Frank McNeill wrote:
> Hi Donald,
> I've used Google to search for messages transmitted via "Sonar"
> normally used for locating submarines, and more recently schools of
> fish. It has also been used to transmit messages, but so far I
> haven't found references to use for remote control, which would be a
> good remote control method for pop-pop boats.
Any submariner can probably tell you about the "Gertrude", a simple
voice-frequency sonar telephone. Take voice from a microphone, amplify
it, and play it through a hydrophone (an underwater speaker), either
directionally or broadcast as suits your need. The other sub (or
surface ship) uses their sonar set's hydrophones to detect and play the
sound through a speaker inboard; switch from receive to transmit with a
simple switch, as on a radio. As a "bonus", anyone swimming in the
water can hear the transmission directly, just as they can hear a sonar
ping. And most of us are old enough to remember the old RCA Space
Command remote control TVs -- they used what amounted to tuning forks to
send the commands from the hand unit to the TV (big step up from aiming
a flashlight at the four corners of the set, but no competition for
infrared pulse code).
One problem with using sound waves for control is lag -- even in water,
where the speed of sound is a couple times what it is in air, by the
time your boat is fifty yards away, you'll have enough lag in the
controls to mess with your reflexes. Likely not a big problem for
slow-moving pop-pop, but I wouldn't consider trying to control a
hydroplane by sound. Not to mention the second big problem (another one
submariners, at least those who worked around the sonar department, are
likely to remember): the faster you move through water, the more noise
the water makes flowing around your hull. A hydroplane couldn't begin
to hear the controller unless it was loud enough to deafen the ducks on
the pond. No, pop-pops aren't that noisy (and certainly not that fast),
but I suspect the "clang" overtones of a diaphragm, transmitted through
the metal hull of the boat or the water in the pipes, would interfere
very badly with an ultrasonic (i.e. not heinously annoying) control,
unless it was loud enough to set off every dog in the neighborhood if
you pulled the controller out of the water.
If, through hard work and perseverance, you finally get what you want,
it's probably a sign you weren't dreaming big enough.
Donald Qualls, aka The Silent Observer http://silent1.home.netcom.com
Opinions expressed are my own -- take them for what they're worth
and don't expect them to be perfect.