining a strong FCU to frame link (little to no control latency thus true dampening versus isolation).  Before we divulge the system, we want the data behind it and several ships to verify it. We are almost there. Stay tuned. The reason for posting this is to just say:

    - forget the foam under the FCU

    - forget foam entirely

    • Come on Forrest, an avant premier pleaseeee!!!!! :D

      • MR60

        a few more days of testing and it will be released ... i promise :-)

    • Hi Forrest,

      Still using the 2 different response rate Zeal combined with O-ring suspension myself, but it is kind of a pain to implement and basically just an OK system.

      I am currently looking at silicone O-ring mounted motor pods and frame arms as well.

      But I am very much looking forward to whatever you have come up with,

      You have come up with a lot of really unique and interesting innovations in the past and I am sure this will be worth the wait.

      Best regards,

      Gary

      • MR60

        thanks Gary. So far the data is a bit non-intuitive (no surprise), so will double check ... redoing all the tests but should be done in a few days

  • I know this is an old topic and has possibly resolved through the multiple pages of discussion.  But I wanted to add some thoughts on Sorbothane application, an alternative usage.

    I have found Sorbo can be used in tension, up to 25% without failure.  In my experience there was no permanent deformation and if allowed to rest would rebound fairly well.

    Unlike other elastic material, Sorbo will control rebound quite well without resonating when partial tension is released.

    My application was using Sorbo as stabilizer band for a gimbal, basically pre-compressing the standard silicone isolators.  It was effective, but securing the Sorbo bands was the point of failure, as I had limited space to create a proper anchor point.

    Effective cutting is another key to its success.  Radius cuts rather than square ones prevents typical tear failures.  Either a punch or water jet can be used to produce the desired shape.  A rounded double wedge shape can be effective in anchoring the material....into a matching receiver.

    @Forrest, I appreciate reading your replies.  Always very insightful and with respect.

    • @RichWest Thanks for sharing your findings. Could you show us some pictures of your mounts, specially some ones about "effective cutting" and shapes?. I have been using Kyosho Zeal Gel Tape system with "traditional" cutting and now the same pattern with 3DR foam (those included with Pixhawk) but  improvements are wellcome

      • Sorry no photos.  The post was more to express the use of Sorbothane in a non-intuitive way, as an elastic band or strap in tension.  How the material is shaped, is more purposed to deter a tear failure.  As an example, an inside corner that is rounded rather than squared.  I just found the alternative use had interesting results and felt it was worth sharing as a general idea towards reducing vibration. 

        It truly may not have application in this present topic, but the overall conversation itself is a googling point to UAV and vibration....I've been reading the thread for over two years, just as an innocent bystander.

  • This a new vers? :D 

    Thank's for share, I'm going to give a try in my newer ntbk to see if I have more success. 

  • MR60

    Tim - Thanks for doing that test. Clearly, the side mount is doing better. Can you post a photo showing how you mounted the FCU? A photo will show size and location of the pads. The difference in Y is probably just noise.

    Also if you want, can you post the logs if you still have them?

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