servo linkage hookup

[bobbiejane]

Am new to plane kits since I began flying helicopters and was not sure which holes in the flap horn, aileron horn and servo horns to secure the rod linkage. There are 4 holes in each horn, which should I use?

[fhhuber]

RE: servo linkage hookup

Select holes to get the desired throws.

Generally I try to use the furthest hole out at the control surface, then about the same distance from pivot at the servo as a start. The further out from the pivot the lower the load on the pushrod, but the further the pushrod has to move.

[Konrad]

RE: servo linkage hookup

Welcome,

May we ask what model you are trying to set the flaps up on?

As was mentioned earlier try to set up your servos so that you give them, or any actuator, the most mechanical advantage and still have the desired motion.  Set up the linkage so that you are using 100% to120% of the servo’s motion. This will give you both power and high resolution at the cost of speed.

You shouldn’t have to worry about this with most of the products sold by MotionRC, but there may come a time when you need to be aware of mechanical differential (Ackermann effect).
https://en.wikipedia.org/wiki/Ackerm...ering_geometry

I use this all the time in setting up my ships. This is done by setting the servo and/or surface horn so that a line drawn from the pivot (servo or hinge) to the pushrod mounting hole is not at 90° to the pushrod
I’ve attached some drawing and photos. The photos are of my glider most are of the Multiplex Cularis.
I hope you can see that as the servo arms goes forward (to the left) for the same amount of servo rotation there is less linear pull on the pushrod. This adds torque. At the same time the horn (on the surface) is becoming closer to 90° to push rod this adds leverage. This torque and leverage are needed as the flap is deflected more and more toward vertical straight down as the air loads will be great at 90° deflection. 
[hr]
Sorry forgot to add some other drawing and photos that might help. I hope they don't confuse the issue. These are of an aileron used on gliders where they are used in crow braking.

All the best,
Konrad

[fhhuber]

RE: servo linkage hookup

Yes... on the helis you worked very hard to make sure the pushrods were 90 deg to the servo arms when the stick is at center... but on fixed wing, you don't always want equal throw both directions.

******

You actually did this right by learning heli before fixed wing, since fixed wing can make you lazy about the throttle and rudder. You can't get away with that when flying helis so you learn the good habit of managing rudder (tailrotor/yaw) for every turn.

Generally 3 or 4 flights to learn that a fixed wing can't stay in the air without forward airspeed... then you're fine.

[Lon]

RE: servo linkage hookup

Welcome,

May we ask what model you are trying to set the flaps up on?

As was mentioned earlier try to set up your servos so that you give them, or any actuator, the most mechanical advantage and still have the desired motion.  Set up the linkage so that you are using 100% to120% of the servo’s motion. This will give you both power and high resolution at the cost of speed.

You shouldn’t have to worry about this with most of the products sold by MotionRC, but there may come a time when you need to be aware of mechanical differential (Ackermann effect).
https://en.wikipedia.org/wiki/Ackerm...ering_geometry

I use this all the time in setting up my ships. This is done by setting the servo and/or surface horn so that a line drawn from the pivot (servo or hinge) to the pushrod mounting hole is not at 90° to the pushrod
I’ve attached some drawing and photos. The photos are of my glider most are of the Multiplex Cularis.
I hope you can see that as the servo arms goes forward (to the left) for the same amount of servo rotation there is less linear pull on the pushrod. This adds torque. At the same time the horn (on the surface) is becoming closer to 90° to push rod this adds leverage. This torque and leverage are needed as the flap is deflected more and more toward vertical straight down as the air loads will be great at 90° deflection. 

[hr]
Sorry forgot to add some other drawing and photos that might help. I hope they don't confuse the issue. These are of an aileron used on gliders where they are used in crow braking.

All the best,
Konrad

Great info/guidance Konrad!

[bobbiejane]

RE: servo linkage hookup

Sorry forgot to mention I am setting up a 1450mm FMS P51D v8 mustang

[Konrad]

RE: servo linkage hookup

Per the FMA manual Page 7 Fig. 8 & 9 for the servo use the 3rd hole on the arm form the center of the servo. Use the 4th hole (nearest the control surface) on the surface control horn. I know it is a bit confusing as FMS in numbering the holes in opposite directing with the arms and horns.

All the best,
Konrad