These articles were submitted to the K-FACTOR by former Dist. 2 VP Bob Richards.
JANUARY 1995
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Futaba 7UAx radio setup.
This following information covers the Futaba 7UA family, including: 7UAP,
7UAF, 7UAPS, 7UAFS. This month I will talk about ATV, Dual Rates, and how
they interact. This information is not intended to replace the manual, just
supplement it.
ATV (adjustable travel volume) is used to set the maximum amount of travel
of a channel. When adjusting the ATV value, remember that there are two
settings per channel, one for each direction of servo travel, ie: up and
down, left or right. Access to both numbers is done by moving the stick/knob/switch
being programmed. For instance, after selecting the ATV screen and moving
the pointer to the desired channel, you will have to move the control for
that channel from one side to the other to get to both numbers.
I prefer having my ATV set for near maximum throw, making any initial changes
in control throw by changing the mechanical linkage on the plane. The reason
for this is that if you reduce the throw by using ATV, you are reducing
the precision of the entire system. If you cut your ATV (or DR) throw to
50%, you are now using a 512 (or less) radio, instead of the 1024 positions
the radio is capable of doing. Also, you are wasting half the torque and
precision of the servo, although the control response will be quicker (less
distance for the servo to move).
I do use ATV initially to determine just how much throw is needed to perform
the pattern. I may fly a dozen flights, doing every maneuver (including
snaps) and adjusting the ATV until I determine the maximum throws needed.
Then, I measure the maximum control surface deflection. I set all my ATVs
and DRs to their maximum (110% on the older radios, 120% on the Super 7)
and adjust the mechanical linkage until I have the same throw as previously
measured. Err on the side of more throw. Then, I fly the pattern some more,
making fine adjustments with the ATV.
Whether to use DR or not is a matter of preference. I don't use dual rates
unless absolutely needed, except on rudder. I always set my rudder throw
to max for stall turns, and set my low dual rate to allow me to hold knife
edge with full rudder stick deflection. I presently use elevator dual rate
to increse throw for spins.
It is important to realize that a change in ATV affects every other function
relating to an individual channel. For instance, reducing the ATV setting
of channel 2 (elevator) will reduce the travel on both sides of the dual
rate switch, and also reduce the available travel when the snap switch is
engaged. So, once an airplane has been setup, it is wise to make minor changes
in travel with the dual rate instead, unless you need to change the throw
in only one direction. The DR setting affects the total throw in both directions,
while ATV allows you to set each direction independently, ie: more down
than up, or more left than right.
Another thing worth knowing about ATV and DR is how they apply to trim authority.
Trim authority (the amount the surfaces move with a given trim lever movement)
increases or decreases with a corresponding change in the ATV. Cut the ATV
from 100% to 50%, and the trim movement is also cut in half. If you leave
the ATV at 100%, but cut the travel by using the DR setting, the trim travel
does not change. For instance, using my Ace Datamaster to measure the pulse
widths, here are some numbers from my four year old Futaba 7UAP:
(center was always 1.52ms)
ATV 100%, DR 100%
Full up = 1.95
Full down = 1.10
Trim up = 1.64
Trim down = 1.39
ATV 50%, DR 100%
Full up = 1.73
Full down = 1.31
Trim up = 1.58
Trim down = 1.46
ATV 100%, DR 50%
Full up = 1.73
Full down = 1.31
Trim up = 1.63
Trim down = 1.40
Notice that the total throw is the same whether the DR or ATV is used to
reduce the throw, but the trim throw is directly affected by the ATV setting,
but not by the DR setting. For the purposes of pattern flying, you are MUCH
better off having a very small amount of trim throw, otherwise you my have
difficulty trimming the plane to hold straight and level flight.
The following is just for comparison:
ATV 110%, DR 110%
Full up = 2.04
Full down = 1.02
110% is the max for both DR and ATV on the older 7UAP radio. The newer "Super
Seven" allows you to go 120%, but (If I remember right) only on the
first four channels.
If you have a Futaba 7UA radio, check your ATV and DR settings for every
channel. If you have an ATV and/or a DR (high side) that is less than 75%,
the precision gain by going to 100% or more, and a corresponding change
in the mechanical linkage, may be worth the effort. The decision to change
it is entirely yours, however.
Next month (if I get a chance) I will cover the ins and outs of two channel
aileron setups. For instance, you CAN have aileron differential AND flaperons,
you just gotta know how! Later on, I will cover the topic of mixing out
roll and pitch coupling.
FEBRUARY 1995
**************
Last month I began talking about the Futaba 7UAP line, and after re-reading
it I decided that I probably need to back up and explain a few of the concepts
pertaining to computer radios.
First of all, let's discuss basically how a computer radio works. The computer
chips in our radios (and most computers, for that matter) are digital, which
means that they deal with numbers. The stick positions, on the other hand,
are analog (linear, or infinitely variable) and must be converted to a number
before the computer can deal with it. The voltage from the stick pots are
converted by an ADC (analog to digital converter) and the digital number
is then read in by the computer. This process is where the concept of "steps",
or "1024 technology" comes into being. The computer processes
the stick positions and sends this information to the receiver/servos as
10 bit numbers, or a value from 0 to 1023.
Futaba often refers to their computer radios as "1024 stepless",
which is a misnomer. What they are trying to say is that 1024 steps makes
their system _seem_ stepless. What this really means is that the radio can
command a servo to go to a MAXIMUM of 1024 positions. Understanding the
concept of "steps" will help you to understand the best way to
program your radio and get the most performance from it.
I made some measurements with some equipment available to me where I work,
and here is the information I discovered:
(Measurements were taken using a Futaba 7UAP and 7UAPS transmitters, FP-R129DP
receiver, and an HP 5314 Universal Counter. Some figures rounded slightly.)
Terms used:
ATV: Adjustable Travel Volume
DR: Dual Rate
7UAP: refers to the older 7UAP/7UAF radios.
7UAPS: refers to the newer 7UAPS/7UAFS "Super Seven" radios.
Channel used: 2 (elevator)
Measured center = 1.525ms
Minimum pulse width change = 1.171us (further referred to as "system
step")
Maximum pulse width range = 1.198ms (2.120 to 0.922)
1023 x 0.001171 = 1.198ms
Setup: ATV 110%, DR 110% (Max on 7UAP)
1 Subtrim step = 1.05 system steps
1 trim lever notch = 4.9 system steps
Full stick travel: 1.023 to 2.043ms (870 system steps)
Full trim travel: 1.396 to 1.651ms (218 system steps)
Setup: ATV 30%, DR 110%
1 Subtrim step = 0.25 system steps
1 trim lever notch = 1.35 system steps
Full stick travel: 1.388 to 1.663ms (235 system steps)
Full trim travel: 1.487 to 1.556ms (59 system steps)
So, what does all of this mean? Basically, the radio has a finite resolution
that it is capable of, but only if the ATV and DR are set to their max.
As you decrease either the ATV or DR, the resolution (number of positions
the system can resolve to) decreases with it. In the above case (ATV 30%)
you have only 235 steps, or 1/4 what the system is capable of. I should
note here that I flew an Ace Micropro 8000 for a short while, and found
out that at best it was a 256 radio. I COULD tell the difference!! My thumbs
could not tell the difference, but the lack of resolution caused the plane
to be difficult to trim for level flight.
Now, lets talk about servo resolution. While I don't have any measurements
to report on (not yet) we can talk in general terms about servos and how
they function. There is no such thing as a perfect servo. Servos have several
characteristics that limit their resolution. One is deadband, or how much
the input signal can change without the servo responding. Another is backlash,
or how much slop is in the gear train. Yet another is "holding torque",
or the how well the servo moves to a desired position under a load. The
better the servo, the less will be the deadband and backlash, and the higher
the holding torque.
The effect of each and every one of these characteristics can be minimized
by using the full travel of the servo. For instance, if you have a radio
set up to only move a servo 30 degrees, and the servo has 1/2 degree of
deadband, then the deadband alone can account for a 1.67% error. Couple
this with the fact that you are working with only 235 steps in that 30 degree
range, and you can add another 0.4% max error for a possible total error
of over 2%. (I won't bore you with the formulas here, trust me.) For a given
control surface deflection, a servo has three times as much power (mechanical
advantage) when set to travel 90 degrees as it does when it is set to go
only 30 degrees, so the servo will work less and be able to move the control
surface closer to the commanded position. And we haven't even begun to talk
about linkage slop! The only downside to using the full travel of a servo
is the transit time.
So, if you are still reading this and I haven't bored you to death yet,
here are my recommendations:
- Use 5 cell (nominal 6v) battery packs to speed servos and increase torque.
- Use high quality control linkage hardware.
- Use long servo arms, and corresponding long control horns, to reduce the
effect of slop in the linkage.
- When possible, use pull-pull cables to remove control linkage slop.
- Program the system to use the full travel of the servos, ie: max ATV and
DR. Reduce control surface throw the old fashioned way: adjust the mechanical
linkage.
- Use good quality, high speed servos to compensate for the increased transit
times with the high ATV and DR settings.
Something else that I have done to my transmitter is to add a 5k resistor
to each end of the trim pots. This cuts the trim authority in half, but
makes smaller trim changes possible. I won't describe how to do this because
I don't want everyone going inside their radio and damaging something. If
you are knowledgeable and proficient at electronics you will be able to
figure out how to do it anyway.
Other interesting facts:
- When using programmable mixers, the ATV setting of the source channel
does not affect the destination channel. The DR setting and the mix percentage
both affect the destination channel.
- The trim lever AND subtrim authority are affected by the ATV settings.
- An unused channel (6 or 7) can be mixed into the flight channels and used
as either coarse or fine trim adjustments, depending on the mix percentage.
Use 3% mix for fine adjustment, one notch equals slightly less than one
system step.
- (7UAP) Full stick travel @ 110% ATV and 110% DR roughly equals 870 system
steps. If full trim is included, then all 1024 steps are used, but with
lost steps at ends (roughly 64 total). Full stick throw = 870 steps, full
trim throw = 218 steps, total = 1088. 1088 - 1024 = 64 lost steps.
- (7UAP) Mix a channel into itself to get more movement with the stick,
(max +16% mix) but with more lost steps at the end if including trim.
- (7UAPS) The max ATV settings for the first four channels are 120%, the
rest are 110%. The max DR settings are 120%. If using two aileron channels,
you should not go over 110% ATV on channel 1 since the other aileron channel
(either 6 or 7) is limited to 110%.
- (7UAPS) When ATV and DR are set to 120%, stick movement gives the entire
1024 resolution, but only if the trim lever is centered and subtrim setting
is 0. If the trim lever is not centered, then there will be lost travel
at that end of the stick movement, ie: with full up trim, the servo will
stop moving before the stick reaches the full up position.
I hope this information is helpful for someone. The main reason I am writing
this is to help the average flier, most of whom are probably flying mid-range
radios. I would like to write something about the JR 347 or 388, but don't
have access to them. If anyone out there that has a JR radio wants to submit
something, please do!
******************
When I discovered that my Ace Micropro was only capable of 256 positions,
I talked to several people about it, including Ace. The response was usually
the same: "256 is better than most servos" or "your thumbs
aren't that accurate". Well, let me talk about each of these statements.
First, it is true that some of the plain jane servos are not very precise.
However, regardless of how good or bad a servo is, having a radio with steps
(whether 256, 512, or even 1024) is simply introducing another error into
the loop. A cheap servo is not going to negate the lack of resolution of
the radio, nor is a good servo going to make it worse.
The statement "your thumbs aren't that accurate" is entirely true
(speaking for myself, of course). However, the centering mechanism on most
sticks are very precise, and this is where the real problem with steps comes
into play. The coarser the granularity, the harder it is to trim a plane.
Anyone who has fought a trim problem and found out they had a bad pot in
a servo knows what I am talking about, and that is exactly the feeling I
got when flying a 256 radio.
MARCH 1995
*********
More on Futaba 7UAF/P
After I re-read my column from last month, I realized that although I talked
about the Futaba 7ch radio, most of the recommendations I made applied to
just about any radio / any plane. This month I will (finally) talk about
two channel aileron setups on 7UA radios.
First, lets define 'differential' and 'flaperons'. Most people know what
flaperons are: the control surfaces on the wing can move together as flaps,
or opposite as ailerons. I have not seen much need for flaperons on pattern
planes, although they can be deflected in small amounts as flaps to help
trim a plane. They can also be deflected up to act as drag brakes during
landing. Differential refers to unequal throw of the ailerons up/down. Differential
is (in most cases) used to counter adverse yaw, especially on high wing/
high lift planes. On pattern planes, differential may be used to help a
plane roll more on its axis.
There are several ways to setup ailerons on the 7UA. First, you can use
just one aileron servo with linkage going to each aileron. However, most
fliers, pattern especially, are using two servos. This simplifies mechanical
linkage and gives a much tighter connection to the ailerons. The simplest
way to do two aileron servos is by using a Y-harness, with both servos working
from one channel. However, there is also the option of using two channels/two
servos, and there are two ways to accomplish that.
Two channel control of the ailerons can be done by either enabling DIFF
(differential) in the setup menu, or by enabling FLPR (flaperon). The second
aileron channel is #6 if using FLPR, or #7 if using DIFF. There are reasons
why you might pick one over the other. If using FLPR, you can use the ailerons
as flaps. You may or may not want to do that, but if you decide to use them
you can trim the neutral point of the ailerons up or down during flight
which might aid you in trimming the plane. However, you can still get differential
throw using the FLPR feature, you just have to adjust the FLPR rate settings
for each aileron channel just like you would with the DIFF feature. One
reason why you would select the DIFF feature is so that you can't inadvertently
move the ch6 knob and throw the centers off. Another reason would be that
you would want to use seperate flaps. Use whichever method you prefer.
I will describe the latter method of selecting FLPR, since the DIFF feature
is a little more straightforward. First, bring up the menu screen and page
over to the FLPR menu and turn on the feature. Now, you should get aileron
output from channels 1 and channel 6. (The manual does not state which channel
should be use for which aileron. It has been my experience that it does
not matter.) Then you must set the direction for each servo. In this menu,
you can also select the amount of throw for each servo, but leave all these
values (four of them, just like ATV) set to 100%. I alway use the ATV settings
to make any adjustments for throw, then use the FLPR rate adjustments to
obtain differential throw, if needed.
When setting up the ATVs, start out by setting the ATV for both channels
to 110% in either direction. Then use a deflection guage to determine which
aileron is moving the least in any one direction. Adjust all the other ATV
settings until both ailerons move this same amount in all directions. This
gives you a starting point of equal throw left or right and zero differential.
If you don't have a deflection guage, you can measure the throw by using
a ruler at the trailing edge of the control surface, although it isn't nearly
as accurate.
For the initial trim flights, use the dual-rate settings to adjust the total
throw until you get the roll rate required. (If you don't have enough throw
with DR at 120%, increase the throw in the mechanical linkage and start
this process all over.) If you use the snap switch, adjust the control throws
until you get the desired snap. (This is a whole subject in itself, which
I may cover in the future). Once you get the throws where you want them,
check the DR and snap settings for the aileron channel. If both of these
are less than about 80%, you may want to reduce the throw in the mechanical
linkage and start this process over. As I said in the January and February
columns, I like to have my ATVs and DRs (high side) at 100% or higher which
will give me the most resolution and torque at the control surfaces.
Remember, while channel 1 can have an ATV setting of 120% (super seven ONLY)
channel 6/7 can only have a setting as high as 110%. So, don't use a setting
of over 110% ATV on channel 1.
Some people prefer having more throw to one side than the other, ie: roll
faster to the left than to the right. This has to be done using the individual
ATV settings for each aileron channel. If you want to roll left quicker
than to the right, use the DR setting to get the desired left-roll rate.
Then, use the ATV settings to decrease the right-roll rate. You want to
decrease the left aileron down-throw, and the right aileron up-throw. (Just
don't 'throw up'). Use a deflection guage to measure each and match them
to each other, ie: the up-throw on the right aileron matches the down-throw
on the left aileron.
So far you should have zero differential. Most of the pattern type planes
that I have flown required little, if any, differential throw. Most people
define differential throw as having more up than down throw. This definition
is only accurate if the right and left ailerons have the same throws, ie:
left aileron up-throw equals right aileron up-throw, and down equals down.
It is more correct to define aileron differential throw as the up-throw
on one aileron being more than the down throw on the other, and vica-versa.
If you think you need differential (again, this is another subject altogether)
then change the FLPR rate (or DIFF if using that feature) settings of the
channels, but always remember where you started so you can return if it
doesn't work. It helps to keep some sort of log book with radio settings
so you can always backup to any given point. The manual that comes with
the Super Seven has a data sheet in the back that can be used to record
all the parameters in the program memory.
Remember, there are now a total of 10 settings which affect the throw of
the ailerons. There are four ATV settings, one for each direction of each
servo. There are four similar settings under either the FLPR or DIFF menus.
Then, there are the DR settings, both low and high. (Kinda makes you want
to say FORGET IT, and just use a Y harness). In the end, however, you can
be sure that you will have balanced throws on both surfaces, and can adjust
for just about any situation.
By the way, did you know that the Super Seven is known as the 'Field Force
Seven' in other parts of the world?
Next month: Correcting rudder coupling using programmable mixing.
APRIL 1995
***************
More on the Futaba 7UAF/P
Last month we covered two-channel aileron setup. I read Eric's column in
which he described the same thing on the Airtronics radio. I am not sure,
but I think he was poking fun at us Futaba fliers. (Then again, maybe he
was poking fun at ME? Nah). Well, I guess Airtronics had to make the two-channel
aileron setup easy, seeing as how they messed up the plug polarity on their
servos. (hehehe)
Mixing: 101.
This month, we will talk about using the two programmable mixers to correct
roll or pitch coupling. Roll coupling is when the airplane rolls with application
of rudder, and pitch coupling is when the airplane pitches with rudder input.
When the airplane rolls in the same direction as the rudder input, this
is referred to as 'proverse' roll, while the opposite is 'adverse roll'.
When referring to pitch coupling, most people will say 'pitches to canopy'
or 'pitches to belly'.
The causes of roll or pitch coupling are easier to understand than they
are to fix. Roll coupling is caused by an improper amount of dihedral in
the wing. Too much dihedral will cause proverse roll, and too little will
cause adverse roll. If you can adjust the dihedral on the plane, this is
the preferred way of correcting for it. Pitch coupling is usually caused
by the placement of the stab being too high or too low on the tail. Too
high will cause the plane to pitch to the belly, too low will cause the
plane to pitch to the canopy. Adjusting the stab height would be the best
way to cure this, although sometimes it can be cured by changing the wing
and/or stab incidence. It is, however, very easy to mix out these tendencies,
especially if the roll/pitch coupling is very minor.
One problem with the 7UAx series is that they only have two programmable
mixers. If you have two aileron channels, you need to mix rudder into each
one to correct for any rolling tendency. This does not leave a mixer to
correct for any pitching problem. SO, I cheat a little. If I have roll coupling,
I mix rudder into one of the aileron channels, and use the other mixer to
correct for any pitch coupling. Get the roll coupling fixed before adjusting
for the pitch coupling, since moving just one aileron may cause a slight
pitch problem in itself. Keep in mind that we will probably be mixing less
than 5%, so any movement necessary should be almost unnoticeable on the
ground. If you need to mix more than that, you should probably think about
fixing the problem on the plane instead of with radio mixing.
First of all, let me mention my philosophy when it comes to checking for
rudder coupling problems. When I trim out a new plane, I always set the
rudder travel for maximum throw on high rate. (I HATE flopped stall turns!!)
I then fly the plane and determine just how much rudder is needed for knife
edge, and adjust the low rate until full stick deflection barely holds altitude
in knife edge. I then determine if I need mixing or not AT THE LOW RUDDER
RATE. (I only use high rate for stall turns or spins). I fly the plane in
knife edge flight and determine any coupling problems. It helps to have
someone to write down which way the plane rolls or pitches while in knife
edge flight. After I land, I figure out which way I need to mix things.
When mixing rudder into the other channels, you need to determine the polarity
of the mix. I have never bothered learning how to determine this without
actually plugging in values. If the mix polarity is + and it is the opposite
of what you need, change it to a -, or vica-versa. You may also need to
plug in a large value for the mix percentage to be able to tell which direction
the servo is moving. Usually the mixing polarity will be the same for both
sides when correcting for roll coupling, but will be opposite when correcting
for pitch coupling. In other words, if there is an adverse roll coupling,
you will need to have the ailerons move in the same direction as the rudder,
for both sides of the rudder mix. But, for pitch coupling, you will have
to have both sides of the rudder cause the elevator to move down if the
plane pitches to the canopy. This is done by changing the mix polarity,
each side of the source stick throw (rudder left or right) will be different.
In some cases the plane may pitch to the canopy on one side, and pitch to
the belly on the other side.
Once you have the directions figured out, then you can dial the mix percentage
back down to around 5%. Fly the airplane some more, and adjust the mix percentages
until you get a straight track in knife edge. Once you are done, you should
be able to roll the plane on its side, kick full rudder stick (low rate)
and fly knife-edge from one side of the box to the other without touching
the right stick.
Remember, as part of your checkout procedure before you start your engine
(you DO check your controls, don't you?) you will need to make sure that
the PMIX switch is on.
I think I have someone lined up to write about the JR mid-range radios.
Hopefully I will have something next month.
MAY 1995
**************
Failsafe w/ 5 cell packs.
It was mentioned a while back that the battery failsafe circuit in our PCM
receivers are programmed to work with 4 cell packs, and won't work with
a 5 cell pack until two cells have dropped - which is probably too late.
While this is true, I did a little checking and found that during normal
pattern flying, the battery failsafe may not work anyway. Battery failsafe
with 7UAP/S takes over 20 seconds to kick in, and is reset every time the
throttle goes below 1/3. Most pattern flights don't have 20 second full-throttle
segments! Custom Electronics makes a device that will work, and can be used
with 5 cells with a special extension (two dropping diodes in series) and
can be used with FM radios as well. However, the circuit can't be reset,
so when the throttle goes to idle you are going to land!. Maybe some other
radios can be programmed to act differently (ok, Eric, put your plug for
the Airtronics here) but I can only speak for the Futaba 7UAP/S.
**************
I just got a couple of the JR super servos. WOW, I am impressed! I may mount
these in a plane to try them out soon. So far I have not checked to see
just how much current they pull. Doesn't matter to me, I'll just use whatever
size battery I need!
JUNE 1995
***************
Eric Henderson was kind enough to send me this bit on JR 347 and 388 programming
tips. Even though I don't fly JR, the information here helps me to understand
more about those radios and what they are capable of. Here's Eric:
In response to Bob's request in a previous issue of K-FACTOR here are is
an explanation of some ways to set up a pattern plane with a JR X-347 or
JR X-388. I currently live near Boston in District-1 but will soon be moving
to southern New Jersey and hope to meet Bob in the near future. Differences
between the 347, read 512 bit resolution and the 388, read 1024 bit resolution
will be highlighted where relevant. (Both radios will support PPM/FM and
PCM 512). To avoid this becoming an instruction manual the steps to set
up a plane are illustrated but the detailed keying etc. has been omitted.
Both radios have step through menus and require some initialization choices.
You are required to select MODEL TYPE before you get into the main body
of programming and servo set up. There are a couple of buttons on the lower
left of the radio that you hold down while simultaneously switching on the
radio. The radio LCD comes on but no RF is produced when in this state.
AERO, meaning power planes is displayed. (For our purposes we shall ignore
the Glider and Heli. options). Two decisions now have to be made. They are;
1) If you want Flaperons - a channel and servo per aileron, step to and
select FLAPERON, and 2) Whether the flap channel is rotary pot driven or
switch selectable, set to and select POT. You also input the model name
at this stage and can copy another model if you wish. This is where you
tell the radio what receiver you are using. The 388 has the option to use
the new 1024 receivers. [I have tried both 512 and 1024 bit resolution receivers
with 4131 servos and to be perfectly honest I cannot really feel any difference
in the air but I can see a minuscule difference in electronic trim resolution].
Then you switch off and on and you are now ready to program!
"Programming" requires you to press two keys simultaneously. This
will put you into programming mode and will produce an RF signal so you
will see the results of your work on your receiver/servos as you program.
You first clear the flap servo rotary POT trim preset down to zero to avoid
inadvertently, (might I hastily add embarrassingly) messing up the two servo
aileron configuration with the Trim Knob. All the servos are default set
to 100% throw and have the option to go up to 150% of their endpoints at
either side of center. The best set up is to have 100% servo throw with
the pushrod about two or three holes out on the servo arm and to choose
horn lengths that give the specified/desired throws.
Next set the direction and centering of each servo so that the arm is perpendicular
to the pushrod. If the centering cannot be done mechanically the programmable
SUB-TRIM option allows very fine adjustment.
Elevator and rudder are easy to set up. The END-POINT, often called servo
throw, is set individually either side of the center, e.g. up and down.
If after flight tests you find that you have too much throw a good technique
is to use the DUAL-RATES option to reduce or increase the throws as desired.
The rate switches have two positions and are default set at 100%. To get
more throw you can go up to 125%, say in position 1 and 110% in position
2 and then try them out to see which setting you like best. This is much
better than changing the end points especially when you are using two servos
on the same control.
EXPONENTIAL is selected by the rates switches. 25% is a good amount to begin
with on elevator. The higher the percentage the less movement you get around
the center for the amount of stick movement. Some may call this an automatic
dual rate but it is not! You use the exponential to desensitize the center
actions of the stick pots. This make for smoother stops and starts in rolls
etc. You will soon know if you have too much exponential because the plane
will respond too slowly. A good set up technique is to begin with no exponential
and set the servo rate first. Then set both the rates positions to the same
percentage. i.e. no matter which position you have the switch then the rates
are the same. Then program in some exponential on rate switch position one
and go fly!. Try the plane with exponential out and then in. You can even
try two different rates of exponential with rates switches. The rudder will
work well at 40% EXPO, it will be pretty soft for takeoffs and landings,
but will respond with authority in stall turns and knife edges.
Throttle was once a "No-brainer" to set up but with the big 120's
some help is needed. First of all the rpm of the engine does not seem to
be proportional to the position of the carb. flap.
To get a linear response use the SUB-TRIM option on the throttle channel.
It allows you to move the centering of the servo and also affect the linearity
of the servo action. If you couple this change with the ability to change
the travel end points it does not take long to modify the resolution of
a servo to meet your throttle response needs. Secondly a difference of 200
rpm on a 15 x 12 at idle can be the difference between a landing or an overshoot.
A practice you might like on the both .61's and the 1.20's is to have a
high/low idle switch. It is very difficult to do this with your thumb on
the throttle trim during a contest landing so if it is pre-set on a mix
switch life can be very enjoyable, read less sweat on finals!.
What you set up is an idle that will not die during stall turns and spins
but can be accurately selected for the final leg of landing or that stationary
moment just before take off on a hard top runway. How you do it is to mix
the throttle channel with itself. With JR this is channel 1 with channel
1. You tell the radio which of the three available switches you want use
and then dial in a small percentage of mix that will lower the idle when
switched in. The YS 61 will idle very slowly for a limited amount of time,
the 120 a bit longer, and it feels great to be able to switch in LOW IDLE
when you are lined up on the final leg of landing and only have to concentrate
on keeping the wings level.
Ailerons with a servo on each control surface help you sleep better at night.
Servos or connectors or gears do fail and a redundant servo will save your
plane. It also allows such niceties as electronic selection of differential
and flap/elevator mixing. A technique that you can use to slow down a plane
is to employ a form of flap using both the ailerons. The JR radios have
a series pre-programmed mixers that you can use. The elevator neutral setting
can be preset to avoid ballooning upon flap deployment. The flaps in this
instance are not drooped. They are set with 5 degrees of UP-flap, yes UP!
select the LAND switch because it also disables the snap roll switch. Not
a good idea to snap roll on landing approach!. What this configuration allows
you to do is slow the plane in a higher than usual nose up attitude without
stalling. It works very well on dead calm days but is usually not needed
on windy days.
Fail-safe is a bit controversial these days but you get RX battery low fail-safe
warning. The JR will give you approx. 30 seconds to land after it senses
a low four cell RX pack. The throttle will cut to idle as a warning. You
can then over-ride it but please, not for long. MHO the biggest cause of
a low pack is a hung gear-leg. If you use the new low profile JR 703 servos
you will get relatively low drain on a stalled servo. (Burnt our fingers
on the servo wheel testing that one!)
Back to fail-safe. A good plan is to choose low throttle, (just in case
you get it back), slight right rudder and half up elevator. The wheels are
best kept up to save the wing in the event of a forced-free-flight landing.
The 388 differs from the 347 in fail-safe options. The 347 allows either
low throttle and HOLD of all other controls OR pre-select of all control
positions. The 388 allows you, nay demands of you, to specify HOLD or PRE-SET
per channel/servo. This gives you a lot of flexibility in emergency options.
SNAP ROLLS can be pre-programmed and selected from a momentary switch on
the top of the TX. The snap roll program lets you set more throw than you
have dialed as available on your control sticks. It is good for snap rolls
on Avalanches etc. You can pre-program all four up and down snaps but can
only have one direction selected at flight time. This makes the option a
bit limited for spins however.
Mixers on the two radios is the same for the first four mixes. The 388 has
two more. The basic program requests you to select the mix identity, A,
B, C or D. You chose a master and a slave channel to be mixed and also the
switch to be used. No switch means ON all of the time. You then select the
mix percentage amounts either side of the center. You can also defer the
mix to only operate when the driving channel reaches a certain point. An
example being that when you mix the throttle to itself you only want the
mix to work on the low position of the throttle and probably only during
the last 10% of the low throttle operation.
There are two extra optional mixes on the 388, called E and F. They have
a special feature called TRIM TRANSFER. This is very useful when you want
to use two servos for elevators. You could just use a Y-lead but this still
gives you a single point of failure. Two channels are definitely better
than one. Anyone who has lost elevator will tell you! You would probably
mix the elevator with Auxiliary Channel 2. Then when you trim your elevator
with the physical trim lever you will get both elevator surfaces to respond.
The electronic SUB-TRIMs and end point TRAVEL ADJUSTMENT can now be applied
per servo to "Tune and match " each elevator control surface.
The rates and pre-programmed mixes will also drive the elevator servo auxiliary
servo as one.
I have gone as far as using four ailerons and four aileron servos in my
Fun-fly machines. You should see a true vertical dive landing approach with
full crow applied. What? that's not an official maneuver???. Regards - Eric
Henderson
* Precision
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