|
Step Four:
Adjusting Servo Travel
Once you
have your linkages set up as shown in the picture, and your
control surface centered, it's time to set your ATV’s,
travel adjust volume, or end point adjustments. JR calls
this travel adjust and Futaba calls it ATV. I’m referring
to Futaba 9Z and JR 10X systems right now. I know many of
you guys are using 8 and 9 channel systems. They'll have the
same functions but sometimes refer to them differently. Now
ATV does not refer to the rates you fly on. ATV’s are the
physical end points of a servo's travel.
On ailerons
we want to start with this matched, meaning we want to the
control surface throw to be same amount up and down on the
ailerons. You'll need a good way to measure the angle
of deflection. CRC Throw Meters work and are quick and
easy. I find that the more accurately I can measure (and
repeat the measurements) the easier this becomes. If you
can’t see 1-3% of ATV change then your measurement device is
not accurate enough. I use a set of pointers I got from
Tony Frackowiak that are about 7” long.
We want the
angles to be the same: 10° up and 10° down. Don’t worry
about differential yet. If you set it up in ATV then all
your flying rates will track. 80% of the throw on dual
rates will still give equal values up and down for both high
rate and low rate. The only difference being that the
low rate is 80% of the high or, in this example, 8°.
ATV settings are independent for each servo. So the aileron
servo plugged into the aileron channel will have its own end
points, and the flaperon servo plugged in as Aileron #2 has
its own end points, too.
We also
want our ATV values to be as high as possible. I know the JR
10X goes to 150% The Futaba 9Z goes to 140%. I usually setup
my ATV values at about 120% as a minimum. Then I adjust to
get the same 10 degs of travel (or whatever the goal
deflection is) both up and down. This is done in ATV.
Example: my
Supreme's right aileron ATV is set at 125% up and 122% down.
The left Aileron servo is 118% up and 123% down. These
numbers will change slightly if I change out aileron servos.
Basically,
the different values are a way to correct for differences in
linkage angles, lengths, or a servo's electronic
differences. We're talking 1024 steps in a roughly 120° arc.
This means that each step is about 0.12° of rotation. That's
a very small difference when you're only talking about a ½”
long servo arm.
You'll want
to get these ATV values to be as close to the same number as
possible, given that the ailerons are actually moving to the
same deflection angle. So make the mechanical changes to
your linkage. Adjust the height of your control horn
connections to get the travels to matched as much as
possible. The radio is for fine-tuning, not for correcting
mechanical errors.
If you have
more than a 10-15% deviation in your ATV values, you need to
improve geometry mechanically. You may not be at the proper
connecting point on your servo arm/wheel, as described
above. Or your control horn clevis connection may not be
over the hinge line. Or you have some funny angles playing
tricks on your linkage. Square everything up and re-do it.
Getting the
servo travel and linkage right is important because once you
fly the model, you'll tweak the rates you fly on. You don’t
want to adjust 65% right aileron and 75% left aileron to get
the model to roll the same each way. The radio can mask or
correct such problems, but it’s so much better to make the
corrections mechanically.
Also, when
your model needs differential, you'll want to increase
differential in logical numbers that you don’t need to
measure at the field. Simply add 5% differential and
you know that the down travel on our example aileron is now
moving 9.5°. If you set up your ATV’s to electronically
correct all the minor deviations then these deviations will
magnify and your model will roll fine on high rates but when
going to low rate it wobbles and the differential is off.
I've seen this happen. I've also watched guys try to adjust
the D/R values all over the place to make the travels the
same. Then they add in expo values, and it drives the
system nuts. You need a BASE and that base is the ATV value,
the end point of the servos travel.
Next: Setting Rates & Testing Linkage
|
