• This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn more.

2 Servos for the elevator of FT Airplanes. Does it work?

MarioGdV

Active member
#1
Hi guys. So, I've seen a few solutions for the classic elevator problem: gluing a piece of wood, gluing a metal bar, 3D-printing a plastic piece that reinforces the connection of the 2 sections of the elevator... I tried those examples, but (from my experience) they aren't effective at all. I also tried to use 2 pushrods in one Servo, but you have to put the Servo arm right in the middle of the fuselage, and it's complicated (specially because of the arm rotates), and the result is one section of the elevator gets higher than the other one.
So, I was thinking about using 2 Servos for the elevator, and connecting them in the same channel (like the ailerons), or using 1 channel for each Servo. I guess it works, but I'm not an expert in electronics, so I have a few questions. If I have to replace a 9g Servo, do I have to use 2 4.5g Servos that are half as strong as the 9g Servo? Will the ESC handle so many servos?

Thank you.
 

FDS

Well-known member
#2
I have had great success with bonded light ply across the thin part of the elevator, laminated with strong PVA like gorilla glue white or Deluxe Materials super tacky. I used a 3mm lite ply on my Sportster tail, it’s survived a lot of crashing and looping. You can also cut it out a bit thicker and put a thin wood or plastic “spar” through the foam core, again with a thin coat of white glue on it.
The Bec might be fine with two servos vs one or it might not, depends on the servos current draw and the Bec output. I wouldn’t want the extra weight or sync issues of two servos, not worth it vs making a better job of the elevator.
Another cause of splitting is poor hinges on the elevator, if you put too much glue in the bevel cut and make it too stiff you are introducing torsional load on the thin part as well, making better, more smoothly operating control surfaces is a skill worth learning too. There’s some great posts on hinge techniques on this forum.
 

MarioGdV

Active member
#3
I have had great success with bonded light ply across the thin part of the elevator, laminated with strong PVA like gorilla glue white or Deluxe Materials super tacky. I used a 3mm lite ply on my Sportster tail, it’s survived a lot of crashing and looping. You can also cut it out a bit thicker and put a thin wood or plastic “spar” through the foam core, again with a thin coat of white glue on it.
The Bec might be fine with two servos vs one or it might not, depends on the servos current draw and the Bec output. I wouldn’t want the extra weight or sync issues of two servos, not worth it vs making a better job of the elevator.
Another cause of splitting is poor hinges on the elevator, if you put too much glue in the bevel cut and make it too stiff you are introducing torsional load on the thin part as well, making better, more smoothly operating control surfaces is a skill worth learning too. There’s some great posts on hinge techniques on this forum.

I will try that. I have cut a piece of wood, but it was balsa, so it wasn't really durable. But the problem I had was using hot glue. With the past of the time, the wood started separating from the elevator. Using other types of glue like the ones you said will definitely work (and it's better than the 2 Servos). Thank you!
 

FDS

Well-known member
#4
You want a glue that soaks into the wood. If using FT board I would remove the paper in the area you are glueing down the wood or whatever. Popsicle stick will work too, it’s pretty tough. Here’s my Sportster tail.
image.jpg
 
#5
Using two servos works fine on a Y cable just as long as they are the same model (both have to be oriented in the same direction or the arms on opposite). I usually calculate each 9g servo at about 300ma, so if you have 5x servos (1 rudder, 2 aileron, 2 elevator) that would be 1500ma or 1.5 amps from your BEC. Most BEC's integrated into ESC's are 2a or greater - most of mine are rated at 3a. The Receiver will also take some power, but that's probably more like 100-150ma unless you have a fancy one that has a gyro/auto-leveling or telemetry (sends data back to your radio to report battery power, speed, etc).
 

Merv

Well-known member
#6
I use a torque rod to connect the elevator halves. Make it from the wire from a marking flag, the kind the utility company used to locate lines. You can buy them at Lowes or similar, $10/100, if you live near a farm supply store, get tile fags, same thing only longer. The also make great servo pushrods.
 

Merv

Well-known member
#8
@Merv How do you secure the rod to the foamboard?
On a single layer. Cut a small groove, trial fit by pressing the wire in, hot glue and press the wire in again. Lately I have been using double layer FB elevator & rudder. Then I install the wire between the two layers before I laminate them together.
 

FDS

Well-known member
#9
Does that cause problems with weight added to the tail? I suppose you could use 2 layers of 3mm board?
 

Merv

Well-known member
#10
Does that cause problems with weight added to the tail? I suppose you could use 2 layers of 3mm board?
No significant problems, just move the battery slightly forward.
It would be a problem if you were out of room for adjustment.
I'm using Adams or Ross FB, if you had heavy FB, it could be a problem.
 

FDS

Well-known member
#11
Thank you, that is all very helpful. The Sportster I used in my picture was very tail heavy, I had to stretch the nose by 50mm and run the battery right forward to balance it. It was done in heavy UK board tho, before I realised how much heavier it is.
 

Merv

Well-known member
#12
I have also lengthen the nose (1-2 inches) of several FT planes to get them to balance. That was before I doubled the rudder & elevator. This does give me plenty of room to adjust CG if I need to.
 
#13
It depends on what the issue is I guess. I save expired gift cards, old credit cards etc and cut kind of a dog bone shape out of them. Then I hot glue them to the elevator. That keeps both halves singing the same tune. Sometimes the control rods are too long and they flex when the servo turns. This can give poor to zero performance. Two ways to solve that problem. One is to tape a piece of bamboo skewer to the control rod to stiffen it up some. Or two, run the control rod through a closed zip tie that you have glued off about half way between the servo and control horn. I have used both methods with success to fix control rod issues. Lastly, make sure the foam board hinge does not have too much glue on it, limiting it's travel. A little sanding in the right spot can make all the difference!
 

sprzout

Knower of useless information
Mentor
#14
It depends on what the issue is I guess. I save expired gift cards, old credit cards etc and cut kind of a dog bone shape out of them. Then I hot glue them to the elevator. That keeps both halves singing the same tune. Sometimes the control rods are too long and they flex when the servo turns. This can give poor to zero performance. Two ways to solve that problem. One is to tape a piece of bamboo skewer to the control rod to stiffen it up some. Or two, run the control rod through a closed zip tie that you have glued off about half way between the servo and control horn. I have used both methods with success to fix control rod issues. Lastly, make sure the foam board hinge does not have too much glue on it, limiting it's travel. A little sanding in the right spot can make all the difference!
You could also use a coffee stirrer/straw as a guide; it'll keep the control rod from flexing too much.
 

Hai-Lee

Old and Bold RC PILOT
Mentor
#15
I do not know if this will help at all but to make a quick and effective torque rod I just use a skewer and "Crack" it so that it assumes the shape I require. When of the correct shape I cut a 3mm channel in the FB to house the torque rod and epoxy it into place/position.

Have used this setup on some planes that have lasted years and been subject to some serious crashes all without a single elevator separation issue. Whilst it does add a little weight it is far lighter than an equivalent torque rod made from wire!

What works for me!

Have fun!
 

BATTLEAXE

Well-known member
#17
I will try that. I have cut a piece of wood, but it was balsa, so it wasn't really durable. But the problem I had was using hot glue. With the past of the time, the wood started separating from the elevator. Using other types of glue like the ones you said will definitely work (and it's better than the 2 Servos). Thank you!
One thing that I have done especially on the minis where there isn't a lot of meat to work with on the elevator surface is to not only cut the bevel into the stabilizer, (which means you need to modify the relief notch in the rudder to get the elevator to get full travel as it passes through the rudder), but to laminate poster board on both top and/or bottom of the elevator right over top of the paper. Either by partially or fully covering the elevator surface using a quality spray adhesive. I found that this really strengthens the DTFB substantially no matter where you use it. I've done this this on the under camber tips of the wings to strengthen them for the event of doing cartwheels on the ground. I hope this helps