BUILDING A WIRELESS VIDEO SYSTEM - UNDERWATER HOUSING

[anonymous]

By David Merriman III


For over a decade I have been working to perfect practical 1/96 and 1/72 scale model submarine torpedo and torpedo launching systems. Mike Dory was the first to enjoy success with his design of a gas propelled model torpedo here in America, but his work was confined too much larger weapons than what I wished to produce. In recent years I found that an all resin, hollow cast, homogeneous polyurethane torpedo could contain a charge of Propel liquid, thereby eliminating the ever present leaks encountered with weapons manufactured of different materials, which required bonding of the various components.

I was finally able to produce massive quantities of torpedoes; torpedoes that would be leak free, easily produced, and of a weight light enough to carry a full charge of Propel liquid yet be nearly neutral in water, at time of launch, and would assume a significant positive buoyancy at end-of-run, facilitating recovery for re-use.

Here you see my first practical small scale launcher and torpedo system]http://sneill.com/merrimans/1.jpg[/img]

[anonymous]

1/96 hollow cast resin torpedoes

1/96 hollow cast resin torpedoes at various stages of construction. The top yellow unit is an unpainted resin casting already outfitted with the propulsion nozzle-pickup tube. Near the center you see a finished torpedo cut-away to reveal the hollow interior and how the pickup tube extends into the body to gather Propel gas rather than liquid – at time of launch and during the run, acceleration force pools the liquid Propel to the stern, so the intake of the pickup tube is positioned near the center of the weapon to siphon off only Propel gas. Gas which is then sent astern to the restricted nozzle where it is expelled to produce the reactive force (thrust) which propels the weapon along a distance of up to seventy-five feet!

Through experiment I found that the nozzle of the small torpedoes (1/96 and 1/72) had to have a restriction equivalent to a #93 drill bit … you have any idea how hard those little bits are to find, and how much they cost!? An alternative is to use diabetic insulin syringe tubes that have a bore just about that small.

I’ve streamlined small-scale torpedo production to the point where I can make up to one hundred units a day. So, if I loose one or two of these things at an outing, it’s no big deal. My innovation, other than making the entire body from resin, was to eliminate the heavy on-board charging valve that Mike Dory and others employ aboard their weapons – the small sized torpedoes just don’t have the displacement to permit a discrete charging valve. My weapons are charged through the nozzle after they are loaded into the torpedo tube and made fast by the stop-bolt mechanism.

[anonymous]

A problem with torpedo stability

A problem with torpedo stability at time of launch quickly manifested itself. Seems that the plum of expanding gas at the stern of the weapon, as it just clears the muzzle end of the tube, is being deflected by the hull (kick-back) acting on the stern of the weapon to swing it off course. The problem was rectified, to a moderate degree, by punching ‘throttling’ holes in each torpedo tube (seen in the launcher system to the left of the model). These holes vent off much of the excess impulse gas before the weapon makes the bubble-water interface.

The throttle holes worked to leave just enough gas pressure behind the weapon to get it clear of the muzzle and minimized the explosive plum of gas. This also had the desired effect of getting the weapon out of the gas bubble and into the water quicker. However, though torpedo accuracy increased markedly, there still existed a stability problem with weapons ejected from the outboard tubes – a situation caused, I believe, do to the extreme asymmetric expansion of the impulse gas plum behind any weapon launched from the elongated openings of the outboard tubes.

With a theory in hand I needed to come up with a means to prove it. The need of ‘real time’ video imagery of weapons launches manifested itself.

(An array of pressure transducers on hull and weapon would be ideal, but such mapping of pressure distribution is way out of my league … hey, I’m just a dumb-### Torpedoman knuckle-dragger. My motto]http://sneill.com/merrimans/3.jpg[/img]

[anonymous]

This article chronicles the creation

This article chronicles the creation of a special housing to contain a micro-video camera-transmitter available today from various sources, and the means of mounting the camera-transmitter antenna above the waters surface.

The video camera system, transmitting at 2.4gHz (gigga Hertz, the frequency of the RF wave in ‘cycles per second’ for you old-school types) doing so at a very low antenna power level, necessitating the placement of the systems antenna well above the surface while the WTC itself was submerged. You only get a good images if the transmitter and receiver antennas are in line-of-site, no obstructions. The obvious solution was to run the antenna up a vertical mast where the transmitter antenna would be in the air as the rest of the model was submerged as I conducted weapons and launcher trials. It’s important to get at least two hull diameters below the surface for such work, as ‘surface effects’ can skew the analysis.

Here you see a test fitting of the completed video system atop the hull of the 1/72 ALFA model. Note that this mount permits extension in height of the watertight container (WTC) from deck level to several inches over the deck. The WTC can also be pitched up and down.

[anonymous]

Once I had a wireless

Once I had a wireless mini-cameras in hand I set about making a series of sketches illustrating just how tight a package I could make of the WTC needed to keep everything dry. The main drivers as to cylinder diameter (going with the minimal 1/16” wall thickness available) and length were the dimensions of the camera-transmitter and 9 Volt battery. I came up with an outside diameter of 1 ¼” and a length overall of 5 ¾” with a cylinder length of 3 ¾”. It was clear that I would be using Acrylic plastic both for the tube and the disc of 3/8” sheet, needed to form the optically clear window at the front. Though Lexan is less subject to stress cracking, that clear plastic is just not clear enough, nor is it available in the variety of diameters and wall thickness as the more common Acrylic.

The major hurdle was to come up with a method of relocating the transmitter antenna from the body of the unit to a position atop a surface penetrating mast. These characteristics of the camera WTC outlined, it became clear what items would be fabricated from Acrylic and what would be cast from polyurethane resin.

The WTC containing the camera system is entirely self-contained, no external power or control inputs required; just work out a means of mounting the WTC to the vehicle and you’re ready to roll tape.

[anonymous]

This is the Swann wireless

This is the Swann wireless video system – it also comes with items not shown here, like wall units to produce transmitter and receiver DC from AC wall sockets. I’ve laid out the stuff of interest to those wishing to employ the unit for r/c vehicle use. Note that the Swann unit is video only. No audio. However, a friend put me onto a site that offers what appear to be the same type units (http://www.wirelessmicrocolorcam.com) but which also transmits and receives audio! You’ll find these things at Micro-Marc, as well as on Ebay.

The modification to the camera-transmitter unit is to install a length of small gauge coaxial cable between the transmitter and remote antenna (atop a tall vertical mast); elimination of the bulky connector between the camera-transmitter unit and its 9 Volt battery. Other than that, the wireless camera system is a ‘plug-and-play’ unit]http://sneill.com/merrimans/6.jpg[/img]

[anonymous]

And here you have the

And here you have the camera-transmitter and battery tapped atop a Radio Shack toy r/c car – just to demonstrate the versatility of the system. Of course this unit can be mounted on a bigger r/c car or truck, boat, airplane, or (with proper water tight enclosure) submarines! This small black and white, battery operated monitor is perfect for field use, shop set-up, and testing of the system. A single high capacity gel-cell battery attached to the bottom of the monitor powers both the TV and the bolted in place downlink receiver.

As used aboard the little car I was able to achieve the advertised 200-foot range with the video link. Keep in mind that these little TV transmitters are very low power so you have to keep the two antennas (camera-transmitter and receiver) in line-of-sight or the signal will drop out. Note how bulky the system battery cable is. That had to go!

[anonymous]

The underwater WTC project was

The underwater WTC project was dead in the water without technical assistance from Lee Smith. I met Lee over at R/C Groups Discussion, http://www.rcgroups.com/forums/forum...?s=&forumid=60 Lee schooled me on the whys and wherefores of high frequency antenna hook-up.

Not only did Lee provide a step-by-step on how to install the coaxial cable between the transmitter and the antenna, he also provided a length of the very small diameter coaxial cable needed, RG-174.

Lee’s assistance was invaluable to the success of the project; guiding me over the net I took his words and made a detailed drawing of how he wanted me to ground both ends of the coaxial cable ‘shield’. Allaying my initial fears that I would have to dig into the circuit boards, it turned out that all I had to do was snip off the existing antenna, insert the coaxial cable (of a length needed to run up through the ‘airfoil’ shaped vertical fairing tube) and trim back just enough shield to produce the antenna of the same length as the original, and ground each end of the coaxial cable shield.

[anonymous]

A completed and outfitted WTC.

A completed and outfitted WTC. The only ‘switch’ needed to turn on and off the camera-transmitter is the connector that makes up to the 9 Volt battery.

Note that there is a modified tire valve in the end of the end-cap. This is used to vent off the slight overpressure created in the WTC when the cap is installed - that slight overpressure, increasing in pressure as the unit warms up (the transmitter does produce noticeable waste heat in operation) the entrapped air could force the end-cap to pop off the cylinder, resulting in immediate catastrophic flooding!

The tire-valve is also used for pre-mission testing of the WTC watertight integrity]http://sneill.com/merrimans/9.jpg[/img]

[anonymous]

Working off the final design

Working off the final design sketch I turned a RenShape 450 plastic end-cap, and cut out antenna, and WTC foundation masters with lathe and milling machine. These masters were then used to create two-piece RTV silicon rubber molds (tools) employing BJB’s TC-5040 type rubber.

An alternative rubber for your consideration is Alumilite’s general purpose 3110. I mention this, as Alumilite is a one-stop source for both the rubber and resin needed to produce cast resin parts.

Oh, one thing before I go on here]http://www.culttvman.com/david_merriman_s_57__seaview.html[/url] part-6.

[anonymous]

Preparing the two tools –

Preparing the two tools – the cylindrical tool to the right forms the tear-drop shaped end-cap, the square tool to the left produced the antenna and WTC foundations – was done by spraying their interiors with a silicon release, rubber banding together the two halves of each tool, mixing the appropriate amounts of A and B of the Alumilite ‘regular’ casting resin (I love this stuff! Very quick cure and rock hard castings that are receptive to machine work and can be finished to a blemish free surface ready for primer).

Most of the BJB and Alumilite casting resins feature a resin and hardener of near equal specific gravity, so these can be measured by either weight or volume. I prefer to use a postal scale to measure the weight of the two parts.

The resin cures through a process of polymerization; as a chemical reaction gets underway after mixing, the resin heats, and the molecules of the material begin a process of linear bonding of the molecules. And it is this change in molecular arrangement that causes the observed change in state of the material from that of a liquid to that of a solid. Neat! But, a word of caution]http://sneill.com/merrimans/11.jpg[/img]

[anonymous]

De-molding the cast resin parts.

De-molding the cast resin parts. Note the massive sprue and vent channel network attached to the WTC foundation and antenna foundation cast pieces on the left. Before putting the two mold halves together prior to pouring of the resin I inserted a short length of K&S streamlined tube into the tool. This ‘removable insert’ forms the bore in which the vertical fairing would later be inserted. In the case of this insert, it was yanked out with pliers and discarded, forming the bore.

Using a set of small side-cutters I snipped away the excess flash and runners from all parts and then hit them with a sanding block and Moto-Tool drum sander to remove flash from convex and concave surfaces. Each resin part was degreased of release agent by a dunking in lacquer thinner, scrubbed with a piece of steel wool, dunked again, followed by a wipe-down with a paper towel and a blow-down with low pressure air. At this point the pieces were ready for machining and/or bonding.

[anonymous]

A holding mandrel (a holding

A holding mandrel (a holding fixture, if you will) was turned on the lathe and the stem of the mandrel used to secure the hollow end of a cast resin streamlined end-cap piece. Two things needed machining]http://sneill.com/merrimans/13.jpg[/img]

[anonymous]

Here we see the transitional

Here we see the transitional stages as a common commercial tire-valve is worked to become an ‘equalization valve’. First, about half of the valve stem is sawed off. Then, on the lathe, the rubber cladding is shaved off. Then the diameter of the threaded portion of the valve is shaved down to a ¼” diameter.

At this point the valve is inserted into the bored out hole in the end of the end-cap and. Pouring CA adhesive from the inside, the tire-valve is bonded permanently in place. The CA adhesive is accelerated to a cure with a liberal sprinkling of baking soda over the pooled glue. Notice that the open end of the Acrylic tube, at the extreme left, is beveled. That bevel is vital; it insures that the end-cap compression o-rings slide into the tube without getting cut, which would ruin their ability to keep the water out of the WTC.

[anonymous]

The majority of the WTC

The majority of the WTC is formed from Acrylic tube and sheet. Acrylic chosen for its superior optical characteristics over the less crack-prone Lexan clear plastic. As the camera will be viewing through the 3/8” forward piece of sheet Acrylic I took care to keep the protective paper backing on the forward face of the sheet.

Fabrication starts with a tube cut to appropriate length. The tube was then secured to the lathe mounted working mandrel (this holding fixture purpose made for the job) and the after edge of the tube given an inside bevel to make passage of the end-cap o-rings an easy matter.

A disc shaped piece of sheet Acrylic was then bonded to the forward end the cylinder with solvent type cement. Giving the weld between cylinder and disc a good twelve-hours to harden assured a trouble free time as I machined the disc to a semi-hemispherical shape on the lathe.