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1/48 G7 Torpedos

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  • #16
    Yeah love your fish vs torpedo video.
    If you can cut, drill, saw, hit things and swear a lot, you're well on the way to building a working model sub.


    • #17
      Can you post a link to where in FB the video is?


      • #18
        It’s on the sub committee’s FB page like I said in the earlier post....


        • #19
          Click image for larger version

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ID:	141323 A couple more photos from today of the G7A type torpedo. Close up of the tail fin detail. The set fitted currently has slightly angled rudders and planes to induce spin.

          The next design I plan to test will be the G7E style tail fin design once I complete the CAD drawings.


          • #20
            Added a horizontal spinning flywheel type gyro driven off the prop shaft just to see what it would do to the running dynamics
            Attached Files


            • #21
              Hi Nick
              Thanks for posting more of your work.
              Could you tell us the source/link for the timer circuit?


              • #22
                That is really nice work!!!


                • #23
                  Beautiful work Mr. Merriman! Thank you for sharing!! Very nice!


                  • #24

                    Got the timer from Bob at nautilus


                    • #25
                      Again Thanks for posting/sharing info.


                      • #26
                        I'm sure by now you have found that buoyancy and weight is critical-so much so that I wound up ditching the aluminum body tube and winding a composite tube from 1/2 oz glass-as a result I saved many grams and gained about a full mm inside for mechanicals. If further weight reduction is needed, consider going with a cap for power which will also eliminate the need for a timer and greatly shorten recharge time to about 30 seconds-but my case was different as I was shooting for 1:64 , good luck with this project-BG

                        Last edited by Bob Gato; 07-10-2020, 11:12 AM.


                        • #27

                          Yes sir you are absolutely correct. I like your design and choices of materials and components. The smaller you try to build these things the challenges go up exponentially as you already know!!!

                          From the very beginning even before making the first part, I’ve been fighting to shave hundreds of a gram anywhere I can while keeping the center of gravity negative in the x axis, zero in the Y and zero to slightly positive in Z axis. Right now the Z axis is adjustable. So far it has been a successful design with buoyancy, running mostly in the direction it was fired (I’ll get to that later), mechanically dependable, water tight and robust. The stupid Bass fish in my pond keep attacking them and swimming off with them, only to spit them out later. The nose has been kept removable and empty for when the time comes to switch out the practice rounds.

                          So far during all the testing and revisions the biggest and last problem to solve has been the torque spin of the torpedo about it’s center axis that is counter to the rotation of the propeller. The original goal was to keep the design simple with running one motor, one propeller and most importantly to me, keeping it’s dimensions and appearance true to the full size originals.

                          The torque spinning is mostly what has driven all the minor revisions since the original design. Things I’ve done to solve this so far are as follows. Keeping the weight as low as possible. I even moved the motor all the way down to the bottom. One revision I machined a miniature spinning flywheel of the appropriate weight and had an active mechanical gyro stabilizer on board. This did actually help but not enough. I’ve played around with different pitches on the propeller blades and again this did help but was not enough to solve the problem. I’ve added varying degrees of twist to the tail fins which I was hoping not to do and it didn’t help as much as I had hoped for. Up until the last revision, I’ve been doing all the testing with a anti clockwise spinning motor and screw. The last revision I made and tested had a two gear 1:1 ratio transmission. This time I used the anti clockwise screw and a clockwise spinning motor. I thought maybe just maybe this might solve the opposing rotation. Hahahahaha hopes and dreams flattened and the stupid Bass grabbed it during one of the test runs and took it down deep before giving it up. Time to arm the damn things!!!

                          Okay so this brings me to the current revision I am designing at the moment while waiting for miniature pieces to arrive from near and very far. I decided to stop screwing around and attempt what I was trying to avoid from the beginning. The latest design has the most tech and hours of design time put into it so far. This version will have a scratch built 2 stage transmission. The first stage is a 5:1 ratio planetary gearbox which drives the 2nd stage counter rotating shaft gear box. I will have lots of machining time invested into this one. The whole 2 stage gear box is roughly only 1/4” in diameter and 1/2” long!

                          I am close to finishing the current design. Most of the work is in correcting the last few hundredths of grams to get everything balanced back to where I had it before adding this transmission. I’ve attached a sneak peek of the almost fishes CAD model assembly. The layout of components will stay basically in the same location with only minor tweaks but the chassis that holds all the bits will likely change a lot by the time the revision is completed.


                          Attached Files


                          • #28
                            Nick-I am so looking forward to seeing how the gearbox works out...if you an pull this off it'll be a game changer! My prototypes were built in the winter and the hard water prevented open water testing, alas I just sold the house With the pool and am presently homeless (waiting on new construction delayed by this damned virus!) All my stuff is in storage.

                            Regarding the spinning- which as you know (and for the other readers) causes the torp to lose fwd thrust because a good portion of the motor's torque is wasted on spinning the body tube and not the prop. My thinking is to not fight it and attach a reverse rotation prop to the back of the tail cone such that when the body tube rotates CW it provides fwd thrust and when the shaft driven prop rotates CCW it also provides fwd thrust conserving the motors power to drive the torpedo, in essence with counter rotating props.(CRPs) I just need some time and water to build it.

                            I have resigned to allow the coreless motor to run wet and seal the interior of the torp from fwd of the motor, eliminating the shaft waterseals and pretty much eliminates water ingress. The motor being full aft causes the CG to be finicky-but with the capacitor full fwd and only a reed switch in between, the torp just floats slightly nose high.

                            Crap Batteries are going on this computer(I have to find the power pack) -keep up the progress-Bob
                            Last edited by Bob Gato; 07-11-2020, 09:44 PM.


                            • #29
                              Bob, will keep you posted on the build. Didn’t want to go with twisted fins for the exact reason you explained. Yes the torp body spin takes away from the forward trust which has been a thorn in my side. After studying many counter rotating design options, I feel the one I went with on purpose is the most replicated possible for most handy folks once I can get it proven. My thoughts were the same as yours with adding a counter rotating set of fins aft of the propeller. In the tests I did it only added resistance and made the problem worse from what I observed. I could be wrong. Most of my tests and revisions have been to isolate and observe behaviors with each change


                              • #30
                                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.