Curious Servo Arrangement
 

OK, cruising the RCU classifieds, I cam across this picture. Can someone tell me what the two servos on the right do and why they are configured that way?

http://www.rcuniverse.com/market/ite...74-10-3903.jpg

I didn't want to email the seller, as I have no interest (actually no cash) to by this awesome plane, but I am puzzled by this servo setup.

I know the servo on the left is to control the RAM lighting system.

RE: Curious Servo Arrangement
 

Looks like dual elevator servos driving one pushrod. Doubles the torque and if one fails, the other works with half the throw.

RE: Curious Servo Arrangement
 

It would help if you could point us at the classified, or if you could tell us the plane's type (flying wing/V-tail/standard/etc).

My initial guess is that it is a manual mix for flaps or something... when flaps are deployed it also activates the right most servo, causing the elevators to change the neutral position so that elevator input is not required with flaps deployed.

Unfortunately, that leaves the very middle servo unaccounted for. The one with two control cables attached is rudder (with one control to the rudder, and the other to the tail-wheel...).
Maybe the tail-wheel is retractable, and that is why there is the servo behind the rudder servo ....

gus

RE: Curious Servo Arrangement
 

I found the classified...

http://www.rcuniverse.com/market/item.cfm?itemId=44815

The plane is pretty well kitted out. I think I am right with my initial guess though. Retractable tail-wheel, and the two servo's on the right... with the flaps down, the right most flap moves to where it is now, with the flaps up, it moves to the opposite position. I am guessing the flap servo's are connected with the right-most servo by a "Y" harness. The elevator controls just the left of the two servos.

as a result, there is a manual/mechanical mixing of the flaps to elevator.

gus

RE: Curious Servo Arrangement
 

Gus,

If you connect your flap and elevator servos together like that, trying to move one independent of the other would just cause them to fight each other to stay on their individual set points. Looking at the description, I have to agree with Flypaper on the dual elevator servos. Looking on the pics, you can see the individual flap servo for the inboard flaps mounted beside the engine nacelle.

Its a neat way to do dual elevator servos, though I bet its a real PITA to get set just right.

Duke

RE: Curious Servo Arrangement
 

Actually, I know now that you are correct ....

If you look carefully, the "coupling" control arm on the servo wheels is not anchored on the right-hand servo. It looks like it just slides through the "ezi-link". The other two links are non-slipping ball-joints. This is what lead me to the idea of the flap-mixed elevator. It also makes the dual-elevator process a non-binding one. Quite neat. I was mislead by the servo's being at different places though, but when in use they will move in tandem.

The classified description confirms the giant-scale servos are the two 134's on elevator. I initially did not get a good impression of how big this plane actually is (none of the pictures have a good scale reference). It is a 114" wingspan plane which is almost 12' It's huge. Makes the "standard" size servos look like minis...

gus

RE: Curious Servo Arrangement
 

Gus,

If you are right about the horizontal arm sliding through the quick link, I'd be real nervous about the metal to metal contact as a possible RFI source. Your theory seems the best though. I hadn't considered that the servos are probably out of position with each other and that they probably do move together through the whole range of movement.