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1/48 G7 Torpedos

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  • #31
    Some compromises I’ve had add to the current design given the weight of the added by the transmission have been switching from running all brass tubes and stuffing boxes to running a carbon fiber main prop center shaft and aluminum secondary Counter rotating secondary shaft. Both shafts are designed to be supported currently by a bronze bushing which I might switch out for Delran. The battle of weight shaving continues.

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    • #32
      One thing I found that fights water ingress into prop shafts is to provide a spiraling profile around the shaft that counter rotates to pump the water out

      nick

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      • #33
        Good idea they used to do something like that on car engines for oil control...

        By the way great backstory on the family...

        So Bob Martin has noted the torpedo tends to curve as it tracks-I believe it's from prop torque or walk. It will curve one way with one rotation and the other way with the opposite rotation of the prop.. these props tend to become surface piercing props because the torp rides so high when it's running so the bottom blade of the prop is scooping the tail of the torpedo one way causing the torpedo to turn the other way like a steering thruster... If you can't go counter-rotating then certainly three blades or more on the prop would help. I really hope this information helps and it's not redundant or annoying... Looking forward to the next post -Bob

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        • #34
          Originally posted by Bob Gato View Post
          Good idea they used to do something like that on car engines for oil control...

          By the way great backstory on the family...

          So Bob Martin has noted the torpedo tends to curve as it tracks-I believe it's from prop torque or walk. It will curve one way with one rotation and the other way with the opposite rotation of the prop.. these props tend to become surface piercing props because the torp rides so high when it's running so the bottom blade of the prop is scooping the tail of the torpedo one way causing the torpedo to turn the other way like a steering thruster... If you can't go counter-rotating then certainly three blades or more on the prop would help. I really hope this information helps and it's not redundant or annoying... Looking forward to the next post -Bob
          Propeller 'walking' is pressure phenomena of a still submerged propeller producing a lateral force at the stern (yaw). But if the stabilizers broach the surface, its the paddle-wheel effect of the rotating stabilizers producing a lateral force (yaw).

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

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          • #35


            I removed my earlier post from last night about my grand father because it was written fairly sloppy as I was headed off to bed. He was a life long Navy man and worked on the the US torpedo development team prior, during and after WW2. They moved around a lot but spent the majority of his time stationed at Mare Island Navy base. He was stationed at Pearl Harbor along with my grand mother and my dad’s brother and sister before my dad was born when the attack occurred. My aunt and uncle although young at the time recall the event and would tell the story of my grandpa running into the house grabbing his rifle and shooting at the planes flying over head. It was a very chaotic story but neat to hear growing up.

            Back to the miniature torpedo topic, I always appreciate any wisdom shared!!! Please by all means keep it coming! This is not meant to be a here’s how you do it topic. I’m just sharing the successes and failures I’ve been seeing while attempting to develop these things. My work background is in senior mechanical engineering, machining, fabrication and manufacturing. So I like to tinker and I get a lot of enjoyment from designing and building stuff. The more challenging the problem to be solved is sometimes the most enjoyable.

            Nick

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            • #36
              Originally posted by He Who Shall Not Be Named View Post

              Propeller 'walking' is pressure phenomena of a still submerged propeller producing a lateral force at the stern (yaw). But if the stabilizers broach the surface, its the paddle-wheel effect of the rotating stabilizers producing a lateral force (yaw).

              David
              The stab fins are definitely a possibility-in my case and tests the track was consistent with prop walk (using bulk drone props-switching rotation was easy) prop walk will track the torpedo the same way as the lower prop blade pushes(ccw turns torp to starboard-tail of torp goes port nose goes starboard) but if it's the stab fins, the same torp will travein a port track( body tube is spinning opposite rotation to the prop)

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              • #37
                Definitely observed the submerged prop walk curve trajectory as well as the paddle wheel effect Yaw in the tests I did. The breaching paddle wheel effect was reduced by adding the 1:1 gear box with low set motor center of gravity but the torp body still spun opposite of the prop being more affected by the prop walk in It’s trajectory.

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                • #38
                  Nick,
                  As I had mentioned my shop and toys are all in storage.. I can do no further testing or building for a couple of months... But I believe that even if you stopped the spinning , the torpedo would still continue to track in a curved Arc. And your solution of counter-rotating propellers might very well be just the thing to cure that... While I do not have the capability or the eye sight to build the 1:48 let alone a 1:64 gearbox when I get back in operation I will pursue allowing the tube to continue to spin and drive a hard mounted counter-rotationally pitched. prop -

                  ​​​​for now will stay tuned. -Bob

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                  • #39
                    Small progress update on the 1/48 G7E two stage counter rotating shaft transmission build. Here are some of the different length motors I’ve been testing to date in the miniature torpedo. The shortest motor is a new one that is yet to be tested but will be in the next couple of days. The black cylinder attached to the short motor is the first stage 5:1 planetary gear box. The black machined stepped part attached to the gears sitting on the Penny is the adapter to drive the second stage counter rotating gear box that I will begin making tomorrow. A .8mm carbon fiber shaft inserts into the end of the adapter (that the blade is pointing at) which drives the aft most propeller, while a custom machined bronze gear presses on over the lager diameter of the same shaft which drives the 2 stage counter rotating shaft transmission. Will post more as progress is made
                    Attached Files

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                    • #40
                      A little more progress on the second stage of the 1/48 scale G7E torpedo’s transmission. The counter rotating part. Going cross eyed making these tiny parts. Hope to finish the transmission soon then testing
                      Attached Files

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                      • #41
                        Does this group even care about this project or am I wasting my time sharing this.

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                        • #42
                          Of course it does. Good stuff. Keep pounding that keyboard.

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

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                          • #43
                            With over 600 views it definitely has interest!!

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                            • #44
                              Nick- don't stop posting! please-
                              I can't quite get the layout.my guess is that there is an additional gear set that meshes with the input and coaxial output shaft gears-accessing those gears thru those housing holes? up coming episode?
                              Last edited by Bob Gato; 07-19-2020, 11:08 AM.

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                              • #45
                                Okay thanks guys for the reply’s of interest. I was starting to have doubts and wondering if I was just wasting storage space on a server somewhere.

                                Bob, yes sir you are absolutely correct about how it works. I’ve attached a screen shot of the basic idea. The pink gear is the input which drives the yellow gear as well as drives the inner prop shaft. The yellow gear drives the green gear. The green gear drives the blue gear that drives the outer counter rotating shaft. I chose this arrangement because it has a lower center of gravity and smaller packaging then using the more common miter gear approach.

                                Also, here’s a couple video from today testing the rough prototype for the very first time.

                                Nick

                                https://m.youtube.com/watch?v=DeVboWjDNrU

                                https://m.youtube.com/watch?v=UZ06B_8o_xA
                                Attached Files

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