Hmm....from the sound of an Autohelm, I was under the impression the
motor drive was a STEPPER motor, which varies with the number of
steps/second delivered from a digital drive. Listen to it run. It
doesn't cut on and off at all. Take it out into the waves and listen
to the FREQUENCY fed to the motor change from that low RPM,
intermittent bzzt,bzzt,bzzt that drives me crazy as it makes little
course corrections in calm waters, constantly, those little jerky
motions, to the full blown hardovers trying to keep up with the swells
offshore. It's not just turning on and off like your water pump.

As to the drive on a hydraulic ram, I believe it is driven from analog
electronics controlling motor speed, therefore hydraulic pressure. We
just installed a B&G Network Pilot with electro-hydraulic A unit on
Lionheart, an Amel Sharki 41 ketch. It looks like a perfect human is
piloting the helm...scary. If you go under the aft cabin bunk and
watch it work, you can hear the power to the drive motor vary as it
runs this way, stops, runs that way backwards. It doesn't come "on
and off" like a relay. To make small course corrections, it comes on
at a low level and power is applied gradually until the rudder
position sensor tells the electronics the rudder is, in fact, moving
slowly in the desired direction. At that point the motor stays at
that level of power until it approaches the correct course, then it
slows to a stop and reverses, bringing the helm, very gently, back to
center as the correction becomes reality. It's the smoothest
operating autopilot I've ever seen, and very quiet unless you're
sleeping on top of its motor.

If someone orders a 10 degree turn on the Pilot's controller, the
motor comes on hard to pull the helm over, but not to the stops. B&G
Pilot's manual says the computer "learns" the boat's handling
characteristics, constantly, and figures out how hard it needs to pull
over to make a nice, coordinated turn. As soon as the boat responds,
felt by B&G's fluxgate, the motor reverses very gently and pulls the
helm back to center....arriving uncannily AT center just as the new
course shows up on the display. Sure wish I could steer it by hand as
accurately as that...never oversteering, which is real easy to do on
the Amel's big rudder...(c;

I don't think any autopilot's control is an on-off simple
switch....Autohelm or hydraulic. Watch carefully when it's working.
It doesn't turn at a set speed on either.



Larry W4CSC

US Supports Apartheid! Vetoes UN resolution
condemning Apartheid Wall.
http://www.antiwar.com/hacohen/h052103.html
http://www.theage.com.au/articles/20...917478560.html
Can apartheid at home be far away?....
Apartheid NOW! Wall off Mississippi!