The linear drive I finally located (haven't purchased yet) is non-marine.
Rather commercial, industrial for gates, wheel chair lifts and positioning
appliactions.

I is presently available from Surplus Center
http://www.surpluscenter.com/item.as...&item= 5-1474

I'm anticipating that I will have to give some attention to marinizing the
unit, but that's what DIYs do.

Steve
s/v Good Intentions

"Steve" wrote in message
...
The linear drive I finally located (haven't purchased yet) is non-marine.
Rather commercial, industrial for gates, wheel chair lifts and positioning
appliactions.

I is presently available from Surplus Center

http://www.surpluscenter.com/item.as...&item= 5-1474

I'm anticipating that I will have to give some attention to marinizing the
unit, but that's what DIYs do.


The other thing you may need is some sort of a clutch to decouple it
whenever the autopilot is not in use.
I know that the raymarine use a sort of a magnetic affair that energises and
locks (by friction) two plates together whenever the autopilot is switched
on.
God knows how you will build that into it!!

garry

The tiller pilots are engaged by simply lifting the end of the linear drive
piston off the tiller pin. With my OEM linear drive, when not engaged on the
tiller pin, it swings out of the way to a storage clip on the stern rail.

BTW. The AH or ST wheel pilot, have internal belt drives with idler rollers
on a clutch lever. Not magnetic (couldn't/shouldn't have mag. around the
cockpit) or friction clutches in these. Trust me, I've had one apart for
voyage repairs in my last boat.

Steve
s/v Good Intentions

"Steve" wrote in message
...
The tiller pilots are engaged by simply lifting the end of the linear
drive
piston off the tiller pin. With my OEM linear drive, when not engaged on
the
tiller pin, it swings out of the way to a storage clip on the stern rail.

O.K I understand, I was thinking that you were going to use it below deck
directly attached to the quadrant.
In that situation you would need some sort of a clutch.
The marinising aspect might take a lot of work, that is usually the bit
where the manufactured models fall down, hence the desire to mount them
below decks if possible


BTW. The AH or ST wheel pilot, have internal belt drives with idler
rollers
on a clutch lever. Not magnetic (couldn't/shouldn't have mag. around the
cockpit) or friction clutches in these. Trust me, I've had one apart for
voyage repairs in my last boat.

Yeah, I know, have had to strip down those friction clutches myself, a real
PITA.
The one on the ST4000 is attached via two tiny roll pins that have a
tendency to shear off at awkward moments.

Re the magnetic clutch, I have seen them on the linear drive of the ST7000
ST6000 and havent noticed any problem with them affecting the compass.
But then I suppose it is fairly minimal, compared to the magnetism created
within the actuator motor itself.


good luck
garry

VERY bad idea. That drive is not going to be any where near fast enough
for an autopilot. It is a screw drive. A LOT slower than a hydraulic.

Also a hydraulic cylinder needs to be a "balanced" type with the rod
going all the way through so the displacement is the same in both
directions. Regular single ended double action cylinders have less
displacement on the rod side because of the volume of the rod. With a
constant pump speed it retracts faster than it extends and with less
force. You would never get an autopilot logic unit to control it properly.

These are more what you will need:
http://www.surpluscenter.com/sort.as...ke yword=HCP1

and the pump has to be reversable like these:
http://www.surpluscenter.com/sort.as...ke yword=HPSD

Steve wrote:
The linear drive I finally located (haven't purchased yet) is non-marine.
Rather commercial, industrial for gates, wheel chair lifts and positioning
appliactions.

I is presently available from Surplus Center
http://www.surpluscenter.com/item.as...&item= 5-1474

I'm anticipating that I will have to give some attention to marinizing the
unit, but that's what DIYs do.

Steve
s/v Good Intentions



--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

I had considered hydraulic and if I already had hydraulic on the engine, I
probably would reconsider it.

Originally I had planned on hydraulic for the anchor windlass but found the
Lewmar 1000 vertical and I'm now happy with that.

Also any hydraulic cylinder and hoses would be right in the cockpit since my
rudder is 'outboard' and no provision for an inboard cylinder.

Additionally, I would have to find or build some kinda electrical to
hydraulic control valve for the AP control head to operate.

After reading Glenns comments regarding the operating speed of the screw
drive, I went to the boat and did a test to determine the rate of travel of
the OEM (AH3000) linear drive. It is exactly 1 inch per min. with no load.
The unit I'm considering is 3/4 inch per min.. 25% slower, however since the
this unit has 3 times the thrust I could move the tiller attachment pin aft
an appropriate amount to increase the rudder stop to stop travel time and
still have the advantage of the increased dynamic and static load.

I'm going to contact the fellows at Surplus Center and see if I can get some
more spec. info on this unit. They have been very help full in the past.

I am however taking Glenns warnings into consideration and thanks for the
heads up.

Steve
s/v Good Intentions

WOW! I am amazed that the AH3000 is that slow. How long does it take
to go hard over to hard over? I was thinking that 15 or 20 seconds
would be the bare minumum. 1" per minute on a 6" tiller arm would take
more than 3 minutes.

Steve wrote:

I had considered hydraulic and if I already had hydraulic on the engine, I
probably would reconsider it.

Originally I had planned on hydraulic for the anchor windlass but found the
Lewmar 1000 vertical and I'm now happy with that.

Also any hydraulic cylinder and hoses would be right in the cockpit since my
rudder is 'outboard' and no provision for an inboard cylinder.

Additionally, I would have to find or build some kinda electrical to
hydraulic control valve for the AP control head to operate.

After reading Glenns comments regarding the operating speed of the screw
drive, I went to the boat and did a test to determine the rate of travel of
the OEM (AH3000) linear drive. It is exactly 1 inch per min. with no load.
The unit I'm considering is 3/4 inch per min.. 25% slower, however since the
this unit has 3 times the thrust I could move the tiller attachment pin aft
an appropriate amount to increase the rudder stop to stop travel time and
still have the advantage of the increased dynamic and static load.

I'm going to contact the fellows at Surplus Center and see if I can get some
more spec. info on this unit. They have been very help full in the past.

I am however taking Glenns warnings into consideration and thanks for the
heads up.

Steve
s/v Good Intentions




--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

I think you misunderstand the typical hydraulic auto-pilot for
mid-size boats where the manual steering is not hydraulic. They
typically have a dedicated reversible hydraulic pump driving (as Glenn
points out) a balanced cylinder. The AP electronics turns the electric
motor driving the pump on and off in the required direction.

Larger vessels, including Fintry, have a setup like the one you
describe below, where an hydraulic pump runs continuously with
hydraulic servos (fluid operated relays) supplying the fluid to the
ram(s) as required. This is similar to automotive power steering.

I think I'd rather have an hydraulic cylinder and hoses back there
rather than an electrically driven screw about the same size. The
hoses would be bigger than the wires, but the Surplus Center drive is
not designed for your environment.

Finally, think harder about the broader design issues here. In
particular, what happens when a big wave pushes the rudder harder than
the AP can push back? This is the touchy area for screw drive APs, as
the drive has to stall safely, and then go on pushing as soon as it's
able. An hydraulic unit does this easily, but a direct electric drive
has problems -- electric motors don't like to stop and you can't just
un-clutch the thing, as it has to stop, not backdrive.

Also think about duty cycle and design life. An AP is working all the
time, back and forth. Very few applications require this kind of
activity, so it may be an area where adapting something from elsewhere
is difficult.

As a complete aside, I wonder about the need for a balanced cylinder
in a hydraulic drive. As Glenn says, with an ordinary single ended
cylinder, you have different thrust in the two directions. But,
modern autopilots are pretty sophisticated and adjusting for that in
software might be cheaper than the extra cost and maintenance (two
seals rather than one) of a balanced cylinder.

Jim Woodward
www.mvFintry.com

"Steve" wrote in message ...
I had considered hydraulic and if I already had hydraulic on the engine, I
probably would reconsider it.

Originally I had planned on hydraulic for the anchor windlass but found the
Lewmar 1000 vertical and I'm now happy with that.

Also any hydraulic cylinder and hoses would be right in the cockpit since my
rudder is 'outboard' and no provision for an inboard cylinder.

Additionally, I would have to find or build some kinda electrical to
hydraulic control valve for the AP control head to operate.

After reading Glenns comments regarding the operating speed of the screw
drive, I went to the boat and did a test to determine the rate of travel of
the OEM (AH3000) linear drive. It is exactly 1 inch per min. with no load.
The unit I'm considering is 3/4 inch per min.. 25% slower, however since the
this unit has 3 times the thrust I could move the tiller attachment pin aft
an appropriate amount to increase the rudder stop to stop travel time and
still have the advantage of the increased dynamic and static load.

I'm going to contact the fellows at Surplus Center and see if I can get some
more spec. info on this unit. They have been very help full in the past.

I am however taking Glenns warnings into consideration and thanks for the
heads up.

Steve
s/v Good Intentions

In article k9elb.83730$sp2.44153@lakeread04,
Glenn Ashmore wrote:

Regular single ended double action cylinders have less
displacement on the rod side because of the volume of the rod. With a
constant pump speed it retracts faster than it extends and with less
force. You would never get an autopilot logic unit to control it properly.

The above is NOT a correct statement considering that most AutoPilots use
an Electonic Feedback Loop for Rudder Position. This is accomplished by
having a Rudder Position Encoder mounted to the Rudder System that then
feeds back to the Pilot Logic directly. In this type of system, the
travel time of the Piston isn't even considered, unless the Hydrolic
Pump that feeds the system is so underrated that the movement of the
piston is slower than the Pulsewidth Modulation of the Feedback Loop.
All the AutoPilot OEM's I am familiar with take this into account when
designing the Feedback Loop in the first place, and therefor it is a
NONISSUE for the end user.

Bruce in alaska
--
add a 2 before @

That's why the quality APs have a rudder position sensor. Good control
cannot be acheived without one.

DOug
s/v Callista

"Bruce in Alaska" wrote in message
...
In article k9elb.83730$sp2.44153@lakeread04,
Glenn Ashmore wrote:

Regular single ended double action cylinders have less
displacement on the rod side because of the volume of the rod. With a
constant pump speed it retracts faster than it extends and with less
force. You would never get an autopilot logic unit to control it
properly.

The above is NOT a correct statement considering that most AutoPilots use
an Electonic Feedback Loop for Rudder Position. This is accomplished by
having a Rudder Position Encoder mounted to the Rudder System that then
feeds back to the Pilot Logic directly. In this type of system, the
travel time of the Piston isn't even considered, unless the Hydrolic
Pump that feeds the system is so underrated that the movement of the
piston is slower than the Pulsewidth Modulation of the Feedback Loop.
All the AutoPilot OEM's I am familiar with take this into account when
designing the Feedback Loop in the first place, and therefor it is a
NONISSUE for the end user.

Bruce in alaska
--
add a 2 before @