SERVO MOUNTING  
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SERVO MOUNTING - 8/20/2007 4:23:15 AM   
combatpigg



Posts: 10108
Joined: 11/22/2003
From: arlington, WA, USA
Status: online 		I've got a question about the best way to mount a pair of elevon servos in a plane that will see a fair amount of vibration. I don't plan on stressing the servos with a lot of wild flying or even pylon-like turns, the plane will mainly be used for speed runs. The servos in question are the Hitek MG digital aileron type. They come with double sided tape and 3 very short wood screws for mounting, no isolating grommets.
Years ago I remember over hearing F-1 flyers talking about mounting servos in puddles of GE silicone, this is something that I've never tried. Is this advisable? This plane has 1/8" thick plywood pads for the servos to attach to, if silicone is the best way to go, does the wood need to be treated with CA or anything before applying the silicone??

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RE: SERVO MOUNTING - 8/20/2007 4:45:49 AM   
djlyon



Posts: 1991
Joined: 12/10/2001
From: Castaic, CA, USA
Status: offline 		If your talking about Hitec 5125s I mount them directly to the fuselage sides of 428 Quickies with wood screws against hard mounts and a layer of double sided foam tape between the servo and the side wall. Two for a V tail. The only down side is the small metal gears don't last a real long time when faced with the vibration of a Nelson turning 23000 to 24000.

Denis

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RE: SERVO MOUNTING - 8/20/2007 5:13:01 AM   
combatpigg



Posts: 10108
Joined: 11/22/2003
From: arlington, WA, USA
Status: online 		Thanks, Denis. Now you've got me wondering if these servos are the right choice. I'm playing with the FAI Nelson, so I want to get this servo deal done the best way possible.

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RE: SERVO MOUNTING - 8/20/2007 8:49:09 PM   
DHG


 

Posts: 896
Joined: 4/24/2002
From: Arvada, CO, USA
Status: offline 		CP,

Those servos look fine to me. I own a couple and was planning to use them on a Q40, although I haven't actually done it yet. My plan was to supply my own grommets and brass eyelets, and mount the servos like any other. Just because the mounting holes are elongated doesn't mean you can't put round grommets in them. In fact, if there's room, maybe you could put two in each hole for a total of 6 mounting screws. As long as the servos are riding only on the grommets, it shouldn't matter that there are 6 of them.

The "puddle of silicone" method works to mount the 1/8" plywood pad that the servo will be attached to, and it will reduce vibration a bit even if you bolt the servo directly to the plywood without grommets. But I'd never glue in a servo directly using silicone -- not because it wouldn't work, but because the servo would be nearly impossible to remove.

Duane Gall
RCPRO

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RE: SERVO MOUNTING - 8/20/2007 9:52:12 PM   
djlyon



Posts: 1991
Joined: 12/10/2001
From: Castaic, CA, USA
Status: offline 		CP
When I said they don't last a real long time I didn't mean that they broke. They just start to develop more play than is generally liked in pylon racers faster than 5245mgs or nylon gears. But if you need the small size and the light weight. They are a good way to go. When the lower weight limit on Q500 was 3lbs 8ozs they sure helped me get a scratch built Quickie down to that weight plus leave a lot of room in fuselage back of the wing for receiver, battery etc.
If you haven't used 5125s or 5245s before, be careful of one thing. Don't let them stall, because of mechanical limits on a control surface. If they do they self destruct, without smoke, in seconds.

Denis

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RE: SERVO MOUNTING - 8/21/2007 12:48:35 AM   
combatpigg



Posts: 10108
Joined: 11/22/2003
From: arlington, WA, USA
Status: online 		Thanks for the advice guys, I appreciate it.
I just had a thought, I'm going to try to cast some oblong grommets out of silicone, with the brass ferrules inbedded.
For what these servos cost, and considering how strong they are, I almost laughed when I saw the included double sided tape and tiny mounting screws that have about 1/8" of reach into the wood.

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RE: SERVO MOUNTING - 8/21/2007 4:11:06 PM   
DHG


 

Posts: 896
Joined: 4/24/2002
From: Arvada, CO, USA
Status: offline
quote:

ORIGINAL: combatpigg

I almost laughed when I saw the included double sided tape and tiny mounting screws that have about 1/8" of reach into the wood.

Yeah, that's for gliders. Things are different with a Nelson F.I.R.E. in the mix.

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RE: SERVO MOUNTING - 8/21/2007 11:38:33 PM   
combatpigg



Posts: 10108
Joined: 11/22/2003
From: arlington, WA, USA
Status: online 		I guess the points to consider here is that the servo is trying to control a much larger flap than a Q40 and the elevon is in the middle of the turbulent prop blast. The Q-40 guys who would use the H 5125 [flat wing servo] for roll control only, aren't asking as much from them as this delta will, so it looks like either the H5955 TGS or the JR DS8611 will get the nod.

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RE: SERVO MOUNTING - 8/23/2007 3:33:19 AM   
Oldbob


 

Posts: 158
Joined: 6/29/2005
From: georgetown, TX, USA
Status: offline 		Combatpigg, Do not, do not, do not use CA as a base for Silicone adhesive. This combination has always come loose for me. For some reason I can not get Silicone to stick to CA. What works really good is a thin film of Epoxy. 5, 15, 30 minute. After it cures wipe the Epoxy surface with alcohol to remove any oil film that may form. Now apply the Silicone, about 1/8 inch thick, let cure over night, and you are good to go. You will have to use a razor blade to remove the servo.

Oldbob

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RE: SERVO MOUNTING - 8/23/2007 5:38:51 AM   
combatpigg



Posts: 10108
Joined: 11/22/2003
From: arlington, WA, USA
Status: online 		Thanks OldBob! I'll be sure to remember that. It makes sense that nothing could be a better base for silicone than something non-porous like epoxy.
I've decided to go with 8611 Titanium servos. I think on a delta, the elevons punish a servo more than your roll control servos will see on a Q-40. If the 8611s fail, there won't be as much second guessing.

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Led Zeppelin is NOT "old fogie" music.

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