Raymarine St4000 with Trim Tab Problem

[GILow]

Originally Posted by Snowpetrel

Damn GI. Cant seem to get android to recognize that compressed file. Even VLC viewer for andriod just goes blank on me... any tips?

It did something odd when I uploaded it. I uploaded a WMV file, but the CF site then reprocesses the file and streams it from the embedded CF player, along with some pretty darn strange advertisement for male growth hormones.

At least the embedded player works using Windoze, but from the App it seems to just give you the header file for the embedded player. I can't even zip it up to attach it either, the system does not seem to allow such sneaky tricks.

Anyway, it ain't exactly David Cameron's finest work, though it does very clearly show the self correction of the setup clearly, so I think it would be well worth viewing for anyone considering such a setup.

Matt

[GILow]

Originally Posted by Snowpetrel

Damn GI. Cant seem to get android to recognize that compressed file. Even VLC viewer for andriod just goes blank on me... any tips?

OK, here it is on YouTube. My first Youtube video, that has to be the start of a slippery slope...

https://youtu.be/GYn5Qu7gz3M

[Snowpetrel]

Thats a great video Matt, it really shows the positive feedback mechanism working. Its interesting how your setup enables the pivot to go anywhere along the tiller, not just at the main rudders axis as I was thinking at first. This should enable a nearly infinate combination of 'ratios' both for feedback 'counterrudder' and rudder or gain. Neat...

Only one small point, I am guessing unless you rudder is very well balanced its not going to quite reach equilbrium at the same angle as your stub tiller due to the water force on the rudder at the angle requiring a small amount of trim tab angle to hold it at that angle. Unless that is you get real flash and go with an autopetre overballanced type. Now that would be a powerful gear, and your mechanism is the perfect system for controlling such a finicky beast.

Just another aside, a freind set up a trim tab to act as a power steering system. He used hydraulics from memory. Very clever.

[Rustic Charm]

Originally Posted by GILow

OK, here it is on YouTube. My first Youtube video, that has to be the start of a slippery slope...

https://youtu.be/GYn5Qu7gz3M

Well done that looks very interesting. Just need to convert it to a drawing that can then be made up.

[Rustic Charm]

Originally Posted by GILow

OK, here it is on YouTube. My first Youtube video, that has to be the start of a slippery slope...

https://youtu.be/GYn5Qu7gz3M

So is the axis for the black colour trim tab on the same axis as the rudder axis?

I've watched this six times now. I'm transfixed on it �� Have you actually made this system? Does it work?

[GILow]

Well thanks to Snowpetrel for suggesting the video. And it was fun doing my first YouTube video. When I reach 1 million views I'll report back.

In answer to various questions....

SP, yes, you are right, the actual point of equilibrium will not be as simple as I have suggested in the video. Depending, as you say, on rudder balance, plus trim tab area, plus weather helm and goodness knows how many factors. But none of these should matter because from the autopilot's point of view this is simply a more or less responsive rudder. Either way, I guarantee it will find a point of equilibrium consistently and predictably.

RC, the pivot point of the arm is slightly aft of the pivot point of the rudder in this particular model. I played around with the pivot point a bit (hence I used a 3 unit stud with end block, which was easy to move and is visible sticking up on top of the arm) The mechanism works well with the pivot point practically anywhere, but seemed to be most "stable" with the pivot close to but aft of the rudder pivot point. The more "dampening" from the ratio of length forward of the pivot to rear of the pivot the better too I felt.

Have I made this in practice? Nope, not even remotely, but others have. These principals are all well documented in various books on self steering systems. I just check the ideas out in Lego.

Honestly, I think this would be so easy to fabricate, with just as much adjustment, even more, available from a few strategically drilled holes.

Either way, glad to have been able to share the idea, and there is a drawing of the fabrication in my earlier post.

Matt



Sent from my iPad using Cruisers Sailing Forum

[GILow]

Well thanks to Snowpetrel for suggesting the video. And it was fun doing my first YouTube video. When I reach 1 million views I'll report back.

In answer to various questions....

SP, yes, you are right, the actual point of equilibrium will not be as simple as I have suggested in the video. Depending, as you say, on rudder balance, plus trim tab area, plus weather helm and goodness knows how many factors. But none of these should matter because from the autopilot's point of view this is simply a more or less responsive rudder. Either way, I guarantee it will find a point of equilibrium consistently and predictably.

RC, the pivot point of the arm is slightly aft of the pivot point of the rudder in this particular model. I played around with the pivot point a bit (hence I used a 3 unit stud with end block, which was easy to move and is visible sticking up on top of the arm) The mechanism works well with the pivot point practically anywhere, but seemed to be most "stable" with the pivot close to but aft of the rudder pivot point. The more "dampening" from the ratio of length forward of the pivot to rear of the pivot the better too I felt.

Have I made this in practice? Nope, not even remotely, but others have. These principals are all well documented in various books on self steering systems. I just check the ideas out in Lego.

Honestly, I think this would be so easy to fabricate, with just as much adjustment, even more, available from a few strategically drilled holes.

Either way, glad to have been able to share the idea, and there is a drawing of the fabrication in my earlier post.

Matt



Sent from my iPad using Cruisers Sailing Forum

[GILow]

Oops. Double post. Silly iPad app.

[Rustic Charm]

Originally Posted by GILow

OK, here it is on YouTube. My first Youtube video, that has to be the start of a slippery slope...

https://youtu.be/GYn5Qu7gz3M

I'm still watching this

I'm contemplating making up a plywood version to scale it looks so simple. Would this make setting up the auto pilot simple.

[GILow]

Originally Posted by Rustic Charm

I'm still watching this

I'm contemplating making up a plywood version to scale it looks so simple. Would this make setting up the auto pilot simple.

Well, as much as I'd like to offer a director's cut, I am not sure you'd get much more from it.

If I were fabricating it for your setup, I would simply find a nice piece of hardwood, about 700mm long, say some 30mm high x 45mm wide Tassie OAK DAR. I'd drill a series of 8mm or 10mm holes through the 30mm axis for the hinge point (so choose a size based on what you will use for the pivot pin), starting around 100mm from one end (call it end A), at 50mm intervals up to about the 300mm point (5 holes). I'd cut a slot in the end of the timber at end A, running vertically, using a broad blade saw or a even a narrow router bit, something around 5 mm or 6mm wide up to a point 75mm from end A. This is to take a vertical pin on the end of the trim tab arm so size the slot to suit whatever you can find for that role. A bit of silicon spray or even grease in the slot should be adequate for testing.

At the other end (end B), I'd drill a series of smaller holes from near the very end, at 50mm intervals, back to a point near the centre. These holes would be sized to take the pin that will be driven by the autopilot ram, so their size will be dictated by whatever pin size the ram needs.

Then I'd figure out how I am going to lash my pivot pin to the side of the tiller and then put it all together and go for a pootle down the river. Probably under engine is easiest at first.

Then I'd play around using the different holes I have drilled for the pivot point first, followed by the different holes I have drilled for the ram pin, until I found what worked best.

Then I'd drill a hole in the tiller for the pivot once id figured out the best relative location.

Test it all again, then if happy, toss the Tassie Oak and get a bit of 6mm stainless flat bar, probably around 30mm wide, and drill the pins based on my timber mock up.

Then go sailing, using half a dozen electrons for each course change.

Neat!


Matt

[Rustic Charm]

$40 to add this. The holes are at 100, 125, 150 and 175mm.

[atoll]

Originally Posted by Rustic Charm

$40 to add this. The holes are at 100, 125, 150 and 175mm.

looks like a work of art!
is the butterfly screw for locking?

[Rustic Charm]

Originally Posted by atoll

looks like a work of art!
is the butterfly screw for locking?

yep. Locks the trim tab tiller to the main tiller. Then I can place the ST4000 on to the locked Trim Tab tiller to operate in the old way.

Unfortunately I'm going to be trialing this on Monday in a crossing of Bass Strait (weather permitting) to Victoria.

[atoll]

Originally Posted by Rustic Charm

yep. Locks the trim tab tiller to the main tiller. Then I can place the ST4000 on to the locked Trim Tab tiller to operate in the old way.

Unfortunately I'm going to be trialing this on Monday in a crossing of Bass Strait (weather permitting) to Victoria.

did you work out how to adjust the YAW,RUDDER and SEA STATE settings on the auto pilot?

[Rustic Charm]

Originally Posted by atoll

did you work out how to adjust the YAW,RUDDER and SEA STATE settings on the auto pilot?

I've read up in the manual yes. But not had a chance to test it as I needed that arm welded on. Five new brass bushes for the other end arrived today, so I also need to arodite them in to the 20mm ply bit I put on the main tiller. Then I'm ready to give it another go.

We are expecting high winds on the weekend, so I doubt I'll get the chance before Monday to trial it. I will if I can on the weekend if weather lets me.