Hi,
I'm having a problem with my Slinger park flyer. It uses a Hitec 555
micro receiver, and two HS-55 micro servos. Everything was working fine
until one of the servos started sticking, as if the gears inside it
were locking up. So I bought another one to replace it. However this
servo doesn't seem to be working either. As soon as I plug it into the
receiver with the battery connected and the transmitter off, both
servos start moving quickly and randomly as if there's some kind of
interference. As soon as I turn the transmitter on, everything returns
to normal.
The problem seems to be this specific servo connecting to this specific
receiver. Plugging the servo into another receiver on a different radio
channel didn't cause a problem, and plugging the servo into a different
slot of the same receiver didn't fix the problem.
Any ideas? Since everything seems to work when the transmitter's on, I
could (in theory) fly the plane anyway, and hope that the interference
doesn't start up when the plane gets too far away from the transmitter.
But I'd rather not risk a crash until I know what's going on.
Thanks,
Jesse
HUH?
You are getting random movements when the transmitter is in OFF position
and you consider that a problem? I consider you lucky one of the servos
hasn't hit a stop and stripped something. Do a proper range check with
the radio on, the antenna down and you ~75 feet away, and if everything
works as expected, fly the plane. Getting random glitches on a PPM
receiver when there is no transmitter on is pretty normal. The normal
order of operations for ANY RC system is to power the transmitter up
first then the receiver. Never the other way around. Especially with
an electric power system.
Jim
Well, as you can see I'm not very experienced in R/C, especially since
I got into the hobby myself without any outside help (resulting in
several planes that had very short flying careers.) I had no idea that
you weren't supposed to turn on your receiver without your transmitter
being on. In fact, that's how I determined that there wasn't any
outside interference! Maybe that's why that other servo died. Hopefully
everything's ok and I'll be able to fly tomorrow.
Thanks for the quick reply and blue skies.
Well, as you can see I'm not very experienced in R/C, especially since
I got into the hobby myself without any outside help (resulting in
several planes that had very short flying careers.) I had no idea that
you weren't supposed to turn on your receiver without your transmitter
being on. In fact, that's how I determined that there wasn't any
outside interference! Maybe that's why that other servo died. Hopefully
everything's ok and I'll be able to fly tomorrow.
Thanks for the quick reply and blue skies.
A lot of receivers do this. Basically its noise. It may be low level
interference, or just 'hiss'
A good design will try and mute the receiver if there is not enough
signal to give a reliable output, but many don't bother.
Transmitter off means the rx is picking up RF noise so the servos jitter.
This is normal. It is also not a good thing to do. You should always turn on
the tx first. That random RF noise can move the servos beyond their normal
range and damage em.
I understand. I taught myself to fly also. It wasn't until I had
several hours in the air that I found a club. The bummer was that they
had a training program and I could have probably saved a few repairs if
I had known ahead of time. Your best bet is to do the one thing we
don't like to, read the manuals that came with your gear. Dollars to
doughnuts the proper order of operations is mentioned in there. That
prop can (and will) bite, you should do the reading first the flying
second.
Jim
Yeah, I have lots of entertaining crash stories due to being self
taught. Looking back, I think I would have saved myself a lot of money
and headaches if I'd gone to the trouble to seek out a club or at least
a more experienced R/Cer. There's still a lot of stuff I don't know.
For example, my most recent crash involved my prized Goldberg Electra
motorglider that was the first plane I ever flew. I thought I had
everything covered in my preflight checks. Unfortunately I neglected to
check the rubber band that holds the motor in, which was apparently so
old that it was at the breaking point. The predictable result was the
motor coming out several seconds after launch, resulting in a spin at
30ft, a head on crash into the ground, and severe damage. Now I know
that ALL rubber bands need to be replaced regularly, not just the ones
that hold the wing on!
On a side note, I flew the Slinger yesterday and everything seems to be
fine, so I lucked out there.
This suggestion is a must for FM receivers. PCM receivers do not have
this issue. In this case I have leared to power the receiver first
(without turning the radio) just to make sure that no one else is on my
channel or I'm not receiving any spurious signals.
This practice is gonna cost you $$, or pain and agony, one day....
The reason that it is standard operating procedure to turn on the Tx FIRST
is to avoid spurious signals to the Rx, which can cause the servos to
overrun their limits and damage themselves.
ALWAYS turn on the Tx first, then the Rx, AFTER checking the board for
frequency use.... Believe me, you DO NOT want to find out you're on the
same frequency as someone else using your method... It may earn you a fat
lip....
Bill
This practise has actually saved me (or the other guy) twice! With the
advent of park flyers, it turns out that in a nearby grass field a
couple of kids were flying their park flyer totally oblivious to the
fact that there is a public field nearby and a frequency board rule in
place. And the second time one of the guys in our field had simply
forgotten to put his card in. With an FM receiver I understand what
happens when there is no signal as servos move all over and you could
could potentially ruin something on the servo or plane. When there is
someone else's signal, your servos would react and in that case there
is a possibility that you could go beyond their travel limit and strip
a gear or break/pull a horn.
With a PCM receiver when there is no signal they do not react so no
chance of damage here. However when there is a signal, well your servos
could react and you could get into trouble like an the FM case before.
Your point is well taken but I rather have my plane experience glitches
and potential servo damage on the ground as opposed to in the air. In
all what I really need is a frequency checker but until I get one, I
will be following my practise.
When you receiver is turned on first the AFC circuit is wide open to any and
all RF in the neighborhood. Sooner or later one of them is bound to be full
throttle. :-(
And here all these years I thought PCM receivers were FM. FM is how it is
modulated, PCM is how that modulation is coded. Receivers are either AM or
FM. If they are FM they can be PPM or PCM but not both at the same time,
some transmitters on the other had can programmed to transmit in either PPM
or PCM mode. At least that's how I thought it worked. Or have the semantics
confused me?
RS
Tower Hobbies sells a 72 MHz frequency monitor, if you are operating in
North America, for around $50. In a couple of replacement servos purchased,
you have paid for the frequency monitor.
Not all servo damage that can cause your model to crash is apparent on the
ground.
Ed Cregger
You're correct as a PCM receiver is indeed an FM receiver. My point is
that a PCM receiver does not misbehave when there is no signal
(basically the fail-safe mechanism). As for my practise, the throttle
could potentially go full on but that is OK because my engine is not
running anyway.
In regard to Ed's comment - yes the purchase of frequency checker in on
my list of things to do. In two incidences that I've experienced my
servos merely moved according to the other guys transmitter. No damages
though because, first servo centers and travel amounts do not vary
significantly from one plane to another and second I turned the switch
off after I noted the signal to my PCM receiver. This is to say with my
practise I momentarily turn the receiver switch on & off to check for
signals and I do this with my PCM equipped planes.
Just because YOU have not suffered any ill effect YET, does not mean
that it is the right way to do things, PCM or not. Bottom line, no
matter what your rationalization is, turning on the receiver first is
the WRONG way to do it, period. I'm happy you have gotten away with it
so far, but if I saw someone doing that at the field they would be
corrected. If it continued they would be reported to the club's safety
officer. Take a look at some of the flap/spoiler setups out there and
tell me they couldn't be damaged by being controlled by someone else's
radio.
Jim
I see your point with flap/spoiler but I don't use them or have them on
my PCM planes anyway. The same safety rules state that one ought to
put his card in when flying and people should not operate a radio in a
nearby field but like many rules, they're broken sometimes. At this
stage I respectfully disagree with your rule as it pertains to my
special case. In future I might be proven wrong as I gather more data
but so far my procedure has saved me (or the other guy) twice in a
3-year period.
It's sad to say, but there are no rules or laws that state that someone
can not fly in a field next to a cub field. They have as much right to
use the frequency as you do.
I see no harm that snipped-for-privacy@yahoo.com can do TO anyone if he sticks to what he
says, let him be. No hard feelings to anyone unless OTHERS safety is
involved.
mk
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