REALTIME CONTROL
SCA3 Small Craft Autopilot Controller
These pages describe a
microcontroller-based autopilot controller
for yachts and boats.
Sufficient detail is included for a
boat owner with electronic and software skills to build it.
Realtime
Control does not supply SCA3s, nor kits, nor parts.
Features:
* Low parts count
* Rudder position inference from motor back EMF, so no rudder position
sensor is required
* Cascaded pair of PID loops, pushbutton configurable to suit a wide
range of vessels and conditions
* GPS, compass or anemometer heading reference
* Soft motor start by PWM of drive current
* Automatic weather helm compensation
* +/- 1 and +/-10 degree pushbuttons for course control
* +/- 100 degree "go about" control
To build an SCA3 you will need:
- Electronic construction skills sufficient to construct an
electronic board from scratch
- Electronic theory skills sufficient to locate any errors in your
construction
- Mechanical skills sufficient to devise a drive system for the
vessel's rudder
- Microchip's MPLAB IDE, V6.60 or the GNU PIC assembler GPASM, and a
compatible programmer for
PIC16F628A devices
To use an SCA3 you will need:
- A heading reference (GPS, compass or anemometer) with NMEA 0183 output
- A 12V PM DC motor and drive train to suit the
vessel's tiller or wheel
- Some understanding of PID control loops
The result of your efforts should be an
autopilot system capable of
steering your boat in most conditions.
Background
Overview
Heading Sensors
Rudder Drive
Hardware
Software
Source code REV 1.1
REV 1.1 (released 1 Oct 05) of the
software fixes an error in the original code which prevented load from
flash and save to flash of coefficients when steering on the basis of
anemometer data. This revision also adds beeper control,
non-reversing deadtime
control, and increasing rudder movement at low speed control. See
main.asm in the source code for details.
GPASM info
Quick and dirty QBasic NMEA sentence generator
Controls
Setup
Tuning
REALTIME
CONTROL
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