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Old 24-04-2016, 23:09   #1
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Homemade tiller autopilot

So, I can't help but thinking ahead to when I get my boat fixed. I have seen stand alone autopilots that take control of the tiller. I thought about it and this is my hardware list to replicate such an autopilot. Arduino board, $10. Wifi shield, (optional, maybe not release 1) $20. Display board with pushbuttons for control, $12. Waterproof box, $6. Linear actuator with position reporting, $135. Hookup wire, $40. 9 degree of freedom sensor with included flux gate compass, $10.


Thoughts? I don't plan on sleeping with this on, so I would see any errors and I could disconnect it easily. But a simple "follow this compass heading" would seem to be fairly easy to implement.

I can see one issue, and that is that a lot of these actuators have duty cycles as low as 25% over 10 minutes. I guess that the program could track how much the actuator has been used and it could get less aggressive if the duty cycle limit is approached. Hmmm.

Thoughts? This is probably a winter project.
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Old 24-04-2016, 23:41   #2
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Re: Homemade tiller autopilot

Sounds like you got the basics of a working system. You might talk to Brian at Pelagic Autopilots. Good guy and he might be willing to give you some guidance, or at least shoot down ideas that are sure to fail
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Old 25-04-2016, 01:20   #3
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Re: Homemade tiller autopilot

Biggest issue I see is the power of the actuator vs the power needed to handle the rudder.
No indication on the boat involved or the power of the actuator. Just make sure you have enough power to overcome max expected load.
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Old 25-04-2016, 01:25   #4
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Re: Homemade tiller autopilot

Quote:
Originally Posted by Brasshopper View Post
So, I can't help but thinking ahead to when I get my boat fixed. I have seen stand alone autopilots that take control of the tiller. I thought about it and this is my hardware list to replicate such an autopilot. Arduino board, $10. Wifi shield, (optional, maybe not release 1) $20. Display board with pushbuttons for control, $12. Waterproof box, $6. Linear actuator with position reporting, $135. Hookup wire, $40. 9 degree of freedom sensor with included flux gate compass, $10.


Thoughts? I don't plan on sleeping with this on, so I would see any errors and I could disconnect it easily. But a simple "follow this compass heading" would seem to be fairly easy to implement.

I can see one issue, and that is that a lot of these actuators have duty cycles as low as 25% over 10 minutes. I guess that the program could track how much the actuator has been used and it could get less aggressive if the duty cycle limit is approached. Hmmm.

Thoughts? This is probably a winter project.
you probably also will need some sort of relays as your circuit boards probably work on 5v at a very low current,and your linear ram would work at 12v at a much higher current,you also probably need some diodes to reverse
the polarity of the current to the linear ram so it goes backwards and forwards
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Old 26-04-2016, 03:54   #5
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Re: Homemade tiller autopilot

You'd also need some sensors like a 3-axis gyro and compass to help anticipate the steering changes required. I had thought that making a pilot should be simple, but ran out of time and bought one. I am surprised at how the thing has "learned" how our boat behaves and steers it so well in rough water.

Chris
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Old 27-04-2016, 02:22   #6
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Re: Homemade tiller autopilot

I am trying to decide between actuators that exert 40 pounds load but which can move faster and actuators which can exert 120 lbs of force but move slower. There are also tradeoffs in duty cycle. Weaker actuators can stand a 40% duty cycle or higher while stronger ones might be limited to a 25% duty cycle. I can probably either calculate duty cycle or get an extra temperature probe. I had thought about mounting the actuator right on the transom, close to the pivot, using a 12" travel actuator, and the 120 pound one to be sure the rudder would work even though I was giving up most of the mechanical advantage in mounting.

There are two fundamentally different approaches I can see taking. One would be to use the arduino. This is a relatively simple device that has a lot of support in an active user community. It is programmed in a variant of C++ and your program is always in control. If it ends it is just started again.

To program it, you need a system that can download the code using USB. The code is stable when it is loaded and can't be changed until the USB is hooked up again.

If you want your program to do multiple things, you need to write your own, possibly simple dispatcher.

The other approach would be to use something like a Raspberry Pi. This allows you to run Linux. You can have multiple tasks running and the system dispatcher will deal with things. As an example, one task might work the autopilot, another task could monitor a GPS, and a third might try to deal with man overboard monitoring. You could run openCPN in spare cycles, say, while giving the pilot program priority.

But I have read about neural network software for Linux, and while I have never used it, it seems like you have an easy goal to conceptualize. You want minimum divergence from your planned path and, as a second goal, minimum perturbation of the boat.

Each axis could be an input to the net. You would probably want some smoothing on the output to the rudder.

You also have a wider choice of programming language, and there are high level languages that can make patching easier.

The hardware cost would be higher. $50 for the Pi, maybe, another $50 for a display. Everything else would be the same.

But the end result could be a pilot that learned your boat and how it reacts to the helm, and after a short period could become an expert handler.

Just thinking ahead. I have a long road in front of me.

I programmed for a living for many years. This will be a large coding task in any case. While getting something that can hold a heading probably will not be hard, (famous last words) I could see it taking a year or more to get some degree of sophistication in the algorithm.

The device I am thinking of using for compass and gyroscopic attitude measurement is the MPU-9255. It has its own on-board processor that can process attitude and direction information. I will be studying product data sheets for sure.

These actuators are typically used, say, to open a window or even the lid of a box. They require a dpdt switch because the DC polarity has to be reversed to control direction. The arduino setups I have seen use pairs of dual contact relays to let the 5v from the arduino control and reverse the 12v supplied to the actuator. I was going to look for something solid state for the relays. My gut feeling is that solid state relays will be more reliable and, well, quieter.
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Old 27-04-2016, 03:50   #7
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Re: Homemade tiller autopilot

about 4 years ago there was a similar thread on the forum by a guy that had sucsessfully built his own auto pilot control unit using a very cheap and simple micro processor.
it might be worth looking for this thread to see what he used,rather than starting from scratch!

edit here is a link to the video he posted
edit here is the thread DIY Autopilot

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Old 08-03-2017, 14:43   #8
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Re: Homemade tiller autopilot

There is another very long thread on this forum that discusses autopilots.. its a must read.

Let me save you some time. PID loops alone are not very effective for autopilots. They work ok in one sea state, but will fail in another. An adaptive PID might work better depending on your algorithm.

There is a huge difference between an autopilot for a power boat and an autopilot for a sailboat. Two entirely different animals.

Think fuzzy logic, adaptive control etc, neural networks, etc. Basically you need to mimic yourself at the tiller and that is harder than you might think.

Fuzzy logic has been proven to for very large power boats (freighters). But teaching the logic is then half the battle.

I have documented part of my first attempt at DC9.com.

Dave
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Old 08-03-2017, 22:51   #9
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Re: Homemade tiller autopilot

RE actuator duty cycles: I suspect that the 25% value is for full power operation. If the actuator is sized reasonably, it would mostly be running well below max thrust, and I expect that the duty cycle limits would be raised considerably.

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Old 04-04-2017, 00:21   #10
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Re: Homemade tiller autopilot

Quote:
Originally Posted by Brasshopper View Post
So, I can't help but thinking ahead to when I get my boat fixed. I have seen stand alone autopilots that take control of the tiller. I thought about it and this is my hardware list to replicate such an autopilot. Arduino board, $10. Wifi shield, (optional, maybe not release 1) $20. Display board with pushbuttons for control, $12. Waterproof box, $6. Linear actuator with position reporting, $135. Hookup wire, $40. 9 degree of freedom sensor with included flux gate compass, $10.


Thoughts? I don't plan on sleeping with this on, so I would see any errors and I could disconnect it easily. But a simple "follow this compass heading" would seem to be fairly easy to implement.

I can see one issue, and that is that a lot of these actuators have duty cycles as low as 25% over 10 minutes. I guess that the program could track how much the actuator has been used and it could get less aggressive if the duty cycle limit is approached. Hmmm.

Thoughts? This is probably a winter project.
I have my own home made unit. Wifi, navionics etc etc. If you want a place to start, type yacht autopilot on youtube. Skim past the model yachts. Autopilots are a simple system in function and software. Outrageous cost though. Make your own, there are plenty of software
engineers that have yachts.
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Old 04-04-2017, 02:26   #11
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Re: Homemade tiller autopilot

Edit: OOPS, zombie thread. Still, just in case anyone is searching my post remains as possibly useful. Would love to know if the op ever got it going.


Went down this path a few years ago using a picaxe chip and a Phillips cm3000 fluxgate on an ic2 bus. A couple of variable resistors are your friend, allows you to tweak response rate and correction factor on the fly till you get those variables in the code about right, then you can hard code them in.

Sounds like you have some kind of hall effect counter for position feedback which is great.

Used mosfets, not relays, plenty of switching power in those.

Steered our 20 foot Austral very well in most conditions.

BUT.....

I never found a satisfactory linear actuator. The speed and force of a good quality tillerpilot like the TP1000 was actually hard to match, and once I did find a match I also found the total cost was about the same as a new tp1000.

But if you have found a satisfactory linear actuator then feel free to drop me a PM if you have any questions. I no longer have the code but it was very simple and I could rewrite it mostly from memory, certainly as pseudo code.

Matt
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Old 04-04-2017, 15:28   #12
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Re: Homemade tiller autopilot

Often thought about re-purposing an old smartphone as a head unit. Has gps, three sensor accelerometers, fluxgate and Gps plus some pretty good brains, wifi and bluetooth. It would need an app to run the Autopilot software and some sort of relay/mosfet driven from the micro USB, or posibly via bluetooth or wifi. To drive a ram.

Prehaps a small motor could be used to drive a servo pendulum vane unit or small well balanced rudder?

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Old 04-04-2017, 18:22   #13
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Re: Homemade tiller autopilot

Very interesting idea, you'd pick up some expensive components for a song.

Making it app based gets around a bit of the trouble with device life span too.

Hmmmm....
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Old 04-04-2017, 18:29   #14
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Re: Homemade tiller autopilot

Quote:
I have my own home made unit. Wifi, navionics etc etc. If you want a place to start, type yacht autopilot on youtube. Skim past the model yachts. Autopilots are a simple system in function and software. Outrageous cost though. Make your own, there are plenty of software engineers that have yachts.
Not so simple if you want a unit that will handle all sea states and steer to wind taking into consideration surfing down wave fronts. A steer around the pond unit is pretty simple.
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Old 04-04-2017, 19:00   #15
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Re: Homemade tiller autopilot

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Not so simple if you want a unit that will handle all sea states and steer to wind taking into consideration surfing down wave fronts. A steer around the pond unit is pretty simple.
I used to write software for a living. I use the same PID formula that raymarine and the others use. You are correct, it isnt simple, but mine works better than my autohelm with extra functions. I can also repair my own equipme t, which was my original motivation. I am a live aboard cruiser so self reliance is important to me.
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