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1/48 G7 Torpedos

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  • #91
    Originally posted by Monahan Steam Models View Post
    Quick update

    Edit: I added a description to each photo but when viewing on a mobile device the full description is not visible. What is the best method for uploading photos to this forum? I’ve run out of curse words trying to sort it out myself
    First off, what a wonderful little mechanism you've come up with. When you start using collets, you're deep into watchmaking stuff!

    I first write the text, then use the 'Upload Attachments' button (below the text block here) to bring up the desired photos from your hard-drive, then plug them into the text as desired. You start with the text, then you plug in the photos -- that way you keep the text AND photos in your post.

    David
    "... well, that takes care of Jorgenson's theory!"

    Comment


    • #92
      Originally posted by coryhenry View Post
      Very nice, any trials yet?
      Not yet with the current design. There has been a half a dozen or more slight design revisions since the last sea trials. Each revision has required making many new parts. If the design didn’t pass the bench test goal then it has been onto the next revision from what was learned without doing any sea trials. Overall the torpedos have worked every time, but the quest has been mostly to perfect the running behaviors, weight, trim and production methods. The earlier designs used longer bodied more powerful motors. As the design has evolved, the length of the 6mm coreless motors has been reduced to save weight and improve running characteristics by not being so overpowered. However these shorter length motors are less forgiving of any resistance in the rotating assembly. Not a problem for the earlier simpler single propeller designs but a significant problem for the later counter rotating propeller designs.

      The last video links I posted of the counter rotating torpedo sea trials went really well but that torpedo was using a slightly longer bodied more powerful motor that didn’t blink an eye at the very minimal resistance that was in that transmission. Also that torpedo’s speed through the water was way over scale. It worked out to be around 90 knots.

      Most of the latest revisions have been focused on improving the precision of the transmission and torpedo tail housing assembly. Normally when I am trying to achieve absolute assembly precision, I would machine every part but I am trying to leverage using a mix of 3D printed parts and machined parts to cut down the labor required to make each torpedo. The problem has been that the 3D printed parts are close but not nearly precise enough to be used without needing additional work done to them.

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      • #93
        Originally posted by He Who Shall Not Be Named View Post

        First off, what a wonderful little mechanism you've come up with. When you start using collets, you're deep into watchmaking stuff!

        I first write the text, then use the 'Upload Attachments' button (below the text block here) to bring up the desired photos from your hard-drive, then plug them into the text as desired. You start with the text, then you plug in the photos -- that way you keep the text AND photos in your post.

        David
        Awesome, thank you David. That is most helpful and I will use that method going forward.

        Having owned and used some large very precision commercial manual and multi axis cnc machine equipment in the past, I’m still amazed at the precision I get using that little jewelers lathe.

        Nick

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        • #94
          Click image for larger version

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ID:	143459 Okay, here is a prime example of the struggle to perfect the perfect 1/48 scale G7E torpedo. After hours of careful design work and machining the last of the parasitic drag in the counter rotating transmission has been removed. The main torpedo chassis design has been carefully worked out to mount each component in the lowest location while keeping the mid ships neutral Buoyancy point slightly aft.



          The main parts being tested here is the new motor, the scale props and the new smaller battery. Normally each change would be isolated and tested individually.
          Click image for larger version

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          The reworked counter rotating transmission an tail cone assembly rotate butter smooth now. The measured amp draw on the smaller motor is much less now compared to earlier tests. Overall weight of the torp is ideal. The torp runs great in mid air. As soon as the props are submerged the LiPo battery over current shut off kicks in.

          And there you have it. Back to the drawing board to rob weight from here to make up for it there because everything has to change again

          Click image for larger version

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          The size change in the battery size. Might add a small super capacitor to even out the amp draw if the weight allows

          Nick

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          • #95
            Latest design revision for the G7E torpedoes.

            The torpedoes are running very straight now. Will start to increase the run time soon. The new scale propellers worked great. The internal chassis was reduced and redesigned to accommodate slight changes to the counter rotating transmission that reduced the last of the rotating friction. Weight needed to be reduced in the chassis to correct the ballast to make up for switching back to the more powerful 6mm X 15mm coreless motor and original sized LiPo. The next tests will be using the same sized LiPo but stepping up to a new 90mAh from the current 60mAh battery. The runtime module is set for 5 seconds but of all the tests done on each version so far running in the pond, the battery’s current draw protection shuts down before the timer. Hopefully the new battery pack will solve that. If it does the revisions following will be to make further improvements on the final design.
            Attached Files

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            • #96
              Hey Nick, things are looking very promising over there in torpedo land! Pardon my ignorance, You state that the motor shuts down as a result of current draw protection? are you using an auto reset fuse(current limiter) or are you talking about a lipo low voltage cutoff of some sort? within the runtime module?-BG

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              • #97
                Hey Good Morning Bob,

                The LiPo does have a built in low voltage protection circuit which I am purely guessing also protects against excessive current draw from what I’ve read on the interwebz.

                These batteries are sourced from sellers on flea bay. Would love to have the actual data sheets for them but I believe these cells are only rated at 1C like most standard LiPo’s not intended for performance applications.

                I am not clear if the timer module also has a protection circuit but if I recall correctly, I believe they are rated for 2A. The motor draws 0.7A with no load (props spinning in air) and 1.49A with the props fully submerged. So far, I’m only seeing premature shutdowns if something gets snagged in the props or towards the end of a run. Even then it has not been reliably consistent.

                Testing the battery after a run, the volt meter shows typically 3.7-3.8 volts. At full charge you can get multiple runs before the voltage noticeably drops.

                The shutdowns due to the battery protection circuit is pure speculation at this point. There may be a brown out situation that is occurring that could be turning off the timer. No idea but will need to do some trouble shooting to pin point the issue. Wish these timer modules had a couple more run time settings than the 3 and 5 second options. Other than that I am very happy with them.

                Would like to listen to what others have to say about their experiences with small LiPo’s and these timer modules.



                P.S. I have a new video of this current design running in the pond. Need to upload it to YouTube so I can post a link here. It is posted on the Model rc-submarines Face Book page currently.
                Last edited by Monahan Steam Models; 09-14-2020, 09:18 AM.

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                • #98
                  Well I see that you have a good handle on it, Nick! -I guess the brownout possibility would be easy to check-just bypass the timer? the other scenarios might be a little tougher-We'll stay tuned...

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                  • #99
                    Ha! I wish I felt I had it well handled but Thank you! Great idea on bypassing the timer. Will definitely try that and report back. Thanks!

                    Comment


                    • Watched your video. Nice straight run! Well done.
                      Last edited by trout; 09-15-2020, 09:02 AM.
                      If you can cut, drill, saw, hit things and swear a lot, you're well on the way to building a working model sub.

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                      • Thanks Trout !

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                        • Video link from last week. They’re running straight now. About to start testing the latest version this week.

                          https://youtu.be/BUV2kb3e_DA

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                          • A bit more testing and I think we are there
                            Attached Files

                            Comment


                            • I'd say that you have nailed it!...what more is there to do? -paint schemes? Nice work, sir!

                              Comment


                              • Thanks Bob! The battery has been stepped up to a 90mAh LiPo that is the exact same size as the 60mAh battery I was using before but is .050 of a gram lighter in weight. I had ordered these 2 months ago and they finally arrived last week. So far the new battery has appeared to solve the over current shutdown issues. I was able to track the shutdowns to the battery and not the timer module. The motor is the heavier 6mm x 15mm unit. This combo works well. The video I posted was still using the 60mAh pack and the torpedo was shutting down 4 seconds into the 5 second runtime.

                                Paint schemes is definitely on the list of things to do. The overall design is about 95% there. It is working out that last 5% that is taking a lot of minor adjustments to the internal bits. The fight now is for weight and ballast. Trying to shave off 100ths of grams. The torpedo is exactly to scale down to the props. This version weighs 11.635 grams. The center of gravity, currently is .060” aft of where I would like it to be. Even so the torp floats at the end of the run and performs well in the water. If this current design turns out to be the best balance of factors achievable, then it simply is what it is.

                                I’d like to try to get the weight down to 11.1 grams with the center of gravity roughly about .010” aft of the center. Most of the weight that needs to be shaved off is in the tail assembly. In order to shave that much weight, I need to once again switch back to the 6mm x 12mm motor, remove the full length aluminum stuffing box and go back to just using a machined short length Delrin bushing where the prop shafts exit the tail cone. There’s a few other minor tweaks that will need to be done but this should get the torpedo to the target weight and CG. The make it or break it part of this next test will be wether or not the 6mm X 12mm motor will play nice or not with the rest of the components. In previous tests it did not due to being slightly less powerful than the 6x15 motor, but I have since been able to remove a small amount of friction that was still in the transmission assembly.

                                Nick

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