Hi All,

I'm trying to decide what is "best" for my application here. The plane is a kit built CG Ultimate with a Saito 150. It will be used for 3D. What linkage should I go with? So far I'm using 1/8" carbon fiber rods with 2-56 titanium ends and heavy duty (but not metal) servo arms. Should I use ball links or clevis? I've got a couple suggestions and they split down the middle so i'm hoping for more opoinion here. If you have a preference, please give specifics as to the brand and model if you can.

Thanks!

Best,
Harold

Well IMO if you have a nice straight shot with no unusual angles there is no need for ball links. A good quality clevis will work fine, dubro or sullivan with the pin clips for example. But if your angle is off a bit or if the hole in the horn is too big and has slop in it it would be a good time to use a ball link

Yep, that's a problem I've encountered with clevises and control horns, the hole is too big for the pin which equals slop. I hate that. I've encountered a few holes that were too tight, but that's not a problem to fix. I really like the Rocket City stuff for the larger planes. Smallfly, you disappoint me. I figured you had already invented the perfect system!

Wade

I filled the hole with epoxy, then drilled a smaller one to fit the clevis. As soon as the snow melts, I'll know if it holds up.

On helicopters, the ball links are popular for their precision, but there is not so great a load on them.

Tom

Tom,
I thought about trying the same thing with filling in the hole and redrilling. Let us know how that works out.

Wade

Ditto

Let us know Greenboot.

My only beef with the clevis is the control horn hole (not servo arm) is just a little to big for the clevis pin. Why don't they make the holes smaller

Whereas I dont see any need to re-invent the wheel you can on some horns drill your own hole between the stock holes

I tried drilling new holes in between the ones already there. Doing this left little "meat" on the horn. I tried drilling slightly rearward but the clevis ends up behind the hinge line.

That little slop due to the very slightly oversized holes on the control control horn is really visible at the surface. Ok, maybe I just don't have enough to worry about

The only slop I want to see is the servo geartrain backlash. I can't do much about that!

Ball links will never give you slop. Clevises routinely develop slop, and need to be dealt with, as evidenced by the replies above. So, if you don't mind spending a little more, the ball links will give you longer service, with less fuss, and can tolerate linkages with larger angle offsets if need be. The Clevises are cheaper, will develop slop, and will need the arm to be replaced or modified every so often.

Basically;

Ball links = no slop, more money
Clevises = less money, will develop slop over time
or
more money, less time
more time, less money

Why does everything seem to come down to this

I personally only use ball links on my larger planes for control surfaces, especially when I use 3D rates. And on smaller ones it really depends on the airplane, and whether or not its really required.

<<...there is not so great a load on them (ball links on helicopters)...>>

?????????????????????????????????????????????

You have obviously never seen a competent 3D guy flinging a ten pound 60 machine around, doing the latest amazing manuevers.

The load on EVERYTHING during this is tremendous, especially the collective servo.

I agree with sfaust; ball links are inherently more slop-free, although they WILL "egg out" eventually; especially if they are not wiped down occasionally. Fuel residue, combined with grit, etc., will erode the contact points, just like it does on a clevis.

I use a mixture of both on my planks, but elevator and aileron always get ball links.

Steve

Steve, I've seen some pretty good stuff, but it was done very smoothly. It seems to me that it wouldn't take very much force to move the swashplate. Don't the blades pivot around the center of pressure? If so, it really doesn't take any force to rotate them. The servo just puts them in any position it wants, with very little force. In fact the blades change pitch each time the rotor head revolves, even if the heli is not maneuvering. So in an extreme maneuver, they just pitch to a different angle. Does this really take significantly more force?

I don't understand why driving the swashplate upward (full collective) would take a large force for the same reason. It certainly isn't the same mechanics as deflecting a huge elevator by 45 degrees.

Tom

There still is a lot of force involved. Even though the servo is only moving the swashplate, the forces are still transmitted from the rotor blades, through the arms, and back to the servos. There are no free rides.

You are right, its not like moving a big elevator 45 degrees. But any helicopter pilot will tell you, use good strong high torque servos on the controls if you are going to be flipping around your helicopter in 3D flight. The forces are there, and good tight linkages need to be employed to create a strong precision linkage.

My big problem is simply finding a clevis and control horn that will fit together with no slop. You would think that if you bought the same brand clevis and control horn then they would fit together with some precision, but many times I've seen this not to be the case. I would expect that with some of that cheap no-name stuff you get with some kits, but I've seen this with top names like Dubro and Sullivan too.

Wade

Well,we could debate which is more forceful all day. I don't have any solid figures to present. What I do know is that only servos I have ever had fail, in 15 years of flying r/c models, have been in a helicopter.

Ask the many, many guys who lost helicopters due to JR 8411 servo failures. JR finally acknowledged the problem and issued a recall. I'm told that this a very popular servo with the big plank drivers. I don't recall hearing any of them complain about failures...

Steve

Then you're not listening! There have been many, and there are complaints. However, they are still the preferred servo for its speed and power. It does help when you have a couple servos on a surface, its not as drastic if one fails

Interesting.

You're right, I haven't been paying very close attention to the large plane threads. This was a topic of discussion on another, heli-specific board, and one of the guys who I know does large planks said that community was quite happy with the 8411.

Guess he wasn't listening either...<G>

But my question is, given that the servo has a known and well-documented propensity to puke at the worst time and trash models, why do guys (the ones who know about the problem) keep using them???

It's not just plankers; more than a few heli guys are (IMO; sorry, but this is the way I feel) slow learners as well.

Steve

What's a planker? I'm assuming that must mean an airplane or an airplane pilot? It must be a heli pilot thing. I don't fly around any heli guys, not many around here.

<<...airplane or airplane pilot...>>

Yup. It's a rotorhead term...<G>

Dunno what to call myself, since I fly both.


Steve

Steve,
I figured the term planker was something like that. Actually, that term sounds vaguely familiar. I've probably heard it before but kind of forgot about it. Even though I really haven't been around any heli guys, I did know they called you guys rotorheads! At least rotorhead sounds better than planker!

Wade

I don't think the plankers are slow learners, its just that the 8411's have the specs they desire. They learn to put up with a bit more fuss, change gears more often, and their servos for the most part are redundant. You can loose one of the four 8411's on the rudder, or one of the two ailerons or elevator servos, and not lose the airplane. When a heli looses its only collective servo, its gonna hurt! With that said, the egg beaters were suffering more catastrophic failures than the guys flying boards. Did I get the terms right

Eggbeaters, boards, plankers, and rotorheads. That sure sounds like a collection of wild names! I can just see a band using one of those names. Yeah dude, we're the Eggbeaters!

<<...they learn to put up with a bit more fuss...>>

Well, I suppose that's another way to look at it. But the motors and pots were failing, not the gears- at least on the helis.

Anyway, I wasn't trying to start a fixed vs rotary wing argument. Each has it's own considerations.

Steve

There is a lot of pressure on the servo arms on a helicopter. I have actually broken servo arms off on a 30 size chopper during "normal" flight. I learned quickly to use heavy duty servo arms.



Dale

I never thought you were, and being a gearmasher as well as a wood stiffy myself, I guess that makes be a cross dres.., er ah , flier. And that makes me politically correct, so I can neither be proven right or wrong