Another torpedo thread?

[cstranc]

Ok time for a quick quiz. What does this look like:


The rest of the world may see this like: http://www.mec.ca/Products/product_deta ... 5747104670 (tent peg)

But for me it screams]http://www.subcommittee.com/forum/mk48.gif[/img]

Note the nice taper on the right end. It even has a little extra aluminum there so you can drill a nice hole and insert a pressurized gas.

Ok so the left end needs a little work, but for a $2 per "tent peg" I can put in the effort.

I have tried to review the other torpedo posts, and spend hours looking at Dave Merrimans instructions via]http://www.rc-submarines.com/id47.htm[/url]

Does anyone have any more details around the firing valves?

The other thing that I guess is obvious, but...
The torpedoes are held in place by the friction. When they are loaded with Propell then pressure inside them overcomes this friction and causes them to launch right?

Any thoughts, or pointers in this area would be greatly appreciated.

[hakkikt]

Diameter is 8.6mm, that might

Diameter is 8.6mm, that might be a problem. Too much for 1/72, too little for 1/48. About right for 1/65, yuck

[cstranc]

That's a very good point

That's a very good point I should have mentioned the scale.

A total co-incidence. The plans for my Sierra came at 1/96 scale, but I wanted something bigger, so I had them enlarged to 1/60 scale...

[daveee]

Torpedos gas powered

I am usually the one asking the questions but this time maybe I can help.
I had to solve these same problems.
The torpedo has a 1/16" aluminum tube sticking out the back with a much smaller tube from a needle glued inside the 1/16" tube.
When pushed into a 1/16" "O" ring, the propel does not push the torpedo out. There is no "piston" to push out on. Instead your firing mechanism has to either pull the O-ring manifold off of the torpedo or you need a pressure firing mechanism to push the torpedo out the tube enough to pass the o-ring seal. (so the gas can release)
The torpedo weight and balance has to float with gas / liquid inside it once charged. The internal 1/16" tube needs to extend forward long enough to only allow gas, not liquid to escape once fired.
I still haven't figured out how to attach and align the curved tail fins.
The toughest problem for me was keeping the tiny O-ring in place inside the firing mechanism. I ended up making a 3 piece manifold that had to be soldered together AFTER the o-ring was inserted.
Still playing with needle sizes. Blue #28 gauge is close.
When the servo pulls the o-ring manifold off the torpedo, the stored propel in the air line blows the torpedo out the tube like a slow bullet. Works in the tub. The picture is incomplete but the servo push rod slides so that it can only pull back on the manifold, not push inwards.
Sorry if this is confusing. Coming up with this stuff consumed a lot of my day dreaming time.
Good luck
Dave

[ramius-ii]

Hi Dave

I like what you wrote and the pictures. I am still a little lost as to the firing mechanism. Do you have a side view mechanical drawing? It just seems that with a propel pressure of 78 PSI, holding the torpedo by o-ring friction would be not be possible. I guess there are a couple of other questions. How do you fill the torpedo? On the fin part, I understood the fins to be installed at a 15 degree angle to generate a spin. That the tail cone was made from a plastic casting with the fins cast into it. Is all this correct or did I miss something?

Thanks, Ed

[cstranc]

Dave,
Thank you for the

Dave,
Thank you for the excellent information, and sorry I did not reply earlier. I have been trying to get my Sierra modified to have a mobile ballast weight to do pitch control. Once I finish that it will be on to other exciting things like... retractable dive planes, working periscope, and of course the torpedoes!

I was at my parents cottage this weekend and made the master for the torpedo nose cone... But still so much to learn about torpedoes.

How could you manage to solder the manifold together with the O-ring in place. You are surely a braver man than I.

Please correct me if I am wrong. Looking at the big picture for torpedoes you get:
- Electric.
- Gas propelled.

The electric always look fun at the start, you can find pager motors and little batteries, but then you struggle with getting them to float and creating a scale prop... Very difficult at scales above 1/48th I think. So that leaves gas powered.

Looking at the gas powered it seems there are two "styles":

Style 1: The Propell is stored in a reservoir, and loaded into the torpedo just prior to firing. (Dave Merriman's setup is an example of this, as is yours)

Style 2: The Propell is loaded in the torpedo on the shore. (I think this is what Mike Dory does).

Obviously style #2 would be a lot simpler to implement. Do people use this style much? Or did I mis-read Mike's implementation. Do people avoid this style because the propell leaks out, or are there other reasons?

Chris

[KevinMC]

Hi Chris,

A point of clarification

Hi Chris,

A point of clarification with respect to "Merriman's setup": So far as I am aware, David has always used "pre-charged" torpedoes in his systems, and even credits Mike Dory with the basic design that he works from. I suspect that the central reservoir you're referring to is the "impulse reservoir" used to dislodge the torpedo from it's seal. Be aware however that firing a torpedo by direct gas impulse is difficult and can be unreliable. David has "moved on" to a firing system which positively latches the fish in the tube before launch and mechanically releases it at launch. (I'm in the midst constructing a similar system.)

[cstranc]

Kevin,
Thanks for that clarification.

Kevin,
Thanks for that clarification. Things make a lot more sense now.

I beleive Mike Dory's model was 1/48 or larger and so he could use modifed schraeder valves mounted within his torpedoes.

Are you going to be using filling valves external to your torpedoes to save weight?

Chris

[Rogue Sub]

Hey Chris,

I dont mean to

Hey Chris,

I dont mean to jump in at a point where its to late but..

Have you thought about using a cigars aluminum storage tube for a torpedo. They are hollow and light. Ofcourse they cost more but you get the cigar too! Ofcourse if your not a cigar smoker you can always send them to me!

Just a thought, i like the tent spike aswell but the tip looks a little to pointy to me. Ofcourse they do look nice and violent. You could use them in those target bb battles they have!

Kevin

[Guest]

Another torpedo thread?

Chris,
I tried the cigar tube route but ended up using a plastic hypodermic syringe for most of the body, and fit a Shrader valve in this Mike Dory style 1/72 scale gas torpedo. It worked well when I pulled the pin manually, but I never installed it in a sub.

[daveee]

Chris
Warning, this is just a

Chris
Warning, this is just a tub tested unit, and I am a beginner!
As you asked, this is a quick sketch of how I built my torpedo launch mechanism.
As for the soldering, the manifold is soldered just around the perimeter as the actual seal is made at the outside edge of the o-ring, not too close to the solder joint.
On the INTERNET I found two other guys that have done similar launch mechanism's but they failed to divulge how they solved the o-ring staying in place problem. (I tried crimping the brass to create a lip to hold the o-ring in but it didn't work.)
Filling the torpedo is done by holding the Propel can upside down and purging the gas out of the line in order to fill the torpedo with mostly liquid. I have had varying success with filling, but expect to come up with a reliable process with repeatable results. These little torpedoes have run for as long as 30 seconds. Getting them to float properly is a balancing act in itself.
At first I tried the shrader valve within the torpedo but it simply weighed way too much. I believe it is simply an impossibility for such a small torpedo. See pic.
I hope this info helps.
Dave

[ramius-ii]

Hey Daveee

I like what you did and maybe I can offer some choices or possible improvements to your design? I was wondering why you did not go to a straight feed of Propel rather than at an angle? As for your o-ring, there are two approaches. One is to use small 2-56 flat head screws to attach a plate to secure the o-ring. the second option is to use a "spot facer" drill for a flat surface for the o-ring rather than an angular hole. This way the o-ring is clamped and slightly compressed.

Best, Ed

[KevinMC]

Hi Chris,

Yes, I'll be using

Hi Chris,

Yes, I'll be using an off-torpedo "schraeder" fill and a firing mechanism very similar to what Davee's shown. I've gone with cast polyurethane heads and tails and an aluminum tube for the body of my torpedoes.

For reference, here is a 1/96 Merriman torpedo along with my brass nose and fin masters:


Here are the resulting cast parts and one assembled fish.


I haven't hit the tub-testing stage yet, but I expect to do so soon. (Gotta get the cover off the test-tank in my backyard.)

[cstranc]

You folks are soo far

You folks are soo far ahead of me. That's great 'cuz I can ask all the nube questions like:

So what type of tube is mounted in the torpedo for the gas pickup / exhaust?

The scraeder valve. Do you just buy the internal valve and make a seat for it? Dave, you seem to have taken something and filed away the threads...

And what about those o-rings? I'm having a hard time trying to figure out where those might come from...

Thank you again for all your insights and help. I cannot imagine the dead ends I would have followed without you folks!

Chris

[ramius-ii]

Questions about construction

I am enjoying all the information and discussion and have been studying as much as possible. There are several construction questions. How on earth do you achieve the groove for the 4 fins at 15 degrees? Next, from the pictures, the amount of plastic to be inserted into the aluminum tube seems a bit much. Is there a reason for this? Do you case several nose cones, for example from the master then use them to create a second mold? Inquiring minds would love to know!

Thanks in advance, Ed