[NSRCA-discussion] Random tip on ATV and setup

[Jon Lowe]

I've run into this over and over again with new flyers.   Using one 
sided servo arms so you can't get the servo linkage centered because 
the splines won't line up exacerbates the problem, so they use tons of 
subtrim.  This is one reason I use wheels instead of arms.  Of course 
using wheels generally isn't possible with giant scale airplanes.   
I've also found that some servo brands have an even number of splines, 
and turning the servo wheel 180 degrees doesn't help things line up.  
My rule of thumb is if more than 10 points of subtrim is required or 
more than 4 or 5 points of end point difference, I change things 
mechanically until things are synchronized again.

Unfortunately, there isn't much out there on basic mechanical setup 
that we can refer people too, especially sport flyers.  I gave a talk 
on ATV and subtrim vs. mechanical setup at our club meeting a couple of 
months ago, and had a lot of people thank me because they had never 
been exposed to the information before.  I am giving another talk on 
proper mechanical linkage set up and servo selection at our next 
meeting.

I've also found out that people just don't understand why you choose a 
standard size servo over a mini servo with equal torque in some 
applications because of gear size.  Some minis, such as the DS3421, 
have lots of torque, but the gears just aren't up to the job in some 
applications.  We had a flye
r show up with a 90 sized Funtana, with a 
huge 4 stroke on it with 3421s with metal gears on the ailerons.  His 
attitude was that the 3421 torque was within specs, but we pointed out 
that the gears were so tiny they'd never last, especially on the huge 
ailerons on that airplane.  Sent him home to get different servos, and 
he returned with 8411's, so it wasn't a problem of not having the 
proper servos available.  He just didn't know.  BTW, I tried 3421's on 
ailerons on a pattern airplane a few years ago, and stripped metal 
gears on one servo in flight after lots of flights.  Landed ok, but 
never again.  Inspecting the gears after the incident showed that the 
vibration of the ailerons had worn the teeth to needle points.  There 
wasn't a lot of slop in the remaining servo, but inspection of its 
gears showed they were also close to failure.

This is one area where we can be ambassadors for the sport by helping 
our local pilots out with proper setup.   If properly done, they do 
appreciate it.


Jon Lowe


-----Original Message-----
From: tocdon at netscape.net
To: nsrca-discussion at lists.nsrca.org
Sent: Thu, 19 Feb 2009 7:32 pm
Subject: [NSRCA-discussion] Random tip on ATV and setup









Sub trim is a function that moves the servo to get the control surface 
centered. This in conjunction with end point adjustments can have an 
adverse effect on servo20speeds. You are basically stretching the number 
of steps for the same amount of travel, among the servos. I was at the 
FARM club helping out a giant scale newbe last fall and he was flying a 
third scale H9 Extra 330 with Futaba 8 channel and Hitec servos. One of 
his servos literally trailed the other one by about 20 or so degrees 
when moving the elevators up and down in a rapid fashion. He said a 
servo was bad. Actually, backing up a bit- when he was flying he asked 
my help to trim his plane and handed me the transmitter
  . When I tried some waterfalls, it peeled off really bad. When I 
landed, that is when I saw the elevators moving at different speeds. 
Upon inspection I found he used the electronic sub trim to get the 
servos aligned and massive atv end point to get the ends the same 
throw. He also had the ATVs set at nealy 150 percent. I think he was 
like, off one complete servo arm tooth and used the sub trim to get the 
servo back to center. After about 2 hours getting everything 
mechanically adjusted, the plane flew so much better. It went from 
something nearly crashing to a competitive IMAC and 3D setup. Any case, 
I had an identical experience when helping a flyer in Vanceboro, NC 
last year
 (after the pattern contest completed). Exact same issue on his (scal

e) plane. He thought the Rx was bad until I showed him what the deal 
was. After mechanically adjusting to g
et it close, all was well.


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