COMBAT
CLINIC
Number 1
This one's from Richard
RADIO PROBLEMS
After noticing that we seem to be
having an unusual amount of radio range and interference problems
(not to mention my fried servo problems), I called Airtronics and
spoke to two of their experts (one of them is the current National
Gas Hydro Racing Champion). From their tutoring came the following
information.
1. ANTENNA INSTALLATION (Fig. 1 &
2)
There's only one best way to do it, especially for our
models and that is to mount the entire antenna vertically. "Dean's"
short antennas are OK for cars because they stay close to the
operator, but for us this will only work occasionally. The "Hayes"
brand of short Rx antenna will work better because it is slightly
longer. Best possible design will be a vertical 1/32" diameter
music wire cut exactly to the length of soft wire removed from the
Rx. This is mounted directly above the Rx if possible. If you do
this, be sure to bend a loop on the high end of the wire so you
don't poke your eye out.
a) The water (and the ground) is a
"ground plane". The closer the antenna is to this ground
plane, the worse the reception. Try it yourself: lay the Rx antenna
on the ground check the range. Then raise it up a few inches on a
box and check the range again. As it get farther from the ground,
the range increases. Supposedly, it's the same with water, even
inside the boat: antenna wire in the hull may be only an inch above
the water's surface. However, if this were true, it would put the
sub guys out of business. They aren't, as you'll read later on.
b)
We've got a lot of metal, servos, servo wires and electric motors,
all of which interfere with clean reception. The point is: keep
the Rx antenna AWAY from all that equipment. One inch
is the minimum separation recommended. This includes servo wires
iside the radio box.
2. RANGE
CHECK
The right way to do a range check is with the Tx
antenna folded/pushed down. Always do it this way. If
everything is OK, your range should be 100 feet. Remember, with the
antenna collapsed. Do this with the Rx out of the model and again,
with it in the model.
3. TRANSMITTER ANTENNA (Fig.3)
The
Tx emits a torodial (donut-shaped) pattern of radio waves. The
emission is stongest perpendicular to the antenna, and weakest along
the lengthwise axis. So, never point your Tx antenna at your model,
always hold it upright.
4. SERVO
PLUGS (Fig. 4)
In the last two months I managed to fry four
servos. Most (maybe not all) servos will overheat and burn some
circuits if one of the power outputs is pluged into the servo's
signal line. Almost all modern Rxs send the signal through the far
left or far right plug-in pin. Also, they design plugs for their own
systems that will fit only one way to avoid this problem. Well, we
end up collecting different brands of servos whose plugs are not
physically compatable and we start customizing things and wires get
crossed. Be VERY careful when soldering a new plug onto a servo
lead. Also, some servos do not have clear color coding on the servo
leads, so indentifying them can be difficult. Usually, the signal
wire is white or yellow. In the case of older AIRTRONICS, all the
wires are black and only the POSITIVE wire has a red stripe on it
and always plugs into the far right pin on the Rx (when looking at
the Rx with the label up and right-reading). I haven't seen their
new Z-Plug setup.
The
following information comes from Skip Asay, owner of SubTech,
manufacturer and supplier to the R/C model submarine community.
5. GROUND EVERYTHING (Fig. 5)
"Grounding"
means to most of us, "connected to the earth". In a car,
the negative battery terminal is grounded to the chassis or engine
block. For model boats/subs it is the NEGATIVE terminal on the main
power battery. Skip recommends grounding EVERY(metal)THING in the
model. Not easy. But the most important is all the motors: Run a
wire from the CASE of the motor(s) to the negative battery terminal.
This does not replace the capacitors (0.47 micro-farad x 3) on each
motor, but gives the collected charge someplace to go. He related
quite a long story to me where this was the only successful solution
to a radio interference problem another modeler experienced on a
surface ship. Grounding all the heavy metal (barrels, ammo, metal
brackets, shafts, etc.) in addition to the motors is the ideal
solution. Skip said they experience no "ground plane" or
vertical vs. horizontal antenna problems, so these may be far less
important than grounding.
6. WET
ANTENNA WIRE (Fig. 6)
If your Rx has a floppy, insulated wire
antenna and it has been sunk, REPLACE THE WIRE IMMEDIATELY. It is
commonly available 22 - 24 guage insulated, multi-strand wire.
Unsolder the old one from the Rx circuit board, cut a new one to the
exact same length, solder the new one on. Why? Because water
(especially under pressure) will go every where, including down the
antenna wire to the Rx or just sits inside the isulation for a month
and corrodes the strands, which effectively shortens your antenna
and your range. Solution: seal the antenna wire tip with thick CA
glue. Do not use adhesive silicon, the vinegar - or what ever it is
that smells so bad - will corrode the copper faster than water will!
Well, I hope
this helps. I'm gonna do all the above, and I strongly advise that
you all do this, too.