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Old Jan 18, 2007, 10:49 AM
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reddog69's Avatar
United States, NY, New York
Joined Jun 2003
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Question
Steering setup

Greetings all. I'm building a tug using the Dumas 45" shelly foss hull.I'm trying to figure out how to mount the steering servo and arms. I have a quarter scale servo that seems to have the needed amount of push to get things moving. I'm not sure if a push/pull setup or laying the servo on its side bettween the rudder arms, one control arm on each end of the horn, would be the way to go. Also, the rudders have a straight shaft with no support on the bottoms. Should I consider some kind of bracket to hold the bottoms of the rudders? I know this would be alot easier to answer if pictures where here. I'll try to post some later today. In the mean time any ideas will be greatly appreciated. Thanks, Reddog.
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Old Jan 18, 2007, 11:24 AM
Veni, Vidi, Feci
patmat2350's Avatar
Motor City
Joined Dec 2004
12,759 Posts
reddog-

Rudder supports- only if the real boat has them! Usually older tugs with a single deep rudder will have a footing in a skeg or extension off the center 'deadwood'. I'm thinking that the more modern tugs with twin props and twin rudders are usually free on the bottom. Exception can be with boats having Kort nozzles, where the bottom of the nozzle can be a convenient place for a footing.
Also, look at the upper side of the rudder at the bottom of the rudder shaft's tube. Imagine the rudder floating up- does it scrape on the tube? Or on the hull? Then glue a ring onto the rudder shaft (same size as the tube) to space the rudder away.

Servo mounting- No best way! Whatever your ingenuity comes up with is good, as long as everything is 'servicable'. It's nice to be able to adjust throw by repositioning the connecting link at different radii on either servo arm or tiller. 35 at the rudder is usually sufficient. Those with 'EPA' on their Tx can also limit throw there.
I've mounted servos upright and on their side, on brackets built into the hull and hanging under the deck.
Long pushrods can be bent around obstacles, just make them beefy enough to not be springy.
I really like using swivel ball-ends instead of those nasty spring clips that are impossible to pry off without breaking something. These also allow for out-of-plane motion without binding.

Pat Matthews
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Old Jan 18, 2007, 12:14 PM
r/c ships and workboats
bellingham, wa
Joined May 2006
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reddog69, the modern Shelly has rudder supports off th base of the shafts for maintaing alignment This would be an upgrade from the time it was designed ( when the origial kit came out).
I agree with Pat on using swival ball end connectors at both ends of the push rod to help eliminate "binding" that happens from misalignment and differnet angles on th eservo and rudders.
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Old Jan 18, 2007, 12:22 PM
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Also, if it's not already clear, you'll want a 90 twin-arm tiller on one rudder if mounting the servo forward of the rudders (the usual case). One arm takes the servo pushrod, the other transmits motion sideways to the second rudder's arm.

Pushrods are usually the easiest way to go; push-pull cables can sometimes offer ways of getting out of a tricky situation.

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Old Jan 18, 2007, 01:03 PM
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United States, NY, New York
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Thanks!

This is why I love this forum! Post before lunch, come back, answers await. It can get no better. Thanks guys. I was thinking ball links since the threaded rod and clips that I have are in fact spongy. Thanks again, Reddog.
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Old Jan 18, 2007, 02:35 PM
r/c ships and workboats
bellingham, wa
Joined May 2006
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on a boat this size and the power that you could put into that tug, it is better to over build the rudder and linkages to handle the stress that could be applied.
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Old Jan 18, 2007, 04:18 PM
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Joined Nov 2005
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1000 Words

As usual, PatMat has hit the nail on the head with "no best way". Since they say a picture is worth 1000 words, thought you might want to see one of many ways to mount a servo driving 2 rudders. Port rudder takes the push or pull and shares with the starboard rudder in this photo. Notice that the linkage between rudders has two 90 degree bends. The step on each end provides clearance between the servo rod and the connector rod to prevernt binding.
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Old Jan 18, 2007, 04:25 PM
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Euclid, Ohio, United States
Joined Sep 2004
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Here's a picture of the twin rudder control set up in my PT boat.
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Old Jan 18, 2007, 06:01 PM
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and an example of a spacer atop the rudder. If you plan ahead, just extend the rudder tube down far enough, but here it was set into the hull. Spacer glued to the shaft also keeps the rudder body from scraping on the tube.

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