Nema 0183 to linear DC

[TreblePlink]

Originally Posted by ilana

I was delivering with another person a boat and due to lightning damage we kept the steering wheel for 45 hours. Not nice.
During the overlapping hours, we thought of a simple solution of a magnetic compass needle and two sensors that would identify a deviation in the path, and would fix the ship's cruise with the navigator's electric motor.
The solution is very primitive but may work.

As long as you have electricity, a bit more complexity using the NMEA gps data or a tilt-compensated electronic compass should work a lot better. Averaging is usually necessary in any case.

I am also considering a homebrew ap. If fast enough to compensate for varying speeds is large swells, it would have to use significant amounts of energy, but in most seas, a correction every 5 or 10 seconds would seem adequate.

I am trying to figure out why most AP controllers want to know rudder angle. Seems like if one could set mechanical limits as to angle, the AP would (lacking PID) just incrementally move whichever way would lessen the error. If error > 30 degrees, stop correcting and sound an alert. This may be naive, but seems like it would work if sails are reasonably balanced ...

[smac999]

Originally Posted by TreblePlink

I am trying to figure out why most AP controllers want to know rudder angle. Seems like if one could set mechanical limits as to angle, the AP would (lacking PID) just incrementally move whichever way would lessen the error. If error > 30 degrees, stop correcting and sound an alert. This may be naive, but seems like it would work if sails are reasonably balanced ...

some don't, but every pilot with one works way better then without one. its not only for the end stops. it knows how fast the boat turns vrs how fast the rudder turns.

[Rapanui]

What you described in your original post is you need to read and convert a NMEA value to an analogue voltage output. To do that you would need to read a serial data stream in, extract the NMEA sentence you need, convert it to the output value you need and then instruct a Digital to Analogue converter to output the desired voltage. So you would need a microprocessor with serial (RS232) input and D to A output and the control software. Pretty well every packaged micro (Arduino, Raspberry Pi, etc) could do this. Whether it would work would depend on what inputs and their update rate you use to provide the feedback loop and the capability of the software. Not a trivial task, just setting it up would take some time. It might be easier to buy a secondhand wheel pilot (the ones that clamp to the wheel) as a backup.

[hzcruiser]

Check out
Jack Edwards Arduino Based Sailboat Autopilot

https://www.youtube.com/watch?v=-nA6wo9PXls

[nohal]

And Sean's one...
pypilot - open source marine autopilot

[ilana]

The solution presented in the video is beautiful. A little too complicated for my needs.
I have tried to plug the NEAA 0183 outport of the seaclear software into the boat's navigation computer and the heading was reasonable.
The next assignment is defined as this. I will try to catch the seaclear exit by software on arduino and see if I can manage a mini DC motor with a small pwm driver.
Hope to succeed. I'll tell you later.
Thanks for all the help. If there are more ideas I'd be happy to keep up to date
Ilan

[ilana]

Hello,If possible a little extra help.
I would like to know what is the content of the sentence sent from the port connection on the navigator's computer to the ship's steering system.
I mean, what is the prefix letters of the sentence which is responsible for the rotation of the ship's stiring/rudder entire contents and the end of the sentence.
http://www.tronico.fi/OH6NT/docs/NMEA0183.pdf
Rgards
Ilan Arbel

[hoolie]

I think it's usually RMB though some systems need RMC as well

[Paul L]

Originally Posted by ilana

Hello,If possible a little extra help.
I would like to know what is the content of the sentence sent from the port connection on the navigator's computer to the ship's steering system.
I mean, what is the prefix letters of the sentence which is responsible for the rotation of the ship's stiring/rudder entire contents and the end of the sentence.
http://www.tronico.fi/OH6NT/docs/NMEA0183.pdf
Rgards
Ilan Arbel

In general you do not need any Chartplotter output to an AP. The AP will steer to a compass course without the Chartplotter connected.

[transmitterdan]

ilana,

There is no NMEA sentence that "controls steering". So I think you are looking for a regular auto pilot which will steer to a heading. Most AP units can accept a target heading input from NMEA but there are some older ones that are purely manual.

[smac999]

Originally Posted by ilana

Hello,If possible a little extra help.
I would like to know what is the content of the sentence sent from the port connection on the navigator's computer to the ship's steering system.
I mean, what is the prefix letters of the sentence which is responsible for the rotation of the ship's stiring/rudder entire contents and the end of the sentence.
http://www.tronico.fi/OH6NT/docs/NMEA0183.pdf
Rgards
Ilan Arbel

there isn't one. the auto pilot computer must do all the calculations.

the software will send out distance to waypoint, bearing to waypoint, and error distance off of that track.