Linkage seal preference - weigh in!

[RCSubGuy]

My 300 Series SubDriver currently uses a linear servo adapter and a cup seal. This works really well, but the drawback is very short throw.

I rigged up an alternative with bellows seals and wanted some input in terms of which version you guys would prefer, given the choice.

Bellows are tried and true and the setup gives about triple the throw that the linear version does. The linear version is true linear motion and uses a cup seal that is easily replaceable. It also uses a 1/8" linkage shaft versus the thinner 1/16".

What do you think?

[JHapprich]

Hi Bob,

I only use Engel-type stiffing boxes with O-rings, both purchased or self-made.

I never use bellows. They deform under pressure. They can easily be damaged. I always considered the a "cheap" solution.

Id go for the cup seal and linear servo in any case.

I usually use a connecting lever to translate the rotation of the servo horn into a linear motion of the pushrod.

Best regards Jörg

[neitosub]

Personally I prefer bellows, they're a bit easier to source where I live and are easy to install. I modify my servo horns so that they can give linear motion. This does require a bushing to be installed through the linkage rod though, but in the age of 3D printing this is very easily accomplished:



Nate

[rwtdiver]

Bob,

I like both methods, and have used the cup seal method mostly until I purchased the 70mm and 80mm WTC.





It may be a less expensive (cheap) way to go, but for someone just breaking into the hobby I think the bellows are a good way to go. The bellows are new for me and I have never used them before now. For me I like the bellows! By the way, the two WTC (70mm & 80mm) are working very well. I have not had any leaks at all....

Rob
"Firemen can stand the heat"

[trout]

Skip it, go for no seals.....

https://youtu.be/kXAmuYTirp4

[Bob Gato]

I have had my watertight linear servo boxes with a one of your cup seals on the output shaft under water for a week...nothing but dust inside...Bellows are made to prevent water ingress due to splashing on the car or boat race course and not to the bottom of the pond-the cheap bellows deform and look like a flat inner tube when taken to the bottom of a swimming pool and the good bellows are quite restrictive due to the thick rubber. The weak link is the seal to the rod be it glue or zip tie-sooner or later it will leak.. Cup seals be my choice.

[He Who Shall Not Be Named]

[Subculture]

Is there no scope to increase the diameter of the racks drive pinion to improve the linear throw?

[RCSubGuy]

Andy, no not to any significant degree. The adapters are already about the width of the servo and I don't want to exceed that.

I feel the linear/cup seal method is the way to go. I just had a customer complain about the throw and wanted to see what a bellows style solution would look like.

All is good! I'm staying the course.


Bob

[QuarterMaster]

To each his own said the Farmer when he kissed the pig.

Chlorinated pool water and electronics do not mix! Page 2

[redboat219]

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Ed

Do you put grease in the space between the pushrod tube and rulon sleeve?

[QuarterMaster]

Yes.

1- I use "Corrosion X" during the initial build. Basically fill the cavity from the "wet" side before I push the pushrod thru from the "dry" side. Have a paper towel ready to catch the excess.
2-A drop of "Corrosion X" on the "wet" side every time I run through my "Pre-Underway" Checklist, then cycle the servo before she hits the water.
3-I repeat Item 1 during the annual "Maintenance Refit" as I pull them to check. All my boats receive an annual "Maintenance Refit" on "Black Friday while others shop lol!

[redboat219]

To each his own said the Farmer when he kissed the pig.

Chlorinated pool water and electronics do not mix! Page 2

Ed,
In your drawing you got a 9/32 " O-rings on the ends of the silicone tubing over the rulon tube yet in the photo of your actual WTC there are none. I take it they are superfluous.

Also your WTC endcap, it looks like it's axially sealed. How do you secure the bulkhead aginst the edge of the cylinder? I don't see any hold down bolts.

[QuarterMaster]

Yes, I found they seal well enough without.

Ask Dwayne Hill regarding the WTC construction. For the record, why would I need that? This is a standard WTC. I am, a simple Gas with Lo pressure snorkel pump Ballast system Sailor. Engel, or OTW or Bladders or any other device that INCREASES the pressure inside is NOT for me.

Technically you can ask the same question regarding any older SubDriver.