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1/48 G7 Torpedos

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  • #46
    I’m back to work this week so I doubt I’ll be able to make any more progress until next weekend. Now that the experimental gearboxes prove to work, I’d like to look at comIng up with much more simplified design that is not so tolerance critical with so many tiny machined shaft bushings and hours of hand fitting parts. A much more simple production method basically. Have a couple ideas so far

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    • #47
      A small amount of soldering work tomorrow morning to get everything connected, then hopefully some wet testing in the pond to see how the counter rotating props affect the running characteristics of this torpedo
      Attached Files

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      • #48
        Test report for the G7E counter rotating torpedo transmission. Here is the good news and the not so good news. Good news is, it works and the counter rotating props appear to have completely stopped the torpedo body from torque spinning around its central axis. The travel trajectory is noticeably much more straight after repeated tests. (Almost perfectly straight. Outer prop was slipping on shaft)

        The not so good news, the decision to swap the 15mm length 65,000rpm motor out for the lighter weight 9.3mm length 28,000rpm motor has proven to be a mistake and the torpedo’s speed has been significantly reduced. The shorter length motor lacks the rpm and torque that the longer motor produces. The picture of the disassembled torpedo show the original 15mm long motor used in past design test and the current 9.3mm long motor used in this current design.

        In the next design revision, I plan to look at using the 15mm motor again or possibly sourcing and testing a new 12mm long motor. Future designs with either motor will either use the current 5:1 planetary reduction gear box or not. The counter rotating gearbox will stay. Thanks for following this developing build!
        Attached Files

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        • #49
          Hey Nick, congrats on the success of the gearbox-at the risk of being redundant-consider upping the voltage instead of changing the motor. With an 8mm 10uf 6.3volt or even a 10volt ultracapicator that little coreless motor would give you all the power you need. The park flyer guys do it all the time you could lose the timer BC the cap would run for about 30sec-1min depending on the charge and with only the motor, cap, and reed switch, it would be all waterproof and light weight I realize that you probably want to just reuse the torp over and over on the battery but you will have the torp in hand between loading anyway whats a quick 20 second charge from a battery pack before slipping it back into the sub?-BG

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          • #50
            BG, I like what you are suggesting! Definitely would be a much lighter setup. I will look into gathering up the components you mentioned and give it a try. How long would you say that the capacitors will store a charge?

            Thanks!
            Nick

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            • #51
              Heck, I really couldn't tell you how long until the charge gets unusable...but if it is any indication-I had one sitting in a magnetic cradle on the bench for a week and it ran when I picked it up off the magnet.
              Yes lightweight...at 1/64 that was my issue, they were borderline bound for the abyss. I was saving weight by the composite body tube, removing the insulation on the ground wires, cutting the all component leads short, using an epoxy covered foam nose cone. Probably not a problem at your scale...I am very stoked about your gearbox-looking FWD to the next post!-Bob
              Last edited by Bob Gato; 07-27-2020, 10:40 AM.

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              • #52
                Wow, that’s impressive! Please educate me on what to look for when searching for suitable capacitors. My experience with using them is almost zero hahaha! I’d like to keep the voltage at 6v incase I still want to use the timer. It seems the easiest thing to try at the moment as per your helpful suggestions is to up the voltage from the 3.7 LiPo battery to a 6 volt capacitor instead by simply swapping the battery out for a capacitor. This would be a super quick modification that could be made to the current design as it is configured at the moment. Thanks!
                Last edited by Monahan Steam Models; 07-27-2020, 10:49 AM.

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                • #53
                  Just got off the phone with a life long close friend who has his master’s degree in electrical engineering and still currently works as a senior EE. Long story short, I got a very thorough instant education on all things capacitors as well as some other EE tips. Got homework to do now!

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                  • #54
                    As I'm sure that you will find out-they aren't just ordinary capacitors-they are classed as super or ultra capacitors-they take and hold a charge like a battery.You'll probably be looking at 8mm in diameter, 6.3volts. the higher the farads(uf) the slower it will discharge you will have to try them to see how they drive the motor-they are quite cheap on ebay-sold by the batch.
                    Nick, ask your friend-this might be a good starting point https://www.mouser.com/ProductDetail...hoC0fEQAvD_BwE
                    Last edited by Bob Gato; 07-27-2020, 08:52 PM.

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                    • #55
                      Awesome thank you again for the info! I’m interested to see how they work with this project. After this morning’s crash course from my EE buddy I searched a couple places that I’ve purchased electronic components from. Both Digikey and Newark electronics had a selection of super caps. 8mm is a great size, so I wound up ordering some 8mm by 13mm long 1F and 1.5F caps from both suppliers. In the 8mm diameter range both suppliers offered various caps in voltages ranging from 2.5, 2.7 and 3.0 volts. I chose the 2.7v caps so they could be wired in series to get 5.4 volts at 1F or 1.5F. I think the 1.5F caps will arrive tomorrow

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                      • #56
                        BG, we must’ve been posting at the same time because I did not see the link in your updated post. Thank you for posting that, I will ask my buddy what he thinks. I like the voltage rating on that one better

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                        • #57
                          HaHa-I hate when that happens...Since I don't need 6v caps I am not sure-the farads are a little high and it needs to be tested on your motor to see how fast they dump their charge-I think they would be good and they're cheap enough-but I like the series Idea...it allows for weight distribution.

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                          • #58
                            BG,

                            I was thinking about other design options last night regarding the use of super caps. The drawback I see to running caps in series is the potential need to charge each cap separately at 2.7volts then switch them to a series configuration. There are probably some simple ways to do this. One simple option for example could be using a jumper to switch between individual charging input then series output.

                            So far I’ve been not having luck finding a 5-6 bolt high farad super cap in ideal dimensions. I’m sure they are out there.

                            Another idea would be to run a single 2.5-3volt super cap with a high farad rating and then use a voltage step up booster. Check these out: https://www.pololu.com/product/2115

                            I have some of these step up boosters already but in a 12v step up for the torpedo launcher micro pneumatic solenoid valves

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                            • #59
                              I am using a 3.3F 2.7V supercap but in a direct drive setting (no gear reduction)-and it goes like hell. I see what you mean about finding the 6v caps-the diameter increases with the higher voltage in order to get the capacitance (F) up -when you get the 2.7Vs that you ordered, I am curious as to how the series circuit works out-I think that you can charge them in series...you might have to trial and error the charge voltage though.

                              And if all else fails-you should be able to use double throw magnetic reed switches to run in series and charge in parallel-no booster necessary
                              Last edited by Bob Gato; 07-28-2020, 02:21 PM.

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                              • #60
                                I was thinking of using a reed possibly too! Nice! I was hoping the parts would show up today but it looks like they didn’t go out last night and were shipped this morning instead.

                                In the meantime I got impatient and pulled the smaller motor and 5:1 gearbox out and put the more powerful motor used in previous tests back in. It’s connected direct drive to the counter rotating gear box. Night and day difference in performance. Think I might’ve had a small amount of prop slippage on the outer shaft. Need to secure them to the shafts better.

                                Here’s a couple videos from this evening. It’s still set to run for 5 seconds.

                                https://youtu.be/Y5ZVUpzDYmo

                                https://youtu.be/DZtCqIuVByw

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