compass/heading sensor needed?

[diama]

hello...confused?? is a compass/heading sensor required to use navico 3g radar with opencpn. thanks diama

[nohal]

Originally Posted by diama

hello...confused?? is a compass/heading sensor required to use navico 3g radar with opencpn. thanks diama

If you for some reason don't have it, you may to some extent simulate HDG from COG, but be prepared that the result will be far from optimal.

Pavel

[diama]

thanks Pavel, at this moment have toughbook cf18 running opencpn with a gps puck....what exactly would we need to have the radar overlayed on the chart screen( or show on a separate screen?) diama

[nohal]

You need to read https://github.com/keesverruijt/BR24radar_pi/wiki and do the stuff you learn there.

[diama]

thank you...reading that link helped...will have to look into acquiring a heading compass

[AuroraGH]

Originally Posted by diama

thank you...reading that link helped...will have to look into acquiring a heading compass

I'm using a pair of these:

https://www.robotshop.com/en/tilt-co...ss-cmps12.html

One on my rudder and one on the boat. Difference is rudder angle. So far, so good.

[seandepagnier]

comparing a compass on the rudder to one on the boat will give very poor absolute accuracy. It's not a good way to measure rudder angle.



Why don't you use a potentiometer or hall sensor?

[AuroraGH]

Originally Posted by boat_alexandra

comparing a compass on the rudder to one on the boat will give very poor absolute accuracy. It's not a good way to measure rudder angle.

Why don't you use a potentiometer or hall sensor?

I don't know how to do that on a transom hung barn door rudder. I'm open to suggestions though.

[seandepagnier]

Just an idea..


You can put a pin either on the tiller or on an arm offset on the rudder, from this, a ball socket to a rod which has another ball socket to the arm of the potentiometer.


You could also potentially mount the potentiometer on top of the rudder aligned to the rudder hinge.


There are probably many other ways as well.. Most people don't measure rudder angle with tillers, it's mostly for hydraulic steering with wheels where they don't actually know the rudder angle.. maybe you don't need it?

[billknny]

You don’t need a separate rudder angle measurement for autopilot control when you have a tiller.

All you need is to measure the extension of the actuator. It has a fixed and essentially linear relationship to rudder angle. Much better than a complex cobble of two compasses.

[AuroraGH]

Originally Posted by billknny

You don’t need a separate rudder angle measurement for autopilot control when you have a tiller.

All you need is to measure the extension of the actuator. It has a fixed and essentially linear relationship to rudder angle. Much better than a complex cobble of two compasses.

Yeah, about that...this is my actual boat. I want an autopilot to handle the helm during periods of protracted motoring. I already have a Monitor that does a great job under sail.

Coming up with an actuator that works with this setup has been a huge challenge. I have looked at electric rams. I can't seem to find one that would allow both a decent range of motion and still fit on within the rails. I already have a line with a length of chain in it that pulls the tiller back and forth.

The only thing I've been able to come up with is to repurpose a powered capstan or winch drum and use a looped line with a chunk of chain in the middle to move the tiller. I haven't had any luck coming up with a servo with encoder and brake at a sensible price so I'm looking to use the motion compensated compass as my rudder feedback mechanism.

I've been looking at this problem and scratching my head over it for a few years now. The usual suggestions generally don't pan out but if someone pointed me to something off the shelf that worked, I'd hop on it.

FWIW, power isn't an issue. This autopilot will only be used when motoring.

[RogerD]

I use a tillerpilot on the windvane to steer while motoring.

An example of this is shown here: Automate the windvane

[AuroraGH]

Originally Posted by RogerD

I use a tillerpilot on the windvane to steer while motoring.

An example of this is shown here: Automate the windvane

I had a conversation about this with scanmar. They do not recommend leaving the paddle in the water in the propellor wash as the vibration from the cavitation tends to introduce stress and abnormal wear.

As I am looking for an autopilot to be used exclusively for motoring, this is a non-starter.

[seandepagnier]

I managed to make several different tiller drivers. I used windshield wiper motors and winch arrangement, ballscrews and lead screws. You could probably use two or even 4 windshield wiper motors in parallel to get much more power in a winch arrangement, or possibly drive a ball screw using one of these motors and get an incredible amount of torque. Typical stainless ball screws use 440 grade which does rust much more easily.



If you have a wind vane for when the wind picks up, the motor does not need nearly as much speed or force to be effective in light wind, so I would imagine using a single wiper motor with ball screw would be cheap and effective drive for you.





Your concern of prop wash on the wind vane oar only verifies that you have an inefficient drive system. Propellors if they be used at all should be much larger than this, or 4-5 feet in diameter in your case turning slower than 100 rpm. Moving a small stream of water very fast is inefficient and wasteful. There is a reason my sculling oar is 16ft long on 27ft boat, and a regular paddle is much less efficient.





I would suggest you use the sails. If you disagree it is likely you need to try a little harder to catch the wind. I found this always works and it's possible to sail everywhere. I often watch people motoring when I am sailing going the same speed, but when they see me and try to sail, they fall behind and start the motor again because they just didn't set the sails correctly. The concept of motoring for extended periods is a poor one.