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    Forum
    Magnetic motors
    No sweat Ed ๐Ÿ˜‰ ALL you have to do is take a brushless Inrunner apart, build the stator coils into an aerofoil section nozzle ring (same cross section as an aircraft wing) with the "underside of the wing" on the inside of the nozzle and the blunt end up front,* then JUST graft some neodymium magnets onto the ends of your prop
    blades
    ๐Ÿ˜ฎ balance and polish. Then just install your nozzles where you would normally fit the rudders. Use a 360ยฐ servo for steering control. Easy peasy ๐Ÿ˜ Interested to see who does it first๐Ÿ˜ Cheers, Doug ๐Ÿ˜Ž * Effect of this is to increase the water pressure inside the ring and decrease it on the outside. Thus improving the efficiency of the prop / impeller.
    1 day ago by RNinMunich
    Response
    Re: STARLET
    Markie, the makers of saw
    blades
    are "starret"
    14 days ago by Wingcoax
    Forum
    CNC boat kits...?
    ".....I have the files to make a dragknife that works with a stanley blade, it is 3D printed and has a steel shaft mounted in ball bearings. Some commercial ones are over 250 quid!....." Sounds like a lot of work. Here is the one I got - I see the price has gone up to ยฃ4.49! This comprises an aluminium housing with a magnetised steel shaft in it mounted on ball bearings, and 15 precision knife
    blades
    in carbide - different angles for different thicknesses of material. I have mounted it in a Delrin collar, and it looks as if it will perform perfectly. Lot less time and trouble (and cost) than making your own... https://www.ebay.co.uk/itm/15pcs-30-45-60-Degree-For-Roland-Cricut-Plotter-Vinyl-Cutter-Blade-Holder/131906788936?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649 I would love to get the plans I drew 'checked out' by a third party who has a precision cutter. My early ones are rather poor - I think I am getting better, but I am still likely to make mistakes. The PT boat would be a good choice - not too much wood and it makes up quite nicely. Of course you would still need to make the fittings - but direction is given on the web site. The figures shown below are cheap Chinese railway figures - about ยฃ2 for a dozen - modded and painted up...
    20 days ago by DodgyGeezer
    Forum
    Hintsand tips - Decals made easy
    "....It's a lot easier and cheaper then buying a vinyl cutter and learning how to use it. It might not cost much more than a pack of decal paper...." I can't report on the 'learning how to use it' part, since I haven't started, but having a CNC machine means that you can add all sorts of tools onto the cutting end. At the moment I just use a small router to cut balsa - I would use a bigger one or a laser to cut ply - and I have just bought a 'swiveling knife' set to cut vinyl. Cost of a mount and 15
    blades
    - ยฃ4.37. Should let me cut any size or shape character out of vinyl (or anything else) sheet...
    27 days ago by DodgyGeezer
    Forum
    Prop size and speed
    Agreed Martin, one thing at a time! BUT: Stuart; I believe we are discussing your 24" Commander here. In which case your results mirror mine with my 24" Sea Scout. Except that my prop shaft did not bind!!๐Ÿ˜‰ It was also reluctant to plane with a 2S LiPo (7.4V nominal) but went very well and planed easily with a 3S (11.1V nominal). I also was using 4000mAH batteries. I published my results using various batteries here in the Media - Video section. Go to the Media Gallery and search for Sea Scout. So, I would leave the motor and prop alone and (after fixing the prop shaft!!!) try a 3S battery. I'm sure you will be satisfied ๐Ÿ‘ Prop technology is complex as Martin said, our old friend Bernoulli raises his head for instance๐Ÿค” But, essentially bigger is better for more speed or same speed with lower shaft revolutions when applied to real size ships. BUT 2: with our electric powered models bigger props often simply increase the load on the motor causing it to draw more current for a fractional increase in boat speed if any. In essence props with fewer
    blades
    are inherently more efficient as you hinted. Minimum being 2 of course ๐Ÿ™„ Two bladers are popular with the Fast Electric guys for that reason. I don't do speedboats, I'm a scale guy and my maxim is; If the real vessel had an XYZ screw then so will my model! Summary; first fix the propshaft; lubrication, alignment with motor shaft, ensure a few thou of clearance between prop hub / locknut and the end of the shaft tube. Preferably with a thrust washer in between. Second, fit a 3S battery preferably crosswise above the C of G of the boat. As you can see in the pic of my Sea Scout 'engine room' in your Commander thread. For those with a mathematical mind, undying curiosity and an afternoon to spare I attach a paper on the Principles of Ship Propulsion from MAN, the supplier of small to huge diesels to probably a majority of ships (commercial and naval) built today. You should find Chapter 2: Propeller Propulsion particularly illuminating! Happy reading ๐Ÿ˜‰ Just remember the paper deals with real ships and real water, we have scale ships but not scale water๐Ÿค” Basic dynamics still apply though. Cheers, Doug ๐Ÿ˜Ž
    1 month ago by RNinMunich
    Forum
    Prop size and speed
    Hi doug and anyone out there.... you mentioned you tried 2 & 3 blade prop what was your conclusion?? did the boat go faster or did it accelerated faster or is there advantage 2
    blades
    are for speed,? and 3 are for power? i have a dumas CC commander 36 inch long. wondering if i should us 3 blade prop. comes with a 2 bladed and going to run twin motors. also should i revers one of the motors, for better control??? thank you samc
    1 month ago by samc
    Forum
    Prop size and speed
    Caution Martin! A larger prop may only increase the current drawn by the motor without increasing speed. in some cases less is more! Rule of thumb is prop diameter not significantly greater than the diameter of the motor. I think the solution here may well lie in the type of prop and/or the battery. Stuart hasn't revealed which battery he is using. The motor and the boat are the same size as my Sea Scout which does pretty well with a 3 blade 35mm prop with pitch approx 1.4. Running off a 3S LiPo. Motor is a Propdrive 1kV ~30mm diameter. In the past I tried a 35 and a 40mm two blade (S type) prop with sedate results compared with the 3 blade. Shaft alignment and lubrication also plays an important role of course. Cheer, Doug ๐Ÿ˜Ž PS "The pitch of the
    blades
    also determine the amount of distance per rotation that the boat will travel but that also has its limitations. This subject can get extremely complex." You are so right Martin! The wood that you are putting a screw into stays put. Water doesn't๐Ÿค” So, amongst other things, you would have to know the 'Slip Ratio' of your prop design!!
    1 month ago by RNinMunich
    Forum
    Prop size and speed
    Hi, Regarding motor speed/prop size. There are so many factors to take in to consideration on this subject. Also the fact that most model boats that you see go a lot faster than there proper scale speed. After looking at your last video I would say that you have it about right, if you were to make it go faster firstly do you have the room to fit a larger propeller? If not then the only course of action you have left is the motor size or blade pitch. If you change the motor you could end up with the motor rotating so fast that the propeller will be next to useless. (If you imagine a wood screw going in to wood the distance per rotation) The pitch of the
    blades
    also determin the amount of distance per rotation that the boat will travel but that also has its limitations. This subject can get extremely complex. If your model is sitting at it's proper waterline then removing weight will not be the answer either. Without getting technical I would personally try a different pitch first then assuming I had the room try a combination of prop size and pitch. I don't know if this has helped. Martin.
    1 month ago by Martin555
    Forum
    Tamar Lifeboat propellers
    Hi Want to change to brass propellers on Model Slipway 1/16 Tamar Lifeboat. Lost one of the original plastic propeller supplied in kit , and looking at Roboesch 40mm brass as replacements . Not sure whether to go for 3 or 4
    blades
    and type A or C Type props. Good speed from the supplied props with kit running with brushless Tornado 3536 1050kv on 3s lipo. Any recommendations of what to go for would be helpful. Thanks
    2 months ago by alan50
    Blog
    HMS Cottesmore in 1/48 scale.
    Hi Guys, As I mentioned the Bridge in my last log I thought that I would cover the Radar on top of the Bridge. As you may have gathered I quite like working with plastic card, so making the Radar was just a case of gluing some layers of card together and shaping. To make the Radar turn I modified a standard servo to continually rotate and by adjusting the pot slightly I managed to get it to rotate clockwise one full rotation at a speed of approximately two seconds. It seemed to be the correct speed, as I have seen on many models the Radars spin like a helicopters rotor
    blades
    and to me that is not correct. The video is 'hidden' in the Invalid File. To view- Click on the Invalid image, Then click the Download button, white arrow on blue background at top left. Windows (App?) offers the choice of View or Save. View with Media Player or equivalent. Martin
    3 months ago by Martin555
    Forum
    Hints & Tips
    Would it be possible to start a topic on hints & tips in building? For instance I struggled for years with filler application , and when going through my old artist type oil paints etc to pass on to my kids , came across some old W&N palette knives. They work a treat from the very small to very large applications. Had bought a cheap set before leaving UK from one of those outlets that pop up from around Christmas, dug that one out and the broad and angled
    blades
    work well for the large applications. The flexible heads push the filler in very well and practically no wastage.
    3 months ago by redpmg
    Blog
    Manufacturing of Paddles
    I started with the paddles. Main reason was that I was not sure the final product would work. I ordered all the brass parts using eBay and google. Templates were photo copied from the drawing (paddle frames) and stuck to 1/32 brass sheet. Centre punched all the points that needed to be drilled. Holes drilled used a jewellers saw to cut out the frames and finish off using files. I had not done anything like this before but patience was need to replace all the broken
    blades
    . I note that the saw came with 120
    blades
    . I then made all the paddles, the spider gear, etc using soft soldering technique. The wheels were then assembled and tested. small adjustments had to be made with a file as some of the paddles were fouling each other. Disassembled them and painted them using car spray paint. I was quite pleased with the paddles so could start thinking about the tug hull. ,
    4 months ago by Hillro


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