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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          • Gary, about those adjustable shocks.

            I had some designs at an early stage incorporating RC car shocks like these.

            3702862929?profile=originalI was thinking of using 3 to suspend the gimbal. They offer so much 'tune-ability' and are quite light but may be better at removing shake and wobble rather than vibration.

            • MR60

              Vince

              - Put one shock onto a scale

              - Tare the scale

              - Orient the shock so you can press downward on the shock

              - Compress the shock by 15% to 20% of it's throw.

              - Read the scale.

              - Weigh the camera and gimbal

              - Divide the camera/gimbal weight by the scale reading

              - That is how many shocks you need.

              - These shocks need to be placed at at 30ish degree angle to prevent x/y wobble

              Because they are adjustable, you can tune the above math. If you do the above math and the answer is 2 shocks, then they are too stiff.

          • Thanks Gary.

            I was doing many 'tuning in' flights when when the things all went missing. Its a laborious process doing flights, adjusting and trying again but things were showing good promise.

            Do you remember my octa that used silicone o rings. They could be easily adjusted by number and tension but I wanted a neat modular folding machine. The electronics unit (ok, lunch box) could be removed and powered separately3702862910?profile=original

            Fortunately I do have all the design files for this 7kg quad but nothing before. Will soon be building another.

    • MR60

      Vince - OMG ... was wondering what happened to you. Sorry about the loss. As Paul Harvey used to say ... "Stay tuned for the Rest of the Story." Can't wait to hear what happens to the perpetrator.

      Impressive setup time and beautiful ship. Glad you are back.

      Do you mind if I forward your video to a company in Singapore?

  • Wow Frantz, 

    Good to see you are still researching and improving years on, you caught a lot of flack for your hard mount suggestions.  I too just ordered up a PixRacer yesterday after seeing Thorsten's results.  Going to try it on a 450 flame in place of an old APM.  Looking forward to see what that team comes up with for a fullsize Pixhawk replacement.  

    It looks like 3DR, or at least their engineers who designed it, are going to release an official diy Pixhawk2. What interesting is how the IMU brain cube attaches into the daughter board, wondering if in a crash if it would detach itself, or that type mounting cause more vibration.

    To Thorsten, 

    Could you give me a few more specs on your small carbon quad you built that is running the PixRacer, motors, battery, size oftubes, if you custom cut all the frame parts yourself or are the motor mounts an off the shelf?  Really would like to make a small P&S camera rig with long flight times.

    -Cheers

    • T3

      Hi Donka,

      all parts are custom cut including the motor mounts. I'll post more details the next weeks.

      • Thanks for the response, that's what I figured, look forward to hearing more about it. 

        I went ahead and ordered up some BLHeli OneShot ESC's to try that functionality.  Been eyeing a Taranis for a while due to it's built in telemetry, now even more tempting w/ the PixRacer's dedicated link.  Yet my Futaba s.bus works really good, so it stays for now.

        Back on topic.....  

        I went ahead and purchased this Ominmac 3d printed 30.5mm pitch mount  by our very own Guy McCaldin to give a whirl along with 50 and 65g balls from HK.  

        Looks like I am going to waiting on the printed mount, so will have to experiment with other options until it arrives in 2 weeks

        Omnimac OP Mount 30.5mm V1.0 by guymccaldin on Shapeways
        Check out Omnimac OP Mount 30.5mm V1.0 by guymccaldin on Shapeways and discover more 3D printed products in Drone Parts.
    • MR60

      any chance when you swap out the FCU that you can do a before and after without making any other significant changes?

      That will tell us if the smaller board (maybe 8x stiffer) is solving vibration issues.  If not, it's back to solving the mysteries of Thorsten's frame.

      • Yeah I'll try, but after a stupid zero throttle 15ft drop during an RTL this bird is not flying quite right.   You can see my original #'s when I first built this copter back on page 16 or 17.  Only thing I changed over the years was putting a nomex platform above the APM to hold the gps antenna and an external mag.  

        I may buy another mag and try flying it again as is.  Maybe even resolder the internal mag trace if that's possible, as it flew well before going to external too.

        Anyone know a good source for a reliable but cheap ublox M8N GPS unit.  The PixRacer guys were selling one, but took it down as they were getting a bunch of negative feedback from people trying to use loiter and other GPS modes, they thought it was the mfg/source, other's thought it was just the location of the GPS on mini racers being so close to esc's, telemetry and video antenna's etc. that it was causing a bunch of electrical interference.

        • T3

          Donka, not sure what cheap is. But Drotek and CSG shop provide good products. The results I presented a while back at http://diydrones.com/profiles/blogs/gps-positional-accuracy-iii are based on GPS from these companies.

          And for sure you have to be careful setting up a small copter since interference of the components can be problematic.

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