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HomeAircraftHelicopterGasser Model RC HelicoptersOther › Predator NX Front mount tail servo kit problem - help!
03-10-2008 03:51 AM  10 years agoPost 1
jschenck

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La Vista, NE.

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I'm about 3/4 through my Pred build and ran into a problem. I started installing the optional front mount tail servo relocation kit:

http://www.heli-world.com/detail.aspx?ID=5490

but it has a serious interference with the new NX style tail transmission case. Now the instructions do say you may need to notch the case or grind some of the screw head down. This may work fine for the old style case but the NX case, it looks like I'd nearly cut it in half to get the clearance. Certainly would have to notch the entire depth of the ridge along the side of the case.

Has anyone else ran into this issue? Do I just space out the plate mount and add longer ball links? I'll call Century's tech's and see what they have to say but thought I'd throw it out here also.

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03-10-2008 05:24 AM  10 years agoPost 2
mcfast

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Quebec Quebec Canada

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I would space it out and use longer ball links.

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03-10-2008 05:35 AM  10 years agoPost 3
Excalibur

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Destination: Earth

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Hi jschenck:

This has been a problem from the inception of the front mounted tail servo kit, not just the NX's.

If I understand you correctly, it is the top socket head screw that is causing the interference. The simplest solution is to replace that one socket head with a button head screw. This provides enough clearance and eliminates the need for cutting. I did this on my Predator Gasser and it has worked flawlessly.

Xcal

Camper Fuel: It's Not Just for Breakfast Anymore

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03-10-2008 05:47 AM  10 years agoPost 4
litespeed600

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St. Charles, Missouri

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Mine came with the front mount rudder servo kit but on mine I need the weight on the boom. I wonder why they even make the darn thing. I'd see how it balances before you go to far on the installation.

Tom

Married with 2 kids, I am no stranger to pain!

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03-10-2008 02:39 PM  10 years agoPost 5
jschenck

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La Vista, NE.

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I want the servo up front more for the protection than the weight, those 9251's are spendy. Though the boom mounted tail servo is simpler to setup I'm a fan of up front mounting.
replace that one socket head with a button head screw
Problem is with the NX tail case the side reinforcement is flush with the frame side. The only way this would work would be with a counter sunk head like the front screw on the transmission case. This is different than the pre-NX style transmission case which doesn't have the rib along the side.

I think I'm going to end up using spacers and longer ball links but sure is frustrating. Your hint with the button head screw make sense, I'll do that so I don't have to space the plate out as far, I do see a potential issue here as this will allow the plate to rock a bit with only two mount points perpendicular to the tail servo force.

I'll talk with Century today and see what they have to say.

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03-10-2008 05:34 PM  10 years agoPost 6
AceBird

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Utica, NY USA

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I do see a potential issue here as this will allow the plate to rock a bit with only two mount points perpendicular to the tail servo force.
Make the spacers one plate between the two mounting holes so the stiffness is not affected. I don’t know why you have to change the ball links to longer. I would leave them short so you don’t add more force on the link bearings.

Ace
What could be more fun?

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03-10-2008 07:15 PM  10 years agoPost 7
jschenck

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La Vista, NE.

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I don’t know why you have to change the ball links to longer.
Longer ball links would be needed to keep the ball links on the same plane they were designed for. Move the mount and ball links out and the pushrods would be at an angle to each other. a couple of mm may not make much of a difference but this would generate a little more side load to the bearings on the pivot besides being geometrically wrong.

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03-10-2008 10:38 PM  10 years agoPost 8
TooBizzy

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Georgetown, Ohio USA

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Heres a picture of mine. Its the old style, but has just enough clearance. I looked at the new style and saw where it has a center rib. I believe I would mark where the cap screw head hits the rib and take a Dremel and cut/grind enough clearance for the head of the cap screw. Or if you know someone with a little milling machine, it would be easy to cut a slot for clearance. That would make it look neater. Another option, as stated above, would be to use a pan head screw. You could remove less material that way. I doubt you will weaken the housing. Mine doesn't have that rib at all....I think I would shy away from spacing the bracket out. It needs to be against the frame for rigidity.

P-Gasser Se, Raptor 50 Se Hyper, Raptor 30v2, Trex450se, 3dx450...

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03-11-2008 05:48 PM  10 years agoPost 9
AceBird

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Utica, NY USA

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Quite the opposite. It is best to keep the ball link directly in line with the bearings in the pivot link like photo shows.

Ace
What could be more fun?

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03-11-2008 10:45 PM  10 years agoPost 10
TooBizzy

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Georgetown, Ohio USA

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What do you mean?
Quite the opposite

P-Gasser Se, Raptor 50 Se Hyper, Raptor 30v2, Trex450se, 3dx450...

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03-12-2008 05:36 PM  10 years agoPost 11
AceBird

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Utica, NY USA

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What do you mean?
If you put longer ball links on, it will move the force farther away from the center line of the ball bearings in the link and create a twisting force on the link. The link is probably strong enough to take it but it is always better to keep the forces in line so the twisting force is kept to a minimum. The slight change in angle of the links going to the servo and the tail is meaningless.

Ace
What could be more fun?

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03-30-2008 05:37 AM  10 years agoPost 12
jschenck

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La Vista, NE.

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Well I finally solved the issue. Not the ideal resolution but it will work and was simple. I put this off to the end waiting to hear something back from Century's support but I did not get a call back.

So, my simple solution was to grind off the head of the screw to about the height of two washers then shim up the plate with two washers. I was concerned that this solution would lead to the assembly rocking on the frame but with the screw head at the same height and ground flat it rests against the tail transmission with some pressure creating a 3 point mount of sorts. Also I couldn't use the fancy screw caps and even ended up putting a button head screw on the top mount side to give clearance for the front pushrod.

I ended up having to move the tail servo to the inside of the frame so that the pushrod would clear the front control assembly. I also had to grind away a fair amount of the rear tailcase screw mount for clearance for the pushrod.

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03-30-2008 03:47 PM  10 years agoPost 13
AceBird

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Utica, NY USA

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You are talking about that end/

If you just turned the link around and had the control rods on the outside it wouldn't clear up the interference?

Ace
What could be more fun?

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03-31-2008 03:32 AM  10 years agoPost 14
jschenck

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La Vista, NE.

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I had to notch the rear tail case. I didn't post a picture of it. I know some guys have posted they fixed the clearance issue back there by using a longer ball link but I didn't have one so I hit the case with my dremel.

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