Auto Pilot Rudder Feedback

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THATBOATGUY
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Auto Pilot Rudder Feedback

Post by THATBOATGUY »

So what I am planning is to run a 33c control cable through a packing gland (or just a hole filled with 4200) following the hydraulic ram out to the rudder post. At the rudder post I'll fab a little tiller arm for a ball mount cable end attachment. I'll have the other end of the cable run under the aft berth to the rudder angle feedback sender. I suppose the other way to do it would have been to purchase the outboard motor angle feedback and rig that up out there but when I was doing marine electronics full time I noticed many failures of these units do to water intrusion. I *think* that my way will be far more reliable and easier. The 33c cable's are inexpensive and I carry a spare for the helm controls anyway.

Anybody else done something else? I don't want to re-invent the wheel here, I just would rather keep the electronics in a nice dry area and use reliable mechanics to bring the motion inboard.

George
George and Kerri Huffman S/V Marquesa Freedom 40 CC CK Sail MarquesaImage

katorpus
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Re: Auto Pilot Rudder Feedback

Post by katorpus »

George

If you center bore the fat clevis pin that holds the ram to the rudder end of the hydraulic piston & thread the hole you can attach the "keeper" for the ball end to that and avoid the "tiller arm" construction. If you center the control cable sheath on the ram barrel, there won't be any lateral motion to deal with, since all you're doing anyway is mirroring the distance that the ram travels at the other end of the cable (which is where you'll need some kind of tiller arm attached to the feedback potentiometer or whatever you're using).

The rest of my plan was to clamp the sheath of the control cable to the barrel of the ram with two titanium hose clamps.

I bought a teflon coated stainless steel bicycle brake cable for this...the idea being that it is stiff enough to handle the 5-1/2" travel required and will provide the least additional resistance to rudder movement.

I've been "pondering" this installation since before 9/11/01...I remember that date because my shipment of the autopilot brains was enroute from Otto at Tecnautic in Zurich on 9/11. Needless to say, it didn't arrive on the expected delivery date.

I haven't completed the install...but my plan was to mount the whole arrangement for the inboard end inside a plastic "tackle box" to keep it from getting banged around by stuff in the lazarette. (I have the aft cockpit Freedom 40 and my plan was to stick it all up into the space in the lazarette where the seatback top meets the aft end of the teak coaming.)


What kind of feedback unit are you using?

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THATBOATGUY
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Re: Auto Pilot Rudder Feedback

Post by THATBOATGUY »

We have a com-nav unit. Unfortunately our ram travel exceeds the travel of the 33c cable so a little tiller arm is in order. That's the easiest thing about the whole job really as there is a big square cut bit of stainless rudder shaft coming out the top of our rudder for the emergency tiller. I only need to make up a bit of 1/4 inch starboard with that square cut at one end and an appropriate arm at the other. I like the reliability of the 33c cable in the marine environment. I've installed quite long ones on go fast boats for tilt/trim indicators on out-drives and they hold up very well in that kind of punishing environment so I figure it should last forever in this application.

George
George and Kerri Huffman S/V Marquesa Freedom 40 CC CK Sail MarquesaImage

katorpus
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Re: Auto Pilot Rudder Feedback

Post by katorpus »

Ok...so your little tiller arm is going to be attached to the rudder head at a point closer to the transom (than the attachment point of the ram), which means that the travel along the arc described by that point (as the rudder swings) will be less than the travel along an arc described by a point located further out on the rudder...

I'm guessing that you're planning to "use up" about all the travel that the cable has available in order to be able to calibrate the autopilot more easily. How much travel DOES that cable have?

If my math and memory are correct, the relationship between the distances along the various arcs from a single point is linear insofar as one radius relates to another...in other words, halving the radius from the centerpoint of a line drawn through the rudder hinge points would halve the distance traveled along the arc for any given number of degrees of the circle... the circumference of a circle of radius = R being half of that of a circle of radius = 2R

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THATBOATGUY
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Re: Auto Pilot Rudder Feedback

Post by THATBOATGUY »

I'll wrap a piece of stiff wire around the rudder shaft with a pointer sticking out where I'll be making my tiller and experiment. Math is *not* my strong point but I love to tinker. I'm not certain the exact throw on that cable but you are right, I'll be using it up. Who ever converted Marquesa to hydraulic steering did a nice job. There is a kind of a cowl made of aluminum covering the ram. I'll make my cable anchor off of that somehow and I have a ball and socket attachment for the cable end at my made tiller arm.

I'll try and follow up with photos if I remember the camera.

George
George and Kerri Huffman S/V Marquesa Freedom 40 CC CK Sail MarquesaImage

katorpus
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Re: Auto Pilot Rudder Feedback

Post by katorpus »

I'm surprised to learn that your boat didn't have hydraulic steering from the "get-go"...mine did. My little "cowl" is made of fiberglass...and my observation is that its only purpose is to prevent rainwater from washing the grit off of the cylinder, thus ensuring that the grit makes maximum contact with the cylinder seal at all times when the boat is sitting in the slip and the ram is "working" in & out due to the normal motion of the boat/rudder/wind...the cylinder gets rebuilt about every 5 years despite my efforts to keep this from happening by lashing the wheel when the boat is not in use...I've also had to overbore the holes for the clevis pin on the rudder end of the ram and have a bigger clevis pin machined to keep things tight and avoid endless clunk-clunk.

I've wondered what the downside might be (other than REALLY stiff steering when it's cold outside) to flushing out the hydraulc system and replacing the ATF with "motor honey" or straight STP...bigger molecules = slower leakage. ;)

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THATBOATGUY
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Re: Auto Pilot Rudder Feedback

Post by THATBOATGUY »

Our first night spent in the aft cabin a while back we discovered the heartbreak of clunk-clunk. Guess I'll have to deal with that soon. For the night i rigged the emergency tiller and lashed it. I ordered two rebuild kits for the ram when I rebuilt it last year. One kit is in the spares bin... Our boat originally had cable steering. Hull number 7. I'll be taking a look at Frank's boat, hull number 4, probably this week sometime over at Kent Narrows and I'll be interested to see what's what.

George
George and Kerri Huffman S/V Marquesa Freedom 40 CC CK Sail MarquesaImage

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