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HomeAircraftHelicopterGasser Model RC HelicoptersOther › Predator Gasser Goes Down Due to 8700G Failure
04-03-2005 09:54 PM  13 years agoPost 21
AGRAV8

rrProfessor

Mosquito Coast......Houston Texas

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Yeah
Not like I have not already been chasing my ass on this one.....

started with 9202's on ccpm. Nope. Not gonna live like that. Waves on the swash.
so. Have some 4131's, one is faster than the other two.....you know what THAT does to a ccpm setup. See above. Dammit !
Now I have some 8231's. I DON'T suggest them for gasser use. BUT..........
I have a set of 8311's with 8417 gears in them. NOT for this stretched machine. And I wanted them with that 601 in the next machine already underway being filmed. GRRRRRRRRRRRRR

8231's or BUST. Might as well put the 401/9254 in it. Maybe. But I have the 8700 already installed.

See, that is why it was 5:15 AM before I went to bed last night. Worry worts !!

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04-03-2005 10:57 PM  13 years agoPost 22
Christopher J

rrElite Veteran

Kansas City, MO Californian lost in land of Oz

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Chris,

I did try your suggestions, they were correct, but I feel the servo was already on it's way out. I'll give Larry a call and get the parts I need and should be back up in the air shortly, and I'll let you know how things turn out. I don't think the problem has anything to do with the heli, I'm just not pleased with the 9254 or 9253 on big ships. I'll fly them in my smaller helis however. I think that for the Benzin and Bergen that I'll use the 601's w/9251's. I can't fly the way Mike at A.I. needs me too if I'm not comfortable with the ship.

Christopher J
same as I ever was
"Still all set & Flying the original"

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04-03-2005 11:01 PM  13 years agoPost 23
JKos

rrProfessor

Redondo Beach, CA

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A 9254 lasted about 4 gallons before it was worn out on my first PG.

I think the gyros are partly or perhaps even mostly to blame by being hyperactive. There is a big difference between holding the tail the way we need them to and being too hard on the servo.

- John

RR rules!

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04-03-2005 11:56 PM  13 years agoPost 24
sgt1959

rrApprentice

Easley SC

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ok agrav8 stop pussy footen around 9252s for ccpm 9251 and 601 for tail take your pick for throttle and be done with it throw out the jr stuff and get some sleep

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04-04-2005 02:41 AM  13 years agoPost 25
dariof

rrVeteran

Henderson, NV / Laguna Niguel, CA

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My 9254 also got very hot with my 401 on my X-Cell gasser. Finally it quit but I managed to save the heli/

I am now running a FUT 9402 with the 401 out of digital mode....high torque and high speed. Works fine.

Best Regards, Dario

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04-04-2005 05:30 AM  13 years agoPost 26
JKos

rrProfessor

Redondo Beach, CA

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I'm thinking of trying a Hitec HS-6965HB which has Karbonite gears and is rated at 111 oz/in and 0.08 s at 6V (which I could run close to). Its deadband spec of 2 us indicates that it should have very good position accuracy.

> I trim my aircraft to hover in normal gyro mode with the tail as close
> to dead still as I can get it, then, while in HH mode, I know the gyro is
> not consistently fighting an out of trim condition

I do not believe that is a factor and let me explain why. When you trim the heli in rate mode and hover, that is the ONLY flight condition (as in hover and at that particular headspeed) for which that trim is valid. Do anything else with the heli and the is now technically "fighting an out of trim condition." In HH, the gyro and servo could really care less about being trimmed in rate mode. The gyro will position the servo wherever it needs to be regardless.

> am now running a FUT 9402

How are the metal gears holding up?

- John

RR rules!

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04-04-2005 06:05 AM  13 years agoPost 27
vetrider

rrElite Veteran

Daleville, AL (Ft.Rucker)

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You know guys, The gassers produce so much torque that I find I'm running a higher gyro gain on my Spectra and GY601/9251 and the same gyros on an Fury Extreme and Freya. 37 to 38% on the gasser and 32 on the nitros.

Could that be some of the problem? I've heard of some guys going to 110mm TR blades to help hold the tail on the gassers. Mine are still 105's? hhmmmm?

I just got 3 of the HS-6965HB's for a Freya/Avant CCPM convertion. They should be great on the tail also.

Nolan

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04-04-2005 06:26 AM  13 years agoPost 28
JKos

rrProfessor

Redondo Beach, CA

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> I've heard of some guys going to 110mm TR blades to help hold the
> tail on the gassers.

We are running 115s on the PGs. It would seem you would need to lower the gain when increasing the blade length, right?

> I just got 3 of the HS-6965HB's for a Freya/Avant CCPM convertion.

Very NICE!

- John

RR rules!

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04-04-2005 09:58 AM  13 years agoPost 29
wolfdad

rrKey Veteran

Southern Maryland

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John,
The question I would have for you, and I agree with your reasoning, is if the aircraft has what I would refer to as an inherent or mechanical out of trim situation (tail rotor), would not the gyro be fighting that in addition to any other inputs the gyro is attempting to compensate for during a flight? My theory, thinking, philsophy (whatever you want to call it) has always been that, by mechanically trimming the aircraft for a stable (no tail swing in either direction) hover in rate mode, you have taken away any inherent correction the gyro has to make (assuming a no-wind, out of ground affect hover) on a continuing basis....essentially a way of double-checking static tail rotor rigging. Also, based on information that came out of one of the Krause/Bennett classes, I try to keep my gyro gain down in the 55-60 range. As I understand it, there is a point, above which, additional gyro gain provides a neglible impact, however due to the high frame rate of the current digital tail servos, the additional gain serves to shorten servo life. Obviously, this is all theory, however, it seemed logical to me and, I have found that it works out fairly well on my nitro heli's. I also think this may be part of the answer that would favor the use of a 601/9251 combination, i.e., components in that system that accept an even higher working frame rate. Another thought that has just ocurred to me is that we all know that gasser's are subject to higher vibration levels (nature of the beast). Could we, somehow, be seeing high frequency vibrations that are approaching servo frame rate frequency or a harmonic of that frequency with a specific servo? And, that the 601/9251 combo's higher frame rate somehow transends or avoids this situation? Quite honestly, I don't know and am open to suggestions/opinions/recommendations. My gyro and tail rotor set-up philsophy/practice has been one of the larger "learning curves" and challenges I have experienced with heli's and it has been a compendium of some of Colin's theory and advice, some of the info gained from Todd Bennett and Jason Krause and some of my own...maybe all in the wrong direction, however, as I said, most of this has worked fairly well with the nitro birds.

Doc

"There are those who have...and, those who will" IRCHA #2117, AMA #70068, Turbine Waiver #105

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04-04-2005 11:00 AM  13 years agoPost 30
AGRAV8

rrProfessor

Mosquito Coast......Houston Texas

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Doc:
I theory....we are taking the assumption that the tail rotor itself WANTS to have, say, 20 degrees of pitch naturally to be in mechanical trim? I would surmise that the tail servo has a working load on it to keep the pitch constantly the same, as the rotating tail disk seeks a neutral state OR the 20 degrees of pitch wants to continue to the stop.

As to the vibration issue, I don't think it is a matter of FREQUENCY that gives us the grief, it is the AMPLITUDE of that vibration. I CAN confirm that some servo's cannot survive long term in a gasser VS a different design of the same manufacturer. 8231's VS 8311's is a case in point.

I think, in part, the level of tolerance by the servo, the mechanical advantage is has (and is against it) and also inherent drag of the components at RPM all play a factor in these failures.

Just my thoughts.

James

GOOD guy list-39, BAD guy list-0

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04-04-2005 11:15 AM  13 years agoPost 31
wolfdad

rrKey Veteran

Southern Maryland

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James,
Good points! I had started thinking in terms of frequency being the culprit based on the fact that, (and, probably, just my perverted way of sorting it out) the greater the amplitude, the more likely the vibration is to become visible. However, the amplitude would be the more likely of the two to "slam-dunk" the servos.

The 8231 revelation is somewhat of a surprise to me since my thinking was that the 8311 was the "beefier" of the two servos and more likely to be resistant to damage. Here again, as in so many other things, we see design play the "key" role...some subtle difference with the inner workings....maybe even the gearing. Over my head for sure, however proven facts (oxymoron) are just that. Something I will note and remember for future reference.

Lots of mysteries and challenges here to play with..maybe even the metal gearing transmitting the vibration loads.

My thinking on the trimming process goes back to my "old" days with the H-2 where the tail rotor was "bungied" to a basic neutral position to assist with a "loss of tail rotor thrust" emergency situation (ability to change pitch in the tail rotor blades was lost). This neutral assist, coupled with forward airspeed was how you maintained straight flight and you turned in the yaw axis by varying the amount of collective (effectively allowing torque or the absence of torque depending on the collective setting) to maintain stability in the yaw axis based in part on the "assumed" neutral rigging of the tail rotor. Interesting to be in the back while "nuggets" did their first "run-on" landings with a simulated loss of tail rotor thrust.

Doc

"There are those who have...and, those who will" IRCHA #2117, AMA #70068, Turbine Waiver #105

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04-04-2005 11:32 AM  13 years agoPost 32
AGRAV8

rrProfessor

Mosquito Coast......Houston Texas

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Well
the 8231's have been shown to NOT survive in the gassers as well as 8311's. This was confirmed by a service rep at Horizon when an autopsy was performed following a servo induced mishap. The other two servo's showed excessive wear and also were not suitable for use.

Note, although I am keenly aware of the 8231 longevity issue, I have made a decision just yesterday to install a set into a machine I am reworking. I don't intend this heli to see much flight time, as it will be used for a scale donor soon. I still stand behind the use of 8311's.

I don't have a problem with 8231's in a glow Predator. They work fine, and longevity has not been an issue there.

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04-04-2005 12:21 PM  13 years agoPost 33
wolfdad

rrKey Veteran

Southern Maryland

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James,
My bust on this one! Thought you had indicated that the 8231 was the better choice of the two and that took me by surprise. Currently, I have gone to the 8611's on my Intrepid for for all but the tail and throttle. 9250 on the throttle and, as of this minute, still have an 8700 on the tail, however that is subject to change shortly.
Doc

"There are those who have...and, those who will" IRCHA #2117, AMA #70068, Turbine Waiver #105

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04-04-2005 05:09 PM  13 years agoPost 34
rafael

rrApprentice

Oaxaca, Mexico

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What type and battery voltage are you using?
I ask this because I have already lost two 9254 tail servos, one on my Intrepid Gas without causing any damage to the heli(it failed on the ground) and the other was last weekend, in my Raptor 50, that I have been flying for more that two years with out any problems. The only common things installed in my two helis are the type and battery voltage and in my raptor was installed before the flight where I lost tail control.

I´m currently using 7.4 Li-ion with a regulator for a 5.3V output.(If you want the brand PM me)

I have read the voltage alone may not be a problem but may be, just may be this combo of battery and voltage is causing my servos to fail.

What do you think? Can this be possible?

Rafael Castañeda
www.helicam.com.mx
www.rcoaxaca.com
www.737-700.com/simuladores/

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04-04-2005 05:13 PM  13 years agoPost 35
dariof

rrVeteran

Henderson, NV / Laguna Niguel, CA

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I am using 6V, regulated to 5.1V. I have had no problems on my other helis with this set-up. Some are NiCd's, some NiMh's, but that does not matter. What matters is the regulated voltage. Your regulated voltage should be fine for the 9254.

THe only problem I had was on the gasser..the 9254 burned up. I changed to a 9402 on the gasser, and thus far, no issues.

Best Regards, Dario

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04-04-2005 07:57 PM  13 years agoPost 36
RUFFYB

rrNovice

HERTFORDSHIRE UK.

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Well you've all got me worried now!
I will put the jr8231 servos for my vario trainer back in their box's!!!
anyone know what the jr8311 equivalent is in the uk market?

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05-13-2005 04:02 PM  13 years agoPost 37
catman3070

rrNovice

Franklin, MA

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9254
I had a 9254 on mine, that failed after 3 gallons. Was able to get it back in 1 piece. After talking with a few others that had failed 9254 servos. I change to the HS6965 on all controls, added a generator regulated at 5vdc and have been having good luck.

Chane

Live Free, Fly Long With Gas Engines

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05-13-2005 05:03 PM  13 years agoPost 38
Stet

rrElite Veteran

Key Largo FL

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I have had servos fail on gassers

I believe the reason was that they were mounted too tight to the frames and engine vibration knocked the boards loose

So now I mount the servos without the internal metal sleeves in the grommets, and use the Raptor servo retaining plates. These plates allow you to dial the squeeze just right on the rubber grommets. Also, since the plates cover the whole grommet, you can use a lot less pressure and still have the same overall stability of the servo.

Also, make sure that the servo is not touching the frame when mounted. If it is and cannot be moved to adjust, open up the frame hole a bit.

Finally, when setting up a heli, the first thing I do is reduce the ATV on the gyro channel (gain) so that I do not sit there at the default gain of 100% for any time at all. I do this before turning on the receiver. As mentioned above, make sure the gyro is left in normal mode until the endpoints are set to avoid binding. Similarly, I always remove the throttle link until I am setting up the throttle endpoints.

keepin' it real

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05-15-2005 08:41 PM  13 years agoPost 39
daggit

rrElite Veteran

Claremont, MN

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I've been running 401/9253 on my X-cell gasser for 3 years in all types of weather with no problems.

I ran Hitecs on the rest of the servos the first year and switched to 4131's because I heard they were more reliable, but I've still never had a servo fail on my X-cell gasser.

This has been all camera work... no 3D stuff.

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05-16-2005 01:25 PM  13 years agoPost 40
FCM

rrElite Veteran

Surrey, England

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Just for your info, I have been running a Gy401 and 9253 (tail boom mounted) on my Benzine based cameraship without problems for 50 logged flight hours. Some of this flight time was when the heli was 'less than smooth' but I have always been careful with setting up the servo/gyro throws and also not to squeeze the servo gromments too tight.

I have now swapped out the 9253 for a 9254 and have run this for 8.3 hours so far without problem - fingers crossed it stays that way

Paul.

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