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04-25-2009 08:19 AM  9 years agoPost 1
Trevor G


Brisbane, Australia

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Has anyone with a Spectra G ever had this happen before???

Last week I re-assembled the throttle linkage to get a more linear response from the engine. I followed the RR thread on it. At the same time I noticed my old stock futaba servo has some slop so I threw in a 9255 I had laying around.

The next flight the throttle was great, but 1/3 of tank in, and an engine failure had me auto it down. The tip of the throttle servo horn had snapped clean off next to the ball.
I replaced it with a new item straight from the packet and the same thing happened again. Same time frame too, 1/3 tank.
Lucky I had installed a kill switch while I was at it...even though the engine went to idle both times. I didn`t have the return spring connected.

Any ideas where to start with this one?

-The 9255 is heavier than the old servo.
-The pushrod is now about 5mm longer with the new setup, which works great!
-The RPM`s are about 12,155 for 1700 on the head, which is where it was running when this happened.
-The servo mount is the stock one, I haven`t doubled it up.
-The only sign I can find of any high frequency vibe is a slight bit of wear on the tail pushrod guides. I balanced the fan and checked runout on assembly, and the heli was fine before the changed linkage and servo.

04-26-2009 02:41 AM  9 years agoPost 2


Gippsland , Australia.

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Hi Trev
I’ve had the same issue a while back using JR & Futaba servos on my 23 & 26 Gassers till I changed to el cheepo Hitec HS 425BB’s there about $25 bucks new and seem to last the longest it’s the high frequency vibe that kills then when running Hi head speeds I feel
What I’ve found that with JR & Futaba servos is the first nylon gear in the servo gear train that comes off the servo motor pinion is a sacrificial gear and the fine teeth break off very easy with excess vibration
Plus I still have the spring on the carby but taken a couple of coils off so it’s not pushing against the servo but will still return to idle if I have a throttle servo failure
Cheers Patty

04-26-2009 03:10 AM  9 years agoPost 3


South Dakota

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I don't know what size threaded ball your using, but if you screw the ball threads into too small a hole in the servo arm it will stress the area around the hole and it will break off with a very light load. You may need to make the hole in the servo arm slightly larger.

Spectra-G, MAH, CSM

04-26-2009 03:55 AM  9 years agoPost 4
Trevor G


Brisbane, Australia

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Thanks Boys.
I ended up putting back a stocky 3003 futaba servo like I had in previously with no issues. It`s much lighter than the 9255 I just tried. I fitted a blank servo wheel to it and drilled to suit.
The horns that broke were the single half arm type with multiple holes at various center distances along the arm. They broke through the next hole towards the centre from the one the ball was in. Now I have a solid disk with only the one require hole in it.
I fitted the return spring as Patty says, so it`s real light but pushes back to idle.
I`ll try it later today with the canopy off and see how if I can get the full tank through it!
Is it common for the servo mounting plate to require doubling up, or does it work fine for most people?

04-26-2009 05:38 AM  9 years agoPost 5

rrKey Veteran

Destination: Earth

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The first thing I would look at in this case is over-driving the the throttle arm on the engine, binding the servo and breaking the servo arm from vibration. I know this sounds obvious, but you need to check that really carefully and make absolutely sure the servo doesn't drive beyond the stops.

As for the throttle servo mounting plate, you will find different opinions depending on who you ask. I did not like the flexibility of the singe frame mount supplied in the kit, so I ordered a second mount and JB-Welded them together. If you search on this forum, you will also find several people who have had problems with vibration on a single-frame mount. Doubling them up makes them incredibly strong, and worth it to me.


Camper Fuel: It's Not Just for Breakfast Anymore

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04-26-2009 07:36 AM  9 years agoPost 6
Trevor G


Brisbane, Australia

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Thanks Excalibur,
There`s no binding in any of controls on my G.
This issue just manifested itself when I put a heavier 9255 servo in.
I must have found just the right weight to tune that mount into the engine. I will look at beefing the mount as well though, I have the materials here.

04-26-2009 10:04 PM  9 years agoPost 7
Justin Stuart (RIP)


Plano, Texas

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Following Excalibur's suggestion, I ordered a second servo plate (and easily removed the PEM nuts with a needle nose pliers), but unlike Excalibur I did not find it necessary (or at least not yet) to JB weld the two plates together. I felt that the bolts passing through the plates was sufficient, at least for now. I feel that the second plate really stiffens things up which makes me feel much more secure. I think vibrations manifest themselves the most in things which are not well secured, and having the throttle servo hanging on the end of a thin CF frame is not sufficient in my opinion.

Avant RC
Scorpion Power Systems
Thunder Power RC
Kontronik Drives

04-27-2009 01:44 AM  9 years agoPost 8



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I would think that would depend on the nature of the vibration. Wouldn't a high freq vibe be more easily transmitted through a stiff component (steel) vs a less stiff component (G10)?

So by stiffening up the servo mount, aren't high freq vibes more easily transmitted to the servo?


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04-27-2009 05:29 AM  9 years agoPost 9


Franklin, MA - USA

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That's what I felt
I did try doubling the servo frame for a while but I felt the vibration was worse with it doubled so I went back to the single stock mount. Other people may have different experiences with their machines.

Been using the 9252 servo with the single mount for quite some time now with good results. No loose or breaking servo screws and the servo is holding up as well.


MA 1005 Hanson 280, 4225 flts
Spectra 27 3DMax, 3325 flts
Whiplash V1-2 Hanson 300, 1650 flts
Whiplash V2 Hanson 300, 504 flts

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