>>>what usually goes wrong with electronic pilots? the
mechanical part or the electronics?
Depends on the type of pilot....if it is a wheel pilot, the
electronics are normally permanently mounted, hopefully sheltered,
and should be reliable. Early motor drive circuits were unreliable
but the new ones should be OK. Nevertheless, a motor that
completely shorts out can still overload and burn out the drive
circuits. The motors and drive belts fail regularly on the wheel
pilots. The ram type or hydraulic type are much more robust.
On the tiller pilots, failure (assuming it is not overloaded) is
usually by water ingress. That is why I recommend keeping them
bagged up at all times. I have used the same tiller pilot for over
15 years but I have sealed the boards inside and covered all the
external seams in "GOOP". Without doing this, it would have lasted
less than a year. Water has come in through the buttons a couple of
times. Newer models have better seals but I still wouldn't trust
them.
On both tillerpilot and wheel pilots they use flux gate sensors.
These are tiny gimballed coils that flex with heel and have wires
not much larger than the diameter of hair. They eventually fail
due to the constant flexing of the wires but if you treat your
autopilot carefully they should last quite a few years. If you move
a tiller pilot around gently you will hear a knocking sound. This
is the gimbals hitting the stops. Always treat them like eggs.
http://en.wikipedia.org/wiki/Fluxgate_compass
I used to repair autopilots in aircraft. The poor build and quality
of most marine autopilots are shocking. They are the typical mix of
great ideas (the electronics-sexy fancy stuff) combined with poor
execution (the hardware- knobbly boring bits). It reminds me of $25
million helicopter I worked on that was regularly grounded for a
cracked door hinge. It only takes one weak link to let you down.
Cheers, Paul