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today's work

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  • Darrin Hataway's 1/15 scale swimmer delivery vehicle (SDV) r/c model kit came to me as 3D printed parts. The six parts that constitute the hull arrived with the lower hull -- itself comprising three parts -- already assembled; the upper hull separate, but outfitted with indexing pins to assure a tight, secure mating with the lower hull; and two SubDriver foundations. The only other parts to this very simple to assemble kit were the single rudder, single stern planes, propeller, and set of bow planes.



    My job was to develop a SubDriver to make the thing go; and to come up with a practical means of spinning the propeller; and getting the control surfaces interfaced with the SD's servos. Once I get the thing into the water I'll make recommendations as to how to improve the 3D files to correct flaws and suggestions as to what it will take to make the eventual product more user-friendly.



    This little r/c submarine will be perfect for pools and small bodies of clear water -- environments where a vehicle of tight turning radius, minimal table-space and requiring only basic support equipment. This little SDV model will fill the bill nicely.

    The actual MK-8 SDV's have been in use for decades. These are wet type vehicles that deploy 'operators' to and from the work site. They can be deployed from submarines, surface craft, or from shore. Typically they are housed in special dry-shelters mounted to the deck of a parent submarine -- in operation the parent submarine assumes a shallow depth, hovers, and the SDV -- assisted by support divers -- is removed from its shelter, readied, manned, and sent on its way.







    Today's task was to manufacture the pushrods, clevis' and control horns that translate the fore-aft motion of a pushrod into a torque that rotates the rudder and stern planes.









    The rudder and stern plane receive a control horn at one end, that horn pined to a pushrod clevis. In actual practice the fore and aft motion of the pushrod swings the control surface by the 'pilot' who sits in the front of the vehicle, in tandem with the 'co-pilot/navigator'. On the model servos move the pushrods through a bell-crank linkage.

    A control horn is simply a soldered sandwich of three pieces of brass strip. The center is .030" thick with the two outer strips .014" thick. Portions of the outboard strips of brass extend past the end of the center strip to form the cavity in which the pushrod clevis is later inserted and pined in place.



    The outline of the horn is inked onto the work and rough-cut to shape on the band saw. From that point on it's hand work with the aid of a rotary tool.



    Final shaping is done with rotary cut-off wheel, files, sanding sticks, and steel wool. Holes are drilled to pass the control surface bearing pin and horn brass securing nails.



    Note that a 'handle' is retained -- the middle length of brass strip -- during shaping of a horn. This makes it much easier to maneuver the work as I hand work it. KISS!



    After tack-gluing the brass control horn to the outboard end of a control surface I drill holes into the control surface, and insert .030" diameter brass securing nails, which are first coated with thin formula CA adhesive. This insures a good, sound union between horn and control surface; a union that should survive handling accidents and the torque presented by the pushrod.



    A unique feature of this little r/c submarine is that the two servo outputs are at the front of the SubDriver, not the back. I'll have to device a pair of bell-cranks to translate motion back to the control surface pushrods. Tomorrow's task.

    Here I've marked out the location of the pivot rod that will pass through holes in the bow becoming the axil about which the two translating bell-cranks will rotate.



    Resident Luddite

    Comment


    • Brilliant !!!!!!!!!

      Comment



































      • Resident Luddite

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        • Super slick. Very clean! You nailed it. Nice work

          Comment


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

            You're one of the few who make good use of the information I and other terribly talented people present to the great-unwashed.

            David
            Completely off topic but need your assistance David.

            I am struggling to comprehend you guys thread system.

            For shafts 1/8 and 3/16 what threads go on those?

            I need to order threaded bushings.

            #6-32 and #10-24?

            Thks & grtz,
            Bart

            Practical wisdom is only to be learned in the school of experience.
            "Samuel Smiles"
            http://scale-submarine.com/index.html

            Comment


            • Originally posted by bwi 971 View Post

              Completely off topic but need your assistance David.

              I am struggling to comprehend you guys thread system.

              For shafts 1/8 and 3/16 what threads go on those?

              I need to order threaded bushings.

              #6-32 and #10-24?

              Thks & grtz,
              Bart
              Hey Bart,

              I don't thread those size shafts, I use set screws to make up items to them. I'll grind a flat at an end of the shaft that will receive a set-screw that secures the item (wheel-collar, propeller hub, or universal coupler) against axial and rotation with a tight fitting set-screw.

              If I were to thread these I would go with a 4-40 for the .025" shaft, and a 6-32 for the .137" shaft.

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              David
              Resident Luddite

              Comment


              • Hi David,
                Are you planning to put o-rings on the drive post to cushion the contact?








                Comment


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

                  Hey Bart,

                  I don't thread those size shafts, I use set screws to make up items to them. I'll grind a flat at an end of the shaft that will receive a set-screw that secures the item (wheel-collar, propeller hub, or universal coupler) against axial and rotation with a tight fitting set-screw.

                  If I were to thread these I would go with a 4-40 for the .025" shaft, and a 6-32 for the .137" shaft.


                  David
                  Ok thks David, your way will result in better centering.....not everybody is able to cut a thread with a die.....most of them will end with a wobbling propeller.

                  Grtz Bart



                  Practical wisdom is only to be learned in the school of experience.
                  "Samuel Smiles"
                  http://scale-submarine.com/index.html

                  Comment


                  • Originally posted by Scott T View Post
                    Hi David,
                    Are you planning to put o-rings on the drive post to cushion the contact?







                    The two sets of magnets don't make contact, there's about a 1/16" space between them. Torque is strictly magnetic, no mechanical contact at all. The inverse square law is our friend in this application -- shimming the distance between the two sets of magnets varies the strength of the bond.
                    Resident Luddite

                    Comment


                    • Very cool David

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                      • Awesome, amazing detail

                        Comment


                        • So those 2 small joysticks control the diveplanes and rudder, one for each. In theory, a pair of 1/16 Navy SEAL action figures can drive this thing. One to handle the dive planes, the other to steer. OR one 1/12 or 1/6 action figure operating a one man SDV.

                          Would be nice to have a scale cockpit with SEAL figures one can drop in in lieu of the WTC when displaying the sub.

                          Anyway, What's the reason for forward location of the servos?
                          Last edited by redboat219; 10-05-2020, 06:06 AM.
                          Make it simple, make strong, make it work!

                          Comment


                          • Originally posted by redboat219 View Post
                            So those 2 small joysticks control the diveplanes and rudder, one for each. In theory, a pair of 1/16 Navy SEAL action figures can drive this thing. One to handle the dive planes, the other to steer. OR one 1/12 or 1/6 action figure operating a one man SDV.

                            Would be nice to have a scale cockpit with SEAL figures one can drop in in lieu of the WTC when displaying the sub.

                            Anyway, What's the reason for forward location of the servos?
                            First I get this thing to work, later I finesse things to permit an open cockpit.

                            The tight confines between stern and after end of the SD precludes the traditional linkages and running gear coupling.

                            David
                            Resident Luddite

                            Comment


                            • David,

                              Is there positive connection between the servo push rods and the "pedals" on the dive planes and rudder control arms, or do they just abut against each other?

                              If its the latter, is there a spring that maintains tension on the pedal arms to move them back when the push rods retract back?
                              Last edited by redboat219; 10-05-2020, 09:57 AM.
                              Make it simple, make strong, make it work!

                              Comment


                              • Originally posted by redboat219 View Post
                                David,

                                Is there positive connection between the servo push rods and the "pedals" on the dive planes and rudder control arms, or do they just abut against each other?

                                If its the latter, is there a spring that maintains tension on the pedal arms to move them back when the push rods retract back?
                                The SD's pushrod pushes against the top end of its bell-crank. The two bell-cranks share a common spring that pushes them at the bottom.

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                                Resident Luddite

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