dual elevator servo
 

Hi,
I am considering to replace my current elevator pushrod ( which is very slopy) on my 90 size pattern,
by dual servo on the tail, the problem is that the fuse is very thin and i can't put two servo's back to back ( even mini servo's )

is that setup going to be ok ? is both linkage travel will be equal ?

Thanks,

RE: dual elevator servo
 

i am trying to upload the image again

RE: dual elevator servo
 

Hello,
If you have a good radio system you will the possibility to adjust the 2 servos travel and end points.
Still after lot of experience I am not sure what is better. Each way has it own advantages and disadvantages. I am tending to think that a single servo is better. Still CG location is also a consideration.

Single Servo
+ Travel is always equal
+ Less parts
+ Simple Radio Setup
- No redundancy
- On long model trimming ,might change on hot day

dual Servo
+ Redundancy
+ Adjustment flexibility
+ Can use small servo (Midi)
+ No trimming changes due to weather
- More part to fail
- Additional channel and more complex Radio setup
- Long wires from RX to Servo

Amram Leshed
F3A Israel

RE: dual elevator servo
 

Thanks Amram,
I have RDS8000 2.4GB which include the option of dual elevator.
in that particular model i have no problem with CG as it's nose heavy.
my concern is about the possbility of unequal throw since both servo's are not back to back. do you have expirewnce with that particular setup?

RE: dual elevator servo
 

Maybe that arrangment will be better choise any comments ?

RE: dual elevator servo
 

If the fuse is thin in the rear, it may be possible (depending upon the design) to cut a hole in the covering and glue in some light ply servo bays inside the fuse, offsetting the bays so that the servo bodies can overlap a bit.

Of course, one servo inside the fuse with a split pushrod certainly looks a lot cleaner!

RE: dual elevator servo
 

Hi
I go for redundancy all the way. It is worth it and independent servos are a doddle to set up and you stand a far better chance of getting your plane home with as much redundancy as possible,

Mike

RE: dual elevator servo
 

Thank you all, but still i am not sure that it answer my question about the whether there is any issue by installing the servo's per the attached pictures.

RE: dual elevator servo
 

i refer to any geometric issue which may lead to unequal throw. i want to avoid tx adjustment as much as possible as it will affect each servo spead. also about the redandancy if one channel act as slave is there any chance that it won't work independent in case of some failure on the master ?

RE: dual elevator servo
 

Hi
I think that as long as you keep the 90 degree angle at the servo and the surface( at neutral) having them directly back to back wont matter. My preference if you are really tight for space is to have them staggered. One further forward than the other on opposites sides. One thing I would watch is to have the pushrods very stiff as the longer of the two will be prone to more flexing then the shorter.

That is my two pence worth.

Mike

RE: dual elevator servo
 

Actually you will introduce differential toward the end of the servo throws as the angle will be different at that point to the control horn. Its best to have the servo's the same distance and angle from the respective control horns.

RE: dual elevator servo
 

I think the second option is the way to go (one servo in front of the other) as it will have less efect on differnt throws, and it should be quite easy to adjust on the radio, the geometry will be sligtly different, but much better than with one servo on top of the other.

Mundo

RE: dual elevator servo
 

selnekav,

As you can see by the pic, there is an open bay rear of my elevator servo. On the other side the other elevator servo is in that open bay 2 1/2" behind the other elevator servo. It is mounted right under the rudder servo. I have no problems with this set up and both elevator servo have the same traval.

RE: dual elevator servo
 

Thanks !

i will install it on the same level like on zippi model.

RE: dual elevator servo
 

One last consideration: mount the servos so that the output shaft are as close as possible (the servo in the front of the airplane with the output shaft to the rear an the servo on the rear with the output shaft to the front) so that you minimize the difference in throws

Mundo

RE: dual elevator servo
 

Is it possible to stack the servo's on top of each other and have the control arms pointing towards each other? this would eliminate the linkage distance irregularities along w/ the angle problems

RE: dual elevator servo
 

I would just rework your existing one servo/push rod set up or replace it with something better.
Many people have been sceptical to the two servo set-up for pattern flying for many years now and many top pilots have stayed with one.
Even those that have gone the twin servo route are now questioning the so called advantages and indeed many are returning back to basics.
Stay ahead of the crowd.... Re work what you have.

RE: dual elevator servo
 

Just my opinion,but I have been flying competition F3A for a long time now.....
Obviously it's ideal to have absolutely equal movements on separate elevator halves, but as long as they're close(say within 1.5mm in each direction),I seriously doubt if many flyers would ever be able to tell,or demonstrate, any flying discrepancies.
And,most importantly, total loss of elevator function, is the one flying control that is virtually certain to result in a written-off model-if you lose one half you'll be surprised how little rolling effect it has-it just reduces the pitching power available.

RE: dual elevator servo
 

Reminds me of the time I broke the down steel cables in one of my earlier designs. The up cables were fine. The model did an extraordinary dance of flying then zooming straight up...flying then zooming up. I realized that I could somewhat control the thing by bumping throttle at the right time or dropping throttle to idle at the right time. Managed to slowly turn it back toward the field and land the thing in a ditch full of water. That was lucky. Timing it just right, I managed to make it pancake in and actually suffered no other damage. No dilusions of extraordinary flying skill here....just dumb luck!!! LOL

I have never used steel cables on my elevator (or rudder) since. Kevlar cable is the only stuff I use for control surface rigging

MattK

RE: dual elevator servo
 

If the tail width is too small to get the servo's back to back then having one above the other on opposite sides is the way to do it, just ensure the servo arm holes (one pointing up, one pointing down) are in the same place relative to the elevator, that way you can have parrallel push rods both sides, when I have had this problem on a slim fus I have used Hitec HS5245MG's which are smaller than standard servo's and allow back to back mounting and both arms pointing in the same direction.

Mike

RE: dual elevator servo
 

""""No matter what anyone says 100% is the maximum you can get. """"


Hmmmmm!!! I certainly hope that statement is wrong. I have no intention in giving back the return on investments that yielded more than 100%. LOL

MattK

RE: dual elevator servo
 

The only way to have the exact same travel at any given time on two servos is to have either a new generation radio or a JR Matchbox, if you have two use a radio mix to use two servos you can actually adjust the sub trim and EPA or ATV to center and match de travel on both servos, but if you lok closely, as the servos moves one will get to the end point before the other, then this has to be corrected on the mix so the slow servo can match the fast.

This slow servo, is not actually slower, but the servos moves in sequence, so the elevator will be the second to move and the aux elev will be the seventh (AUX 2), on the new radios this is not the case, 12MZ,14MZ, 12X, ie.

On the match box you can adjust the independent EPA and SUBtrim, but there is only one single input signal coming from the receiver, so this speed problem goes away.

In two servo application this is the all the choices and only choices to make it work.

Regards

RE: dual elevator servo
 

This is the only thing that I have found to be above 100% and its fantasy. LOL

RE: dual elevator servo
 

Son, you haven't lived

RE: dual elevator servo
 

Perhaps not, but if you click on the picture you will find she does, Oh and by the way I am over 60, so if I am your son??????

Mike