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  • Stephen Vick
    Lieutenant
    • Nov 2018
    • 67

    Dave,
    I am curious as to the KV of your outrunners? I have a pair of Graupner 500 KV outrunners, which I am installing in a Robbe U-47. I will try them direct drive initially, but I might need to go to gear reduction or belt drive if that doesn't work out. This is my first try at Brushless motors in anything but a plane. They are always so bloody fast! The 500KV Graupners are comparable to the outrunners being used by Engle in a couple comparably sized boats so fingers crossed they aren't stupid high RPMs . Up side is low current draw and longevity.
    Cheers,
    Steve

    Comment

    • gantu
      Commander
      • Apr 2009
      • 360

      Hi steve better use the engel brushless motor with 300 Kv. The graupner 500Kv is too much.




      Regards Gantu

      Comment

      • He Who Shall Not Be Named
        Moderator
        • Aug 2008
        • 12256

        Originally posted by Stephen Vick
        Dave,
        I am curious as to the KV of your outrunners? I have a pair of Graupner 500 KV outrunners, which I am installing in a Robbe U-47. I will try them direct drive initially, but I might need to go to gear reduction or belt drive if that doesn't work out. This is my first try at Brushless motors in anything but a plane. They are always so bloody fast! The 500KV Graupners are comparable to the outrunners being used by Engle in a couple comparably sized boats so fingers crossed they aren't stupid high RPMs . Up side is low current draw and longevity.
        Cheers,
        Steve
        Temper my comments by knowing that I'm new to the black-arts of brushless motors.

        So far my only practical experience is with the D3548-6. Rated to run off a 11.1 - 18.5V source this motor will yank up to 60A stalled. This outrunner is 790 KV, which I understand means it has a relatively high torque at a lower than 'normal' speed. I have bare-fisted this thing at 11.1- volts and must say it has considerably more ass than a brushed 555 motor!

        That said, I would assume you're 500 KV motor is even better in the torque department. For direct drive the old rule-of-thumb for brushed motors was that if the propeller diameter was not too much more than the can diameter, then it was OK to go direct-drive without over-loading the motor. With these more efficient brushless units we can assume an acceptable motor:propeller diameter ratio to be 1.5:1.

        What's your Robbe U-47 propeller diameter? I assume its close to your Graupner motors diameter, so direct-drive should be OK for you installation (assuming a dedicated motor per propeller).

        The big practical fly-in-the-ointment with outrunners is the need to suspend the motor by its mounting spider. As demonstrated here:





        Remember the gear-splitter we came up with for your little TRUTTA? I've done pretty much the same thing to get two shaft output from the single D3548-6 motor:















        Andy!!! Help us out here, pal.

        David
        New-to-this-****!
        Last edited by He Who Shall Not Be Named; 02-21-2020, 04:08 PM.
        Who is John Galt?

        Comment

        • Stephen Vick
          Lieutenant
          • Nov 2018
          • 67

          Awesome trip down memory lane Dave ! I just did some shopping on McMaster Carr and think I have a pretty fair 2.5 : 1 ratio belt drive being shipped to me... I am expecting a lot more torque from the little 500KV's than from the stock 600 brushed motors. My only concern is the motor RPM's, but I think the reduction will be sufficient. Its all experimentation really. A dash of experience and a spoonful of guesswork... I'm totally gonna steal your mounting stud method!
          Cheers,
          Steve

          Comment

          • He Who Shall Not Be Named
            Moderator
            • Aug 2008
            • 12256

            Originally posted by Stephen Vick
            Awesome trip down memory lane Dave ! I just did some shopping on McMaster Carr and think I have a pretty fair 2.5 : 1 ratio belt drive being shipped to me... I am expecting a lot more torque from the little 500KV's than from the stock 600 brushed motors. My only concern is the motor RPM's, but I think the reduction will be sufficient. Its all experimentation really. A dash of experience and a spoonful of guesswork... I'm totally gonna steal your mounting stud method!
            Cheers,
            Steve
            Yeah! Back when photography was chemically based. Only visuals I have from those days are scratched and faded emulsions on 'film'. Mid-80's was when we were all terrorizing Lake Trashmore?

            Don't think you'll need to up the torque with a reduction unit, Stephen. But, as you so correctly observed it's all a good helping of guesswork.

            Too late to rip me off on the studs -- I stole that mounting arrangement years back from one of my betters. Nothing new under the sun, only varied applications of the same tricks.

            Loved the mounts GANTU illustrated. That guy is a wealth of good stuff! I would employ the same trick if I ever figure out how to beak the set-screws that secure the motor shaft from the rotating bell without turning everything into slag.

            David
            Who is John Galt?

            Comment

            • He Who Shall Not Be Named
              Moderator
              • Aug 2008
              • 12256


              Sheet metal work today.













              Who is John Galt?

              Comment

              • trout
                Admiral
                • Jul 2011
                • 3545

                I like sheet metal. It really sets your Sub-Driver apart.
                If you can cut, drill, saw, hit things and swear a lot, you're well on the way to building a working model sub.

                Comment

                • He Who Shall Not Be Named
                  Moderator
                  • Aug 2008
                  • 12256

                  Originally posted by trout
                  I like sheet metal. It really sets your Sub-Driver apart.
                  Thanks, Tom. I've always been fascinated by what can be done with sheet-metal. Particularly today, when you watch how their working stainless steel plate into compound and simple curves to make Elon Musk's Starships.

                  Whenever it comes time to do sheet-metal work and I settle into the routine, I'm reminded of those few happy times I had in high-school -- shop class, where I was introduced to mechanical-drawing, machine-shop, welding-shop, wood-shop, and metal-shop. Back when such classes were routine for boys, but today replaced by black-history-month (every frig'n month of the school year) and other completely useless and sometimes counter-productive drivel mandated by screaming Liberals who reside in the Swampland of Federal agencies run by thieves, Congress Critters, cronies, and lobbyists.

                  David
                  Who is John Galt?

                  Comment

                  • He Who Shall Not Be Named
                    Moderator
                    • Aug 2008
                    • 12256
















                    Who is John Galt?

                    Comment

                    • He Who Shall Not Be Named
                      Moderator
                      • Aug 2008
                      • 12256








                      Who is John Galt?

                      Comment

                      • He Who Shall Not Be Named
                        Moderator
                        • Aug 2008
                        • 12256














                        Who is John Galt?

                        Comment

                        • He Who Shall Not Be Named
                          Moderator
                          • Aug 2008
                          • 12256








                          Who is John Galt?

                          Comment

                          • gantu
                            Commander
                            • Apr 2009
                            • 360

                            Loved the mounts GANTU illustrated. That guy is a wealth of good stuff! I would employ the same trick if I ever figure out how to beak the set-screws that secure the motor shaft from the rotating bell without turning everything into slag.

                            Like this with this tool allen key













                            Regards Gantu

                            Comment

                            • Scott T
                              Commander
                              • May 2009
                              • 378

                              The video I watched where the motor shaft was reversed; stressed using only high quality allen / hex wrenches. He stated anything else would round out the set screws. He did mention maybe heating
                              the set screws first. No harbor freight allen wrenches allowed.

                              Comment

                              • He Who Shall Not Be Named
                                Moderator
                                • Aug 2008
                                • 12256

                                Originally posted by Scott T
                                The video I watched where the motor shaft was reversed; stressed using only high quality allen / hex wrenches. He stated anything else would round out the set screws. He did mention maybe heating
                                the set screws first. No harbor freight allen wrenches allowed.
                                I tried the heat-trick. No soap. I've come to terms with the need to work with the motor shaft as-is.







                                David
                                Who is John Galt?

                                Comment

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