Correction::

That was suppose to be 1"/sec. for the AH3000 linear drive.

The ram (if you wanna call it that) total travel is 10.5 inches and it take
a little over 10 sec from stop to stop.

Sorry about the error.

Steve
s/v Good Intentions

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 @

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.

I was kinda thinking the same thing. Infact, at first, I thought this unit
was a electro-hydraulic unit.

Since I'm not going to drive the hydraulics off the engine I really need to
find a compact efficient 12vdc power unit.

I don't think I need to get into a continious running pump since the boat
has a full keel and maintains it's course very well. 90% of the time, the AP
linear drive is just holding the tiller in position (static load). Something
that a hydrualic cylinder it very good at. The main reason the AH3000 linear
isn't satisfactory, is because in heavy weather, the rudder tiller exerts
enough force against the linear drive to force the motor to turn in reverse.
I'm afraid of what this is doing to the planetary gear reduction.

Thanks to your comments and that of Glenn, I will look farther for a 12vdc
(reversiable) PowerPack.. If anyone knows of something like this, please let
me know.. The pumps that Glenn referenced were just the pumps.. gotta be a
complete unit someplace, like truck power lifts, etc.

Steve
s/v Good Intentions

Steve,

You might contact WH. The power pack I have is a simple 1/4 HP
DC motor the drive a hydraulic pump via a belt. Pretty compact.
I suspect they would sell you a unit for a reasonable price. Motor
only runs when moving the runner. But that is a function of the
controller rather than the powerpack itself.

Doug
s/v Callista

"Steve" wrote in message
...

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.

I was kinda thinking the same thing. Infact, at first, I thought this unit
was a electro-hydraulic unit.

Since I'm not going to drive the hydraulics off the engine I really need
to
find a compact efficient 12vdc power unit.

I don't think I need to get into a continious running pump since the boat
has a full keel and maintains it's course very well. 90% of the time, the
AP
linear drive is just holding the tiller in position (static load).
Something
that a hydrualic cylinder it very good at. The main reason the AH3000
linear
isn't satisfactory, is because in heavy weather, the rudder tiller exerts
enough force against the linear drive to force the motor to turn in
reverse.
I'm afraid of what this is doing to the planetary gear reduction.

Thanks to your comments and that of Glenn, I will look farther for a 12vdc
(reversiable) PowerPack.. If anyone knows of something like this, please
let
me know.. The pumps that Glenn referenced were just the pumps.. gotta be a
complete unit someplace, like truck power lifts, etc.

Steve
s/v Good Intentions

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 @

The 12VDC powerpacks like Barnes and Fenner are not designed for
reversing. Will Hamm's system is simple and and an elegant use of off
the shelf parts. It looks like a fairly standard 2" bore steering
cylinder mounted at one end on a custom made swivel. The power unit is
a very small pump with a belt drive to what looks like a 1/4 HP DC
permanent magnet motor. The motor would have to be compatable with the
control unit but that means either a PM (2 wire) split field (3 wire) or
series wound (4 wire).

The thing is you have to balance the tiller arm length to the throw of
the cylinder to get 72º of movement then match the displacement of the
cylinder with the capacity of the power unit to get an acceptable hard
over time with suficient force. Then you do it backwards using
available parts to get the final tiller arm length. The thing is any
compromise reduces efficiency so components made for the purpose usually
work out better.

Here are some handy formulas. I did the calculations for Rutu and it
took 3 pages of scribbling and then decided to let a pro do it. :-)

Maximum pressure on the rudder = 1.6 x area of the rudder in sq. ft. x
boat speed in knots squared. If the hull is capable of surfing double it.

Torque = max pressure X distance from the cneter of force of the rudder
to the centerline of the rudder post. (The center of force on the rudder
is usually about 30 to 40% of the cord length. )

Cylinder force required = Torque/tiller arm length

Hydraulic pressure required (psi) = req'd force/net area of piston in
sq. in. Net area is the area of the cylinder less the area of the rod.

Hydraulic volume required (GPM) = net area of piston x throw length/231

Output of pump (GPM) = displacement x RPM/231

Horsepower required = GPM x PSI/1714 x .80 (efficiency of pump)
(multiply by 4 for a 15 second hard over time)


Steve wrote:
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.


I was kinda thinking the same thing. Infact, at first, I thought this unit
was a electro-hydraulic unit.

Since I'm not going to drive the hydraulics off the engine I really need to
find a compact efficient 12vdc power unit.

I don't think I need to get into a continious running pump since the boat
has a full keel and maintains it's course very well. 90% of the time, the AP
linear drive is just holding the tiller in position (static load). Something
that a hydrualic cylinder it very good at. The main reason the AH3000 linear
isn't satisfactory, is because in heavy weather, the rudder tiller exerts
enough force against the linear drive to force the motor to turn in reverse.
I'm afraid of what this is doing to the planetary gear reduction.

Thanks to your comments and that of Glenn, I will look farther for a 12vdc
(reversiable) PowerPack.. If anyone knows of something like this, please let
me know.. The pumps that Glenn referenced were just the pumps.. gotta be a
complete unit someplace, like truck power lifts, etc.

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

That is fine if you are designing from scratch and can program the
controller for PWM to run the motor faster in one direction than the
other but for a home brew match up it would be close to impossible.

Bruce in Alaska wrote:

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

--
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

Thanks for the formulas Glenn.

I ran the numbers to get some idea of what I might be looking for.

Seems I should be using about a 2"X20"X1.5" cylinder, 318psi @ .186gpm.

Using a slightly oversize pump at a lower RPM, I would need a 1/4hp motor to
achieve the 15 sec. hard over time.

Seems do-able on paper. I just don't know what the max current draw might be
for this motor. I'm sure someone has a formula for this as well.

Steve
s/v Good Intentions

Sorry, another typo..

"Steve" wrote in message
...

Seems I should be using about a 2"X20"X1.5" cylinder, 318psi @ .186gpm.


Should read .... 2"X20"X 1 1/8" cylinder, .......

Steve
s/v Good Intentions