Here comes the vibration again

[hareedy]

Hey guys
Suddenly out of the blues the vibration started appearing badly on my ap bird
It's a trex 700 stretched to 800 with a symmetrical spin blades 690 mm and ace one the main controller and photoshipone 2xpt
Everything was working perfectly with out balancing the main or tail blades
And suddenly all this shit started to appear
Ps the only thing that I have made was moving the video sender and battery over the mount ?
Can this be the reason ?
Anyways after taking the head apart I found that the bearing block for the main shaft is rough I will change it with boka ceramic bearing that I am ordering tonight
Also I am going to increase the bearings on the torque tube and I am not going to leave equal space between them
I will post the videos before and after the vibes later tonight
Any thoughts will be highly appreciate it
Cheers
Zidan

[hareedy]

here is the link to the video
http://www.youtube.com/watch?v=jUKhv...ature=youtu.be

[smankleo]

Hi
I have some time these problem and at the end I found that was the batteries that loose the power . If are old looks powerfull and when you make a minuets just hover count it and you will see that lost enough power that loose rpms

Hope help you

Regards

Smaris

[hareedy]

Originally Posted by smankleo

Hi
I have some time these problem and at the end I found that was the batteries that loose the power . If are old looks powerfull and when you make a minuets just hover count it and you will see that lost enough power that loose rpms

Hope help you

Regards

Smaris

thanks smaris for your reply
but the batteries are fairly new thunder power 65c i fly them on my logo 600 3d with no problem maintaining the head speed at all
but what i did notice that in some locations there is no vibration in some others there is
and i found out that the two bearings in the bearing block for the main shaft are kinda rough
i just finished changing them i will try it tomorrow and c how it goes
cheers
Zidan

[pc3associate]

Here is what i see- huge vibe at spool up, begin with looking at your blade grip bearings and work down from there. Is your pitch perfect for both blades 360 degrees? Check your pinion gear mesh as well. Any imperfection in main gear area?

During flight when your camera angle changes your vibe increases- is your camera cg perfect with that lens? Do you have gyros on any axis of the 2xpt?

[pc3associate]

When i asked about cg, i meant is your camera cg perfect on the gimbal?

[hareedy]

I have a gyro on the pan tilt axis only , sorry I don't get what has the gyro to do with the vibration
And the cg of the gimbal what do you mean exactly i put it on the end of the camera tray of the 2xpt the camera is a 5d markII with anion 20 mm lens
Please explain more

[hareedy]

Ps I am still working with the stock head dampeners which are intended for 3d
Any idea where can I get a softer dampeners ?

[pc3associate]

The gyro can compensate too slow causing it to work against itself if not setup right. Disconnect gyro and fly without gyro on gimbal to see video.

With tilt axis servo removed test your camera on gimbal. Make sure it spins with same smoothness throughout whole range. Once the perfect mounting point is found mark where the camera is for that lens. Be sure lens is set how you will have set.

[hareedy]

Alright will do that and let you know what happens
Also I am thinking about getting the slant gear do you think it will make any difference ?

[hareedy]

Also where can I find the softer trex 700 e dampeners
Do you think the f3c dampeners will be softer?

[pc3associate]

You must be running black dampers. Just look for grey dampers. Reds are even softer but i would start with the greys.

[pc3associate]

I personally am not a fan of the align slant gear. Not a good design. Puts too much stress on the bearings. If everything is setup and tuned correct the gear type should not matter. Better spending more time perfecting what you have than swapping around gear types.

Now if there were gears with the v-slant like logos then it would be a for sure upgrade IMO.

[R_Lefebvre]

Do you have any data about slant gears putting stress on bearings? I've seen that a number of times, but never any data. I actually did a calculation and determined that the thrust load is not really that high on the motor. The thrust load is comparable to the propeller load if you were using the motor on an airplane.(ie: propeller thrust all going through the bearings). It seems like really not a big deal. Maybe I have missed something, but again, I've never seen any data either way.

Now, that doesn't mean I'm a fan of the helical gears. Theoretically they should be quieter, which means less vibration, but the fact is the modulus is higher, so the gearing is coarser, and that brings in more vibration again.

I am running the slant gearing on my 450 and it's really not great. In fact I suspect it may be worse. It's certainly not much quieter.

The other thing to be aware of is the bearing quality. I've gotten Align bearings that are actually not smooth right out of the package. I recommend getting quality bearings such as from Boca.

[hareedy]

I am getting a full gearing set from boca in a couple of days

[pc3associate]

Rob that was just an opinion. Not a fact with any data. Even if there were data the time and money to change the gearing to slant would have a greater rate of return invested in other areas of the heli (for an ap application). By the looks of the video and to address his main concern here slant or straight gearing should not be debated. Get the vibe levels down then talk about slant vs straight.

[Goldenhour]

I've found that the top motor bearing and the top main shaft bearing wear rather quickly. For me within 20 flights. Its the same if I'm at 1800rpm or 1280. I've used ceramic balled bearings and got the same results as say all steel quick UK bearings. That play in the bearings caused by the pinion wanting to walk out of the main gear and the forces of the head on the top main bearing have been a big source of vibration.
But not the only source.
I've gotten good at changing out bearings now.

Hey, nice pictures of Cairo. Hope all goes well with your country.

[R_Lefebvre]

Originally Posted by pc3associate

Rob that was just an opinion. Not a fact with any data. Even if there were data the time and money to change the gearing to slant would have a greater rate of return invested in other areas of the heli (for an ap application). By the looks of the video and to address his main concern here slant or straight gearing should not be debated. Get the vibe levels down then talk about slant vs straight.

Ok. I know this isn't the source of his problems, but since it was mentioned decided to ask. I had been interested in the slant gears to get rid of vibration, and I've heard about the wear thing so I decided to check and I couldn't see a problem with the axial load. I just want to know if there's something I missed.

Looking at his video, and I don't think this is a problem from high frequency vibrations such as from bearings or gears. This is much lower frequency. I'm guessing it's something like blades being out of track, the blade grip bearings the swashplate... something that is passing down vibes closer to the rotational speed of the head. When bearings fail, the vibes are actually at a very high frequency.

It could also be a problem with lack of stiffness of the mounting, or even high frequency vibration messing up his gimbal controller, and it's not actually a vibration per se, but the servos jittering around because gimbal controller is having difficulty seeing through high frequency vibes.

[FSAMedia]

The most prolific sources of vibration I have encountered with any of my AP birds (trex 700/800/logo/one off custom birds) have been the head and motor bearings. Obviously there are numerous sources i.e. blade balance, tracking, gear mesh, etc... but the fore mentioned problems were the root of my biggest frustrations.

The motor

There's tremendous load being placed on the top bearing of our motors and this is the number one cause for hard to find vibration and should be a major concern for anyone. Without utilizing a double shear bearing arrangement you WILL experience serious bearing wear, as golden put it, visible wear after 20 flights. This doesnt mean the bearing will fail after 20 flights, it just means the potential for failure and unwanted vibes drastically goes up. Good bearings, a double shear bearing block, good gear mesh, and regular maintenance should cure this problem

The head

I'm a cnc machinist and I know what goes into making these heads. They're not all perfect and it doesn't always show at first. I'm sure you're all accustomed to tearing down and rebuilding your heads on a regular basis. Sometimes, this goes for align and rjx heads, you can tighten everything up and the head spins true, sometimes it doesn't. Fact is, the bore in the head is slightly over the size of the main shaft and there's a relief cut in the head that compresses to the shaft when you tighten the Jesus bolts. This method has room for wiggle, and I'm sure some of you may or may not have noticed a smooth bird one week and a rough one after you've rebuilt the bird the next. Careful attention is required when you tighten down the head. Use even and alternating thread tightening methods to try and get good results. If you can, use a micrometer or calipers to match the main shaft (they're not perfect either) with the head.

My last bit of advice is to switch over to turnbuckles instead of the stock linkage rods. This allows for infinite fine tuning for blade tracking....you'll be glad you did.


That's it....back to work.

[helicek]

Hi guys,
I have followed this thread with great interest. Let me tell you about my recent experience with my old and trusted Vario brew front mount heli that I use for aerial photo:
One day I noticed the pictures were coming slightly out of focus no matter what I did with the system. I took the main shaft out and checked its trueness on the lathe. It was out 0.025. I tried to straighten it (the ancient method) but I noticed that it had softened in the middle. So, I got a new shaft and checked before mounting for trueness. That was out too. But I managed to straighten it to 0.005 which I think is acceptable.
This shows many faults can develop during regular flight (no mishaps or crashes) so we end up spending more time servicing our machines than flying.
Right?
By the way, I will be flying this t-rex 700 I have converted to a front mount AP ship very soon. If the main shaft on a new heli is not 100% true it may cause unexpected wear out. So make sure shafts are straight and true.
Thanks again for a very informative thread.
Ahmet