1/48 scale Type VIIC U-201 build

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  • redboat219
    replied
    Originally posted by Monahan Steam Models
    the cooling effect of the servo being in the drink may help reduce some of the heat build up.

    Nick
    maybe add some heat sinks or a U-shape brass tube for the oil to circulate by natural convection to cool the servo?

    Leave a comment:


  • Monahan Steam Models
    replied
    Originally posted by He Who Shall Not Be Named

    Yeah, O-rings present a lot of friction to rotation. A cup-seal would be ideal, but that means inserting a very short length of brass tube over that portion of the splined output shaft, and then working out a means of mounting the cup-seal to the top of the servo body so its lip can engage the brass tube. (A fools-parade at that point, I'm afraid, Nick. We start chasing our own tail. Diminishing returns for time and effort).

    David
    Rube Goldberg is my Personal Savior
    Because I have a habit of doing things my own stubborn way, I chose a o-ring that had an ID much smaller than what would typically be used in a ideal rotating fit. The shaft splines already presented a less than ideal smooth sealing surface for the o-ring so I chose to significantly undersized the ID of it in order to stretch it doing two things. First the stretching would reduce the o-rings overall installed height and second would force it to seal better on the splines. The sealing is now dependent on the squish between the bottom of the servo horn surface and the servo case surface. So the O-ring travels with the shaft. Drag is adjusted by the squish factor. A better chosen o-ring thickness could help reduce drag more perhaps. The mineral oil does seem to help provide lubrication to the O-ring so far.

    Nick

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  • He Who Shall Not Be Named
    replied
    Originally posted by Monahan Steam Models

    I completely agree with everything you have said. In regards to the heat build up, another source to add is the drag created by the servo horn pressing down on the o-ring. This is an area that could be dialed in a bit better to free up a small bit of resistance. Also the cooling effect of the servo being in the drink may help reduce some of the heat build up.

    Interesting stuff regardless. Collaborative experiments like this and shared knowledge is what makes this sort of thing fun! We all learn from one another! I certainly wasn’t the first to try this. I followed what Bob Gato, Sub Ed, Bob Martin, Steve H and others did way before my attempts and now have implemented your recent piece of the tech puzzle into the equation. Good stuff!

    Nick
    Yeah, O-rings present a lot of friction to rotation. A cup-seal would be ideal, but that means inserting a very short length of brass tube over that portion of the splined output shaft, and then working out a means of mounting the cup-seal to the top of the servo body so its lip can engage the brass tube. (A fools-parade at that point, I'm afraid, Nick. We start chasing our own tail. Diminishing returns for time and effort).

    David
    Rube Goldberg is my Personal Savior

    Leave a comment:


  • Monahan Steam Models
    replied
    Originally posted by He Who Shall Not Be Named

    Nor I. But, thinking it through: the viscosity of the oil dragging down the motor armature and the 'water-hammer' between gear teeth is making the motor pull more current, hence the heating. You're taking us all to school, Nick. A most interesting (and well presented) thread. Tribel knowledge is the better for this kind of work. Nice thing about r/c submarines is that servo response speed is not critical.
    I completely agree with everything you have said. In regards to the heat build up, another source to add is the drag created by the servo horn pressing down on the o-ring. This is an area that could be dialed in a bit better to free up a small bit of resistance. Also the cooling effect of the servo being in the drink may help reduce some of the heat build up.

    Interesting stuff regardless. Collaborative experiments like this and shared knowledge is what makes this sort of thing fun! We all learn from one another! I certainly wasn’t the first to try this. I followed what Bob Gato, Sub Ed, Bob Martin, Steve H and others did way before my attempts and now have implemented your recent piece of the tech puzzle into the equation. Good stuff!

    Nick

    Leave a comment:


  • He Who Shall Not Be Named
    replied
    Originally posted by Monahan Steam Models

    Thank you sir! That diaphragm you suggested trying, came in handy for the heated oil expansion! Didn’t see that one coming but, duh!
    Nor I. But, thinking it through: the viscosity of the oil dragging down the motor armature and the 'water-hammer' between gear teeth is making the motor pull more current, hence the heating. You're taking us all to school, Nick. A most interesting (and well presented) thread. Tribel knowledge is the better for this kind of work. Nice thing about r/c submarines is that servo response speed is not critical.

    Leave a comment:


  • Monahan Steam Models
    replied
    Originally posted by Bob Gato
    Great post! I love information like this- nice job..
    Thanks BG!

    I’ll admit that I was a little skeptical if I still needed the diaphragm equalizer if I was able to achieve the 100% oil fill. Yes, David don’t kill me, I’m just being honest and look, boy was I wrong! Yes it the diaphragm equalizer definitely helps!

    Going to go eat some humble soup now…

    Nick

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  • Monahan Steam Models
    replied
    Originally posted by rwtdiver
    Nick,

    I received my Arkmodel 1:48 scale Vll today. I have a question for you about the hull sections! Did you use the provided screws and the Plastruct Bondene solvent cement to glue the hull half sections, or just the solvent cement?

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    Rob
    "Firemen can stand the heat"
    Rob,

    I used both types of solvent only because I was originally having trouble with the orange label solvent. David helped solve the issue and that was due to oil contamination of the molded parts. Scrub the hell out of them with scouring powder and degreaser before you do anything. I have yet to do this to my parts as I stopped glueing parts together after this was discovered and switched my attention back to design and rough assembly work. I do plan to use both the solvent as well as the screws provided when the time comes to bond everything together. I recommend dry assembling the kit a few times with the screws. This will familiarize you with how things go together and allow you to see what screw holes need opening up and adjusting. Better to solve those issues now.

    Nick

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  • Bob Gato
    replied
    Great post! I love information like this- nice job..

    Leave a comment:


  • rwtdiver
    replied
    Nick,

    I received my Arkmodel 1:48 scale Vll today. I have a question for you about the hull sections! Did you use the provided screws and the Plastruct Bondene solvent cement to glue the hull half sections, or just the solvent cement?

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    Rob
    "Firemen can stand the heat"

    Leave a comment:


  • Monahan Steam Models
    replied
    Originally posted by He Who Shall Not Be Named
    Well done, sir!

    David
    Thank you sir! That diaphragm you suggested trying, came in handy for the heated oil expansion! Didn’t see that one coming but, duh!

    Leave a comment:


  • He Who Shall Not Be Named
    replied
    Well done, sir!

    David

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  • Monahan Steam Models
    replied
    This morning I continued experimenting with the water proofing attempts with the SG90 style servos. Now that the RTV sealant used yesterday had overnight to cure, I could move on with the next steps.

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    The first step today was to replace the standard type connectors on the servo wires with 2mm bullet style types.

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    These were then sealed up with heat shrink tubing that has heat activated glue inside them. Water or oil will travel through the wires if measures are not taken to seal the ends. I’d rather solder the connections on now than try to do so when they might be filled with oil.

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    Once the wire connections were completed, the next step was to begin filling the servo with mineral oil with the lower hole that was drilled into the case while the opposite upper hole allows air to escape. The servo was filled as much as possible. Here I am using the blunt applicator needle to point out a small air pocket still trapped in the servo.

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    The servo was then placed submerged in a jar of mineral oil and placed inside the vacuum chamber. Here’s where things I think became interesting.

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    This photo was taken after about 5 minutes into initial drawing down the vacuum chamber. I thought this would be a few minute job in the chamber….

    Here is a short YouTube video taken at the same time as this photo.



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    28” of Mercury was reached immediately and held there during the degassing of the servo. Now here is the interesting part. The servo continued to release lots and lots of tiny to larger air bubbles for the next almost 45 minutes! I had to stop and reposition the servo a few times until the bubbles being pulled out of it became just about zero. Key word just about zero. The bubbles were micro at this point and very few.


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    After the visit to the vacuum chamber, the servo was removed from the jar of oil and kept in this position with the fill holes pointing up. I had left the o-ring and servo horn off of the splined during the degassing but quickly installed them after the servo was pulled from the oil and placed like this. Next I carefully took a a paper towel soaked with isopropyl alcohol and cleaned off just the area around the fill holes. It is also interesting that the equalizer diaphragm is still in a puckered position. I’m assuming it stretched this way and took a set like this.

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    Next I used some baking soda and CA glue to seal up the fill holes.


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    Once the CA cured the whole servo and wires where submerged in a jar of isopropyl alcohol and wiped off.

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    After all that, there are still two very small air bubbles trapped inside. It’s not the 100% fill that I was shooting for but it is darn close! Btw, the motor puked a ton of air bubbles during the vacuum session. That was one of the main areas of monitoring that was done during the entire process.

    Okay one or two more interesting things witnessed today…

    Although the equalizer diaphragm is puckered inwards, this is not a bad thing! The next step was to hook the servo up the servo tester to see if this thing still was alive. Yes it was! The travels where full in either direction but the response speed seems slightly slower to me.

    After moving the servo back and forth many times with the tester, I noticed the servo heat up.

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    This is where the puckered diaphragm came in handy I think. As heat built up the expansion of the oil inside had somewhere to go besides being pushes out of the seals. This slight bulge in the diaphragm was only after few dozen full travels with the tester. The returned to its puckered state less than a minute after I stopped operating that servo.

    Anyways, interesting stuff I think.

    Nick


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  • Monahan Steam Models
    replied
    Yesterday I started experimenting with making the servos waterproof. This was basically taking it the servo apart to rtv the different sections of the case together and make additional holes between sections of the case to allow mineral oil to fill the cavities and air to escape. Got the bulk of the air out but was still left with a couple tiny air bubbles trapped inside. The good news is the servo still works and hasn’t lost a drop of oil in the last 24 hours.

    Today I am at it, trying again.

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    First I disassembled the servo and soaked everything in a jar of 99.9% isopropyl alcohol to remove oils and grease.

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    After the parts soaked I removed them and dried them off.

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    The motor’s case has holes in it, but they are blocked off by the plastic servo case.

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    To allow oil to flow in and air to flow out of the motor, I drilled small holes through the plastic servo casing.

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    Sealant is added to the edges of the servo housing sections using a syringe filled with black RTV gasket sealant.

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    Example of the sealant bead applied to the housing edge.

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    Next I drilled a 1/4” hole in the center of the servo case. This is for adding a thin rubber diaphragm that will act to equalize pressure internally with outside pressure .This feature is thanks to David M suggestion for it’s addition.

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    Here are the 3/8” diameter rubber diaphragm disks punch out from a party balloon.

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    A bead of RTV is used to glue the rubber “party” diaphragm to the case.

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    Here’s the servo reassembled waiting to be filled with mineral oil. I’m going to wait to do so until the RTV has had time to fully cure.

    Nick

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  • Monahan Steam Models
    replied
    Bob,

    The mount assembly for the servo is somewhat of an artifact and a design compromise left over from the way that I had originally chose to locate the components in the hull using the first WTC. Post #188 goes into some explanation of what all it does.

    In a short summary, it holds the servo and allows me to still use the original linear forward plane linkage I came up with last year. It also holds the adjustable pressure regulator for the torpedo solenoids. It will aid in keeping the forward data cable connection in place from being bumped around.

    Most importantly it locks the forward end of the new WTC in place in the hull while also pulling that area of the hull halves back into the original shape and location with the use of dowel pins. (The horizontal waterline cut caused the saddle tank area to spread apart a small amount.)

    Nick

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  • RCSubGuy
    replied
    Nick,


    Maybe I missed something in the thread, but what is the assembly that the servo is bolted to? Is that all for the sake of creating linear movement for the forward dive plane linkage shaft? My gut says no, and you likely explained it earlier, so sorry if I missed something.


    Bob

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