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britinusa
Web Editor

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USA
5404 Posts
Initially Posted - 03/14/2015 :  13:41:11  Show Profile  Visit britinusa's Homepage
It has always amazed me that Garmin did not come up with a simple add on to their chart plotters to provide auto pilot control out put to drive an Auto pilot power head.

Or am I missing something?

Paul
Joint Decision. (Sold)
PO C250WB 2005 Sail # 841.


Moved up to C34 Eximius

Updated August 2015

delliottg
Former Mainsheet C250 Tech Editor

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USA
4479 Posts
Response Posted - 03/14/2015 :  18:53:39  Show Profile  Visit delliottg's Homepage
I'm able to control my ST1000+ with my Garmin 276C. It took me a while to figure out the pinouts from my GPS into the AP.
David
C-250 Mainsheet Editor


Sirius Lepak
1997 C-250 WK TR #271 --Seattle area Port Captain --
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britinusa
Web Editor

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USA
5404 Posts
Response Posted - 03/14/2015 :  19:17:15  Show Profile  Visit britinusa's Homepage
David, you have to share!

Paul
Joint Decision. (Sold)
PO C250WB 2005 Sail # 841.


Moved up to C34 Eximius

Updated August 2015
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TakeFive
Master Marine Consultant

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2272 Posts
Response Posted - 03/14/2015 :  19:45:48  Show Profile
It sounds easy in theory - the chartplotter just tells the the power head to turn left or right. But there needs to be PID controller logic to prevent cumulative errors from building up, and to damp out oscillations caused by wave motion of the sea, etc. All that logic is typically built into the autopilot's control head, and that function would need to be programmed into the chartplotter if there was no control head.

Plus, the most popular operating mode of an autopilot is simply maintaining a steady compass course, so the autopilot comes with its own fluxgate compass for that. That would have to be built into the chartplotter also.

The standard way of doing this with a traditional autopilot in "track mode" is for the chartplotter to feed data on bearing to waypoint and cross-track error to the chartplotter, which uses its PID logic to maintain a steady course to the waypoint and minimize cross-track error without causing wild oscillations. Like David, I've done this with my Raymarine ST4000+. Instead of a turnkey chartplotter or GPS, I use OpenCPN on a Windows tablet. And I managed to do it all wirelessly via Bluetooth, so I can move the tablet anywhere on the boat without a bunch of wires dangling around.

There have been a couple times when I managed to run an all-day pre-programmed course from the Chesapeake Bay, through the C&D canal, and up the Delaware River. I did keep a constant watch to make sure the course didn't take me right thorough a buoy or a freighter's path.
Rick S., Swarthmore, PA
PO of Take Five, 1998 Catalina 250WK #348 (relocated to Baltimore's Inner Harbor)
New owner of 2001 Catalina 34MkII #1535 Breakin' Away (at Rock Hall Landing Marina)
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awetmore
Master Marine Consultant

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USA
1144 Posts
Response Posted - 03/16/2015 :  05:53:04  Show Profile
quote:
Originally posted by TakeFive

It sounds easy in theory - the chartplotter just tells the the power head to turn left or right. But there needs to be PID controller logic to prevent cumulative errors from building up, and to damp out oscillations caused by wave motion of the sea, etc. All that logic is typically built into the autopilot's control head, and that function would need to be programmed into the chartplotter if there was no control head.


The control head also includes the motor driver, a component that isn't generally a part of a chartplotter. The motor driver takes a low level analog signal and uses that to provide a proportional amount of drive to a high power motor (what actually turns the wheel or pushes the tiller).

The plotter also doesn't have the necessary fluxgate compass, and may not be positioned in the best place to have one (especially since most plotters include a magnetic latching door to hold the memory card closed).
Alex W
Seattle, WA
Express 37 "re-Quest"
previously owned 1984 Catalina 25 "Lutra"
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Notice: The advice given on this site is based upon individual or quoted experience, yours may differ.
The Officers, Staff and members of this site only provide information based upon the concept that anyone utilizing this information does so at their own risk and holds harmless all contributors to this site.