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Low Head Speed Helicopters Low Head Speed Helicopter Setups and Flying info


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Old 11-11-2017, 05:44 PM   #21 (permalink)
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Quote:
Originally Posted by etherbatxx View Post
nice!

what is the rhythmic squeaking sound?
i have the same noise on my SAB 700 at 1000 rpm and i can’t figure out what’s causing it.
I don't know yet. I have analyzed the sound and found that it has peaks at almost exactly 2040 Hz, at 4080 Hz and some smaller peaks.

I have a 13T pinion and a 153T main gear.
The tail gear (front pulley) is 42T. The gear on the tail shaft is 9T.
That gives tail RPM = main RPM x 4.667.
I have tried to do the math.

710 RPM -> 11.83 RPS (main rotor)
x 153 = 1810 Hz (each teeth on main gear/pinion)
x 42 = 497 Hz (each teeth on tail gear)
x 4.667 = 55.2 Hz (tail rotor)
x 153/13 = 139.2 Hz (motor)

The motor have 12 windings and 8 magnets (possibly 16).

139.2 x 8 = 1114 Hz
139.2 x 12 = 1671 Hz
139.2 x 16 = 2228 Hz

One suspicion I have is related to the fishbone gear/pinion. If the gear is not exactly flat there would be a strange effect that I would expect to manifest itself as a 1810 Hz noise. I have not found good instructions, but would guess my main gear should have a vertical play that allows it to move a little up and down to always match the pinion. I have very little vertical play now.

Onother suspicion is that a bearing is causing the noise. Depending on the bearing damage, that could multiply a rotation frequency with a factor. The noise peaks are at what could be 4 and 8 times tail RPS. With a 2% error, that could be in my RPM measurement.

One way to find the cause of the noise is to eliminate. Eg.
1. Run just motor.
2. Run motor and main, without tail belt.
3. Run tail without rotor head.

I'll let you know what it is when I find it!

/Bo
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Last edited by svensson_bo_l; 11-11-2017 at 06:09 PM..
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Old 11-29-2017, 12:58 PM   #22 (permalink)
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Just buy a optical tachometer to find the rpm.

That's amazing you are able to fly that low of head speed. Don't you have tail issues at this low speed ?

What main gear are you using (153T) ?
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Old 11-29-2017, 01:38 PM   #23 (permalink)
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Flying at low rpm brings out noises that you don't hear at high rpm? It is probably the pinion as suggested. The art of making pinions is gone from the RC hobby. If you compare an ancient Schluter, Kalt, Hirobo pinion to a modern Align pinion, the difference is obvious. Pinions used to be polished and then hardened. It may be motor or esc noises that you don't normally hear.

KSJ / K&S used to sell QUIET pinions as replacements many years ago!
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Old 11-29-2017, 03:17 PM   #24 (permalink)
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Default Low RPM maiden with a Logo 600SE

besides the high pitched squeak, my G700 also makes a softer swish-swish rubbing sound when i add a lot of cyclic input.
but almost no sound when i add collective.

i’m thinking swash or maybe blade grip bearings, but shouldn’t slow turning bearings be quiet?
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Old 12-05-2017, 08:34 PM   #25 (permalink)
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Quote:
Originally Posted by Freeskiken View Post
Just buy a optical tachometer to find the rpm.

That's amazing you are able to fly that low of head speed. Don't you have tail issues at this low speed ?

What main gear are you using (153T) ?
Sorry for not looking here for a while…

Yes, I have tail issues. Tail does not hold in pitch pumps or even in flips.
I have not decided what to do about tail yet.
Here are the options I am considering:
– A three bladed tail. I don't think that would be enough.
– A longer tail shaft so I can increase tail pitch.
– Change tail speed with a smaller (aft) tail gear. A SAB pinion have been suggested, but I don't know yet if it will fit.

Perhaps I need all three...

I don't want longer tail blades, since I am close to too little distance between main blades and tail blades. I currently have 710 mm main blades and 107 (or 110, I'm not sure) tail blades.

I don't want to reduce pitch on main blades since already with 11.5-12° that I have now (if I remember correctly) I don't get a lot of lift with RPM way under 900…

I use the 153T/modulo 0.7 gear on this heli. 0.5 might work, given the low power. But, I have seen 0.5 used on Logo 500 with 520 mm blades where it stripped very easy, so 0.7 "feels" a little safer...

/Bo
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Last edited by svensson_bo_l; 12-06-2017 at 03:50 AM.. Reason: Main gear...
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Old 12-05-2017, 08:41 PM   #26 (permalink)
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Quote:
Originally Posted by Four Stroker View Post
Flying at low rpm brings out noises that you don't hear at high rpm? It is probably the pinion as suggested. The art of making pinions is gone from the RC hobby. If you compare an ancient Schluter, Kalt, Hirobo pinion to a modern Align pinion, the difference is obvious. Pinions used to be polished and then hardened. It may be motor or esc noises that you don't normally hear.

KSJ / K&S used to sell QUIET pinions as replacements many years ago!
I have tried to polish a couple of pinions recently, to reduce noise and friction. It feels better, but I have not measured.

I bought a polish kit like this one (biltema.se):
Polerset, 5 delar - Polermaterial Polerskiva Polertrissa - Biltema
and spent some 20-30 minutes to get the pinion real shiny.
I will try that on this 600 SE too, when I get to it.

/Bo

PS1: I have noticed that sometimes the Mikado gear, even it it is perfectly flat, does not get flat after mounting. When I have seen this the reason have been that the gear have not "settled" perfectly on the "Autorotation Hub". The plastic may need some "cleaning" around the screw holes.

PS2: For the fishbone gear to center perfectly around the fishbone pinion there are two requirements:
– The mounting of the pinion must be so it exactly matches the gear.
– There need to be a little vertical slop on the gear so it can settle where pinion and gear match perfectly.
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Last edited by svensson_bo_l; 12-06-2017 at 02:11 AM.. Reason: PS1 + PS2
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Old 12-10-2017, 12:26 PM   #27 (permalink)
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I have ordered a three bladed tail to try on my Logo 600SE. See how that works.
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Old 12-11-2017, 10:48 AM   #28 (permalink)
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Quote:
Originally Posted by Freeskiken View Post
I have ordered a three bladed tail to try on my Logo 600SE. See how that works.
What three bladed tail was that?

I know Align have one, where a modification is suggested (here on HF) before use.

Looking forward to hear about your result!

/Bo
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Old 12-11-2017, 07:49 PM   #29 (permalink)
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It is the I2RC TBTL56 LOGO 500/600 High Performance Tri-Blade Tail Grip Assembly

Welcome to RC-TEK Ltd. - i2RC Ultra High-End Products :: Tail Rotor Assemblies<br> :: I2RC TBTL56 LOGO 500/600 High Performance Tri-Blade Tail Grip Assembly
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Old 12-11-2017, 07:50 PM   #30 (permalink)
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I would still like to try a lower KV motor as well.

edit: I ordered a Hacker A50 14L 400 KV Motor.
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Last edited by Freeskiken; 12-11-2017 at 11:34 PM..
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