Below deck autopilot

[AngusMcDoon]

Another post about the £4.5k cost of a below deck autopilot got me having a look at linear actuators. What about this one?

http://www.dcactuators.com/Detail.asp?Product_ID=306.160_6112C

Would 200 lb-force and 1.5" per second travel be enough? The 1000 lb ones are very slow, but you could always use it to pull yourself off a sandbank like the winch on a Landy in a bog. That's assuming your sandbank of embarrassment had a handy tree to use.

 

[pvb]

Another post about the £4.5k cost of a below deck autopilot got me having a look at linear actuators. What about this one?

http://www.dcactuators.com/Detail.asp?Product_ID=306.160_6112C

Would 200 lb-force and 1.5" per second travel be enough? The 1000 lb ones are very slow, but you could always use it to pull yourself off a sandbank like the winch on a Landy.

Raymarine's Type 1 linear drive is 650lbs thrust. Don't think 200lbs is enough.

 

[AngusMcDoon]

Bah! Only tiller pilot suitable then.

 

[ianj99]

Another post about the £4.5k cost of a below deck autopilot got me having a look at linear actuators. What about this one?

http://www.dcactuators.com/Detail.asp?Product_ID=306.160_6112C

Would 200 lb-force and 1.5" per second travel be enough? The 1000 lb ones are very slow, but you could always use it to pull yourself off a sandbank like the winch on a Landy in a bog. That's assuming your sandbank of embarrassment had a handy tree to use.

Without a clutch, you'd need to disconnect it from the tiller for hand steering.

 

[lw395]

Raymarine's Type 1 linear drive is 650lbs thrust. Don't think 200lbs is enough.

Surely the force required to turn the rudder depends on the length of the tiller arm?
Essentially it comes down to power. Power=force times speed. At least in metric units.
A bloke on the tiller might do 50lb force and 20? 40? inches per second fighting an overcanvassed boat in waves.
A well balanced boat on flat water needs very little, especially with a balanced rudder.

 

[pvb]

Surely the force required to turn the rudder depends on the length of the tiller arm?

True, but both the Raymarine Type 1 linear drive and the one which AngusMcDoon suggested have a maximum travel of 12", so the length of tiller arm they could drive would be the same (and would be determined by the angular movement limits of the rudder). Raymarine think that they need 650lbs thrust. I'd guess that 200lbs thrust might well be OK on a smallish boat in some conditions, but it might not be ideal. As someone else pointed out, I don't think the cheaper one has a clutch either.

 

[prv]

Surely the force required to turn the rudder depends on the length of the tiller arm?

Yes, but below-decks pilots operate with alarmingly short tillers. Partly to avoid taking up too much space in what is often a cramped location, partly to avoid needing unfeasibly long travel on the actuator, and partly to reduce the linear speed required to meet a given hard-over-time spec.

Pete

 

[AngusMcDoon]

It has no clutch so no good for below decks, but I imagine it would do for a tiller pilot if sufficiently waterproof.

 

[maxi77]

Surely the force required to turn the rudder depends on the length of the tiller arm?
Essentially it comes down to power. Power=force times speed. At least in metric units.
A bloke on the tiller might do 50lb force and 20? 40? inches per second fighting an overcanvassed boat in waves.
A well balanced boat on flat water needs very little, especially with a balanced rudder.

It is however not as simple as that, try for example going astern, and rudder balance to minimise effort will lead to other problems

 

[testmonkey]

howabout a different approach: I wonder what could be done with parts from an electric bicycle? Old bicycle parts readily available for low cost and in the end bicycle/motorcycle chain is what many steering pedestals are using today with no problem.

 

[ianj99]

howabout a different approach: I wonder what could be done with parts from an electric bicycle? Old bicycle parts readily available for low cost and in the end bicycle/motorcycle chain is what many steering pedestals are using today with no problem.

You still need a clutch - anything using a geared motor whether rotary or linear will be immoveable once the juice has been switched off.

Unless of course you go totally electromechanical and just have a mechanical system as backup (requiring manual disconnecting of the ram from the tiller when it fails) and use the AP to steer all the time using the + - buttons.

 

[testmonkey]

You still need a clutch - anything using a geared motor whether rotary or linear will be immoveable once the juice has been switched off.

this got me into thinking - what electromechanical part readily available at any scrap yard has a built-in clutch you drive with 12v power? Well any automotive or motorcycle starter! So how about salvaging e.g. a fiat uno flywheel, removing excess weight, bolting it to the rudder stock under deck, then build a bracket for the starter. To engage the autopilot apply voltage to the solenoid and by providing positive/negative voltage to starter from control head steer the boat. Automotive starters come in many sizes so with some experimenting or calculation an optimal size might be found... If this works all mechanical parts could be found for very low cost. Then some diy electronics to drive it. To get a head start in autopilot software & control board the ArduPlane & DIY drone projects might help http://diydrones.com/profiles/blogs/ardupilot-mega-home-page https://code.google.com/p/gentlenav/

 

[knuterikt]

this got me into thinking - what electromechanical part readily available at any scrap yard has a built-in clutch you drive with 12v power? Well any automotive or motorcycle starter! So how about salvaging e.g. a fiat uno flywheel, removing excess weight, bolting it to the rudder stock under deck, then build a bracket for the starter. To engage the autopilot apply voltage to the solenoid and by providing positive/negative voltage to starter from control head steer the boat. Automotive starters come in many sizes so with some experimenting or calculation an optimal size might be found... If this works all mechanical parts could be found for very low cost. Then some diy electronics to drive it. To get a head start in autopilot software & control board the ArduPlane & DIY drone projects might help http://diydrones.com/profiles/blogs/ardupilot-mega-home-page https://code.google.com/p/gentlenav/

The speed of this contraption will be a problem, the drive units of the shelf has geared down the speed a lot, yours would have to high a RPM i think.
Here is a video showing the Jefa unit

 

[harstonwood]

Why not use an innertube as a lifejacket whist your foraging!

Though not been sailing long, the autopilot is a the very top of my safety on board equipment list

I would not be without a well engineered and reliable system

Fiat starter motor? Yiu having a giraffe?

 

[Upnorth]

Above decks homemade unit, looks like a battery drill to me.
http://www.youtube.com/watch?feature=player_embedded&v=AdpxTa__YCw

 

[ianj99]

The clutch on inertial starters only works in one direction to stop the engine turning the starter once it starts.

You could use a pre engaged type but do you want that orrible clunk every time the AP engages it? You'd also need some pretty hefty switches to handle starter motor currents. If it ever went wrong the torque would probably break the rudder shaft or rudder.....

 

[testmonkey]

The clutch on inertial starters only works in one direction to stop the engine turning the starter once it starts.

yes actually the clutch should be disabled. The key part is the solenoid which pops out the starter wheel to engage against the flywheel. This is the functionality needed from the starter so that disengaging the autopilot would allow free movement of the rudder when autopilot not in use...

Here's another approach, self-made autopilot actuator based on a bus wiper motor. What it just needs is a clutch to disengage when not in use. Maybe starter solenoid would do?

http://www.boatdesign.net/forums/onboard-electronics-controls/homemade-autopilot-30075-17.html

 

[AngusMcDoon]

I would not be without a well engineered and reliable system

You will soon find that it isn't and it isn't.

 

[prv]

You could use a pre engaged type but do you want that orrible clunk every time the AP engages it?

It wouldn't engage and disengage for every movement - if it did that, the rudder would be free to swing about when it should be held steady. It would engage when you pressed "Auto" on the head unit and disengage when you pressed "Standby" - I think I'd actually find a slight clunk as I pressed the button reassuring rather than orrible.

My main worry about doing this would be how much current the servo draws to keep it engaged - in terms of both power consumption and overheating. Fundamentally a starter motor is not designed for continuous operation, and the same presumably applies to the servo.

I think you'd also need a worm gear in the system rather than just welding a flywheel to the shaft and engaging the motor with it. Partly to reduce speed and increase torque, but also because you need the system to hold the rudder still when engaged but not being driven - the rudder mustn't be able to backdrive the motor.

Pete

 

[NickRobinson]

Why not use an innertube as a lifejacket whist your foraging!

Careful, didn't I buy your lifejackets?

I thought about using an car window power lifter motor as an actuator, my son rolled his eyes until I dropped the idea-

Nick