fheppenheimer

My Feedback: (11)

I posted this in the AIRPLANE/BEGINNERS Forum and got a lot of good advice BUT Question #1 below wasn't answered, so I'm reposting here.

Assume the elevator's mechanical linkages throw 1.5" each way, and that 1" is desired. The clevis is at the absolute top of the elevator control horn (away from the elevator surface), and on the servo arm the rod linkage is three holes out from the servo spindle (so throw could be reduced by moving the rod linkage in two holes closer to the spindle).

1. SUPPOSE THAT, FOR WHATEVER REASON, I DON'T WANT TO OR CAN'T CHANGE THE MECHANICAL LINKAGES SO I WILL NEED TO MAKE MY ADJSUTMENTS ON THE COMPUTER RADIO, FUTABA 9CAP. I see 2 approaches:

APPROACH A: I could use the computer radio's end point adjustment to reduce the elevator throw to 1" -- assume the EPA adjustment needs to be set at 66% to do this. APPROACH B: But I could alternatively leave the EPA set at 100% and instead reduce the throw to 1" by reducing the high rate setting on the dual rates menu from 100% to, say, 66%.

QUESTION: Is there any difference at all between Approach A and Approach B?

2. If I move the servo arm linkage in as far as possible, to the arm's innermost hole (next to the servo spindle), I can get closer to the desired 1" setting. Should I do this before attempting any computer EPA/dual rates adjustments? (Putting the linkage right next to the spindle seems like it would give very little power to the control surface.)

3. Is the EPA set as a % of the regularly available servo arm movement?

4. If I use dual rates to set a high rate of 80% -- does that mean it's 80% of the EPA setting? Suppose I had set my EPA at 90 and the HR at 80

5. Is the regularly available servo arm movement about 40 degrees each way, that is, describing an arc of 80 degrees?


Thank you for any help you can give.

laryboy

My Feedback: (2)

the epa is used to make up and down movement the same( or different if you want ). dual rate adjustment will adjust up and down a percentage of epa movement

bentgear

I thought you got quite a few answers to your questions, it just seems everybody that answered chose a different question to answer.

Ed M.

JohnBuckner

My Feedback: (1)

Always better to set throws as close as possible mechanically before touching any kind of electronic reduction be it: end point, Travel volumn or dual rates. Using excessive electronic reduction to get throws where they need to be will result in reduced servo resolution and centering accuracy. The result of this will be a curious hunting action on the axis which is controlled by that servo. If I have to go lower than say 60% then its definately time to rethink my mechanical linkage.

John

rusirius

In this case, you would be best to adjust the the EPA to the amount of travel you want for a "high" rate... Then adjust the dual/rates down to match the 1" throw on low rates... This way, if for some reason you get in the air (say it's the maiden flight) and you find that your 1" throw isn't enough to control the plane well, you can go to high rates and have say your 1.5" throw... If you use the EPA to knock the travel down, there is no way to "get it back" without reprogramming the radio.... A feat not easily accomplished while trying to fly a plane around that doesn't have enough authority on the control surfaces!

[/quote]
QUESTION: Is there any difference at all between Approach A and Approach B?
[quote]
See above...

Actually it's the exact opposite... There are three effects that take place as you move the linkage FURTHER away from the center of the servo... First, the mechanical leverage of the servo is reduced.... This mean the servo is actually developing LESS torque against the linkage... So the closer you move to the inside of the servo, the MORE torque the servo has to move the surface... The second is that you SLOW the travel time FOR A GIVEN DEGREE OF MOVEMENT of the servo... In other words... If you were in the outter hole and wanted 1.5" of movement, then went to the inner hole and STILL wanted 1.5" movement, the movement would be slowed down because the servo would need to move FURTHER to get the same throw... But in this case, since the throw would change from 1.5" to 1", and the servo movement would stay the same (let's say 30 degrees) the speed will not change.... The last effect is that the "precision" of the servo is better... The resolution that is... The centering and preciseness of the movements will be more accurate the close in on the servo arm you are...

"Normal" movement on a servo is considered 60 degrees... 30 in each direction from neutral... The EPA is set as a percentage of that 30 degrees movement from neutral... 110% would be 33 degrees, while 90% would be 27 degrees...

Yes, dual rates are a percentage of the total throw available AS DEFINED BY THE EPAs...

The servo can move much further, the "normal" (100% EPA) is 60 degrees (30 each way)... You'll find that the servo is actually capable of moving about 180 degrees... (the reason you can set EPAs OVER 100%...)

fheppenheimer

My Feedback: (11)

Bentgear - You are 100% right, I did get quite a few answers in response to questions I asked -- and to questions I didn't ask plus setup tips and advice. All the responses were helpful and gratefully received, and thanks to all. BUT, interestingly, QUESTION #1 is still unanswered!! HELP!

I must not have asked Question #1 in a clear enough way. Maybe I should have stayed in the Beginners forum, but as long as I'm here, let's try again:

THE UNANSWERED QUESTION. All computer radio (Futaba 9CAP) adjustments are now at 100%. The elevator throw is 1-1/2!QUOT! but the maximum desired for actual use is 1!QUOT!. For whatever reason, assume that the specific mechanical linkages can't or won't be changed. THE QUESTION: Is there any difference at all -- for example, in terms of servo resolution, resolution of trim adjustments, torque, etc. -- between (A) reducing the EPA until the 1!QUOT! is achieved (I guess this means that all dual rate settings remain at 100%), or (B) leaving EPA at 100% and reducing the high rate setting on the dual rate menu to reduce throw to the desired 1!QUOT! maximum throw?

Thanks to you and the others who have had the patience to read my questions and took the time and effort to help.

bentgear

Reducing throw using the EPA settings will allow the maximum resolution compared to having a high EPA setting and then reducing the throw via dual rates. This is optimal, however in the real world it does not always work out as practical. However, any reduction at the radio end so that the full servo travel is not used reduces resolution at the servo end. ie. its always better to stay as close in on the servo horn "as possible" to allow the most movement of the servo so that both the radio and the servo stay in sync as close as possible.

Does that do it?

Ed M.

aeajr

My Feedback: (2)

QUESTION: Is there any difference at all between Approach A and Approach B?

rusirius has given you the correct answer for both one and two.

End point is to set the maximum throw I would ever want. Do that first.

If you want the option of having that maximum AND a lower setting, you can use the 9C's dual/tripple rates to set these with EPA having defined the maximum or highest rate setting. Dual rates allows you to switch between that maximum an some lower rate that you might want for a different flying condition.

aeajr

My Feedback: (2)

If that Still does not answer your question, perhaps this will.


Part 1

SETTING SURFACE THROWS - EPA AND ATV
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 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/ATV 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/ATV on the radio.

When you go looking at radios, I encourage you to make sure it has this
feature.

Clear skies and safe flying.

aeajr

My Feedback: (2)

Part 2


DUAL RATES AND EXPONENTIAL EXPLAINED AND COMPARED

by Ed Anderson
aeajr on the forums

Perhaps you are buying your first plane. Or perhaps you are thinking about
upgrading your radio. You read all those feature lists and don't understand
what they do for you. This may help you understand two of the features that
are listed so you can get the radio that will really help you enjoy this new
plane and the electrics, glow, gas or gliders to follow.

Dual rates and exponential allow you to change how responsive the plane is to
your stick movements. If you have them set-up on a switch, you can make these
changes while the plane is in flight. This might be useful as you move from
take-off to normal flight. Perhaps an instructor has a trainer plane she would
like share between new pilots and more experienced pilots. It would be
convenient to be able to change the plane's behavior depending on the pilot
without having to move the linkages.

Changing how the plane responds might be useful if we move from normal flight
to highly aerobatic flight. The large throws for aerobatics might make the
plane "twitchy" or hard to control during normal cruising around. Dual rates
and exponential, when tied to a switch, or some other trigger can be changed
while the plane is flying. They are used for similar reasons but accomplish
the task in different ways.


DUAL RATES

Of the two, dual rates has been around longer and is simpler to understand.
Dual rates are based on changing how much a surface can move. Let's use rudder
set-up to illustrate this.

If your instructions say to set 1" of throw left and right, that would be the
recommended surface movement at full stick movement. When you move the stick
1/4 of the way, you would get 1/4" of rudder movement. At 1/2 stick you would
get 1/2" of rudder movement. You get a direct, proportional and linear
relationship between stick movement and surface movement. At 100% stick
movement you get 100% of the maximum surface movement that you have set. In
this case 100% stick equals 1 inch.

With dual rates we can change to a second maximum at the flip of a switch.
Let's assume you have the standard throw set as the high rate. Then, using a
menu in the radio, you enter a percentage of the high rate to create a low
rate, say 50%. At this setting, when you move the stick all the way over you
will only get 1/2" of surface movement. However stick movement and surface
movement remain proportional. So at 1/2 stick movement we will get 1/2 of the
1/2 inch maximum or 1/4 inch of surface movement. Your rudder movements remain
directly proportional but are now based on a smaller maximum.

We can say that control and response are both proportional and linear. That
is, all the way through the stick movement the rudder will move with us in a
linier fashion. If we move the stick 20% we gets 20% rudder. Move the stick
62% and the rudder will move 62% rudder movement. If we plotted a graph with
stick movement on one axis and rudder movement on the other, the graph would
have all points along a straight line at a 45 degree.

How does this effect the handling of the plane?

Continuing the example above, we have high rate, at full stick movement equals
1" and low rate set at 1/2" maximum rudder movement.

On low rate, for each small movement of the stick, we get less movement of the
tail surface. So, on low rates the plane will be less responsive to the same
amount of stick movement. This may make it easier to fly as we can make
smaller adjustments when we move the stick. We have finer grain control. On
high, we get more movement of the rudder for each unit of movement of the
stick. We get a faster response from the plane for the same stick movement. If
you have ever worked with a precision tool or instrument, this is like having
course adjustment and fine adjustment.

As new flyers often have a tendency to over control the plane, it is not
uncommon to set-up the plane with smaller throws so that the pilot is less
likely to get in trouble by over controlling the plane. Later when she gains
confidence and the right feel for control, surface movements can be increased
to make the plane more responsive. Originally this had to be done on the
plane. Many RTF planes come set-up this way. They are set for mild response
for initial flights. Then the manual explains how to increase the rates as the
pilot gains experience. Some RTF planes now include a dual rate style control
on their radios.

With dual rates on the radio, this can be done at the radio rather than
working on the plane itself. This is much more convenient. Dual rates can even
allow the instructor to take control, flip to high rates and pull the plane
out of a tough situation that the student could not handle. Dual rates can be
very helpful during training.

Of course we can always have it the other way where the low setting is the
"standard" recommended by the instructions and a high setting might be our
aerobatic setting or our 3D setting where we want 1.5" of deflection at full
stick. This allows us to take the plane from mild to wild at the flip of a
switch. However having it set to high might make the plane uncomfortable for
"normal" flying so we switch to low.

OK? You with me so far? If not, go back and read through it again as the next
section is based on your understanding of dual rates. Imagine how your plane
will behave on high and low rates. When you are comfortable then you can go on
to the next section.


EXPONENTIAL

Exponential changes the relationship between stick movement and surface
movement. When using exponential, stick movement and surface movement will no
longer be linear. What does that mean?

Exponential is going to allow us to shift some of the rudder response so that
we get a different amount in the early part of the stick movement as compared
to the later part. Let's stay with the rudder example above.

At 100% stick movement we would still get 100% surface movement, but at 50%
stick movement we might only get 25% rudder movement. This would be like
having low rates on the first half of the stick travel and high rates on the
second half of the stick travel. That would give us a "softer" response around
the center of the stick area, and a faster response toward the end.

How is this beneficial? This gives us finer control when we are making those
typical small adjustments to the plane when we are cruising around, just like
low rates. However if we suddenly want a big surface movement to get out of
trouble, to respond to a gust of wind or to perform that big stunt, we still
have the big surface movements we need without having to manually switch to
high rates. One of the criticisms of using a low rate for "flyability, is that
it limits the pilot's ability to get out of trouble when you are on low rate.

Let's look at that aerobatic or 3D pilot we mentioned above. He has BIG
surfaces and BIG throws set which makes the plane very responsive to small
inputs. If he were to set exponential rather than dual rates, then he could
have a very soft center to the stick. He could make fine adjustments when
needed to but get big response when he needed it and there would be not need
to flip a switch during the flight. Cool?

Let's try some examples that involve numbers. The numbers I am going to use
may not map directly to your transmitter as different manufacturers have
different interpretation of exponential and what the numbers mean, but the
overall impact on flying is the same. They just express it differently.

Let's say that under standard set-up conditions exponential will be expressed
as zero. This means we have the same linear response we have always had. Now,
if I put in -50% exponential, that might mean that for a 50% movement in the
stick I only want to get 1/4 surface movement but when I move the stick to
100% I want full 100% surface movement. An input into the set-up menu of +50%
might mean that for the first half of the stick movement I want more of the
total surface movement. This would make the center area very responsive while
leaving find grain control at the ends of the stick movement. I am not sure
where this would be used, but that is how it would work.

It is important to note that exponential does not imply a sudden change in
rate. Rather it is a smooth change in rate. So the further we move the stick,
the faster we get more stick movement. If we were to plot the percent stick
movement to percent surface movement we would not get a straight line as we
normally get. We would get a curved line indicating that the further we move
the stick the less linear the relationship between the stick and the surface.

This is one of those things you are just going to have to try to fully
understand. At first it seems it would make it difficult to predict how the
plane will behave depending on how much you move the stick. However in fact
most people tend to fly more by input response. You move the stick and watch
the plane. After a while you develop a good understanding of how the plane
will respond to a given stick movement, but you know that it will be
influenced by wind, air speed, and other factors.

I typically set up my controls with about 35% exponential so that I have a
softer response around the middle but gradually faster response as I move
toward the extremes of stick movement. On my radio I have dual rates and
exponential available and I can use them together. I can also set them by
surface.

Computer Radios

While I have seen dual rates on a few "standard" radios I have never seen
exponential. So for this discussion, we are going to assume that exponential
is a feature of computer radios. If you don't have a computer radio, this
might be a reason to move up to one.

Whether you ever use dual rates or exponential is, of course, is up to you.
However I would encourage you to give them a try if you have them. They are
just tools and like all tools, it takes a little while to get the feel of how
to use them. So, if the first time you try dual rates you don't see an
overwhelming benefit, don't walk away. Try different settings.

Some radios will allow you to set different rates to each surface. So, for
example, my ZAGI flying wing slope glider has dual rates set up on the
elevator. Tailless planes like this tend to be very sensitive to pitch, so
under normal circumstances I find I like to have the elevator controls set on
a low rate. However when I want to "crank it up" and get aerobatic that low
rate does not give me the action I want, so I flip the switch and get the kind
of pitch control I want for stunts.

On my 3M sailplane I find I like to have high rates set up for launch where
the plane can get in trouble very quickly and I might need a fast response,
but then switch to lower rates for normal flying. I even have a third rate set
for working thermals which is lower so I can make very find adjustments and
more easily to get the most lift I can out of each thermal.

On my electric planes, I tend to have a mild and wild set-up for cruising and
for stunting.

I have been experimenting with exponential and find that I like it. I could
see myself going totally to using exponential and doing away with dual rates
all together, but that is not the case today. Right now I am having fun trying
out different settings to see what works for me. I encourage you to do the
same.

Clear skies and safe flying!

aeajr

My Feedback: (2)

Part 3

This is what you do BEFORE you start adjusting EPA, exponential or dual rates

FIRST TIME SERVO SET-UP
by Ed Anderson
aeajr on the forums

If I am setting up the plane for the first time, I make sure all the settings in the radio are at zero or 100, whichever is the radio default so that the radio is not providing any adjustments. Trims are centered. If there is a reset adjustment to get everything back to zero, that is where you want it all to be.

All sticks, switches, dials should be in their zero or centered position. throttle all the way to zero.

If you are working with an existing plane and want to "start from scratch" start a new set up on a new memory location so you don't screw up the set-up you have now. Then you know the settings are all at default.

Mount the servos solidly in place. Make sure that control arms can swing with no interference. Get the control rods to approximately the length they need to be to reach the servo control horn when the servo is centered and the surface is at a neutral position.

Now, take the control horns off the servos.

Turn the radio on. (always turn the radio on first)

Apply power to the plane - the servos should all jump to center.

Now put the control horns back on the servo in such a way that when the
surfaces are centered, the control horns are centered along the path they are going to travel as you use them. This may take some trial and error. I usually tape or clip the rudder and elevator at neutral position during this process..

The control arm should be at approximately 90 degrees to the direction of travel when the control rod is attached.


Photos:

See the photo of my Sagitta 600, "servo set-up spoilers down" - red fuselage with yellow wings. The two servos that are side by side are at zero/neutral rudder and elevator position. The small servo to the left is in the extreme end of its travel which is spoilers down for that servo. Ignore that one.


Forward Electronics area - that is my Spirit. Again those servos are
at neutral position. Elevator and rudder are aligned with their surfaces.
Trims are at zero and servos are centered.

Tail control horn detail photo.

Now, you will probably have to adjust the length of the control rods so that
you can put the servo arms back on the servos in this position. See the metal/nylon
ends on my control rods? they screw on and off the rod to allow me to adjust
the length of the rod. I may have another like it at the surface end.

If you have Z bends on both ends, you will have to make new bends, or make a V bend somewhere in the control rod. This is a common practice or small planes. This can then be narrowed or widened. However be aware that a shot to the surface might stretch or compress this V, so check you allignments before every flight.

You must do this with the radio on and the plane on or you can't be sure what
position the servo is sitting in. So, if your rudder is centered the control
arm should just drop right onto the servo and look something like mine, plus or minus a little. Same for all the rest of your servos.

Any adjustments you do from the radio once you have this set should be minor
and only need to be done to make minor corrections in the way the plane flies.

Hope that helped.

fheppenheimer

My Feedback: (11)

Ed - Wow! That's a lot of info, all useful! Bentgear said: !QUOT!Reducing throw using the EPA settings will allow the maximum resolution compared to having a high EPA setting and then reducing the throw via dual rates.!QUOT! Is that true? Why? Thanks to you and to Bentgear, for the help and persistence.

aeajr

My Feedback: (2)

I think he is saying the same thing we are, just expressing it differently. Here is your sequence.

Mechanical first

EPA/ATV next

Rates and exponential last.