Servo geometry ?
 

I am doing the final setup of my control surfaces and I have a question
about the servo linkage geometry...

I will use the elevator as an example:

With the servo arm set to 1.25" from the center of the servo,
and the elevator linkage set to 1.25" from the hinge line to
the linkage point (a 1 to 1 ratio) I have to adjust my radio
as follows....

High rate 88% Low rate 25% - It seems to me that I am loosing
a lot of servo resolution doing it this way.

Now if I set the servo arm to 1.15" to maintain a 1 to 1 ration I
need to move the elevatro arm in aslo to 1.15". It helps a little,
High rate now at 94% and low rate around 30%.

Am I mistaken that I should be trying to keep a 1 to 1 ratio on the
servo arm and elevator linkage?

What rates are you guys getting?

I would think this would be ever worse with the 1.5" arms some of you
are using?

Thanks for the help

RE: Servo geometry ?
 

What you want is to use the lowest ratio of servo arm to control horn length that you are able to use and still have it fly the way you want. 1 to 1 is not a magic ratio. The shortest servo arm and longest control horn that will get the job done is what you are looking for.

Pro pilots will first set up their ATV to its maximum to get the most travel out of their servos. Then set high rates to 100%. Now adjust the mechanical ratio to give you the throw that you want on high rates and not a degree more.

Now that you have the best possible mechanical setup that will give maximum push/pull power, adjust the low rate to whatever you want that to be by tweaking the transmitter.

By doing it this way you put the least load on all the parts like pushrods, servo gears, etc. Doing it the other way is just "leaving money on the table", you are stressing things more than tehy need to be stressed.

TF

RE: Servo geometry ?
 

anyone try the new line of dubro servo horns?

RE: Servo geometry ?
 

Thank's Tom, I understand now.

RE: Servo geometry ?
 

I just finished setting up the control throws on my 28% WH Extra 300LX and I use a homemade protractor-like tool to measure the degrees the surface is moving. On the elevators, to continue with your example, I am using the hole 1-1/4" from center on the servo arm and the length of my control horn is 1-1/4" from the hinge-line to the center of the pivot point. This gives the elevator pushrods perfect geometry...the pushrod is 90 degrees off the servo arm and the line between the servo arm pivot point and the hinge-line on the elevator.

I can get 60 degrees of throw giving it everything I've got. I am going to set 45 degrees up and 50 degrees down elevator in the 3D flight mode. That gives it a little buffer before the elevator hits the stops.

From setting up the geometry on helicopters, it is extremely important to have the pushrod 90 degrees to the servo arm and the control horn. This is not possible on the ailerons on the 28% WH Extra and get the recommended high rate throw.

Edit: It is only off by a little bit, but that's rough for us perfectionists. ;)