Screechy noise from heli @ 1150 head speed

[johncclayton]

Hi

I maddened the E7SE the other day, on 6S simply because I didn't have a 12S pack.  Very cool - I like low head speed :-) Huzzzaaaah!

Anyway, I tached 95% throttle on the Jive 120 HV at 1040 RPM (remember: 6S).  My problem/question is this when I run 98% (1150) I hear a screeching noise from the drivetrain.  The hell still flies, but as soon as I back off the RPM a bit, the noise goes away.  I've flown 450's, an X5, an X7 and a Goblin 570 - so I'm not utterly a newbie.  This definitely does not sound right.

I should mention I have no, and I mean absolutely zero vertical play in the main shaft assembly - and I wondered if I should take out the main shaft shim (109-110) in case that's the cause.

Or perhaps its gear mesh too tight on the main gear / tail? 

If anyone else has had screechy (I know, suck description) noises and solved it - keen to know what you did.

Thanks
--
John Clayton
Switzerland

[okanor]

Yay for trying low head speed! I enjoy it quite a bit.

I do not run Kontronik but I was under the impression they did not like to run over 85ish % on the throttle when using their governor? It sounded like it was fine @ 95% but not at 98% so that would be my guess. I run 7s which gives me a bit more head room for things like this (I know a lot do not have 7s packs laying around).

[Danny Dugger]

Try flying it with a 12s pack to see if it's RPM related. If you don't hear it while governed properly at higher 12s headspeeds, try flying with a very low (around 40%) throttle setting on 12s and see if it makes any noise then. If not then it could be something about high PWM rates with your motor. Even when I fly low head speeds on my kontronik units I like to leave overhead for the gov. Which means I typically don't go above 70-75% throttle on my 14SG when using Jives or 80-85% using Kosmiks. 100% shouldn't make it squeel tho, something sounds fishy. I usually look at bearings first if I hear screeching. Is the motor new?

[johncclayton]

Thanks for the info DoubleD

I'll give 12S a shot for sure - once I'm back from holidays in Italy.

The 4525 isn't new - it's had about 100 flights on it.  It was also salvaged from a horrendous crash that totally destroyed the X7 that used to be its home.  It spins OK, but that's all I know.

High PWM rates can cause motors to squeal / screech?  First I've heard of that...

--
John

[Danny Dugger]

High PWM rates can cause motors to squeal / screech?  First I've heard of that...

--
John

No it shouldnt, you may have misread my post. I was thinking along the lines of the motor bearings possibly being damaged and youre only hearing it at a certain motor rpm? Running at a higher headspeed with 12s should rule out all the other hardware if you don't hear anything at normal and lower throttle %. Not sure without hearing/seeing it but I hope you get it squared away Let me know what you find. If you can capture the noise on video post it up or PM me a link and we could see if that tells us anything.

[johncclayton]

I'll attempt to remember that when I fly next, which will be in about two weeks as I'm off on holiday without the helis... thanks for the offer of listening and trying to work out what it might be.

[johncclayton]

I took off the blades and spun the E7SE up on 12S this morning before leaving for holiday.  There was a faint screech as she spooled up, which might have been close to the 1050 rpm mark. In ID1 she's at 1380 and satisfyingly silent, at ID2 somewhere closer to 2000 from memory.

I suspect I won't know if this is just resonance until I put blades back on and fire it up for real. Time will tell!

[Ross Lawton]

Hi John,

I have not come across your particular issue before but i have come across something similiar, in your motor installation does your pinion ride against the bearing of the lower motor shaft support? If it isn't then it may be possible that the bearing has become dislodged from the bearing support and is shifting around on the motor shaft which could be causing this screeching.

Hope this helps and let us know how you go.
Cheers,
Ross

[RichH]

I have a similar screeching resonance on my E7. It's at a higher rpm than yours, but below my typical 1800/2000 rpms that I fly with.  Fortunately it doesn't resonate at my standard head speeds.  This is with a well secured lower bearing.


Rich