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Minimal Tiller Pilot Adaptation
#1
I'd like to get some feedback on a DIY auto pilot to see if there are some safety or reliability issues I'm overlooking.  It is basically a Tiller pilot, but I want it inside the boat.  The goals:

  1. Safety
  2. Cheap
  3. Get the non-marine hardware out of the elements - protects the hardware and get the clutter out of the cockpit.
  4. Not have to manually removed the tiller mechanism when needing to immediately go to manual control.  Well... it's below the deck so I wouldn't be able to get to it in a timely manner.  I also want to avoid some Rube Goldberg contraption to remove the tiller pilot below the deck.  

I'm assuming I'd use the full suit of OpenMarine, PyPilot, controller, drivers, etc... and hook it up to something like these that are made for moving solar panels and cost less than $40US.  They're only IP54 and not salt water tolerant, so I'd like them inside the boat.  Besides, I'm trying to reduce clutter in the cockpit.

[Image: 71HLyl3Y1-L._SL1500_.jpg]


Here is a schematic in case the verbiage isn't clear.

   
  • The linear actuator would simply replace the connecting rod that is currently in this location.  
  • When the autopilot is engaged, the tiller is placed in the cradle to keep it stationary.  The actuator works the rudder as expected.
  • Taking over manual control (emergency or not) lift the tiller out of the cradle and press the button disengaging the autopilot.
  • If the autopilot was at some off-angle, it would be nice for it slowly return to its center point before going inactive.  



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#2
Is your tiller really offset from your rudder post that much? I've never seen that on a sailboat before. Do you have any photos? Maybe I'm misunderstanding your diagram.

The standard stroke for tiller actuators is ~12" (300mm) at a distance of 18" up the tiller arm, so to have your actuator work as a linkage like you depict here, it seems like it would have to be a very large offset to allow the actuator to be at the midpoint when centered and have room to extend and retract when in operation. Beyond that, by leaving the actuator connected to your steering system all the time, I would be concerned that the constant push/pull on the actuator arm when hand steering in big seas would wear out your bearings very quickly. Finally, those actuator speeds seem on the slow side unless they are very powerful and very close to the rudder post. My tiller actuator is 45mm/sec and 300N by comparison, attached at the 18" distance from pivot on my tiller.

For my money, I'd go with one of the $80 actuators from ebay/aliexpress and build a waterproofing shell around it for placement in the cockpit. Less engineering and fewer points of failure that could affect your baseline ability to steer.
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#3
(2024-02-02, 06:52 PM)MacKludger Wrote: Is your tiller really offset from your rudder post that much? I've never seen that on a sailboat before. Do you have any photos? Maybe I'm misunderstanding your diagram.

The standard stroke for tiller actuators is ~12" (300mm) at a distance of 18" up the tiller arm, so to have your actuator work as a linkage like you depict here, it seems like it would have to be a very large offset to allow the actuator to be at the midpoint when centered and have room to extend and retract when in operation. Beyond that, by leaving the actuator connected to your steering system all the time, I would be concerned that the constant push/pull on the actuator arm when hand steering in big seas would wear out your bearings very quickly. Finally, those actuator speeds seem on the slow side unless they are very powerful and very close to the rudder post. My tiller actuator is 45mm/sec and 300N by comparison, attached at the 18" distance from pivot on my tiller.

For my money, I'd go with one of the $80 actuators from ebay/aliexpress and build a waterproofing shell around it for placement in the cockpit. Less engineering and fewer points of failure that could affect your baseline ability to steer.

Thanks for responding.

Actually, the boat has dual rudders with a cross-link.  I just simplified the schematic for illustration.  So, there is plenty of room for any of those actuators to go from centerline to the cross link.  It's been a while since I've been under there, but I believe the arms are around 8".  I'll have to check.  But the 1000N at 14 mm/sec version would almost be equivalent to your numbers.  I'll need to check the arm sweep, but my gut feel is I won't even need the full 12" version.   Also, the rudders are balanced and be fine tuned to require zero load, though I put a little just for rudder feel.  

Another savings grace is this is a small boat and won't ever be out in big seas.  Likely it'll only be in lakes, ICW, bays, and an occasional costal sailing.  

BUT... your comment of the constant wear and tear just acting as a pushrod is an important consideration.  I'll need to dig up what these things look like.  I assumed a simple threaded rod with big honk'n nut making the connection... pushing the piston in/out.

Thanks.
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#4
It doesnt auto-center, but by code it could, but what if it did not? If there was some problem and it was stuck all the way in or out, would this make hand steering difficult?

I use those actuators... and I leave mine out in the rain. It still works but is rusting pretty bad now. I should bring it out of the rain but I have left it out in a bunch of storms now.

https://www.aliexpress.us/item/2255800497051447.html

I dont think it would affect the bearings to move them when off, because they are lead screws so should remain locked

Anyway, I would suggest considering waterproofing the actuator better. Replace the steel screws with stainless and coat the whole thing when you get it, and perhaps build a nice cover for it. It should be possible to build something around it to ensure it never gets wet but can still be used normally. It is good to be able to remove it and steer normally.
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#5
(2024-02-02, 07:47 PM)seandepagnier Wrote: It doesnt auto-center, but by code it could, but what if it did not?    If there was some problem and it was stuck all the way in or out, would this make hand steering difficult?

...

Anyway, I would suggest considering waterproofing the actuator better.  Replace the steel screws with stainless and coat the whole thing when you get it, and perhaps build a nice cover for it.  It should be possible to build something around it to ensure it never gets wet but can still be used normally.    It is good to be able to remove it and steer normally.

I don't think the auto-centering would be an issue.  As for safety, even if the AP was at full lock and I had to go manual, I'd still have plenty of tiller room to go the full range.  It'd just be off center.  It would be a nice-to-have and if/when I get to that point, I try digging into your code.  

Only part of the desire to put it down there is for weathering.  I highly desire to de-clutter the cockpit and adding a AP just makes things worse.  As it is, I'm changing helm, sail-plan, boom and sheeting for the main to get the traveler out of the cockpit.  

Thanks.
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#6
If you do this, it would be great to hear back about it once it is set up.
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#7
(2024-02-03, 05:05 AM)seandepagnier Wrote: If you do this, it would be great to hear back about it once it is set up.

I think I'll be haunting the forum off and on.     Smile   I have lots to learn from real sailors.
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