small diameter static-diving type SubDriver

I’m finalizing the design of the 1.25” static diving type SD. It’s been a long and frustrating road. The work started over ten years ago. There have been design changes, brought on by new products needed to populate the system.

A quick summation of what has happened to alter the design of this static diving type 1.25 SD over time:

1.  Devices aboard the SD have drastically reduced in size and improved in function over time
2.  Because of the smaller sized LPB I came up with a much improved routing of the snort plumbing
3.  A more practical arrangement of the devices to limit wire-runs

Below is pictured the original proof-of-concept SD, just below the 1/72 Type-23 hull. As you can see it has been populated with all the devices, and has been  tested and works fine. However, that version of the static diving 1.25 SD is a bitch to wire, and some of the devices take up a lot of real-estate.

The unpopulated SD below -- it’s devices arrayed under it – is built to take advantage of these new developments. The most significant improvement is a much reduced in size low pressure blower (LPB) that permits internal running of the induction and discharge hoses. Also, much smaller, linear type servos free up room that now permits placement of the receiver under them, within the cast resin servo box. Substitution of the toggle mission switch with a tiny, magnetically actuated mission switch makes the wiring within the servo box a lot easier. And, finally elimination of the Lipo-Guard/Battery Link Monitor has simplified wiring and frees even more space within the cylinder.

You’ll notice that this new arrangement results in nearly a 25% increase in ballast tank size for a given SD cylinder length.



The big game-changer is the new (new to me, anyway), much smaller two-stage, diaphragm air pump. Unlike the stock LPB, this smaller pump fits easily within the SD. Also, as this 3-volt unit draws much less current, I’m able to eliminate the dedicated LPB motor-controller. Now the LPB pump is run through a simple servo controlled limit-switch.



Of course I first conducted some testing to insure that water ingested into the pump would not migrate anywhere else. The same testing protocol used for the big original LPB was employed to validate the smaller unit.

What I’m determining the value of the voltage dropping resistor needed to get this little motor down from the 7-volt line voltage to the 3-volts. Ohm’s law is your friend, but it never hurts to breadboard the circuit to see if it does the job.

The syringe is used to send pressurized water first into the pumps inlet port, then the outlet port – if there is any leak between the pump body and pump foundation, it will be revealed through the weep-holes drilled into the pump foundation.

Ten of these little LPB’s checked, not one leaked. A much improved batting average than the bigger LPB, which exhibits a failure rate of 20%.



This is the big deal: Where before I was compelled to build a dedicated forward bulkhead to house the big LPB and run its plumbing (induction and discharge hoses) external of the cylinder, now – with the smaller LPB – the plumbing is reduced to a short internal run of induction and discharge hose between pump and ballast tank forward bulkhead.

Note that the induction hose continues within the ballast tank, up into a manifold where the induction hose stands vertically where it will be at the topmost portion of the model submarines sail. We’ll be able to empty the ballast tank the moment the sail broaches the surface.

The brass tube running through the ballast tank is a conduit between forward dry space and the servo box. Through this will pass the power cable and wires between LPB motor and its limit-switch.



Though the LPB is now internally mounted, there is still room under it to place the after end of the battery. For a length of 1.25”cylinder that can comfortably fit the 1/72 Type-23 hull, the new design increases the length of the ballast tank over that of the original design.

Note how the simplified plumbing works: Air is drawn in from the broached sail down the vertical length of induction hose; through the manifold atop the ballast tank where another length of hose makes up to a nipple that directs the air forward through the forward ballast bulkhead; and then through another short length of induction hose into the suction side of the LPB. Compressed air is then sent aft through the short length of discharge hose; through the forward ballast bulkhead nipple; and into the ballast tank, blowing out the water through the open flood-drain hole at the bottom of the ballast tank.

(The lengths of Acrylic cylinder here are simple place holders and will be replaced with Lexan cylinder lengths – with complete ballast tank machining and function – once all the details are worked out).



The low-current drawing smaller LPB motor can now be controlled through a simple (and cheap) mechanical switch; a limit-switch that is actuated at the extreme ‘ blow’  position of the ballast sub-system servo. This arrangement reduces the need to route the three-wire lead between an (expensive) motor pump controller and receiver.

In this arrangement I need only run power from the limit-switch to the LPB motor.

Note the tan color of the internal forward ballast bulkhead. It’s a turned master being test fitted here. It will be used (with the other new masters) to create rubber tooling from which resin parts will be produced.



The LPB motor limit-switch is closed when the ballast sub-system servo magnet shuttle travels forward to the extreme ‘blow’ position. The switch is open in the ‘vent’ and ‘neutral’ positions.



The white platform, with a dedicated foundation for the LPB limit-switch, is a master that will be used to eventually produce parts like the earlier version seen above slapped together to prove out the concept of using a limit-switch to control the LPB.



The three servos needed to control the rudder, stern planes and ballast sub-system are mounted on a platform that sits within the cast resin ‘servo box’. The tops of the servo magnets -- each set within a shuttle that makes up to the linearly running servo bell-crank -- are even with the bottom of the G-10 cover.



The coupling between external push rods and servos is magnetic. An uncomplicated watertight linkage between servo and item being moved by that servo, no seals involved.



David

Are you planning on offering this for sale?

Nautilus Drydocks had a 1.25" OD watertight cylinder advertised for $125 (https://www.rc-submarine.com/product-page/1-25-wtc-single-prop-dynamic-diving). I tried talking to them about a twin shaft version (which is on the YouTube video they had). After several weeks, they told me the fellow who makes these was suffering some serious ailments. I waited, then I was told they wouldn't make the twin shaft version. Then I decided to buy the single shaft, but they said they couldn't make that either.

I don't fault the guy, his health needs to take priority.

Anyway, I look forward to hearing more about your experiments.

Cheers,
TXGR

TXGR wrote:Are you planning on offering this for sale?

Nautilus Drydocks had a 1.25" OD watertight cylinder advertised for $125 (https://www.rc-submarine.com/product-page/1-25-wtc-single-prop-dynamic-diving). I tried talking to them about a twin shaft version (which is on the YouTube video they had). After several weeks, they told me the fellow who makes these was suffering some serious ailments. I waited, then I was told they wouldn't make the twin shaft version. Then I decided to buy the single shaft, but they said they couldn't make that either.

I don't fault the guy, his health needs to take priority.

Anyway, I look forward to hearing more about your experiments.

Cheers,
TXGR

Currently we are selling just the dynamic type (no ballast sub-system) SD. However, I'm nearing freezing the design of our new static type (snort type ballast sub-system) SD. So, that item will be in the catalog soon.



Both the static and dynamic type SD's can be rigged for single or dual, counter-rotating shafts.













I'm the fellow who makes the SD's. I'm fine and ready to kick-ass.

Watch the skies!

David

I had no idea this was you. Cool. I am very happy to hear you're doing better and look forward to your finalizing the static SD.

Cheers,
TXGR

David

Looks like you are extremely close to "sea trials." I hope you have a chance to take some videos.

Cheers,
Brian

TXGR wrote:Looks like you are extremely close to "sea trials." I hope you have a chance to take some videos.

Cheers,
Brian

I have other projects to attend to, but come next month I should have this thing in the water -- pool water, so we can see it running in its element.

You bet I'll shoot video.

David

David

David

I was just wondering if there were any updates on this SubDriver and maybe so "sea trials" in your Type XXIII U Boat?

In looking at pics, I think your proof of concept model has about 13"-14" of usable interior hull length, maybe 15" depending on the taper at the end. How long is the prototype SD?

I don't have the model will me now, but I am hoping I might be able to squeeze this SD into the Trumpeter 1/144 USS Gato. That model has a pressure hull, which IIRC is about 1.25" OD. The overall hull length is about 26," but I can't find my notes on the dimensions of the interior, pressure hull, etc. Of course, even if I can get the SD in there, I'll need additional room for rigging. We shall see...

Cheers,
Brian

I was just wondering if there were any updates on this SubDriver and maybe so "sea trials" in your Type XXIII U Boat?


As to providing you with an update on the SubDriver (SD) and the eventual ‘sea trials’ of the 1/72 Type-23 model submarine: Can’t put it in the water till the model structure is done and the SD properly integrated with the hull. And that means finishing the model proper; indexing and making fast the SD within the hull; working out the running gear between SD motor and propeller; and developing the linkages needed to position the stern planes and rudder.

One major improvement, that has taken some time and ingenuity, during hull assembly has been the incorporation of six practical limber hole/hand-grabs atop the diesel muffler fairing astern of the sail. As represented on the stock kit they are very shallow indentations – an artifact of the injection molding process, where sunken features cannot be adequately represented on tool cavities of deep draft.

Here you can see how I’ve dug open the oval openings and inserted a length of styrene square stock to form the hand-grabs that make these six limber holes unique from those on the hull and sail.



A single indexing pin within the hull engages a hole at the bottom of the SD’s ballast tank. This prevents any fore, aft, and rolling of the SD within the models hull. Without the pin it would be a constant battle adjusting the linkages as the SD slide within the hull. That done I addressed the running of the linkages pushrods to the control surfaces; and a preliminary look at how I would arrange the running gear.

I’ve denoted the main spaces within this little 1.25” diameter SD. Of note is how I employed magnets to translate the motion of the internal servo output arms to the external pushrods. The ballast vent, rudder, and stern planes are positioned as a consequence of magnet motion atop the servo box.



The servo box contains little, slightly modified linear motion servos (the kind used in those little indoor flying model aircraft). The shuttle/bell-crank of each servo has attached to it a magnet that is positioned under a thin fiberglass box-top. It’s the magnetic attraction between the inner and outer set of magnets that accomplishes the task of linking the internal (dry) magnet to the outer (wet) magnet, thus eliminating the need for any traditional pushrod seals.

Illustrated below is an old-style arrangement. Today the toggle mission-switch has been replaced by a magnetically actuated electronic switch located in the forward dry space of the SD. Other than that, the servo box on the Type-23 SD is pretty much the same arrangement.



The right-angle bends at the forward ends of the pushrods are there to permit fine adjustments of pushrod length during set-up. The rudder pushrod runs through the hollow rudder upper skeg, and the stern plane pushrod is directed low engage that control surfaces bell-crank.



I was getting cute here: trying to keep the rudder linkage hidden within the upper skeg section of hull. No small feat on a model submarine this small.

This may, or may not work. My inspiration here is the magnificent work of Tom Chalfant and Manfred Reusing. Two masters of making very small r/c submarines work in a credible fashion. I blame both for this little slice of insanity!

Specifically I’m investigating the viability of using a magnet engaging an iron bell-crank element atop the rudders operating shaft as the means of translating the axial motion of the pushrod to a rotation of the rudder. Unfortunately the short moment arm and relatively weak magnetic ‘pull’ may not be enough here to hold up against the propeller flow forces acting on the rudder. If this does not pan out during ‘sea trials’ I go old-school and run an external bell-crank to the rudder with a hard-and-fast mechanical union between pushrod and bell-crank. We’ll see.

The stern planes are also connected through a magnet working an iron piece incorporated within the stern plane bell-crank.



The little magnet engages an iron bell-crank. It’s as simple as that. I cut away a bit of the upper skeg to get access to the rudder bell-crank, but once I’m happy with the linkage I’ll permanently attach the removed piece and fair it in. In the event I find it better to go with a traditional hook-up between pushrod and rudder bell-crank I’ll simply pull the magnet equipped pushrod and replace it with a pushrod that will run externally to the rudder. Always have a fall-back position when drying something new.



Hopefully this mock-up will demonstrate to you how the magnets are used to connect the linkages in an almost non-kickback fashion.



In looking at pics, I think your proof of concept model has about 13"-14" of usable interior hull length, maybe 15" depending on the taper at the end. How long is the prototype SD?

I found that I only had room for a 13” long SD for this model. Just long enough to provide a ballast tank with enough floodable volume to produce the buoyancy needed to get the model up to designed waterline.



I don't have the model will me now, but I am hoping I might be able to squeeze this SD into the Trumpeter 1/144 USS Gato. That model has a pressure hull, which IIRC is about 1.25" OD. The overall hull length is about 26," but I can't find my notes on the dimensions of the interior, pressure hull, etc. Of course, even if I can get the SD in there, I'll need additional room for rigging. We shall see...


I can get a 14” SD in there, but that’s it: I have to leave plenty of room at the after end to provide a low angular-offset between SD output shafts and propeller shafts. And that extra inch on an SD dedicated for 1/144 GATO model use will be needed as additional ballast tank volume if I’m to have any chance of getting that model even close to designed waterline in surface trim. There’s a lot of above waterline structure to that kit that has to be accounted for in the ballast tank!



A fortunate occurrence is that the foundations within the two hull halves of this 1/144 GATO model kit are sized to fit a 1.25” diameter SD. Perfect! The task with this model submarine kit, like the Type-23, is working out a means of getting at the SD for maintenance, adjustment, or repair.



The running gear for this model will make use of the kit provided propellers and shaft struts. The only trick was to snip the propellers away from the styrene propeller shafts and substitute stainless steel shafts. Simple! Ahead and astern loads will be taken at the SD’s motor and idler gear bearings.



The universal between SD motor shafts and propeller shafts are lengths of flexible surgical tubing. Slick! Note the use of an idler gear driven by the main shaft – that extra gear producing the counter-rotating motion to achieve a two-shaft drive off of one little motor.



Note the sloppy fit between drive and idler gears. This permits water to squirt out of the meshing teeth. If the fit was tight, the unit would water-hammer to pieces (or more likely, just come to a screeching stop). Remember: water is an incompressible fluid.



David

That post probably took you hours to put together, including taking all the specific photos. I really appreciate all the detail and explanations. Watching your build is a real education

I was so focused on whether I could squeeze the SD into the hull, I completely forgot about sizing the ballast tank for proper buoyancy.

I'm very fortunate you're also working on a Gato, that will make following in your footsteps much easier for me. I almost feel guilty.

Thanks for the update. I'll keep following along.

Cheers,
Brian

TXGR wrote:That post probably took you hours to put together, including taking all the specific photos. I really appreciate all the detail and explanations. Watching your build is a real education

I was so focused on whether I could squeeze the SD into the hull, I completely forgot about sizing the ballast tank for proper buoyancy.

I'm very fortunate you're also working on a Gato, that will make following in your footsteps much easier for me. I almost feel guilty.

Thanks for the update. I'll keep following along.

Cheers,
Brian

Thank you for the acknowledgment, Brian. Yes, I put in some effort to document my work and present it to the Great Unwashed. And there's a reason:

I stand on the shoulders of the giants that came before me.

I was taught by many the techniques I now employ in my model building. Those Craftsman too took the time to write and illustrate about the techniques they learned; they made the effort to pass the Craft on to others.

I'm honor bound to do the same -- to pass the torch to those who come after me.

As a young man I devoured all the magazines, lectures, seminars, contest, and trade-shows that had anything to do with the Craft. And there were (not so many today) the model clubs, national and local, where questions could be asked and other peoples work examined in detail.

My Dad was a sculptor and model builder. To this day I study his work and notes, and continue to learn from him.

Working out the amount of water the ballast tank has to hold is an easy one if the structure is GRP or polystyrene: Those materials have a specific gravity very close to 1. Therefore, if you take all the above waterline structures and weight them, that gives you a close presentation of the weight of water the ballast tank has to hold to get the entire structure in a state of near neutral buoyancy. Just to be sure, tack on ten to fifteen percent more water and you're good to go.

I have several other projects ahead of the 1/144 GATO, but hope to eventually get to it.

Stay tuned, Brian.

David