SETTING SURFACE THROWS -
End Point Adjustment or Adjustable Travel Volume
by Ed Anderson
aeajr on the forums
After you have built your model and installed your electronic
components, you will want to set your surface throws. If they are too
large, the model will be overly responsive and hard to handle. If they
are too small, you may have not adequate control of your model.
Mechanical Adjustment
Regardless of what kind of radio you have, I feel it is always best to
do your first adjustment mechanically, at the servo and control horns.
The simple rule is that the further the control rod is from the hub of
the servo, the more movement you will get on the control surface. The
opposite applies to the control horn at the surface. The closer you
move the control rod to the control surface the more movement you will
get from the surface. By making a combination of changes at the servo
and the control horn, you can maximize or minimize your control throws.
Let's assume you have your control rod at the outermost hole on the
control horn of the servo, and the control horn hole closest to the surface.
This
will be your max throw position. If we stay with the rudder as the
example, measure the throw of the rudder when you move the control stick
all the way to one side. How does this compare to the recommended
throws in the instructions. If they recommend 1 inch left and right and
you have 1.5 inches, you want to reduce the throw or your model may be
too responsive.
In this case you can move the control rod at the servo and/or the
control horn to minimize the movement of the surface. Let's say you
move 2 holes up on the control horn and one hole in on the servo and you
hit the 1" mark, you are all set. However I have found that sometimes I
can not hit the desired throws. Either the movement is too large or too
small. Now what?
Staying with the mechanical approach you will either have to lengthen
the arm of the servo if you are trying to get more throw, or lengthen
the control horn if you are trying get less throw. While there may be
some formula for doing this, for the most part this is a trial and error
process and sometimes it doesn't really yield the desired results.
ATV and EPA
Today, all computer radios and many standard radios have End Point
Adjustment, EPA, or Adjustable Travel Volume, ATV features. Essentially
these are the same feature by different a name. They allow you to
control how far the servo arm moves when you give a full stick command.
This allows you to adjust how much surface movement you get by using a
dial, or by entering numbers into a menu. For convenience I am going to
call this feature EPA from here on, but you will understand that EPA and
ATV are essentially the same.
Mechanical First Please
First, I encourage you to make mechanical adjustments first, within the
limits of your standard servo and control horn. Use ATV and EPA after
you have done this. You will get the best service out of your servo if
you do the mechanical adjustments first.
Staying with the rudder as our example, you have gone to the innermost
hole on the servo arm, and the outer most hole of the control horn but
you still have to much throw. Using EPA, you go into the menu, or turn
a dial that controls how far the servo moves in response to a full throw
command. In other words, when I move the rudder stick all the way to
the left, how far do I want the servo to rotate in order to give me the
right amount of surface throw. On many radios this is expressed as a
percentage with 100 being full movement by the servo and 0 being no movement
of
the servo.
When I was setting up my ZAGI slope wing, I was planning to use standard
servos and a three channel standard radio that did not have EPA as a
feature. No matter how I moved the control rods, I had way too much
movement on the elevons. This was going to make my plane very very
responsive; too responsive. I had to reduce the throws. I could have
moved to larger control horns on the elevons, but I felt this would create
more
opportunity for damage due to large horns that stuck out far from the
surface.
Fortunately I own a computer radio, so I changed the receiver to one
that was compatible with my ZAGI wing and my computer radio. I had
moved the control rods to minimize the control throws already. All I
had to do now was make some adjustments from the radio to get the
control throws I wanted. The operation took only a few minutes.
Summary
I have found that EPA/scriptTV is a very very valuable and useful feature.
Without it my models would be hard to adjust and I would have to go
through some difficult or inconvenient manipulations of the servo horns
or control horns. It is so much easier now with EPA/scriptTV on the radio.
When you go looking at radios, I encourage you to make sure it has this
feature.
What you need to know about receivers:
http://www.rchangout.com/forums/radio-electronics-motors-and-accessories/t-what-you-need-to-know-about-receivers-12151.html
Clear skies and safe flying.
Best regards,
Ed Anderson
aeajr on the forums
Long Island Silent Flyers |
Radio Set-up - EPA or ATV
Forum Locked
Posted - 09/20/2006 : 12:58:06 PM
