Model Forum / Radio Controlled / Water Models / September 2003

Definitely the best way to go.  Definitely.  Better quality, better
range, greater frequency stability, ability to work with any device
(servo, ESC (electronic Speed Controller, etc) designed to respond to
the signals meant for standard servos.  Just better all round.  And no
I dont sell'em. :)

Yup.  "Centre" is just for the operator's sake.  Servos (and control
sticks) are continuously variable from endpoint to endpoint.  And
"centre" doesnt necessarily have to be half way between the two.  If
you have your control stick set up as a "ratchet" control (ideal for
rudder control on scale models) the stick stays wherever you move it
to, as does the servo.  If you have the stick set for spring return,
letting go of the stick allows it to spring back to "centre" - again,
the servo just follows it obediently.

Yuck.  No offence, but yuck.  Been there, done that - digital
(non-proportional) radio set ripped from an el cheapo toy buggy and
used for my very very very first model boat, more years ago than i
care to admit.  3-setting rudder control:  hard to port, midships,
hard to starboard.  It was not good.  Eventually made good landfill
though.  Proper proportional servos provide what you have now (stays
where you leave it) plus more... move the stick slowly, the rudder
will creep around with the stick.  Slam the stick back and forth and
the rudder will do its best to keep up.  Nudge the stick away from
centre just a little, the rudder follows it.  Want to fine tune it
from that setting without returning to centre?  no probs - just nudge
the stick a tiny bit and the servo will follow.  Can't ask for more
than that.  :)

(People will climb dowm my throat for that last one - the one thing
more that could be asked for is auto side-wind adjustment.  Anyone
played with a gyro out of a heli?  I'd like to hear how you went;)

???

Spot on re pulses and duty cycle.  Each pulse is 2ms wide, including a
deadzone at the end of each pulse frame.  "Minimum" setting (drives
the servo to one end of its travel) is a positive pulse of 0.5ms.
"Centre" is 1.0ms.  "Maximum" (drives the servo to the other end of
its travel) is 1.5ms.  Voltage, off the top of my head, is whatever
supply voltage the RX and servo is using.  It's a positive pulse,
btw... signal is at ground level for most of the time, rising to Vcc
for the duration of the pulse.  Important note:  though the pulsewidth
varies according to stick setting (0.5-1.5ms), the duty cycle remains
the same: 2.0ms for the frame, regardless of the pulsewidth.  In other
words, its only the mark-space ratio that changes, not the framerate.
Frequency is dependant on the number of functions your radio has.  If
it's a 2-channel (sorry, 2 *FUNCTION*) set, it sends a frame for
function 1, a frame for function 2, a sync frame, then restarts the
cycle.  if it's an 8-function set, it sends each of the 8 function
frames sequentially, then a sync frame, then starts again.  (the sync
pulse isnt sent to any servo, btw - its only sent for the benefit of
the RX, so the RX doesnt get confused as to where the hell the TX's
pulsetrain is up to.)  As the frame duration is fixed at 2.0ms, the
more functions, the greater the time between each frame per function.
In reality, this isnt an issue - im yet to meet a servo fast enough to
keep up with even 10-function sets (which by nature send one pulse to
each function/servo every 22ms (2.0 ms per function, plus the 2.0 100%
mark-space ratio sync pulse - or is the sync pulse 2.5ms?  anyone?).

I hope reading this confused you as much as writing it confused me.
;)

*Dreamscape*

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