Beginner need help with propeller / motor vibrations!

[raf]

Hi.
This is my first post so I would like to say hello to everybody.
As per title I'm having a trouble with my first multirotor (quadcopter) build. I can't get rid of vibrations on my propeller / motor?
Please have a look at the video below.
I have ordered all parts from HK due to price and availability.

Parts used:
- NTM 2830 800kv motors (inc. accessory pack for NTM 28 motors)
- 12x4.5 SF Carbon Fiber Propellers (I have also tried 10x5E Carbon Fiber Propellers - even worst vibrations)
- X580 quad frame
- Multiwii Pro (2.3 firmware)
- 30A Afro ESC (SimonK firmware)
- turnigy 5000mAh 4S Lipo
- turnigy 9x transmiter +receiver


I have used "HobbyKing Universal Magnetic Propeller Balancer, For T Style And Standard Hub Propellers" to balance propellers blades and hubs.


As you can see on the video even after balancing propellers I'm having extremely strong vibrations. I have no idea how to eliminate them... Any thoughts please help!


P.S. Sorry for my language but my native language is Polish

Ohh.. And one more question, when having let say over half a throttle for some time it seems like the motor slows down and as per video above when the motor got those serious vibrations it seems like it is shut down? The red light on ESC comes on and the motor stops.. Is it normal FC and ESC behaviour?

 

[Hugh Hemington]

There is always the issue of spacers between prop and shaft. If they are too close in size to fit a spacer, it is a problem. The motors you are using I found on HobbyKing and have 3mm shafts. The props I think are adapted to 5 or 6mm. Do you have correct adapter?

I notice in the video, you have the motor adapter (silver colored aluminum 'x') UNDER the motor plate. I would suspect the fiberglass motor plates are not stiff or solid enough to hold the motors. Where the screws go into the motor is a very small circle -- smaller than the 28mm diameter. I think the motors are allowed to move too much. (also a sign of imbalance in the motor/prop)
I would try screwing the adapters to the bottom of the motors, with the supplied screws, then bolting the adapters to the top of the motor plates. You may also want to buy another set of those X adapters and put them on the bottom of the plate too.

When you run the motors up high without the props, do they vibrate by themselves?

When the motors shut off, are they hot? Too hot to touch?
I see the motors are rated for 4S and that size prop, so matching should not be a problem, but vibration puts wear on the motor which can produce heat.

 

[raf]

Hi and thanks for your reply.
As you have wrote above I have to use adapters with those props / motors and yes I use correct adapters. The only thing is that the on two out of four motor shafts / prop adapters those little prop adapters are quite tight, I mean the motor itself is short shaft version so I have to use prop adapter with them (mounted with 3 screws on top of motor) and it seems like those shafts / adapters are not equal to each other in thickness as I can fit the shaft size adapter on 2 of them without any problem and on another two I need to use a bit of force to press fit them? - hope you know what I mean

Just like you have wrote above those fibre glass motor mounts are not stiff enough in my opinion. Unfortunately there is no other way to mount those motors to arms / mounting plates (please have a look at pictures below). I have thought about buying another set of those adapters and double them to make it stiffer. Unfortunately I have no access to any workshop where I could cut to shape some aluminium / metal brackets / motor mounts.

When I run the motors without the props they vibrate but just a little bit - nothing close to what you can see in the video. I have tried to balance those motors with some vibrometer app on android but I could not get any better than it was out of factory so I assume they are fairly balanced.

When the motors shut off they are warm / hot, but I can hold them in hand without any problem so I assume the heat is not a problem...
And again as you have said they are rated for 4S and for those props. I have tried using them with another 10inch props but the vibrations were even worse...

Any other ideas?

What I'm planning to do is:
- I'll order a Du-Bro prop ballancer as the magnetic one I have from HK makes me feel it may not balance props perfectly
- I have ordered some plastic SF props to see if there will be any difference

All I can think of is either: propellers, motors or frame?

 

[Hugh Hemington]

Those motor plates are held on by two bolts? Can you make NEW motor plates? And work again to balance props. I think the short motor shaft isn't helping either. The adapters are working like big washers. You cannot use outside holes because the slots in the motor plate are too long.
And yes, these box aluminum and fiberglass frames from HobbyKing are known for being cheap in every sense of the word. I like the Alien 560 frame a lot better, but they have been out of stock forever.
If you can get a new set of the SAME motor mount plates -- the fiberglass ones, and epoxy them together, I bet two of them would be strong enough, but having two bolts on the arm is not really good either. Maybe you can epoxy that too?

 

[raf]

Just to correct my mistake this frame is GLASS fibre and aluminium instead of CARBON fibre - my bad
Yes. Motor plates are held by two bolts - is there any problem with that?
Unfortunately I have no access to any workshop where I could cut new motor plates out of aluminium / metal. And to get the new set of those motor plates I would have to buy a whole new frame... So I would better off buying a different frame like HobbyKing H.A.L. (heavy aerial lift) which looks / seems to be a lot more sturdy. I know I should do it in first place but I have watched few videos on YT about my frame and some people managed to get it to fly, so I though I'll go for it...

Thank you for your current help / advice.

 

[Hugh Hemington]

I watched your video several more times, stepping through slowly to try and see if the vibration begins at the prop hub or motor plate. at 47 seconds, it's vibrating too much, but between 48 and 49 seconds, the vibration reaches a resonant frequency that is sympathetic to the deflection -- it increases greatly at that time and speed.

Is it possible for you to make another video, with the camera STILL (on a tripod, or just held against something) and at the same level as the motor plate? We may be able to see if the plate deflection starts first, or follows the hub deflection. I know they both have to appear to begin at the same time, but it's this resonant frequency you are fighting, and I don't know if it comes from the plate or the motor/prop/hub.

Another idea is to remove the motor from the arm (and quad maybe) and attach it to something that will not move at all! Like a heavy object? Then run it up again and see if/when the vibration starts. You have to separate the plate flex problem from the motor vibration problem to see which one is happening first, or making the other one worse. If the motor/prop/hub vibrates like this when attached to a platform that DOESN'T flex, then you know the problem is probably in the motor bearings. If it was anywhere else, the vibration should increase as the speed increases, and not go crazy as in the video at 49 seconds.

If the plate won't work, maybe you can drill another hole in the arm and mount the motors right to the arms with just 2 screws? I think they use 3mm screws. You could drill larger holes in the bottom to pass the screw through, or use needle nose pliers to get the screws into place, sliding the screwdriver through the holes.

 

[raf]

I have made another video:

I'll also remove whole motor off the quad and just like you wrote I'll try fixing it to something heavy anr run it then.
Seriously I have no clue what is going on there. As you can see just at the end just before I stopped motor it hit the edge of the aluminium arm and therefore motors looks now like they had been crashed or something you can even see that earlier in video they have scrathes.

I have tried balancing my props and motors once again and I really think they are quite good balanced (I have seen many videos where people are flying their quads without balancing anything ant they're having just the fraction of the vibes that I'm having) and this video was made after balancing...

regarding mounting those motors to the arms directly I have thought about it, but there is a guy on YouTube who did that before and I think one of the motors flew away or something for him. I have contacted him through YT and I'm now waiting to see if he will respond.

I just cant understand why I'm having such vibes... All of the parts were recommended for this build and I have watched many videos and have never seen such strong vibes... I have spent quite a bit of money for this baby and I have to have this quad up in the air or my wife will kill me

Thanks again for your interest and help!
Raf

 

[Hugh Hemington]

Yeah, THIS isn't good!
Going frame by frame, at :15 I see the first vibration go harmonic. At :30 I see the first large deflection beginning. At :31 the motor is deflecting about 30 degrees!
I think this motor's bearings were defective to start with. Does it happen more or less the same way with the other motors?
Another possibility is that the prop isn't tight -- SOMETHING with weight is throwing this off. Are you sure you cannot rotate the props when holding the motor body still?
If you have a drill, you might want to put a prop on a shaft and spin it that way and see if it goes out of balance.
Obviously the fiberglass plate is allowing the motor to deflect in that wide arc that forces shutdown, but it wouldn't have to endure it if the motor/prop wasn't doing it to start with. There is also the possibility that the flexibility of the plate allows a small vibration to build into a larger one by letting it go harmonic.
I think in any case, the fiberglass must have been compromised by all the forced bending, which may be making this problem worse as you diagnose it, so even if it turns out to be bad bearings, the plate is probably not safe to continue using. I'd remove it and see if it bends easier than those not tested like this.

So, at this point, I'd recommend you ISOLATE. Spin up the motor without the prop, and using a drill motor, spin up the prop off the motor. Of course, if you can do that OFF the arm/plate it would be best. If the motor runs up without deflection and the prop runs up fine too, I'll be surprised. I think the weak plate is making things worse, but it has to be bad on its own to induce this vibration. If you spin the motor without the prop right where it is, that would be the easiest test to do first. Of course, if the bearings are bad, that might not show up with no weight on them, as the prop may act as the counter weight making bad bearings go critical.

If you can do the off-arm mounted-to-weight test, do it with TWO motors. This one and one that hasn't been thrashed. There is a solution, and your quad (with some parts, maybe not these) will fly!

 

[Hugh Hemington]

Looking back on this thread, I noticed you have tape on both sides of a prop to balance it. But the tape is on the leading edge of one side and the trailing edge of the other, so the weight is all on one size of the shaft hole. I can't say that is a factor, but at some speed it will be applying force, unless it corrects balance in that direction. Usually I only see balancing tape on one side of a prop.

 

[Hugh Hemington]

I'm going to post this on the HobbyKing forums and see what others say. Since all the stuff comes from HobbyKing, that should make me some friends over there.

Here's a link if you want to track the responses. http://www.hobbyking.com/hobbyking/forum/forum_posts.asp?TID=58416&PID=278095#278095

 

[raf]

I'll try to do some more testing today with different props/motors/arms configuration as to be honest I have spotted two out of four motors going that bad and when they reach this vibes I simply shut them down because I dont want it to brake the mounting and make some more damage or even injury. so I'll check the other two motors to see if they have any vibes at different speeds and then I'll try few combinations prop/motor/arm...
The prop is defo tight fit I wouldn't risk running not properly tightened prop...
I'm not sure if I know what u mean by running prop on drill... I don't have any spare shaft so do you think that I could put the prop on my ballancing shaft then tighten it down with the cones and then put it into drill? I'll try that
Well when I run this motor without propeller I don't have this problem but just like you said it may be invisible without prop.
Yeah I do have tape on both blades on this propeller but I don't really think it cause the problem as I have previously used 10" props and now I'm on 12" ones and the problem is the same...
I thought about posting this on HK forum so thanks for that

 

[raf]

|Hmmm.... So I performed few tests and it's quite interesting...
1. I have run each motor separately to see how many of them will have those bad vibrations and.... all of them had those vibes. I have not seen them before on all 4 motors because 2 of them got those vibes a bit earlier than other two and when I reached those first bad vibes I simply stopped motors immediately so I couldn't see vibes on last two motors. What's interesting is that one motor had those vibes slightly weaker and once I moved the throttle stick a little bit up those vibes has gone - unlike with the other three motors...
2. I have made few swaps (propellers on the motors, direction of spinning etc.) and those bad vibes were there all the time regardless of swaps...
3. I have spinned propeller fixed on balancing shaft with my drill and all I can say is that I need new balancer (I'll defo go for DU-Bro this time) as i could see my balancing shaft is making slight circles while spinned by drill - so I assume it is slightly bent (not visible for eye)? But... I didn't feel any strange vibrations or couldn't see anything strange while holding the spinning drill...
3. Have a look at the video I have fixed exactly same bad motor to piece of timber (long enough so I can hold it in hand if needed) and there is no vibes? I can feel very little of vibes on this timber / piece of wood but come on those motors are spinning really fast so it is almost impossible to have no vibes at all... And I could do whole throttle movement from 0 to 100% and as you can see in the video there is nothing happening apart of lifting this piece of timber

4. I have told you before I'm awaiting response from the guy from YouTube and he did wrote me that he would buy different frame for example H.A.L. form HK as he had whole bunch of problems with those motor mounts on X580...

So... what do you think? I think I'll give it (H.A.L. frame) a go a see if it will sort me out...

 

[Hugh Hemington]

Congratulations. It seems you have isolated the issue. And it seems to be centered on the cheapest part of your quad to replace (apart from the props). You're getting the H.A.L. quad -- 585 frame? It looks good. No fiberglass anywhere on it!
So it appears that when the frequency of flex in the fiberglass motor plate met a sympathetic frequency in motor/prop deflection, the two acted together to grow the deflection. Looking back, it's pretty obvious that the plate was too weak if it allowed the motor to deflect over 30 degrees in your videos, no matter how out of balance anything on the motor may have been. (I have frame stills from the video that are pretty wild! A blurry horror. I'll upload to HK for that frame. Probably get me banned for life.)
It's too bad you can't find a way to stiffen those plates, or replace them with something better, because as cheap as it was, the rest of the frame is probably serviceable. Ideally, they should have been aluminum to start, with folded edges along the edge of the arm to stop rotation (so the bolts just hold in place), and a raised or lowered lip around the circular area to stop deflection. But that would have cost an extra three cents each. They make diving boards out of fiberglass, because fiberglass has SPRING to it!!! You'd think this would be the LAST place you want springiness!

 

[Hugh Hemington]

The international listing for the x580 - files area includes two CNC motor mount diagrams! So that's a pretty clear admission that the fiberglass plates are a failure. I uploaded the deflection still anyway, but nothing I've uploaded to HobbyKing has made it into the files areas, and most of my discussion posts get deleted, so we'll see what happens with this one.
There is also a picture of a x580 modified as a tri-copter with the motor plates not used and the motors on the arms. It's pretty clear those plates are junk.

 

[raf]

Well... I like the tarot frame but I want to go cheap with first quad as I'll probably brake it anyway that's why I think h.a.l. will be all right. It have quite weak landing legs but that shouldn't be a problem.
That's a great idea... I can use this frame to make tricopter later
I haven't done enough research before I bought x580 as I simply believed it will be ok.
Thank you again for your support and help and I'll let u know next week how's new frame.

 

[Hugh Hemington]

You're welcome! And we all want to see your quad fly. Maybe if you put pieces of "pool noodle" on the land gear legs, it will land easier and maybe even float.