Can you help me choose a linear actuator?

[MigGat]

Hello everyone,

For quite a long time already I've been wanting to get my own autopilot using pypilot. Several things have been pushing me back (like money, time, overall knowlegde), but now I think I'm ready for it, except that I don't know how to choose a linear actuator.

I know this is quite a wide topic, so i'll try to narrow it down as much as I can. This  is my boat: https://sailboatdata.com/sailboat/puma-29/?units=metric . As you can see it displaces 3,368kg and is almost 9m length. I currently have installed an Autohelm ST2000, which is basically the same design as new Raymarine S2000: https://www.raymarine.com/es-es/download...ve-manuals

As advised by @seandepagnier, I require something rather powerful to be able to use it in heavy weather conditions. I also read a couple of times this thread https://forum.openmarine.net/showthread....r+actuator so I know there's plenty of options in AliExpress, Amazon, etc...

I know too that I will need to purchase a motor controller (hopefully the small one) from @seandepagnier's  store: https://pypilot.org/opencart/index.php?r...ry&path=59  (I don't even consider buying that anywhere else, because of trust, and the "opensourcefullness" of his job).

Also, this is a couple pictures from ST2000 manual so you can see how it is mounted. It's mandatory for me that I can keep using this autopilot in case pypilot fails, so it would be great if I can reuse the mounting socket and the tiller pin somehow.

   
   

That being said, I don't know where to start choosing the linear actuator. 

1) How many Kg/N (N stands for Newtons?) does it need to push?
2) How do I measure what stroke lenght do I need?
3) What speed show i have?
4) What am I missing?

I like this type of actuators because they are alreadyy waterproof, so I don't need to sew a canvas bag, but that is NOT my primary concern at all, is just an idea where I started.

[stelian]

Many people were disappointed by the Aliexpress tiller drives.

I recommend you this one: https://pcnautic.nl/nl/autopilot/raymari...ent-detail . It's not cheap, but it is good quality and will also fit your existing socket and tiller pin mounts, so when you consider this the price does not seem so big. I have one of those and I'm really happy with it.

[seandepagnier]

I got a drive off aliexpress with the specs of 170mm/s 50N force it cost $80. So far it has worked well but all the screws are steel and they are already rusting so much I cant remove them. Then the end stops got "stuck" it had automatic end stops to prevent the motor stalling which worked well until it didnt, and I had to bypass these since they are in series (with diodes most likely) with the motor. The pypilot motor controller stall protection seems to work well enough and prevents the motor from stalling.

It is a little fast but good on my boat. Can move the rudder 30 degrees per second. This is useful when surfing the ocean swells. I have built my own balanced carbon fiber rudder. Most people want something in the 50-70mm/s range with more force.

Without a balanced rudder the forces can be high especially with weather helm. I have in the past broken the wooden tiller and replaced it. So in a worst case situation you could need 500N of force on that size boat at 0.5 meters from the rudder hinge. Any tiller pilot will struggle with this, but by reefing the sails a smaller motor could manage with a small reduction in boat speed.

The faster the autopilot can move the rudder, the faster it can react and (assuming it is working well) this saves power as the boat holds a better course and the total power consumed is less (to a point). This is why I am looking at using motors that are 20 or 30 times more powerful than what is in a typically tiller pilot (but only $50 for the brushless motor) for the future since it would have better efficiency, but could also have much more force and speed, only if needed.

One option to have a small motor on slower boats that dont have balanced rudders is a mechanical wind vane. The wind vane's performance improves with stronger wind exactly when a weak autopilot motor struggles. The weak motor steers easily and better than the wind vane in lighter winds.

[MigGat]

Many people were disappointed by the Aliexpress tiller drives.

I recommend you this one: https://pcnautic.nl/nl/autopilot/raymari...ent-detail . It's not cheap, but it is good quality and will also fit your existing socket and tiller pin mounts, so when you consider this the price does not seem so big. I have one of those and I'm really happy with it.

This looks really cool and ready-to-use enough for my basic skills. The 245€ cost is quite a bit more than what I was expecting (100€-150€) but I can figure that out if that's the best option.
It also says it doesn't comes with a plug, so i would have to add that to the shopping list.

---

I got a drive off aliexpress with the specs of 170mm/s 50N force  it cost $80.    So far it has worked well but all the screws are steel and they are already rusting so much I cant remove them.    Then the end stops got "stuck"  it had automatic end stops to prevent the motor stalling which worked well until it didnt, and I had to bypass these since they are in series (with diodes most likely) with the motor.  The pypilot motor controller stall protection seems to work well enough and prevents the motor from stalling.

It is a little fast but good on my boat.  Can move the rudder 30 degrees per second.  This is useful when surfing the ocean swells.  I have built my own balanced carbon fiber rudder.    Most people want something in the 50-70mm/s range with more force.

Without a balanced rudder the forces can be high especially with weather helm.    I have in the past broken the wooden tiller and replaced it.    So in a worst case situation you could  need 500N of force on that size boat at 0.5 meters from the rudder hinge.  Any tiller pilot will struggle with this, but by reefing the sails a smaller motor could manage with a small reduction in boat speed.

The faster the autopilot can move the rudder, the faster it can react and (assuming it is working well)  this saves power as the boat holds a better course and the total power consumed is less (to a point).    This is why I am looking at using motors that are 20 or 30 times more powerful than what is in a typically tiller pilot (but only $50 for the brushless motor)  for the future since it would have better efficiency, but could also have much more force and speed, only if needed.

One option to have a small motor on slower boats that dont have balanced rudders is a mechanical wind vane.  The wind vane's performance improves with stronger wind exactly when a weak autopilot motor struggles.  The weak motor steers easily and better than the wind vane in lighter winds.

From what you say, buying a cheap one from aliexpress is not an option for me, since I wouldn't know how to fix the issues you faced.

I sail in the western mediterranean, so there are no big swells, just very fast choppy waves, which prove to be quite tricky to handle for the ST2000.

Regarding the windvane, I look at it as something else in addition to the autopilot, not as a replacement. Something I would like to have, to be honest, but I think is for next season.

[MigGat]

I measured yesterady the lenght of my the installet autopilot yesterday and it's 600m 
   

The pcnautic's one has a 600mm version, so it sounds like a match.

@seandepagnier Can you confirm me that whis will work with this motor controller? https://pypilot.org/opencart/index.php?r...duct_id=50

If so, i will start ordering the products

BTW @stelian, since you already installed one of those, what socket/plug did you use?

[stelian]

I used these ones: https://aliexpress.com/item/1005003072474781.html

[MigGat]

Nice, thanks!

[seandepagnier]

You should measure the stroke, or difference in length from fully extended to fully contracted.

[MigGat]

I did measure that, it's 310mm

[seandepagnier]

I guess what is more important is what angle this can turn the rudder to and how fast since you can change.

If you had more than one pin, or position to attach the tiller pilot, you could have more force for upwind, and more speed for downwind as well as compensating any helm by adding an offset port or starboard to allow operating with a shorter travel..

Most people just find a position that works and use it in all conditions.