the SubDriver becomes modular

[RCSubGuy]

Here's the sketch Scott posted up "over there".

[Scott T]

http://subcommittee.com/forum/attachment.php?attachmentid=7938&d=1572369026&thumb=1

Posted very bad sketch at Sub Comm. copy paste the link if you want to see. But I think you already got the idea.

[He Who Shall Not Be Named]

Thanks Tom! You are very quick with that sketch up!
Another way to get rid of the air bubble is to have the casting slide over the outside of the tube instead of inside.

Now THAT's a concept worth looking into. Good work, guys.

I'll sketch it up tonight and present it to the mob. Continue to use the sharp knife, you bums!

David
Student

[Scott T]

Thanks Tom! You are very quick with that sketch up!
Another way to get rid of the air bubble is to have the casting slide over the outside of the tube instead of inside.

[trout]

No routing out polycarbonate tube necessary now.

[trout]

This is to see if I can upload for Scott (who is one of the most brilliant people I know!)

[Scott T]

Well I can't get this drawing to upload. But I sent an email to Tom just now to see if he can upload it.
My sketch has the same problem with the air bubble.

Scott

[He Who Shall Not Be Named]

Just to add to the thought process......
The more you can take off the cylinder, the more modular it is.......In other words, less time needed to manufacture (less drilling into the tube) and maintenance is easier to work on the vent in the bulkhead instead of trying to go into the tube or needing the tube on to check travel. Plus once the vent is set, changing tubes will not impact the vents function.

Good, sound points, Tom. And your arrangement does the job of evacuating all the air when the vent is open.

However, I still have to mill out a slot in the Lexan tube to girdle the vent body, and since there are no O-rings, I have to RTV the tube to the Union.

I well appreciate your arrangement -- particularly the rigidity of the linkage between servo and vent valve. As you say, in so many words, ' once set you don't have to mess with it if a cylinder change is needed'. I'm almost convinced, but not swayed yet. Keep pitching. Good stuff, Tom.

David
The Horrible

[Subculture]

the OTW version don't fully vent.

True, but it has a solenoid actuated valve pinching off water pressure- effectively a kingston valve, preventing air pressure pushing water back out through the pump, and preventing water pressure getting in.

Dave's cylinders are open at the bottom, so an air bubble will squish. This was always the main caveat of the old Craycraft systems, in an average pond where you're getting little below periscope depth it doesn't make much difference, but in a swimming pool, if you explored the deep end the boat could go negative if you had it dialled with only a small amount of positive buoyancy.

[trout]

Just to add to the thought process......
The more you can take off the cylinder, the more modular it is.......In other words, less time needed to manufacture (less drilling into the tube) and maintenance is easier to work on the vent in the bulkhead instead of trying to go into the tube or needing the tube on to check travel. Plus once the vent is set, changing tubes will not impact the vents function.

[He Who Shall Not Be Named]

Whiney baby.....here. Like that? If you want to be fancy, I could put a lip around the vent that would go on top of the vent and facing the exterior of the tube.

Great! Now I have to glue the cylinder to that union half. Don't like that!

But, on a less cantankerous note: I do appreciate the thought exercises, I certainly don't have all the answers and your challenges to my thinking makes me...….. err ……... think.

David

[trout]

Whiney baby.....here. Like that? If you want to be fancy, I could put a lip around the vent that would go on top of the vent and facing the exterior of the tube.

[He Who Shall Not Be Named]

I like that idea a lot!

Andy, I get what you're saying about the trapped air, but I don't know that it's a big concern. The amount of trapped air would be very minimal. Many successful ballast systems such as the OTW version don't fully vent. Yes, you'll lose a very slight amount of capacity, but the benefits in manufacturing complexity and ease of transfer between models would more than make up the difference...

Bob

Andy put his finger on the biggest reason I placed the vent valve atop the cylinder, not below it.

And that being that any bubble of air that is not vented overboard will change the displacement of the boat with depth. Air is compressible, water (as a practical matter) is not. A bubble in the ballast tank will reduce in volume as the boat goes deeper, water comes into the ballast tank to make up the lost volume, and the boat gets heavier -- the situation only exacerbating as the boat goes deeper and deeper.

As a navy diver that phenomena was brought home when I was being trained as an instructor at the Submarine Escape Training Tank at the Groton submarine base. You took in a lung full of air topside. And sure enough you floated on or near the surface. But, swim down some twenty feet, and that lung full of air has squeezed to the point where you SINK! The tank was 118-foot deep. An alarming lesson in gas physics. One never forgotten!

https://youtu.be/ffOJEJwWSbs

A lesson applied here.

I don't want any air in that ballast tank when it's supposed to be full. That lip traps air. I don't like it.


David

[RCSubGuy]

I like that idea a lot!

Andy, I get what you're saying about the trapped air, but I don't know that it's a big concern. The amount of trapped air would be very minimal. Many successful ballast systems such as the OTW version don't fully vent. Yes, you'll lose a very slight amount of capacity, but the benefits in manufacturing complexity and ease of transfer between models would more than make up the difference...

Bob

[Subculture]

If incorporating the valve into the endcap, I think it would have to fit like a sleeve around the outside of the lexan tube, to avoid some sort of step (however minimal) between the valve and the inside of the tube,preventing the tank from fully venting.

A sleeve won't look as elegant, but it would also be easier to seal.