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Brutus

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  • #49618
    Diede van Abs
    Participant
      @diedevanabs87670

      Luckily I have never had molten connectors in any of my boats, but I did see the pictures of some who had.

      I however did have a burning ESC in one of my tugs, and I ruined a brushless motor + ESC so badly the insulation was completely gone, and the wires along with it – due to a shorting in the motor, I pushed it waaay beyond its limits…

      Edited By Diede van Abs on 12/06/2014 17:50:14

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      #49627
      Amy jane September
      Participant
        @amyjaneseptember49770

        Nice to see Brutus running along Bob, Well done!cheeky

        #49630
        Bob Abell 2
        Participant
          @bobabell2

          Thank you, Amy

          Some of the wiring was a bit suspect, but was good enough to demonstrate to Paul, how the model performs, especially the fast turns, which were not on the video unfortuneately

          Working on Phase two now…..The new exciting ABELL twin drives…….More fun in the pipeline

          Have a nice day

          Bob

          #49636
          ashley needham
          Participant
            @ashleyneedham69188

            cor. I have gone over to Deans connectors for batts now, much more reliable than the tamiya sort, and the few high power machines I have , have got 4mm gold connectors fitted. With thick wire you should never have an issue.

            The KM Ecranoplan batteries get very hot when it is running, the motor and ESC are watercooled. The wires get very warm..they are big chunky items same size as fitted to brushless motor tails.

            Ashley

            #49637
            Bob Abell 2
            Participant
              @bobabell2

              Thank you, Ashley

              Can you post a photo of the Deans connectors and the Gold Conns please?

              I didn`t think 7.2 volts would cause such a fuss!

              When your stuff starts getting hot….Doesn`t the fuse blow?

              What size of fuse are you using?

              Thanks matey

              Bob

              #49639
              Colin Bishop
              Moderator
                @colinbishop34627

                It's not the volts that are the problem Bob, it's the amps!

                Colin

                #49641
                ashley needham
                Participant
                  @ashleyneedham69188

                  Bob. Pictures of the KM Ecranoplan. Brushless motor with watercooling jacket, Gubbins spread out where it will live in the hull. The connectors are a bit like banana plugs but shorter. Wires are a bit long due to the need to thread everything through the centre wing bit. ESC watercooled and has thermal cutout and overload protection. Wire gauge matches that on the motor and get quite warm. Motor stays cool, ESC stays cool. ESC cant remember about 50A capacity..battery 35A discharge they say and I recon we are probably up to 30A but this is just a guestimate.

                  Motor 3Kv on 9.6V…almost 30.000 RPM……..motor safe for 3s lipo..whats that….15v or something??? times 3=rpm….. The KM is just so fast… Ellie going fast?? Brutus going fast??? dont think so.

                  Brushless motors, easy. I only had to set up the esc cutout voltage with a program card and i have not touched it since.

                  Ashley

                  KM ecranoplan motor

                  KM ecranoplan layout

                  #49643
                  Bob Abell 2
                  Participant
                    @bobabell2

                    Thanks Ashley

                    I`ll stick with the Tamiya stuff, just one more time, then reconsider the future

                    I won`t be charging about that much

                    Thank you, Colin for the Amp info

                    How many amps is 4600 mAh with 7.2volts?

                    Bob

                    #49645
                    ashley needham
                    Participant
                      @ashleyneedham69188

                      Ah…Bob, there we have it. Using that combination of battery (4,3 A/hr CAPACITY) and 7.2V voltage, in a boat with a speed 280 motor driving a 25mm prop it might be 3 amps or so (3 amps being taken out the battery, that is)

                      BUT if this battery was to be put in, say, my hovervan (speed 300 motor plus a 540 motor) it would have to give approx 10A,

                      THERE AGAIN…in the Ecranoplan we may well see 20+A being consumed.

                      It all depends on the motor that is connected to the battery. NOT FORGETTING most batteries have a recomended max output or draw..in most cases I think for Nimh type sub C cells, it is usually around 35A or so.

                      This is one of the reasons really fast boats are using Lipo batts, they can discharge a lot more amps.

                      Ashley

                      #49646
                      Colin Bishop
                      Moderator
                        @colinbishop34627

                        Bob, the Amps drawn depend upon the power demanded by the motors and props at the delivered voltage. If the motors are overloaded by the props then heat will be produced in various components and the battery will be flattened in short order. It's all about getting everything in balance as other people have mentioned in their posts.

                        Colin

                        #49649
                        Paul T
                        Participant
                          @pault84577

                          Bob

                          In very basic terms

                          4600 mAh = 4.6amps which in basic terms means that the battery pack can provide 7.2volts at a current load of 4600mAh (4.6amps) for one hour.

                          If your 700 size motors take a current load of 9amps to make them turn the propellers then your battery pack will provide 7.2volts for less than half an hour.

                          The problem with using a low amp battery to provide power to a pair of high amp motors is that the battery pack becomes exhausted to quickly and will generate heat (the batteries get hot…the wires get hot)

                          Ideally a pair of 9amp motors should be powered by a minimum 9Ah (9000mAh) battery pack.

                          #49650
                          Bob Abell 2
                          Participant
                            @bobabell2

                            Colin

                            See Paul`s latest thread about this subject

                            The props on my Brutus boat are too small btw

                            Bob

                            #49653
                            Colin Bishop
                            Moderator
                              @colinbishop34627

                              I would doubt that the props are too small. It's the props that put the load on the motors and generate the heat which suggests that they are too big for the motors to cope with.

                              Without props the motors will be running free and draw only a low current which will certainly not generate heat.

                              Colin

                              #49654
                              Bob Abell 2
                              Participant
                                @bobabell2

                                Do these props look too big?

                                g2.jpg

                                #49655
                                Colin Bishop
                                Moderator
                                  @colinbishop34627

                                  They look like racing props to me with a large pitch on them. Matching the props to the motors and also the motor revolutions is the key to efficiency. Are the motors getting anywhere near their rated working RPM? If not then they are struggling and will create heat. This is where gearing down can help as you know yourself. Even on much smaller, sedate models I have always found that gearing down by around 2:1 or 2:5 :1 allows the motor to rev and the prop to deliver better efficiency. The same thing applied in the early days of steam turbines. The old Mauretania had direct drive to the props which were relatively small and required a lot of fuel to achieve her record speeds. When geared turbines were introduced, the mechanical losses in the gearing were more than offset by the gains in efficiency in allowing the turbines and the props to each run at nearer their most efficient speeds.

                                  Colin

                                  #49657
                                  Paul T
                                  Participant
                                    @pault84577

                                    Bob

                                    This is all getting very confusing so I would suggest that we start at the beginning by taking an ammeter reading from your motors whilst they are running in the bath and from that reading we will be able to answer all of the questions.

                                    Paul

                                    #49658
                                    Bob Abell 2
                                    Participant
                                      @bobabell2

                                      For starters…..I haven`t got an ammeter

                                      The motor blurp says the motor is rated at 55.62 Watts……..This works out at…. 7.7amps x 7.2volts

                                      What does this tell us?

                                      What figure will the bath test give us?

                                      Bob

                                      #49659
                                      Paul T
                                      Participant
                                        @pault84577

                                        Hi Bob

                                        The bath figure will provide an amp reading with the motors under the load (strain) of turning the shaft and props, the factory figure of 7.7amps will be its unloaded rating. I would expect that the loaded reading would be around 8.5 to 9amps.

                                        From this assumption we can now have a good guess at what the correct batteries and wiring sizes should be.

                                        I'm signing off now but I'm sure that all of the answers will be provided by morning.

                                        Paul

                                        #49660
                                        Bob Abell 2
                                        Participant
                                          @bobabell2

                                          OK, Paul

                                          Thanks for the info

                                          Bob

                                          #49662
                                          lnvisibleman
                                          Participant
                                            @lnvisibleman

                                            Speaking as a newbie, how do we know what to do without investing in a PhD first ?

                                            Mike

                                            #49664
                                            Colin Bishop
                                            Moderator
                                              @colinbishop34627

                                              As said on the other thread, have a read of Dave Milbourn's article.

                                              Colin

                                              #49670
                                              ashley needham
                                              Participant
                                                @ashleyneedham69188

                                                Bob. Those props look MUCH TOO BIG..if they are 50mm as i FINK THEY ARE. Overheating on motors this size should just not happen with the correct size prop and adequate ventilation (which at least you have)

                                                The motors you have fitted would best have plastic two bladed "S" pitch 40mm on, or even 35`s….

                                                Theres absolutely no doubt that a pair of MFA 850 motors on 12v and running X50 props would be just then thing for this, absolutely, in my opinion, but I am not sure they would fit in your situation.

                                                Ashley

                                                #49671
                                                Bob Abell 2
                                                Participant
                                                  @bobabell2

                                                  Thank you, Ashley

                                                  The props are actually 40mm dia…..Paul has suggested going for 50 dia

                                                  The wiring I fitted last week where really a temporary lash up with any old wire that was lying about and was rushed into sailing right away by a close well meaning old pal

                                                  I am quite confident that today's wiring and plugs will be ok

                                                  Bob

                                                  #49672
                                                  Bob Abell 2
                                                  Participant
                                                    @bobabell2

                                                    Thank you, Ashley

                                                    The props are actually 40mm dia…..Paul has suggested going for 50 dia

                                                    The wiring I fitted last week where really a temporary lash up with any old wire that was lying about and was rushed into sailing right away by a close well meaning old pal

                                                    I am quite confident that today's wiring and plugs will be ok

                                                    Bob

                                                    #49675
                                                    Bob Abell 2
                                                    Participant
                                                      @bobabell2

                                                      Brutus is now rewired using the new plugs and wiring and runs with frightening ferocity! Reaching top speed is not for this chicken!

                                                      Almost approaching the brushless motor speed, which sounds a bit far fetched!

                                                      So I don`t think we have chosen the wrong motors after all?

                                                      Got two spare props, one is 55mm dia and the other is 45 mm dia a poor match, but feel sure we can run a few tests when the Cavalry arrive tomorrow?

                                                      The current props are 40 mm dia

                                                      Bob

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