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Thread: Vibration Dampening & Isolation Solutions - Guide

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    Banana Drone Flying Monkey's Avatar
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    Vibration Dampening & Isolation Solutions - Guide

    For the last six months I've been testing different materials and techniques in my quest to eliminate vibrations. I was hoping that the newest materials that I tested over the weekend would be the ultimate solution, but it seems we still have some fine tuning to do. With the dampening solution I've been using I have had the KK board gyros set to 90% without any oscillations... Which makes the thing so stable it's silly. I've actually let go of the controls and just let it hover in place! If the KK board had a barometer it could compete with some of the other boards like OpenPilot, MultiWii, NAZA, etc.

    First, you need to know the difference between Vibration Dampening and Vibration Isolation. A good vibration isolator lowers the natural frequency of a system to below the excitation (or disturbing) frequency. Keeping these two frequencies "out of sync" greatly reduces the problems of vibration. A good vibration damper takes mechanical energy out of the system. Properly designed metal springs and rubber mounts can be good isolators but have almost no damping capability. Oil dampers (dashpots) have good damping capability but no isolation capability. Foam products can be good isolators but have limited life. The short answer is that dampening occurs when the energy is absorbed and removed from the system... This is what my motor mount does. When mounting your gyros, you should Isolate them from the rest of the system. This tends to be tougher to do but you should use a different material (like Neoprene) because it will counter different frequencies. My experiments using Sorb on both the motors and kk board were way worse, the vibrations "crept" back in.

    I have tested so far...
    Neoprene foam (of different thickness)
    Silicone foam
    Silicone tubing
    Silicone bobbins
    Cork
    Insulation Foam (from Home Depot)
    Rubber (pads, grommets, washers, etc)
    Wood vs. carbon fiber tube ARMS (carbon wins!)
    ...and finally... Sorbothane
    ...& Kyosho Zeal mounting tape

    Sorbothane is a proprietary, visco-elastic polymer. A thermoset, polyether-based, polyurethane material. The energy it absorbs is then turned into heat (but not enough to notice). http://www.sorbothane.com/material-properties.php

    What is a Durometer?
    Durometer is a measure of hardness used for polymers. For a given polymer a higher durometer frequently indicates a stronger material and possibly other properties. Sorbothane is softer than rubber and most other polymers. The 30 duro Sorbothane is much softer than 50... etc.

    The two best materials I've tested...
    http://www.amazon.com/gp/product/B00...00_i01_details
    http://www.amazon.com/gp/product/B00...00_i00_details

    For the 2213N motors the Kyosho Zeal mounting tape gave the best vibration dampening... almost to the point of not being able to feel any vibs at the KK board! However, it is a bit softer than the Sorbothane 30 duro and if your props are imbalanced you'll see the motor swinging around a bit, and I would NOT suggest it for the DT motors. The 3/16" Sorbothane 30 duro works great for both 2213N and the Hextronix DT series (DT700, DT750, DT850). These are the motors I have and so the only motors I've tested so far. Different motors have different vibration frequencies and you'll have to test out different thickness and durometer to find the best (30 and 50 duro are good, 70 duro is usually too hard).

    Now for some pictures...


    Sorbothane 30 duro is pretty STICKY and feels a bit like meat.









    With this type of Sandwich clamp mount the motor is ONLY connected to the frame via the Sorbothane!



    Make sure the zipties don't touch the frame! You can use bolts too, but zips are lighter AND they break away in a crash, usually sparing your motor damage!



    The Sorb should be compressed to 75% of its original thickness for best dampening results. So for 3/16" then 0.14" should be close enough. Use a caliper for best results, but it doesn't have to be perfect.





    To test it against the "baseline" of a hard mounted motor...



    Testing the Zeal in an Isolation method... When the motors are hard mounted, this works... when they are mounted with Zeal, not so much.





    Better conservation of an expensive material... works just as good.





    With the motors mounted with Sorb or Zeal... this was the best result for mounting the KK board. Good old outdoor mounting tape (5+ pull, hence the little squares so I can get my kk board back someday!) folded over twice so the pins on the bottom of the board don't interfere.





    To see if David's (rcexplorer.se) method of folding the tape over 7 times would help. With the motors hard mounted, yes... a little. With the motors mounted with Zeal or Sorb... NO! It was worse, just use the tape folded twice!



    And finally some pictures of the DT700's mounted using the Zeal... The zeal is thicker so it should be compressed to 0.17"



    I haven't gotten around the cutting the shaft on this motor as I just got it two days ago, but it should be cut as short as possible to reduce the chances of the shaft getting bent in a crash and increasing vibrations.



    At this point I still have a few more ideas to try and will continue experimenting but the performance is pretty damn good already. Perhaps with the community playing around with this stuff too then one of you can improve on my R&D...!
    Last edited by Flying Monkey; 6th March 2012 at 10:07 PM.

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    Banana Drone Flying Monkey's Avatar
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    Great work buddy, I've not seen any footage from my tri yet but I'm sure there will be vibes!
    Thanks

  5. #5
    Very interesting work bud.

    Wonder if Moongel http://www.rtom.com/moongel.htm is similar to Sorbothane?

    What are you using to test vibrations?
    Ive found smartphone apps really usefull! Tie the phone to the arm & run the vibration app to see the waveforms!

  6. #6
    Banana Drone Flying Monkey's Avatar
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    Quote Originally Posted by Badlands View Post
    Very interesting work bud.

    Wonder if Moongel http://www.rtom.com/moongel.htm is similar to Sorbothane?

    What are you using to test vibrations?
    Ive found smartphone apps really usefull! Tie the phone to the arm & run the vibration app to see the waveforms!
    Usually I just use my fingertips... I wish I had a smartphone but whenever there's a choice between buying a new smartphone or some FPV gear.... Well... Perhaps you could use yours to test these out? Another way I've tested them is to stick a 401b gyro on the arm connected to a servo, then just watch how wildly the servo arm swings. With the Zeal tape the arm hardly moved.

    Moongel is on my list of stuff to test. I think it could work great as an isolator for the kk board, but it looks way too soft to mount motors with. One material that actually removed ALL of the vibrations was the Window Clings I got from a craftstore one day. But it was too soft and the gel would squish out after a couple of flights. It's not as sticky so I'm not sure you could mount the KK board with it alone, but perhaps with some rubberbands keeping it on... might work with the moongel that way too.

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    Lumenier.com timnilson's Avatar
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    Have you done much flight testing with this set up yet and have you recorded any video? As you point out as well, I am worried that your motors will loose position under prop load. If the motors can twist under load it will start to impact flight characteristics -- the FC won't be able to control the stability of the quad/tri if the response is not there or is inconsistant. What you see is FC compensation movements even though the overall vibrations are a lot less -- so it's a balance of both. It would be very helpful to see some flight videos with your solution.

    Here is a video I took that had the motors hard mounted and the vibrations killed within the center frame plates with vibration bobbins and a GoPro vibration mounting pad. In this video I am using the same motors as you and I am using the Pro Tricopter Delrin kit. So, it's very comparable to your set up. There are definitely multiple solutions to killing vibrations and I am interested to learning from you what you see the drawbacks and benefits of your solution are!

    Last edited by timnilson; 7th March 2012 at 10:39 PM.

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    Banana Drone Flying Monkey's Avatar
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    Quote Originally Posted by timnilson View Post
    Have you done much flight testing with this set up yet and have you recorded any video? As you point out as well, I am worried that your motors will loose position under prop load. If the motors can twist under load it will start to impact flight characteristics -- the FC won't be able to control the stability of the quad/tri if the response is not there or is inconsistant. What you see is FC compensation movements even though the overall vibrations are a lot less -- so it's a balance of both. It would be very helpful to see some flight videos with your solution.
    Been flying with the sorbothane 50 duro 1/8th" for about six months. After talking to one of the engineers at Sorbothane he suggested the 30 duro 3/16" and I've done a couple flights with it but am still testing it. With the zeal and the 2213n's I could turn the gyros up to 90% and it was dead smooth... can turn the gyros up all the way for more aggressive and aerobatic flights! But that made it a bit jumpy in the wind. The zeal with the dt750's isn't working as well... I think the motor is just too heavy, too much thrust and too much torque for it... but the sorb 30 duro works great with it. With the sorbothane compressed as much as they are there really isn't a whole lot of movement. On the thrust stand you can definitely see the motor torquing with rapid & large throttle changes... But it doesn't seem to bother it in flight. I can fly smooth and stable or aerobatic and it stays put... I have yet to have the mounts come undone or even shift.

    Will try a mounting method later that will restrain the motor to prevent the torquing to see if there's a difference. I also want to try hard mounting the motors, then using this sandwich clamp style to mount the kk board + cameras.

    Alas I'm still saving up for a Gopro so I can't shoot any video right now. I had a Panasonic point and shoot that I was using to shoot video but in a crash the ccd came loose. Here's a video I shot with it... Using DT750's and the 50 duro sorbothane 1/8th thick.


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    Lumenier.com timnilson's Avatar
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    Quote Originally Posted by Flying Monkey View Post
    Been flying with the sorbothane 50 duro 1/8th" for about six months. After talking to one of the engineers at Sorbothane he suggested the 30 duro 3/16" and I've done a couple flights with it but am still testing it. With the zeal and the 2213n's I could turn the gyros up to 90% and it was dead smooth... can turn the gyros up all the way for more aggressive and aerobatic flights! But that made it a bit jumpy in the wind. The zeal with the dt750's isn't working as well... I think the motor is just too heavy, too much thrust and too much torque for it... but the sorb 30 duro works great with it. With the sorbothane compressed as much as they are there really isn't a whole lot of movement. On the thrust stand you can definitely see the motor torquing with rapid & large throttle changes... But it doesn't seem to bother it in flight. I can fly smooth and stable or aerobatic and it stays put... I have yet to have the mounts come undone or even shift.

    Will try a mounting method later that will restrain the motor to prevent the torquing to see if there's a difference. I also want to try hard mounting the motors, then using this sandwich clamp style to mount the kk board + cameras.

    Alas I'm still saving up for a Gopro so I can't shoot any video right now. I had a Panasonic point and shoot that I was using to shoot video but in a crash the ccd came loose. Here's a video I shot with it... Using DT750's and the 50 duro sorbothane 1/8th thick.

    That video is very promising!! I think most people here care to reduce vibrations to clean up their HD video, but your point to remove vibration to remove the 'noise' for the FC is really good. The FC has to fight with enough between wind, gravity, torque -- adding noise from vibrations is definitely bad for performance. Not only is your video very clean, your flight characteristics are nice and smooth as well.

    One point on durometer from my experiments... I find I get better results with a slightly harder durometer. A 50 works better for me than a 30. 30 is too bouncy and you start seeing rubber bounce vibrations that are amplified at the right harmonics of the frame. Also, the way you are mounting your motors, you are compressing the material substantially, which in turn ups the durometer. So a durometer 30 rubber under load really behaves much like a 50 durometer or more, depending on the pressure you apply. The way you mount your motors, you don't have much of a choice but to apply force to the sandwich to hold it together... I'll soon be sharing my own experiments along the same lines of what you're working on here, but I'm going about it slightly differently. Once I'm far enough along, I'll post my results for you to comment on. Good work!

  10. #10
    Sky Pirate & FPV Outlaw SecretSpy711's Avatar
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    Cool experiment. LOTS of variables that could all affect each other, though.

    One thing to note... there should be some effort aimed at eliminating the source of vibrations. I.e, are you using *REAL* APC props, or cheap knockoffs? The APC's make a world of difference over the HK cheapo's.

    Also, I've noticed that inertia of the camera, sensor type, and camera quality have a lot to do with it. Field of view too. (Super-wide fisheye GoPro = less noticeable vibrations). Derrick has a GoPro on his tricopter that's nearly identical to my own tricopter... he has almost zero vibrations in his video. However I still notice some vibes with my $40 "HK HD Wing Cam" which is much lighter, has a CMOS sensor, and isn't quite as wide. I started out with a Fuji point and shoot, which didn't handle vibration very well at all... to the point that it would not only cause the video to look bad, but cause the camera itself to malfunction and stop recording.
    Last edited by SecretSpy711; 8th March 2012 at 01:43 AM.

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