What is the size of the magnets please.
Today's work on the little Revell SKIPJACK fittings kit
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David,
Not to be a killjoy here, but I reckon that your 1.25 SD would be restricted to littoral (< 1 m )and not blue water ops. That 1/16" lexan cover (I assume would be siliconed to the top of the servo box) being flat and thin would have a tendency to deform inwards with increasing depth/water pressure which might affect the magnetic couplers movement leading to loss of control of the stern planes.Last edited by redboat219; 02-24-2009, 05:50 AM.Make it simple, make strong, make it work!Comment
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David,
Not to be a killjoy here, but I reckon that your 1.25 SD would be restricted to littoral (< 1 m )and not blue water ops. That 1/16" lexan cover (I assume would be siliconed to the top of the servo box) being flat and thin would have a tendency to deform inwards with increasing depth/water pressure which might affect the magnetic couplers movement leading to loss of control of the stern planes.
The testing protocol will go like this: A servo box will be outfitted with cylinders containing a battery and receiver and the unit will be 'on' during the test, i.e. I'll be able to control the servo via r/c during all phases of the test; a fitting will connect the test article to a volume tank that has been evacuated, the tank outfitted with a vacuum gauge and stop-valve; I will open the valve to partially evacuate the test article and will check operation of the servo at three foot increments (translating pressure differential to feet of fresh-water); performance evaluation will be conducted (providing there is no structural catastrophic failure of the test article) to the maximum of thirty-feet fresh water, which is one-atmosphere, the maximum differential when employing a vacuum at sea-level.
David,Last edited by He Who Shall Not Be Named; 02-24-2009, 08:02 AM.Who is John Galt?Comment
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I get my magnets from this outfut (great service!):
Gaussboys Super Magnets - Your source for high quality neodymium rare earth magnets. Custom shapes and sizes available. Now accepting bitcoin.
3mm x 9mm N38 Nickel Plated Cylinder Magnet
Model: C0309
$0.17 (€ 0.12)
Great crafts and small projects. This one is easy to handle and will not pinch at all. It is not quite strong enough to be a great fridge magnet, but jewelers and woodworkers will find it is a great size and strength for most small jobs.
Details
Model: C0309
Size: 3mm dia. x 9mm thick
Grade: N38
Plating: Nickel
Max Temp: 80° C (175° F)
Surface Gauss: 3500
Magnetized: Axially (through 9mm thickness)
Max Energy Product - (BH)Max: 36.9 MGOe
Pull Strength: 7 Oz.
Weight: 0.0176 ozWho is John Galt?Comment
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Last edited by toppack; 02-24-2009, 03:45 PM.Rick L.
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* Asking Questions is a 'Good Thing',
Since Learning is Always a 'Good Thing' *Comment
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OK, I'm done with the masters and it came time to develop the production tools, start making some castings, and see if the new 'fittings kit' parts would integrate correctly with the little Revell SKIPJACK kit.
The propeller and weight masters were embedded in clay, about one-half of their form was masked off by the clay -- this done to create a half-tool, you don't want to encapsulate the master, that would be a useless task unless you are prepared to come in later and cut the master out (done with specific 'slit' type tools, but not here). First you make a halve of the tools, then you scoop out the clay, apply a mold release, and pour the second half of the rubber tool -- producing a two-piece. tool.
I used BJB, TC-5050 high-temperature silicon rubber for the propeller and weight tools as I would eventually be casting molten metal into those tools. The tool that would be used to produce the resin pieces of the little SKIPJACK's fitting kit was made from the less heat tolerant (and cheaper) TC-5040.
The containment dam for the propeller tool was a length of Lexan tube. Masking tape was used to hold in the liquid rubber around the weight and fittings kit tools.
Resin casting requires careful tool design: you have to quickly introduce relatively thick resin and at the same time insure that the displaced air within the tool cavities has a route out of the tool. Laying the masters onto a paper towel I arrange them in a fashion that will involve the minimal amount of resin to cover them, also keeping in mind that I have to respect Newton, i.e. gravity has to do the work of getting the resin into the cavities and the displaced air out. Once I have a good sound fill-vent network down on paper, I transfer the masters to a mold board and I embed them into the clay.
After I embedded the fittings kit masters into the clay I scribed into the clay the vent and sprue network, then later punched in dimples into the clay (with the shank end of a drill bit). The outlines of the vent and fill channels guided me later as I cut away those channels in the flange face of the two hardened tool halves. The dimples form an indexing network that holds the two tool halves in perfect registration.
Listen up: I don't show off how to make duplicate parts -- be they resin or metal -- so that you idiots can take commercial parts and make copies of your own. That's called piracy, and you had better not let me hear of you doing it! This discussion is presented so you will know how to make copies of your own work -- or the work of others once you have secured the permission of the owner of that property to make said copies. Don't steal! And don't use that BS argument, "It's for my own personal use". You want a duplicate part? Then go buy another kit!
The last shot shows off the completed two-piece resin fittings kit tool and next to it a shot of cast resin parts. Those parts were de-greased, flash filed and sanded off, and assembled/integrated with the Revell SKIPJACK hull and things checked for fit and functionality. I'm glad to report that everything fit just fine and I now have finished the control surface and linkage installation and test of the first little r/c SKIPJACK. The fittings kit should be on the market soon. Stand-by!
David,Who is John Galt?Comment
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The shot of resin parts shown here reveals, to good effect, the design of the filling (sprue) and vent channeling cut into the rubber tool flange faces. The central cylindrical pouring sprue receives liquid resin at the top, gravity causes it to drop; the height of the liquid equates to the pressure it exerts, so I put the most difficult to fill cavities (the two tail-cone cavities) as low as possible in the tool -- doing so insures maximum pressure on the most difficult to fill cavities. Note that as the shapes of the resultant parts get simpler, they are arrayed higher off the main sprue cylinder?
Outboard of the cast parts you see the narrow vent channels, leading up from the high points of each cavity (where the air-bubbles would collect if not vented off), where the displaced air is pushed up and out at the top of the cavity as resin enters the bottom of the cavity. Even with careful tool design like this I take the extra step of pressurizing the resin (while still in the liquid state) to one-atmosphere. This to crush any remaining bubbles either entrapped in the mix or not vented through the vent channeling provided. The differential pressure is maintained till the resin cures (changes state from liquid to solid). My pressure pot is a simple spray-painting accessory (industrial grade, not hobby crap).
Now here's some work that wold make Fabergé proud: the stern plane and rudder linkage sized to fit the little Revell SKIPJACK kit. Note that I flattened and punched a hole in the end of the .020" brass push rods, forming the connecting clevis.
There is no bell-crank on the yokes, I simply ran the respective push rods up to the high point of each yoke and jammed them there with little pieces of plastic tube (actually, little pieces of electrical wire insulation), the white tube retainers held in place with dabs of CA adhesive.
In these shots I've yet to install the upper half of the cast resin stern-cone piece provided with the fittings kit.
Here you get a better perspective of how the stern stabilizers and control surfaces are arranged around the stern of the SKIPJACK. The forward end of each push rods will terminate in a magnet, that magnet will fall under the influence of another magnet which is set into a servo bell-crank magnet -- the two separated by a 1/16" clear Lexan cover that forms the watertight barrier between servo and external pushrod.
And here we have the same shot, but this time with the cast white-metal propeller installed. Note how the propeller shaft runs through the center of the two control surface yokes. Non-interference is the name of the game here!
Pretty neat, huh!?...
David,Last edited by He Who Shall Not Be Named; 03-01-2009, 12:39 PM.Who is John Galt?Comment
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vent channeling cut into the rubber tool flange faces.
My wife makes miniture doll body parts using pressure-pot, similar rubber molds and resin, and I've made a few ship parts that way also, when I needed many of the same parts.
We've never done any casting of metal tho.Last edited by toppack; 03-01-2009, 01:27 PM.Rick L.
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* Asking Questions is a 'Good Thing',
Since Learning is Always a 'Good Thing' *Comment
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OK, with the preliminary 'production' parts (metal and resin) in hand, time came to assemble five r/c SKIPJACK'S. Why so many? Because during this initial run of 'alpha' test products I would identify shortcoming in method and materials, identify fixes, and incorporate those into the methodology I would publish for the fittings kit, and through physical changes to the tooling, if need be.
Doing so many like models at once also gives me the luxury of staggering the assembly steps between them a bit. This permits me to take shots of different phases of assembly -- more information conveyed per picture taken.
The two-piece cast resin stern is attached to the aft end of a kit hull once it's out-of-scale stern is chopped off with a razor saw. Only the bottom half of the new tail-cone is permanently bonded with CA adhesive. Later, the upper half of the tail-cone is glued atop the lower half -- but only with RTV adhesive. If need be I can, with relative ease and no damage, pop the upper tail-cone off for servicing of the rudder or stern plane yokes.
Before applying the CA to permanently secure the lower tail-cone to the lower polystyrene hull piece I ran a 1/16" rod through the propeller shaft bore and aligned that rod with the hulls longitudinal center line -- a wad of clay up forward centered the rod. Once assured that the propeller bore is centered with the submarines center line, glue is applied, baking soda brushed into the union to accelerate the cure of the adhesive and bridge any gaps, and the aligning rod removed.
The kit provided sail is pretty close to scale. I used the excellent Deep Sea Designs drawings, penned by Greg Sharpe, as source, I know these are based on BuShip's sources. Greg's work is the industry standard and are recommended for anyone wishing to produce accurate kit assembly jobs or scratch-built models.
However, the kits sail leading edge is rounded off. It should be knife-edge sharp. This error is corrected easily by first shaving away plastic either side of the leading edge and then building up the knife-edge with CA and baking soda, which was filed and sanded to knife-edge. Some putty, sanding, priming, and a I had a re-contoured sail. The Sharp sail leading edge is a defining characteristic of the SKIPJACK boats and should be addressed if you want a faithful model of it.
The only real contour mistakes Revell made on this model was the sail leading edge, and rather blunt bow -- both fixable problems.
Oh, and the sail planes are too long of span and a bit out of profile. I took a set from a kit, shaved them down and will use them as masters so I can add correctly shaped cast resin sail planes to the SKIPJACK fittings kit. Again, the Greg Sharpe drawings were used as source as I made the corrections that turned the kit parts into production masters.
Here's Ellie holding the first completed conversion of the little Revell SKIPJACK kit. Tiny!
David,Who is John Galt?Comment
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Originally posted by redboat219Now the wife can come up to you and say; "Is that a Skipjack in your pocket or are you just happy to see me?"
I'll make a point NOT to pass that one on to Ellie, thank you very much.
David,Who is John Galt?Comment
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David,
I'm eager to see how this little baby of yours perform. I have been looking over those wonderful photos and several questions popped into mind.
Being a dynamic diver don't you need to make the stern planes a bit larger than normal to be effective in getting her to dive?
Will she incorporate a pitch controller?
If not, how do you think she'll behave?
Have you conducted the vacuum testing of the subdriver already?Make it simple, make strong, make it work!Comment
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David,
I'm eager to see how this little baby of yours perform. I have been looking over those wonderful photos and several questions popped into mind.
Being a dynamic diver don't you need to make the stern planes a bit larger than normal to be effective in getting her to dive?
Will she incorporate a pitch controller?
If not, how do you think she'll behave?
Have you conducted the vacuum testing of the subdriver already?
There's a false assumption that's been in the r/c submarine community for decades, that the control surfaces have to be over-size in order to get the model to respond to control surface deflections in a timely manner. False.
Over-sized control surfaces are no substitute for a properly trimmed boat -- a boat that has the c.g. and c.b. correctly positioned. And too often I see a dynamic diver trimmed still way too buoyant.
A dynamic diver, to operate at all well underwater, its deck has to be below or even with the waterline when at dead-stop, only the sail above water. Over-sized control surfaces are used to force an overly buoyant model beneath the waves.
Now, with a dynamic diver you have to contend with the need to keep the hull at a negative pitch angle to the water flow -- the hull producing the downward force needed to counter the buoyant force. That situation induces unique forces that have to be countered with a specific trim and control surface deflection. Typically a boat trimmed to run well submerged in near neutral buoyancy is not properly trimmed to operate dynamically (the boat still in a buoyant condition). Two different animals.
The scale sized stern planes, rudder, and sail planes on the little SKIPJACK model will be more than adequate to operate the model underwater in the dynamic diving mode.
Yes, at the speeds I'll operate this thing, an angle-keeper is a vital piece of gear. Typically, dynamic diving submarines tend to be a bit more manageable without artificial stabilization about the pitch axis, but the quicker you go, more rapid the depth excursions, so at some point (relating to underwater speed), you need the angle keeper to prevent porpoising.
Nope, no differential pressure test on the 1.25" SubDriver's yet. I'll let you know how that goes.
David,Last edited by He Who Shall Not Be Named; 03-03-2009, 01:24 PM.Who is John Galt?Comment
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I think these are really going to sell like hot cakes if you can get the price right on this, Dave.
A lot of model submariners over here are interested in weeny boats lately, as exhibitions are increasingly supplying very small pools for display (if you're lucky), which confine larger models to drydock.
The Skipjack won't look out of place with just the tower out of the water- they must have one of the lowest freeboards of any sub short of a Holland class.Comment
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