REALTIME CONTROL
SCA3 Autopilot Controller
Background
We lived two years and sailed
some 11,000 miles on our 32 ft cruising yacht along the East coast of
Australia and to New Caledonia, Vanuatu and the Solomon Islands.
The first year our only automatic steering system was an Aries wind
vane. This performed well while there was sufficient breeze, and
impeccably in extreme conditions, but we needed a system to steer in
light winds and under power.
At the end of the first year we obtained a broken Autohelm Tillerpilot,
replace the failed electronics with a simple 555-based "bang-bang
with deadband" controller and linked it to the Aries. This setup
steered us many miles and used little power.
We now mostly day sail from our home port, and fit the Aries only for
extended trips. This left us with no automatic steering system for day
sailing. We were
given and fitted an Autohelm 3000. However, while it performed
adequately much of the time, it was useless in some conditions. Except
in light weather it either consumed power in unnecessary, frequent
movement of the rudder, or did not respond in time to hold a course,
depending to some extent on the setting of its "Rudder" control.
We obtained a second Autohelm 3000 controller with dead electronics,
removed these, and fitted a control board of our own design based
around a PIC 16F628 microcontroller. This system can accept heading
data from the VDO fluxgate compass, the Navman GPS or the Rotorvane
wind instrumentation. We have found that this controller
can be tuned to steer the boat in almost any conditions for which the
Autohelm rudder drive system is adequate. The SCA3 is a
development of this controller, with modifications which reduce the
parts count and eliminate the rudder position sensor.
Overview
Index