1/48 scale Type VIIC U-201 build

[Monahan Steam Models]

With the bow plane, stern plane and rudder servos in the wet and recently swapped out for the waterproof IP67 micro versions, the last servo in the wet that needed to be swapped out was the main ballast tank servo. Just like swapping out the other three sub-micro SG90 servos for the IP67 rated micro servos, this called for a redesign of the original equipment. The main ballast tank servo probably had the least forgiving area to work within for redesigning the conversion to the slightly larger servos.



This was the original Sg90 servo design for the main ballast tank. Was fairly happy with the layout of components and their functionality. The recent water proofing experimenting of the Sg90 servos and their current draw measurements made me want to formulate a plan B for their use.



Here is the result of the redesign that now uses the IP67 rated larger micro servo for the main ballast tank. It fits within the original design and works well. Happy with the results so far.

Nick

[Monahan Steam Models]

With the aft compartment wiring sorted out I spent some free time today focusing on getting the forward compartment wiring sorted out. This mainly involved modifying the internal main power cable to work with the new waterproof bulkhead connection on the forward end cap. The other part of the task was wiring up the new 17 position waterproof data cable bulkhead connection also on the forward end cap.



Here is the 8 wire ribbon cable connection that was used in the original WTC design to send the data signals back and forth between the forward compartment and the aft compartment. The ribbon cable passed through a conduit in the central ballast tank.



Here I’m starting the process of solving each of the color coded 26 gauge wires to their respective pins. It’s easiest to start in the center and work your way around to finally the outermost pins.



Here’s the finished solder up bulkhead connection.



Silicon tubing comes in handy for creating wire looms when dealing with a lot of wires in this small size gauge. The group of nine wires to the left replace the 8 wire ribbon cable with one other going to the signal output side of the ballast control module . Of the seven wires in the center loom, six of those are for the five torpedo tube solenoids with one extra unused wire. The last pink wire to the right connects to the output signal side of the forward bow plane depth controller.



The finished result with the ribbon cable replaced with the new data wires. The TCP or torpedo controller hooked back up as well as the servo signal outputs wires for the bow planes and ballast tank.



Earlier I had made up the new connection for the main power cable but the photos I took did not save. Here you can just make out the yellow plug inside the forward module.



The underside of the forward module is a lot less busy by removing the 3 wire main power cable connection.

I’ll need to choose what the next battle of this build I take on will be. I still need to finish up the work on the external data and power cable harness as well as the water proofing final work to both the forward and aft end caps. But hey, pretty soon I’ll be right back to where I was months ago having a functional WTC before I decided to split everything up into separate modules….. Face palm.

As much as I liked the original design, I do like this design better for a number of reasons. Looking forward to testing it in the tank. The dive times should be be greatly improved. The current draw from the servos should be much less and the ease of working on everything is already paying off.

Nick

[Monahan Steam Models]

Very nice Nick!

Your work is so clean and organized. Your education and understanding engineering concepts sure dose show up in your surface boat building, steam powered systems, and for sure submarine techknowledge! I look at your work and only wish I could understand let alone be able to reach your level of expertise. Your Type VllC is a masterpiece for sure.

Rob
"Firemen can stand the heat"

Thank you for your kind compliments Rob!

The design of these things is really driven by the components, the space available and the desired function in the end. Once all the needed components are well known for the desired function, work begins to find the optimal grouping and placement in the space that is available. Sometimes the process is quick and straightforward. Other times the process takes many unsuccessful mock ups before discovering the optimal placement.

The aft lower equipment shelf is an example of experimenting many times with component placement mock ups before arriving at what was finally built. I always try to kill as many birds with one stone so to speak when grouping components or designing something but with every design there will almost always be a compromise. It’s just finding the design compromise you can accept the most.

As far as the type VII being a masterpiece, thank you but let’s see if I can do it justice when it comes to the cosmetic portion of the build!

Nick

[rwtdiver]

Had a couple hours today to focus on finishing up the aft WTC upper equipment shelf. The last wiring connection that needed to optimized was the main 3 wire power connection to the rear end cap. I took the opportunity to slightly modify the design and remake the aft equipment upper shelf. The new design features a hole in the upper shelf for the 3 wire power connection to pass through as well as short vertical 3mm thick walls added at the outer edges of the shelf to help keep the overall surface flat and ridged. Keeping the upper shelf flat is important because it is parallel to the keel and waterline and secured to it is the main gyro and pitch controller for the stern planes. Early in the WTC design I opted to remove any deflection or vibration causing devices from equipment shelf as it would effect the accuracy of the gyro and pitch controller.

Okay now onto the actual work that was done today.



Okay here’s the new upper equipment shelf already populated with the same old junk you’ve seen a million times. The last 3 power wires trimmed back waiting to be united with the appropriate plug.



New plug soldered into place.



The overall view of the finished assembly.

Nick

Very nice Nick!

Your work is so clean and organized. Your education and understanding engineering concepts sure dose show up in your surface boat building, steam powered systems, and for sure submarine techknowledge! I look at your work and only wish I could understand let alone be able to reach your level of expertise. Your Type VllC is a masterpiece for sure.

Rob
"Firemen can stand the heat"

[Monahan Steam Models]

Had a couple hours today to focus on finishing up the aft WTC upper equipment shelf. The last wiring connection that needed to optimized was the main 3 wire power connection to the rear end cap. I took the opportunity to slightly modify the design and remake the aft equipment upper shelf. The new design features a hole in the upper shelf for the 3 wire power connection to pass through as well as short vertical 3mm thick walls added at the outer edges of the shelf to help keep the overall surface flat and ridged. Keeping the upper shelf flat is important because it is parallel to the keel and waterline and secured to it is the main gyro and pitch controller for the stern planes. Early in the WTC design I opted to remove any deflection or vibration causing devices from equipment shelf as it would effect the accuracy of the gyro and pitch controller.

Okay now onto the actual work that was done today.



Okay here’s the new upper equipment shelf already populated with the same old junk you’ve seen a million times. The last 3 power wires trimmed back waiting to be united with the appropriate plug.



New plug soldered into place.



The overall view of the finished assembly.

Nick

[Monahan Steam Models]

Manfred,

Thank you. Yes waterproof instant connections would be a great addition but I have not found anything on the market I like so far. The connections I’m using now are waterproof but still require physically disconnecting them. I am already enjoying the new split WTC as I can work on each compartment section with much more ease.

Nick

[MFR1964]

Nick,

Nice work on splitting the WTC, what you really need is instand connect waterproof connectors, really don't know if they are availible in the market.
All that work to split the WTC has paid off, in the near future you can work much more easely at your electric modules.


Manfred.

[Monahan Steam Models]

Nick, are you leaving the antenna bundled up? Very smooth...I mean it is just SMOOOOTH!!!

Steve, thanks!

The antenna is just bundled up for now. There is a hole for a brass nipple to be installed in the aft end cap that the antenna will pass through. Still need to finish the work needed on the end caps.

Nick

[SubDude]

Nick, are you leaving the antenna bundled up? Very smooth...I mean it is just SMOOOOTH!!!

[Monahan Steam Models]

Was able to spend some time today on the WTC’s aft module section.

Before deciding to break the original WTC up into three separate modules, the order of operation to gain access to the batteries was to disconnect all external hoses and electrical connections and then pull the whole WTC out of the vertical split at the aft of the hull. The next step was to to pop the forward compartment end cap with it’s equipment shelves attached to the end cap and disconnect the data and power connection. Then I could remove the aft end cap, disconnect the data ribbon cable and pull the aft equipment shelves out to gain access to the batteries which still required removing two small long bolts that doubled as fasteners to hold the upper equipment shelf to the lower as well as act as a stop to keep the batteries from sliding out. This process wasn’t hard and was relatively optimized in the original design. It would only take a few minutes to do. Still it wasn’t ideal.

The new horizontal water line hull cut made removing the original WTC a lot easier but I felt there was still an opportunity for improvement with the complex original WTC system. This brought the sectional modular WTC design revision into play which further reduces the amount of stuff that needs to be disconnected and removed from the hull each time the boat is serviced or operated.

Today’s work involved replacing the lower aft equipment shelf with a design that allows the two LiPo battery packs to be removed from either side without the need to unbolt anything or disconnect any wires other than the battery plugs. It was also time to get rid of the 8 wire rainbow ribbon cable which was the original data connection to the forward WTC compartment. The new 17 wire water proof connection in the aft end cap now carries those data signals along with the data signals, positive/negative power for the rudder and stern plane servos and the four wire usb connection to the Arduino control on board. So that wiring needed to be done too.



Here’s a side view of the newly populated lower equipment shelf. The short side rails that kept the batteries in place have been removed from the design.



The new side rails feature a tongue and groove installation with the lower equipment shelf.



Here is one of the new side rails slide into place about halfway.



And another photo of it in place.



The wiring mess that I started out with this afternoon for the new 17 wire connection. Note the ribbon cable is still in place.



The new lower equipment shelf populated with all the gear. No space is wasted. This area features both the 12 volt and 5 volt main busses. The main fuse. The main battery connection. The remote on/off board as well as the high amp on/off switch. The 3 amp 5 volt reduction board as well as the BLM module.



One of the last soldering job connections to the new 17 pin harness was the usb data plug for the on board Arduino unit. Now I can modify the PID settings and Kalman filter code used in the static diving routines while the boat is water tight.



The following photos show the aft module sealed up. Again no space was wasted. The last bit of wiring tidying up work needs to happen to the main high/low power connection at the lower right of this photo.





Other than that, I’m happy that now all the aft module takes is sliding off the outer acrylic tube and removing the batteries for servicing.



Well that’s besides pulling these four connections…. Still way simpler than what I had before…..

Nick

[Monahan Steam Models]

Since the last update of this build thread where I was experimenting with waterproofing sg90 servos, I redesigned the aft motor/servo mount to accept a pair of Savox IP67 rated micro servos. I made this choice to use these servos instead of the sg90 type servos based on the fact that they are better constructed out of the box and draw much less current during normal operation compared to the sg90 servos.



Here’s the new version of the aft motor/servo mount with the slightly larger Savox micro servos installed. Linkages to the stern planes and rudder pushrods still need to be made up.



The new forward servo mount with the Savox micro servo and bow plane linkage installed in the type VII hull.

Other work with this build has been focused on the “in the wet” wiring harness build as well as the aft WTC main battery access simplification. Have made great progress in these areas and will share those build updates soon once I get a chance to document and complete the work.

Nick

[He Who Shall Not Be Named]

This morning I wanted to get some real data regarding the drag or resistance the newly waterproofed servo was experiencing since the modification. Real data is always better to look at verses guessing or lots of arm waiving.

I used the bench top power supply set to 6 volts constant output and set the current draw at variable. This allows you to view the amps or in this case milliamperes or mA draw in real time. I also used a servo tester set to the automatic function in order to get repeatability across each servo test.

First up was to test a standard unmodified SG90 servo. The current draw in automatic mode averaged about 120mA.

Next up was to test the modified servo as is from yesterday. The current draw in automatic mode averaged about 485mA.

The next test to the modified servo was to remove the servo horn and o-ring. The current draw in automatic mode averaged about 235mA.

The final test to the modified servo was to reinstall the o-ring and servo horn to find the optimal amount O-ring squish or sealing without leaking oil and still having the equalizer diaphragm work. The current draw in automatic mode for this scenario averaged about 260mA.

Nick

Excellent test protocol, Nick; you verified -- and segregated -- the two causes of drag on the drive train: fluid viscosity drag (mechanics working in a liquid environment); and mechanical drag (the O-ring drag on the output shaft). Your observations and application of your findings led you to the adjustment of the O-rings tension between horn and servo case, which reduced the off-the-chart half-Ampere draw to a quarter-Ampere draw (still about twice the in-air current draw, but reasonable).

The scientific method on display here! Good stuff, sir. The output transistors of the PCB's H-bridge thanks you!!

Observe and record the characteristics of a system -- work out a hypothesis on what is the likely cause of the observed characteristics -- formulate a theory of how that system works and apply theory to change the systems characteristics.

https://youtu.be/bTlXZf5qsZI

David

[Monahan Steam Models]

This morning I wanted to get some real data regarding the drag or resistance the newly waterproofed servo was experiencing since the modification. Real data is always better to look at verses guessing or lots of arm waiving.

I used the bench top power supply set to 6 volts constant output and set the current draw at variable. This allows you to view the amps or in this case milliamperes or mA draw in real time. I also used a servo tester set to the automatic function in order to get repeatability across each servo test.

First up was to test a standard unmodified SG90 servo. The current draw in automatic mode averaged about 120mA.

Next up was to test the modified servo as is from yesterday. The current draw in automatic mode averaged about 485mA.

The next test to the modified servo was to remove the servo horn and o-ring. The current draw in automatic mode averaged about 235mA.

The final test to the modified servo was to reinstall the o-ring and servo horn to find the optimal amount O-ring squish or sealing without leaking oil and still having the equalizer diaphragm work. The current draw in automatic mode for this scenario averaged about 260mA.

Nick

[Monahan Steam Models]

Romel,

The amount of heat that built up was not very much and I was stressing the servo a lot more than what it would normal see during normal operations. Adding special features to help cool the oil are likely not needed.

Rob,

No problem at all and ask as many questions as you need. I do follow your builds so if you want to ask a question that specifically relates to your build in your thread, I will see it and do my best to help. Or if you want to ask a question here on this thread that works too.

Nick

[rwtdiver]

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 gluing 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

Nick,

Thank you very much for getting back to me, I really appreciate your advice, and will certainly follow it.

I am going to start my own build blog on this forum of my Arkmodel, so as not to interrupt yours or anyone else's theme! I am sure I will have a lot of question, so I hope you do not mind if I chime in on your build with some of those questions?!

Thanks again Nick for all your help and input!

Rob
"Firemen can stand the heat"