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Merriman's Submarine Modelling

merriman

David Douglass Merriman lll
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Today was spent machining the motor bulkheads to fit the Lexan cylinders that house the items within the model submarine that have to be maintained in a dry environment. Most of the work dedicated to mounting the outrunner type brushless motors within the MB's.





To facilitate motor testing and MB certification I assembled this test rig comprising a battery, electronic speed controller, switch, and servo-setter (pressed into service to act as a 'throttle').





Tomorrow I explore what it takes to assemble, test, and certify a MB equipped with the gear-splitter.



 

merriman

David Douglass Merriman lll
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Old and new r/c submarine operating systems on display here. Each type embodies the means of control, propulsion, and ballast water management needed to make a scale model submarine work in a credible and reliable manner.
The system on top is the old, single cylinder type SubDriver (SD). The two bulkheads that divided the cylinder into three spaces are fixed in place with machine screws -- screw holes that sometimes resulted in cracks that would migrate over the seals causing water leaks into the dry spaces. And this type SD compelled me to select one diameter size cylinder for the entire length of the SD, this often not the ideal utilization of annular space between it and the interior of the model submarines hull. And the single cylinder system had just too many hoses and manifolds sitting proud of the cylinder, all potential points of failure.
Many of the SD shortcomings have been eliminated with the next step up the evolutionary ladder: the Modular SubDriver (MSD), seen at the bottom of the picture.
No mechanical fasteners to hold bulkheads in place. Instead, only O-ring friction holds three separate lengths of Lexan cylinder in place -- this innovation making access for repair, maintenance, and adjustment a much easier task. As an added benefit the MSD’s ballast water management sub-system has been consolidated into a tight, accessible package, eliminating most of the external plumbing which plagued the original SubDriver design.


The MSD contains the same devices as the earlier SD but does it within an envelope that can quickly and easily be changed in length and diameter to suit a specific application. As exemplified with this tear-drop shaped hull the arrangement of the three separate cylinders has been selected to make maximum use of the available space within this free-flooding model submarine model.

With few exceptions an r/c submarine makes use of the traditional devices as other r/c controlled vehicles. However, only air-ships and submarines require a means of changing the vehicles displacement within the fluid it operates; and only a submarine requires an assured means of autonomously sensing and correcting its pitch angle. The main destinguishing burden an r/c submarine has over all other vehicle types is the need to keep things dry at all times.


There are many ways to move water in and out of the ballast tank if the intent is to change the submarines displacement by taking on an amount of water weight equal to the weight of water the above waterline structures displace when immersed.
My SemiASperated (SAS) ballast water management sub-system pushes the water out of the ballast tank by displacing it with air. Air either scavenged from within the dry spaces of the system or from atmosphere. Pictured is an old SubDriver system employing the SAS cycle -- a Rube Goldberg delight, to be sure.


This better illustrates the SAS ballast sub-system.
A vent valve atop the ballast tank (not shown) opens, venting the air from within the ballast tank, allowing water to fill the tank and the submarine is totally under water. The formerly above waterline portions of the submarine, now fully immersed in water, produces a buoyant force equal to, but opposed to, the weight of the ballast water taken on. The boat assumes the state of ‘neutral buoyancy’.
To surface the water in the ballast tank is blown out with air compressed by the LPB. Air is initially scavenged from within the SubDrivers interior (the snorkel valve is closed). Once the sail broaches air is taken from atmosphere.
Internal air is only good for a partial blow of the ballast tank, but it’s enough to broach the sail above the surface. Once the snorkel head-valve opens the partial vacuum created within the dry spaces is back-filled with surface air and the blow continues with air from the surface.


Two-valve protection is an almost religious tenant within the submarine community – you always want a back-up stop to any line subjected to sea pressure. That philosophy has carried over to my model submarines as well. The ‘safety float-valve’ is the back-up valve within the induction side of the SAS ballast sub-system. The primary stop to water ingress to the induction line is the snorkel head-valve up within the sail. The safety float-valve is the backup, it prevents any water that gets past the snorkel from leaking into the SubDrivers dry spaces – it only closes if there is water in the line, otherwise it passes air going in or out of the systems dry spaces.
Here I’m testing a unit by injecting first air, then water. It must pass the air, but immediately block the flow of water.


Within the safety float-valve a float, with a rubber disc atop it and a weight within it will remain clear of the air passage between the nipple at the bottom and the nipple at the top of the device. However, should water get into the safety float-valve, the passage is blocked, keeping water from getting into the dry space of the SD/MSD.


The body of the safety float-valve is formed from a short length of copper pipe and two copper caps. The lower cap is permanently soldered in place; the top cap is removable for servicing and is secured and made watertight with RTV adhesive. Here I’m cleaning parts for soldering. The end-game: I’m holding a completed, ready-for-issue unit.




The air-pump used to discharge the ballast water is this small diaphragm pump, modified to make it suitable for handling water as well as air – if, and when, water gets into the induction line (and it will!!) I don’t want any of it to get out of the pump and into the dry spaces of the SD/MSD. The elastic elements of a diaphragm pump prevent ‘water hammering’ of the mechanism should it encounter a non-compressible fluid. Though technically described as positive displacement type pumps, because of their slight ‘give’, the diaphragm type will move water or air with great enthusiasm and without hammering itself to death.
Each pump -- I revert to submarine-speak and call them Low Pressure Blowers (LPB) – had its rubber seal, which isolates the pump workings from the pumps surroundings, mashed tighter within its housing through a few modifications of the assembly. This work to insure no water leakage past the pump body and into the dry space.


Each modified LPB was then subjected to about 15 psig of water pressure at the discharge and induction sides of the pump and the pump body examined for water leakage past the seal.


Once a LPB had passed its leak-check it was then outfitted with two spark-suppression .01 micro Farad capacitors. Electronic ‘noise’ within the tight confines of an r/c vehicle has to be avoided; spark-suppression of brushed motors and switches is a necessity.


Final check of the LPB’s was to spin the motor under load (dead-header test), followed by an affirmation of correct discharge rate. At this point I declare the units, ready for issue.


The new MSD design has greatly streamlined the integration of the SAS elements. Here you see a typical MSD ‘after ballast tank bulkhead’, or ‘union’ along with the fasteners that hold things together, servo, linkages, LPB switch, safety float-valve, plumbing, and LPB.
Unlike the earlier SD with its many externally running hoses, nipples and manifolds, the new MSD’s SAS plumbing is all internal with only the flexible induction hose running from the system to the snorkel head valve located high up in the submarines sail.
The union is of two-piece construction which permits me to mix-and-match different diameter lengths of Lexan cylinder. This particular union provides interconnection between a 2.5” diameter after dry space cylinder and a 3” diameter ballast tank cylinder.


After assembling the two union halves the ballast sub-system servo – that opens and closes the ballast tank vent valve as well as activating the limit-switch that turns the LPB on and off – is strapped in place. The servo pushrod passes into the ballast tank through a watertight seal and works the linkage that opens/closes the vent valve atop the ballast tank.


The LPB and safety float-valve mount, as a unit, in front of the servo. Note that the LPB induction is split between the safety float-valve and nipple which connects to the snorkel head-valve through a long length of flexible hose. The LPB discharges directly into the ballast tank.

 

merriman

David Douglass Merriman lll
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When I got into the r/c vehicle game, in the mid-60’s, the vehicles receiver, unless it was of the super-heterodyne type suffered from low selectivity; it was most susceptible to adjacent frequencies, ‘electrical noise’ and unwanted RF from other devices in close proximity to the receiver. Back in those days, when dinosaurs still roamed the Earth, all electrical and electronic devices within the model airplane or boat had to be well distanced and spark suppressed if any credible range was to be achieved between transmitter and receiver. The devices could not be packed in close proximity to one another; the inverse square law was (and still is) your friend.
Flash forward to today: We are now using receivers that not only feature very selective detectors, and the signal they are tuned for is ‘processed’ to weed out both external and internal RF energy not emanating from the controlling transmitter. And it is these advancements in receiver technology – and the introduction of brushless motors, servos that are suppressed at the factory and other device improvements -- that permits dense crowding of electrical and electronic devices within the tight confines of a SD or MSD.


Once I had settle on a rational placement of the devices within the after dry space I set about designing and proofing a means of mounting those devices within the cylinder. The eventual foundations would be fabricated from .031” thick aluminum sheet, in the form of trays and circular bulkheads. Sheet metal work 101. Of course, it did not go according to plan.
Good practice: Before committing to the metal one should first mocked-up the foundations using cardboard cut with knife and scissors – easy to work with and easily modified as problems of fit and placement were resolved. I started with an initial cardboard template, and from that marked out a cardboard mock-up; that mock-up to affirm fit within the after dry space.

I took advantage of the motor mounting studs, using their forward ends to make a four-point attachment to the after vertical face of the eventual device foundations.


Once I had constructed the cardboard foundation mock-up and worked it – along with the template – to fit the cylinder, I quickly shaped scrap pieces of 20 lbs. RenShape to stand in for the actual devices that would eventually populate production MSD’s. I make it a practice to slightly over-size stand-ins like this to account for mounting tape, leads, heat-shrink wrap, and other unaccounted for obstructions. In other words: if I can get the stand-ins to fit, I won’t have any trouble getting the actual devices to fit.
IDIOT!
Nothing revolutionary here in the design process; shipyards have been doing this ‘try it before you buy it’ mocking up for centuries. I don’t invent ideas. I steal ideas (but, only the good ones). Though, sometimes I don’t apply those ideas very well.


The MSD will accommodate five servos. On in the after ballast tank union, two at the forward end of the forward dry space, and two back in the after dry space – the space I’m working up the device foundation for.

As this size MSD is for the intermediate-to-large size r/c submarines we wanted those two after servos to have the ass to move substantially sized control surfaces, so I sized the servo stand-ins to represent ‘standard’ sized servos. Sure, they’re big bulky things with a substantial foot-print. But, what’s a guy to do? Once those stand-ins were in place there was precious little real-estate left for the other device stand-ins.
And this brings us full-circle back from my observation about the ability of today’s receivers to tolerate other electrical and electronic devices in close proximity without being swamped with RF ‘noise’. The packaging illustrated here would have been impossible back in the 60’s! Some things do improve with age.


But will the organized chaos fit?.... Hell no!


Well … what worked in mock-up, did not work when I started to mount the actual hardware. Servo leads got in the way; the receiver pin array stood too proud and would not fit the narrow slot I had initially assigned for it. Little things like that, not accounted for in mock-up spilled all the beans. A re-think of how things would be arranged was in order, on the fly. Chaos management 101.
And this, boys and girls, is why you test fit before committing to a permanent install.


This is as far as I got with the real-deal install: the two big ‘standard’ sized servos and that rather chunky Mtroniks brushless motor ESC. I found that the forward end of the aluminum foundation was not getting it done. The vertical attachment to the motor mounting studs was good, as was the long running horizontal base. But the forward, starboard plate, where I planned to mount the receiver was too tight a fit. So the forward end of the foundation needed a re-work, and I had to find a new home for the receiver – I elected to raft it over the ESC.


A little sketching to skull out the new forward area of the foundation and in no time I had my plan-B. A little sheet-metal-thinking-on-paper and it was worked out that a single piece of sheet could be bent to produce the receiver raft, as well as two vertical faces to mount the smaller devices. Origami for idiots!


From brain, to sketch, to template, to laid-out sheet aluminum, to band saw, drill press, and mini-break.

 

merriman

David Douglass Merriman lll
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The electronic devices within the cylinder are commercial products with leads usually longer than required to reach the receiver. Aboard the Modular SubDriver the receiver is the nexus from which most propulsion, control, and ballast sub-systems receive their intelligence.

To get everything to work as a system its good practice to first arrange all the electrical and electronic devices outside of the very cramped MSD and get things operational. Problems are identified and corrected easily at this stage and some of the setup protocols performed. Some setup tasks have to be differed until the devices are installed within the MSD.



Longer than necessary leads within the tight confines of the cylinder not only makes for a messy arrangement, they also act as antennas that capture spurious RF energy and pump it into the receiver where that noise could swamp out the transmitted signal.

Long leads bad.

Short leads good.

Each lead is shortened but for a little slack to alleviate any strain on the wires, plug and PCB. Getting rid of all that spaghetti makes for a much tighter assembly within the cylinder and greatly reduces the possibility of RF noise causing self-glitching.



Dykes, wire-stripers, solder, 25-Watt soldering iron, non-acid flux, heat-shrink tubing, and patience, outside door secured so that screams of rage don’t disturb the neighbors, and the leads are sized to suit the devices distance from the receiver.



Gathering, testing, programming, and integrating the electrical and electronic devices – wrangling all the magic gizmos that make the damned thing work, are tasks I loathe doing; these aspects of r/c model submarine building and operation interest me not in the slightest!!!!

I’m competent enough when it comes to donkey-work like hooking up receiver to servo or ESC, that basic stuff I can handle, any moron can do that! BUT, what frosts my butt; what drives me nuts; what sets my hair on fire, is the task of ‘setup’ of the two devices unique to r/c submarines: the Battery Link Monitor (BLM) and Angle Driver (AD2).

I’ve read and re-read the instructions and simply cannot get a setup to work right the first time. To be fair to the product, I can think of no better word description than what Kevin has authored in the instructions.

Apparently I’m not wired to translate written instructions into the perfectly choreographed button-pushing, and transmitter stick twiddling actions needed to get the devices to talk to one another in a civil manner. I NEVER get it right the first time. But, I’m a special type of hard-head; I eventually get the damned things working right. Given a choice between chewing broken glass and setting up these devices I would have to think about it a few moments.

I hate this shit!

Don’t get me wrong. No one on this planet appreciates the availability and utility of these devices more than me; particularly the units produced by Kevin McLeod of KMH. His devices present small foot-prints, are rock solid, and consume very little current. But, because of the sophistication of their operation and enhanced capabilities, these devices -- specifically the Battery Link Monitor (BLM) and Angle Driver (AD2) -- demand full attention as you attempt to follow the instructions. Programming is specific to the model, r/c system, and battery type. One size does not fit all.



Only r/c submarines require a device to autonomously drive the stern planes to keep the model horizontal when running underwater; and a fail-safe device to blow ballast water if the signal is lost (not a unique requirement in itself to r/c submarines), and also actuates if the battery voltage drops to a dangerous level.
(The ADF2 pictured below is an older type that featured an integrated fail-safe circuit, but that chore is now handled by the BLM).



Setup of the BLM can be done before putting it into the cylinder, but if care is taken to make it assessable once mounted – you have to get at it to push the ‘set-button’ – there’s no problem programming it in situ. As you can see I’ve mounted this device on the side of the starboard (stern plane) servo.



A simpler setup routine is employed to get the Depth Commander (DC) device up and running. This optional piece of gear drives the bow/fairwater planes to maintain the last commanded depth setting. It can be commanded off and on from the transmitter. Slick! This device is not vital, but something I’ve come to embrace.

You see, I’m a bit of a cow-boy when it comes to mixing it up with surface craft (targets) at the lake. The DC greatly reduces operator work-load as one weaves in and out and under the surface pukes. Much good fun to be had busting up the regimentation of a nicely arrayed battle-group.

“What? Something spooked you guys? There were collisions? You all should work on your group discipline … just say’n”.
RHIPMF’s



The AD2 has to be set once mounted on the MSD’s device foundation. This is because the devices reference plane is gravitational force and the basic setup operation tells the devise which-way-is-up.



The Battery Link Monitor is a device that, in the fail-safe modes, autonomously commands a ballast tank blow if there is a Loss Of Signal (LOS) between transmitter and receiver; and/or the battery runs down to a preset low-voltage point.

The monitor mode logs the number of LOS events occurred during the last sortie. Informing you to what degree the body of water you are operating in is attenuating the transmitted signal. Good to know stuff as you prepare for the next patrol. It’s been my experience that any body of water, be it pool or lake, has its radio ‘dead spots’ which when identified should be avoided when operating the model submarine submerged. The BLM’s monitor is a very useful feature in that it helps you survey the patrol area for these no-go locations.

 

Grey Havoc

The path not taken.
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You see, I’m a bit of a cow-boy when it comes to mixing it up with surface craft (targets) at the lake. The DC greatly reduces operator work-load as one weaves in and out and under the surface pukes. Much good fun to be had busting up the regimentation of a nicely arrayed battle-group.

“What? Something spooked you guys? There were collisions? You all should work on your group discipline … just say’n”.
RHIPMF’s
:D
 
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