700 DFC tail issue

[marc8090]

Originally Posted by nynextel88

Guys I'll just have to chime in here for a moment - Marc has been in this game for 15+ years and he certianly knows exactly what he is doing and like he stated both of his Nitros are 100% the same. Not ONE thing is different.

If he says the main blades didn't hit then I can assure you it most certianly did not hit.

Only thing I can think of is maybe a bad batch of tail fins you got Marc? Although your issue seems to be resolved now by adding the additional carbon fiber it would be nice to have a complete explanation as to what exactly happened and how to prevent it.

Thanks for the kind words Rob. I think I still have some sort of a hidden high freq vibe that is just being masked by the stiffer fin, but what is crazy is that there is nothing visible or audible. It is something that happens for just a split second, not giving me a good chance to diagnose it.

[marc8090]

Originally Posted by Dino Spadaccini

have a question your not using the E boom on the N as the N boom is longer by 10mm on the new dfc if this happens again i like to take a ride out to Li and see this in person


Dino

Hey Dino. My 700's are original "V1" Nitros (if you want to call them that) converted to flybarless with V2 NON DFC heads, V2 tail parts, and the 4.95 V3 gear ratio. Using the original boom length, not the longer Nitro DFC boom. Original size 693 mains and 105 tails.

[marc8090]

Originally Posted by dchekas

Marc, have you swapped the entire boom/boom support assembly from the "good" 700 to this one that's striking the vertical fin to see if the issue persists?

No I have not. I have thought about doing this just in case there is some sort of an invisible vibe being caused by the engine or clutch.

[mattox]

Hello, Ive been reading through this thread and have found multiple fixes. I am wondering why it is when I changed to the new hub and grips and black tail gears i get the hum.
the tail WAS setup like this. v2 tail case (with big metal silver bar in between the plates), new dual silver pitch slider, White rear tail gears, and v1 tail hub and grips..
with that setup i am still currently using the black front tt gears(faster ratio) and black auto gear.. and finally the original align 105s.--- Now with this setup I was running up to 2300hs on the head with absolutely no hum. the tail was smooth as it could be in the air..With no issues or HUM ever!!!!

Just recently I changed the rear TT gears to the black ones with the new hub and the silver tail grips. I now have the hum.... everything else on the heli was untouched.

Im trying to figure out why the previous setup worked? And now the new setup does not.? parts changed were all brand new... If the tail blades worked with the previous setup, then i suspect it wouldn't be the blades..

Any ideas? Questions?

Thank You
Mattox

[PetJumper]

Originally Posted by mattox

Hello, Ive been reading through this thread and have found multiple fixes. I am wondering why it is when I changed to the new hub and grips and black tail gears i get the hum.
the tail WAS setup like this. v2 tail case (with big metal silver bar in between the plates), new dual silver pitch slider, White rear tail gears, and v1 tail hub and grips..
with that setup i am still currently using the black front tt gears(faster ratio) and black auto gear.. and finally the original align 105s.--- Now with this setup I was running up to 2300hs on the head with absolutely no hum. the tail was smooth as it could be in the air..With no issues or HUM ever!!!!

Just recently I changed the rear TT gears to the black ones with the new hub and the silver tail grips. I now have the hum.... everything else on the heli was untouched.

Im trying to figure out why the previous setup worked? And now the new setup does not.? parts changed were all brand new... If the tail blades worked with the previous setup, then i suspect it wouldn't be the blades..

Any ideas? Questions?

Thank You
Mattox

Hi Mattox,

the only thing that is proven here is that the new tail shaft is not a fix but in the best case just a cover-up of the tail issue. That's confirmed by your experience.

I am afraid, the issue arises from the combination of a number of factors in the tail assembly. I had the hum with "old" plastic tail grips, and when I changed to the silver metal grips, it was gone. On another heli, I had the hum with Align tail blades, and when I changed to Rotorchtechs, it was gone. I had a very smooth tail with almost no vibes (vbar vibe test) without tail blades, and as soon as I put the blades on, I had terrible vibes. The same blades worked just fine on my second heli.

So, I think it is trial and error - but change just one part at a time. Otherwise you cannot find out what the critical piece is in your case.

Pls, keep us posted!

Best
Peter

[marc8090]

Originally Posted by mattox

Hello, Ive been reading through this thread and have found multiple fixes. I am wondering why it is when I changed to the new hub and grips and black tail gears i get the hum.
the tail WAS setup like this. v2 tail case (with big metal silver bar in between the plates), new dual silver pitch slider, White rear tail gears, and v1 tail hub and grips..
with that setup i am still currently using the black front tt gears(faster ratio) and black auto gear.. and finally the original align 105s.--- Now with this setup I was running up to 2300hs on the head with absolutely no hum. the tail was smooth as it could be in the air..With no issues or HUM ever!!!!

Just recently I changed the rear TT gears to the black ones with the new hub and the silver tail grips. I now have the hum.... everything else on the heli was untouched.

Im trying to figure out why the previous setup worked? And now the new setup does not.? parts changed were all brand new... If the tail blades worked with the previous setup, then i suspect it wouldn't be the blades..

Any ideas? Questions?

Thank You
Mattox

Same torque tube? On a side note, if the tail hum is weight related as has been suggested, the aluminum grips are heavier than the plastic if that's what you meant by "V1" grips.

[ranchhand]

Weight seems to be one problem, but take a black TT gear and see how it fits on the TT before you assemble everything, it's a pretty bad fit and has to be causing some vibration.

[rcflyerheli]

Originally Posted by ranchhand

Weight seems to be one problem, but take a black TT gear and see how it fits on the TT before you assemble everything, it's a pretty bad fit and has to be causing some vibration.

I don't disagree that the TT wobbling around inside the umbrella gear could be causing vibrations. On my 3 setups, I just put one wrap of clear scotch tape around just the metal splined end of the TT. That kept it centered in the umbrella gear and removed the play.

I haven't had any hums on my two 700s, and one I did for a friend. We have run either Rails, or Edge SEs from the get go.

[mattox]

Originally Posted by marc8090

Same torque tube? On a side note, if the tail hum is weight related as has been suggested, the aluminum grips are heavier than the plastic if that's what you meant by "V1" grips.

I have never used plastic grips. Lol by v1 grips I mean the solid black metal ones.

The TT was not changed.

Mattox

[ranchhand]

Originally Posted by rcflyerheli

I don't disagree that the TT wobbling around inside the umbrella gear could be causing vibrations. On my 3 setups, I just put one wrap of clear scotch tape around just the metal splined end of the TT. That kept it centered in the umbrella gear and removed the play.

I haven't had any hums on my two 700s, and one I did for a friend. We have run either Rails, or Edge SEs from the get go.

I did the same to the TT, works out great.

[PetJumper]

Originally Posted by rcflyerheli

... On my 3 setups, I just put one wrap of clear scotch tape around just the metal splined end of the TT. That kept it centered in the umbrella gear and removed the play.....

I did that, as well. Didn't reduce the vibes in my case.

[rotceh_dnih]

Originally Posted by songer121

these blades weigh in at 5 grams a piece. anyone tried these yet?

http://www.amainhobbies.com/product_...l-Rotor-Blades

Just got a set yesterday. mine where 6.10 gram's each ,did a test flight today with the same results as rails installed.

i knew it would still be there at that weight but i had to try!
i have send of an email to HH about the weight as i was expecting them to be lighter then rails when they state there ment to be 5g's

[songer121]

Originally Posted by rotceh_dnih

Just got a set yesterday. mine where 6.10 gram's each ,did a test flight today with the same results as rails installed.

i knew it would still be there at that weight but i had to try!
i have send of an email to HH about the weight as i was expecting them to be lighter then rails when they state there ment to be 5g's

oh man no joke!? i would def send them back and contact horizon. that's kinda false advertising if you ask me. especially in our situation where weight MATTERS lol.

just get your money back and move back to whatever was working before...rails i guess lol

[rotceh_dnih]

yea ive sent an email off i guess ill have to wait till the new week to hear anything but ill be sure to update when i do . as far as the blades go there pretty nice and if it was for any other heli they'd be fine however in my situation where rails dont even fix the hum for me @ anything over 2150 i was keen to try them ... i will give them this, there no worse then rails in my case i couldn't tell the difference. ill post a video tomorrow of a test flight

[rotceh_dnih]

heres my flight , much the same as the rails maybe a little worse in id2 but not bad ...wish they where really 5g's still haven't heard from HH i got a case number at the start of the week but nothing since

700e Pro DFC HH 105mm tail hums (5 min 20 sec)

no worse then rails yea?

[AbdulBasit]

Originally Posted by rotceh_dnih

heres my flight , much the same as the rails maybe a little worse in id2 but not bad ...wish they where really 5g's still haven't heard from HH i got a case number at the start of the week but nothing since




700e Pro DFC HH 105mm tail hums - YouTube

no worse then rails yea?

Hi,
Just saw this issue & remember solving it by changing PWM of the motor as I'm using CC 120 or 160 ECS changed setting from outer run to 8hz or 12hz.... hope this can help if you wish to have a try

Abdul

Sent from my GT-N5100 using Tapatalk

[ddj74]

Originally Posted by AbdulBasit

Hi,
Just saw this issue & remember solving it by changing PWM of the motor as I'm using CC 120 or 160 ECS changed setting from outer run to 8hz or 12hz.... hope this can help if you wish to have a try

Abdul

Sent from my GT-N5100 using Tapatalk

PWM has nothing to do with this tail hum. Also recommended setting is 12hz. Shouldn't be in outrunner setting.

[AbdulBasit]

Dear,
I didn't mean nothing except trying to give some help & I wish I had the video which I took for the problem. ..

Sent from my GT-N7100 using Tapatalk

[rcflyerheli]

Seeing the above post also got me to thinking and remembering when I first built my 700V2. I didn't initially experience what I guess everyone is referring to as tail hum, but I sure did get tail surging. Scared the hell out of me the first time I ran it up. Those issues however had nothing to do with the mechanics of the tail, but had everything to do with the ESC/motor setup. I was running too high a gain on the governor setup in the Castle, and it was causing the motor to rapidly change rpm, and was causing the tail to chase it.

Now fast forward to today's tail hum issues. Could it just possibly be caused by governor gain that is just a tad bit too high, not real high like mine originally was, but just high enough to make the motor change rpm enough to hear it?

It seems like we have tried everything else???

[michael503]

Originally Posted by rcflyerheli

Seeing the above post also got me to thinking and remembering when I first built my 700V2. I didn't initially experience what I guess everyone is referring to as tail hum, but I sure did get tail surging. Scared the hell out of me the first time I ran it up. Those issues however had nothing to do with the mechanics of the tail, but had everything to do with the ESC/motor setup. I was running too high a gain on the governor setup in the Castle, and it was causing the motor to rapidly change rpm, and was causing the tail to chase it.

Now fast forward to today's tail hum issues. Could it just possibly be caused by governor gain that is just a tad bit too high, not real high like mine originally was, but just high enough to make the motor change rpm enough to hear it?

It seems like we have tried everything else???

an interesting theory. I can see a rapid surge induce a lead/lag that with the right blade weight and the right rpm could set up a harmonic.

That said, we should have seen that at a lower HS with heavier blades, and I'm sure that there are peeps who have had the issue running a curve vs a governor.

Still, I remember reading where someone had the hum, and they swapped every part at the field with a known good bird, and swapping the boom block+gear assy fixed it. Now to me, that sounds like a cyclic bind on the drive gears, inducing a torsion load/unload of the TT, with the TT acting as a torsion spring, storing the energy. With the right mass blades, with tight screws, I can see a harmonic being hit at the right rpm. Lighter blades, or loose screws would make it better, which are known to help the issue.

Gears being out of round can cause the TT to accelerate and decelerate slightly/revolution too, but once again, I saw TT gears WAY more out of round than these on my 600N (The old gray gears were really really bad) and never saw this issue, and neither did anyone else, as far as I know, so who knows

Same theory as yours really, just different causes.

I feel like we're all grasping at straws on this one.