DIY Autopilot

[Lake-Effect]

Great story, Matt.

I always thought a cordless drill turning a cog that moves a toothed bar would be a low-budget linear actuator. But I'm sure that by the time I had worked out all the bugs, the hours would pay for a commercial tiller-pilot two or three times over.

Fun stuff to mess with though.

[GILow]

Originally Posted by Lake-Effect

Great story, Matt.

I always thought a cordless drill turning a cog that moves a toothed bar would be a low-budget linear actuator. But I'm sure that by the time I had worked out all the bugs, the hours would pay for a commercial tiller-pilot two or three times over.

Fun stuff to mess with though.

Lots of fun! Perhaps TOO MUCH fun... I really should have been doing more important things...

But, I actually I DO use a AU$19 cordless screwdriver spinning a 3 foot long threaded rod to do my solar panel tracking. The thing is, solar tracking does not need speed, it just needs force.

Steering the boat, even the lovely little 20 footer I was sailing at the time, needed force AND speed (ooh look, the equation for power!). I tried building an actuator for that and produced a lot of bent rods, stripped gear wheels and hot motors. Sometimes, you just have to give up and let the pros do their thing as you suggest.

I wish I had a lathe.

I am not sure it would help with this particular problem, but I would feel better about my failures.

Matt

[GILow]

Originally Posted by Lake-Effect

I always thought a cordless drill turning a cog that moves a toothed bar would be a low-budget linear actuator.

I had to think about this one a bit, but I reckon you would need a really big stepdown from the drill before driving the cog.

Looking at a basic cordless drill from a reputable manufacturer I see between 600rpm and 2000rpm depending on the gear chosen. Even 600 rpm would produce an actuator speed of 37 meters per second from a 20mm drive cog.

Heck of a response rate , but I would hate to be hit by a tiller travelling at 135 km/h!

Still, the average cordless drill gives you a bit more power than my $19 screwdriver.

I have been looking with interest at how people use right angle drills to drive winches, one to follow up.

Matt

[goboatingnow]

Originally Posted by wellin

I agree with the previous post. I think a fast response time to keep an exact heading, would just drain the batts. Would be nice on a calm day motoring but in waves and wind, not good. Motor would run back and forth and never stop. So i think an averaging over time and then make a small correction and "wait" to see if the correction worked would me my method. You constantly get knocked back and forth heading wise so no point in correcting when the next bounce might straighten your heading out. Maybe record headings every second, then average them over 10 seconds. Ignore any angle change under 5 degrees and only move the rudder if average heading changed more than 5 degrees. Then do a "preset" rudder deflection, then return to center. The amount of deflecton tuned as needed to not spill drinks. Then wait till the next 10 second cycle and compare the new average heading. Also record the direction of heading corrections so that if the autopilot corrects the heeading 2 or more times in the same direction then make a small shift in the neutral rudder angle so next correction is smaller than the last one so any weather helm would be tuned out in a few cycles. Relieving the autopilot from constantly correcting for the same thing.
All of the perameters for "turn rate" "delay time" and so forth could be adjusted "on the fly" with pots making setup real easy.
I love working out logic problems and programming stuff like this.

Andy

Sent from my SCH-I415 using Cruisers Sailing Forum mobile app

Yes bit that's algorithm is no use running down the back of a wave under autopilot. Al, that happens is the autopilot will allow the boat to broach and then attempting the correction.

The autopilot has to use the yaw rates to regain control. It certainly can't wait 10s. The holy grail of good autopilot design is down wind , high wave performance

Dave

[DeepFrz]

I think early and quick response with small corrections is what works best. Motor only works for a short time with some very small corrections needed after the initial motion. I once sat watching an autopilot work its wonders and tried to match my steering to it. It won the contest hands down in rough seas between Cuba and Isla Mujares.

[Rabadak]

Hi All,

Just started my DIY Autopilot project (April/2015).

The idea comes after I installed a linear actuator to my outboard motor:
"Why not control the linear actuator by a GPS?"

The project status is like:
https://www.youtube.com/channel/UCCX...LqT3z413--VgOg

The water tests will start July/20.

Please comment and interact:
knowledge from 1 + knowledge from 2 = knowledge (powered) by 2

Warm regards,

Rabadak

[Brasshopper]

Originally Posted by GILow

In the end it was the lack of a good (affordable)durable linear actuator that scuttled the project and I went out and bought a tiller pilot instead.

Matt

Would you mind sharing what pitfalls you ran into with the linear actuators? They seem ideal for my purpose, and, while I had already planned on avoiding really low end ($65) ones, I was looking at the https://www.firgelliauto.com/product...inear-actuator. This Actuator can be had in longer or shorter throws and in 40 or 150 lb force.

The other alternative might be the https://www.firgelliauto.com/product...near-actuators, if I can figure out how to use the optional optical position reporting interface. My current guess is that they have put this on their web site but they don't really have any idea how this works. They may not actually have one in hand. Sigh.

Anyway, if you care to share. On a positive note, the man who did the original autopilot mentioned here has already reached out to share his code repository.

[Bertie68]

Originally Posted by Lake-Effect

Is instantaneous heading change the grail, though? From thinking about my time hanging onto a tiller, it seems the best control comes from observing how the boat heading is oscillating around the desired direction, and how the heading relates to travelling the desired line, and the feedback was a combination of observation and pressure from the tiller, and the most efficient control was a series of well-timed nudges. What we learn to do almost instinctively. Possibly too complex to push into an Arduino.

(I did take control systems 35+ years ago but it wasn't my favourite subject)

Been there also... The complexity would mainly lie in accurately modeling the boat's physics, but once you obtain the control function, it's just a matter of discretizing the system (Z-transform) and programming a controller in the Arduino, which would be fairly easy. In the video it seems to be a rather simple algorithm, but with a control systems approach the result would be much better.

[GILow]

Originally Posted by Brasshopper

Would you mind sharing what pitfalls you ran into with the linear actuators? They seem ideal for my purpose, and, while I had already planned on avoiding really low end ($65) ones, I was looking at the https://www.firgelliauto.com/product...inear-actuator. This Actuator can be had in longer or shorter throws and in 40 or 150 lb force.



The other alternative might be the https://www.firgelliauto.com/product...near-actuators, if I can figure out how to use the optional optical position reporting interface. My current guess is that they have put this on their web site but they don't really have any idea how this works. They may not actually have one in hand. Sigh.



Anyway, if you care to share. On a positive note, the man who did the original autopilot mentioned here has already reached out to share his code repository.

That actuator has a few problems. The speed for a start is a bit slow. The IP rating is also a bit on the low side for marine work I think, mainly the second figure but dust protection loosely translates to salt saturated air protection in my books.

I played around with the numbers on lots of these devices and by the time I found one with the properties I felt were adequate for marine (external) use I was pretty much at the price of the TP1000 so I bought it instead.




Sent from my iPad using Cruisers Sailing Forum

[RaymondR]

Originally Posted by goboatingnow

I think since rate gyros have been added, future improvements will be limited to small advances. The issue t now is clearly the physical dynamics of moving the rudder quick enough to respond to big perturbations in vessel position. Thats not easily solved.


dave

I have been pondering on this question for a number of years now, usually when going downwind in a big quartering sea.

I tend to the opinion that a second, well balanced spade rudder with an electric linear motor could respond quickly enough. Perhaps the software could be written for a lagged response on the main rudder, the balanced spade being used for anticipatory corrections.

I have also concluded that using a three axis accelerometer to measure vertical accelerations might provide an input for the anticipatory control.