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-   -   gps + autopilot (http://www.sailnet.com/forums/gear-maintenance/15677-gps-autopilot.html)

bigpic 04-24-2006 10:39 PM

gps + autopilot
 
I am interested in purchasing a gps unit to which I can interface with my Raymarine ST1000+. I would like the gps to notify the autopilot of course corrections to navigate to one or more waypoints. This application would be for day/weekend use.. nothing fancy required. Does anyone have any suggestions regarding a gps device to buy? Do you have any personal experience intefacing these products? Does this sound like a feasible solution?

Thanks

Ryan

Faster 04-24-2006 10:50 PM

Find out what interface your auto helm supports, (likely NEMA). Most GPSs sold nowadays will offer various communication interfaces, just make sure that the GPS you choose can "talk" to your autopilot. The wiring is simple enough, and the GPS and the autopilot documentation should have a wiring diagram for just that purpose.

It's an easy thing to set up.

Silmaril 04-25-2006 08:50 AM

You will be pretty much stuck with a Raymarine, as their proprietary SeaTalk interface does not follow NEMA very closely. It would make everything easier to interface.

You can do it, but you will have to get the listing of what NEMA "words" the autopilot recognizes, and match them up with the "words" the gps transmits to the data bus.

Think about what the system has to accomplish, the autopilot needs to maintain a heading that it receives from the gps. Because the AP does not know where it is actually going, just a reference point on a fluxgate compass, the gps needs to feed deviation information to the gps, ie, "go +2deg". then the AP needs to respond. When interfacing such a system, it is usually best to have a server involved, which is a device that looks at all available data, (AP Wind, True Wind, Boat Speed, compass course, GPS course, etc.) then resolve it to make a judgment call on course corrections. There is usually a feedback device involved telling the server rudder position, so it can know if a suggested course correction is even feasible.

Pretty complex stuff! Not for the faint of heart, or technically challenged, and best left for the pro's. But if you are a techy hobbiest who loves a challenge, go for it! Be advised, it took months of fiddling with data settings, NEMA version settings, bus speeds etc. for me to integrate my electronics, Wind, Boatspeed, Dual Fluxgate Compass, GPS, VHF, PC Mapping Software. Some from different vendors. The server saved the day, making sure everything worked and played well together. And I have left the AP out of "The Loop" because of the added complexity the wiring, rudder position sensor, and tuning would have caused. That, and I like to steer myself!

TrueBlue 04-25-2006 09:01 AM

I had a similar experience as what Simaril described with my '99 vintage Raytheon ST6000+. After exploring possible ways to integrate the AP with the Raytheon chartplotter (forget the model #), I decided this was way too complicated, so I use the components separately.

sailingdog 04-25-2006 09:53 AM

The newer Raymarine Autopilots do have NMEA capability, without using a SeaTalk to NMEA converter box. I've got a ST1000 tiller pilot talking to a Garmin GPS without any trouble.

hamiam 04-26-2006 12:10 AM

Autopilot + GPS
 
Ive gotten all my raytheon (now raymarine) autopilots to interface with my the various garmin units ive had over the years. I wouldn't trust it in close quarters or leave it unattended for very long but, in my experience, it has been quite reliable.

sailingdog 04-26-2006 12:35 AM

Anyone who trusts an autopilot in close quarters or leaves one unattended for any length of time deserves to have their boat scuttled out from under them.

rptrsn 04-26-2006 03:06 AM

Saildog is absolutely correct about leaving it unattended. But if you're stuck motoring in calm weather with plenty of sea room, it will keep you on track. I have ours Garmin 128 nmea connected to a RayMarine 6001 autopilot and it works fine.

Some issues you need to be aware of before you go to great expense. When you engage Track on the autopilot, it will drive the boat to make a 20-30 degree course correction to get you immediately on to the track. It can be quite a surprise as you try to figure out where it's taking you. This happens even if your cross track error is only a tenth of a mile. Then it can take up to ten minutes of snaking through the water before it finally settles down. You really don't want to use it under sail.

Pete
s/y "Brilliant"
Moody 425

Jantar 05-07-2006 11:00 AM

I want to connect my Raytheon ST1000 + tiller pilot to my Magellan 315 GPS. The ST1000 + has NMEA +/- and the GPS data in and out. What should I connect to what? Thanks. Ivo

sailandoar 05-07-2006 07:03 PM

No problems
 
(1) NMEA is supported. If there is anything in the NMEA vocabulary that is not included you will probably not miss it. Sea talk is there if you need it (probably NOT)

FROM: ST1000 Plus & ST2000 Plus Tiller Pilots - Owner’s Handbook

Information on NMEA 0183 data words:
Cross Track Error:: APB, APA,RMB, XTE, XTR
Bearing to Waypoint:: APB, BPI, BWR, BWC, BER, BEC, RMB
Distance to Waypoint:: WDR, WDC, BPI, BWR, BWC, BER, BEC, RMB
Waypoint Number:: APA, APB,BPI, BWR, WDR, BWC, WDC, RMB, BOD, WCV, BER, BEC
Speed Through Water:: VHW
Apparent Wind Angle and Speed:: VWR


(2) CABLING

Go to the owners manual for the pinout. It will be 3-wire (a) common (12V ground) (b) Data in (recieve) , (c) Data Out (transmit).

Get the common correct and the rest will fall into place. You can't hurt anything switching the data wires so just give it your best educated guess and then switch the data wires if that does not work. Serial communication has some issues with terminology that constantly causes confusion so don't feel bad.

Example: Equipment is divided into two types DTE and DCE and between them you connect trans-a <=> recieve-b and recieve-a <=> trans-b, HOWEVER if the items are both DTE or DCE you then have to cross-over the two data wires.... i.e. transmit<=>transmint // receive<=>receive. They labels are just words so don't let them throw you.
DTE - Data Terminal Equipment
DCE - Data Communication Equipment

************************
Most any GPS will work, just set the communication protocol to NEMA.
Comments about 'seatalk only' do apply to the older units but anything inthe last 5-8 years will talk NMEA.


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