Hi,
I have measured very good Zaccel vibrations with this mounting system. It consists of a suspended acrylic base plate (3mm thick) on which a silicon pad (6mm thick) is placed. The APM case is placed on it with a little pressure from a velcro band.
The O-rings go through holes on each corner of the acrylic plate and are attached to the black nylon spacers. In order to avoid that the o-rings would move up/down the nylon spacers, I used flat metal nuts to block the o-ring (it is screwed between the first 10mm spacer and the bigger 30mm spacer).
The acrylic plate is suspended about 2mm above the fiberglass mounting plate. In order to shield the EMI interferences that could come from the PDB/ESCs, I added special EMI tape on this bottom fiberglass plate.
I show below the obtained results with motors 100% throttle:
This AccelZ measurement in the logs show an average of maximum 0.5g deviation, which is I guess quite good!
Other pictures:
Hugues
Comments
Hughes,
Could you please post a dataflash log of your copter in flight. I think you have you good ideas here regarding the vibe isolation, would love to see the 'live' results.
Hello,
yes very effective against EMI. In fact I purchased this at a company called SERTIM in France.The metal braided thing you see cmies from the inside of a EMI heat shrink tube (i removed the heat shrink part to have a very flexible wire wrap (not to convey vibrations).
Hugues
Can someone tell me what those metal braided wire wraps are called?
Plus, are they effective in shielding?
@Chris : you can balance the motors by sticking on the side a piece of tape (alu tape or copper tape or even standard plastic tape, so long as it has enough weight). The position of the piece of tape on the circonference of the engine case must counter act the weight inbalance. To find the right position, you must do trial and errors by moving the piece of tape by 90° (quarter of a turn), then you fine tune in the quarter you found reduces best the vibrations.
Brenton - could you please let me know how do you balance the motors itself (without prop). I know about balance the prop, but wonder how/what need to be done for balance the motors.
Thanks
Another method of motor/prop balancing is to use a smartphone with an app such as iSeismometer. I balance my motors with this, then I mount the prop and do it again (after having balanced the prop on my Dubro balancer). It's surprising how much more work they can sometimes need once they're on the motor and spinning!
@Dave, not flyed yet. I'm now ready to try it in flight after having fixed my throttle issue thanks to Randy. Will keep you posted.
This is one of my favourite subjects, and I'm impressed with this mount and others like it that I've seen and made. It does seem like a solution, even if a bit fiddly.
I really feel like I'm missing something here though. How are you measuring these vibrations with your motors at full kipper. I presume with no props on?
Have you got any graphs of it flying? Or is this thing tethered down hard when you are measuring?
Yes I agree with you that the O-ring suspension is cumbersome and probable not the best mechanical option. I have another issue with my setup here : as I have cut the silicon pad in four little cubes, I have less friction between the already slippery silicon pads and the also slippery acrylic plate =>I risk having my APM case move in case of shocks. I tried different glues and/or double sided tapes but nothing seems to stick on that silicon. I moulded this silicon pad myself mixing pure liquid silicon with a catalyser (purchased on a crafting/hobby web site : www.artificina.com). I would be very interested to replace this by fixed absorbing grommets.
I also wonder if I could not isolate/dampen now my motors by adding some o-rings on the screws ?
@Jim : yes this is a bench test I did, not a flight. The props are balanced , not the motors.
I will later balance also the motors with a laser test I saw on a forum : motor by motor you attach a small mirror on the active copter arm. You then project a laser (presentation pointer for example) at this mirror to have a reflexion of the laser dot on a distant enough surface (for example the wall of the room). Then you start the engine of that arm and check if the laser dot stays a dot or if it becomes rather a segment. If it remains a dot, the motor is balanced. Otherwise you stick some tape (random I guess) on one side of the motor and check the dot again. As long as the laser projected segment does not reduce its size to a dot, you move the piece of tape around the motor (I would say by 90° each time). You repeat the procedure for all other motors individually.
Hugues, clearly it does seem to indicate even a further improvement with your full throttle vibration now at approximately 0.02G.
Your beginning and end transitions, although still completely excellent at about 0.05 G are indicative of a less tractable aspect of vibration control in multicopters: Resonance.
Multicopters are inherently non-synchronized (because the motors need to move at different speeds for normal flight maneuvering).
And of course as you are accelerating and decelerating the motors and props are speeding up and slowing down at slightly different speeds, whereas once you get to full throttle they are in rough synchronization.
There are likely always going to be areas of higher vibration during maneuvering and normal flight due to this effect and with your system you have finally gotten the overall vibration down to the point where this effect is clearly visible.
Nonetheless, superb results and I would very much like to see the results in a normal hover just trying to hold it as stable as you can, I suspect you will see results very much like your full throttle experience, which is great.
Basically, I would presume that if we can come up with a viable reproducible system that can achieve the results you have achieved we have pretty much solved the problem.
I realy like the 2 zone isolation system with the dampened board on the dampened plate using differing dampening techniques.
Even though I am using the O-ring suspension system myself, however I don't really like it very much because it is cumbersome to install properly and O-rings aren't really designed for this use.
I am, however going to convert one of my O-ring suspension mounts to a system like yours with a separate plate and some various pad type secondary supports for the APM.
I am also going to build a system where the intermediate plate is supported by vibration absorbing grommets rather than O-ring suspension mount and give that a try as well.
Your results are the "grail" at this point and I will report my results.
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