I think you might need pointing in a direction, so I had a quick look on Hobbyking, and this motor is the sort of thing you can use, although this particular one would need you to swop the shaft around, this is just a guide, other s will no doubt add comment, its the right size, 5mm shaft, right kv and watts. https://hobbyking.com/en_us/turnigy-g15-brushless- style='background-color:yellow;'>outrunner-810kv.html brushless esc https://hobbyking.com/en_us/hobbyking-90a-boat-esc-4a-sbec.h... you don't need the high amp capability, but its reversing, programmable, water cooled, and has an sbec, so the main battery power this 5 mm shaft, move your motor to the centre section meaning weight distribution is more central, and you can now use a shorter shaft, and get a couple off plastic "x" props, I would say 40 to 45mm will be the one. This will give a good speed, and you can power on 3 cells or 4 cells lipo, get higher c rating (40c or more) and higher mah so you have fuel in the tank available https://hobbyking.com/en_us/turnigy-battery-3000mah-4s-40c-l... This is just a guide, a starting point, as I feel you are unsure where to start, others with more knowledge will come in regarding this, having experience with lipo, brushless, 3 foot ply boats, and esc's, depending on budget, this would be the sort of thing I would be getting.
Hi Graham If we are talking about the Graupner Brushless Speed 500 ECO no 7295 https://www.graupner.de/Brushless-Speed-500-ECO/7295/ then yes the Kv is 500 which equates to 7500 at 14.8v. It's 50mm x 80mm with a 6mm shaft so really a heavy duty motor and in a Aeronaut Queen 36" still much too big and powerful. You really need to resolve the drive train and shaft problems and this will be easier if you choose a motor of smaller diameter and power. A 36xx or very similar size motor at about 1000Kv or less (500Kv with 14.7v) will be ample. The prop should be less diameter than the motor. There are many examples of 36" model boats on this site and I do believe the majority of our members have used similar set ups, to those we have suggested, in their models with a large degree of success. It could be we are talking about a different motor as you refer to " the small outrunner motor". If so please post a link to a pic of the motor.
Hi all, what do we all think of the Graupner 500 ECO? it only does 7500 rpm but high torque, about 1500 watts, 14.8 volts. The say it is especially built for boats. I would like to know your thoughts on the small outrunner motor? Regards Graham
Graham - don't tell me you ran the boat at anything like full throttle. If so, it wouldn't just be the prop shaft that you'd have to worry about! If you did it must have been virtually uncontrollable! I take it you bought the boat with the motor already in it? Whatever, it couldn't really have been a worse choice! With such a high kv and being an inrunner (if I've got the right motor) it's really meant for a lighter, race type boat running on 2S to keep the revs down to a reasonable level. As you now know, for your type of boat you need a kv around 1000 or even a bit less as torque is what you need and also go for an outrunner. 3S or 4S is fine and if it is too fast limit the amount of throttle. Without seeing photos it's impossible to say if your existing prop shaft is up to the job but as you've removed it anyway and if you don't mind the expense I'd change it for one of the Raboesch maintenance free ones. I'm using these for my builds and my Fairey Swordsman at 33 inches is a similar size and weight. These are rated for 10k. and 15k. rpm, I've gone for the latter and in 5mm shaft size to be on the safe side. I doubt that a shorter prop shaft will be feasible as usually the motor is already pretty low in the boat and a shorter shaft will increase the angle and you don't want it too steep. Also you would have to redrill the hole for the different angle. What dia. is the existing prop shaft? The other thing you need to consider is the prop. What are you running at the moment? A photo of the boat would be good. Chris
Hi peter, do you want a brass 3 blade prop for cosmetic reasons, if so they do look nice. I did extensive testing with my 3 foot fireboat using brushed, then brushless motors, and then prop testing. I was using eagle tree data logging for watts, amps, gps speed etc. The plastic two blade cheap as chips props actually produce similar readings to the more expensive brass 3 blades. Personally, as you are at the "guess work" stage, just use the plastic two blade ones, but use "x" pitch, standard wont give you the speed. Get a few sizes, 30, 35 40 mm and test. When you have the optimum set up you can then go to the expense of the brass prop. I sent Simon Higgins (ex prop shop) my readings and he made a specific prop for my boat, its a 35mm cleaver 3 blade. He has his own company now but I've forgotten what it is! He was at Blackpool last year so someone might have the list of traders. His props are balanced and one piece, very nice. I also experimented with a belt driven gearbox. The set up I have at the minute is this motor https://hobbyking.com/en_us/turnigy-t600-brushless- style='background-color:yellow;'>outrunner-for-600-heli-880kv.html overkill really! but my 3 footer is an original very heavy aerokits boat.
Looking at the specs ROXXY BL Outrunner 4240/10, 980rpm / Volt, 130g For electric sailers up to 4500g Scale and sport models up to approx. 2900g. If you have the 34" Fire Boat then this is too big. Mark suggested above a 3542/1000 and I agree. The smaller model is very light with a small transom and I found it has tendency to lean under the tork effect of the prop. Turning had to be slow and gentle to avoid capsize. This is not such a problem on the 48" version. Props should be no greater in diameter than the motor and should be chosen to keep well within the motor and ESC ratings. A wattmeter will help you check this and a good rule of thumb is to run at about half max current for best results.
I' doing somehthing very similar, rebuilding one from the 60s, when I get time to finish it. I picked up a Brushless outrunner, Robbe/Roxxy Outrunner 4240/10 - is this about right? - Will it be OK with a 4S/5000mAh lipo? - What prop would you suggest to start with?
No, that's less powerful than in Pilot's opening post and like his suggestion is an inrunner motor. The consensus is that a 50 mm diameter outrunner ( the first part of the model No.) is what is required for a big boat like the Huntsman. The second part of the No. is the length of the motor. That size plus a kv figure of around 700 to 1000 will provide plenty of torque to get it moving and high enough revs to get it on the plane. Once you start getting a kv figure well over 1000 you start to get into higher revs which is useful for smaller batteries (e.g. 1000kv x 7.4v = 7400 rpm) which as said is good for fairly small, light, sports and race type boats. Conversely if you have quite a big displacement boat then you want quite a big motor but with a low kv figure as you don't generally want to tear along but want torque! Chris
The 46" Huntsman is a big old beast and I'd be looking at something different. You want good speed but not manic. The one you mention is an inrunner brushless which doesn't have as much torque size for size as an outrunner. If it was me (and it will be at some stage as I have a 46" Huntsman with an MFA 850 brushed motor in it) I'd be looking for a 50 diameter outrunner around 700kv which will give plenty of torque. There is a Turnigy just under that which might do. I'm building a 33" Swordsman and am fitting an Overlander Tornado Thumper V3 4250/06 800kv outrunner. It is probably a little oversize but my thinking is that the motor will have an easy time, run cooler and the battery (4S) will last longer. If it is too fast I'll limit the throttle. Better to be too big than too small in my book. Overlander do a 5045/10 720kw which should be good on 4S which could always be increased to 6S if necessary. See what others say though. Chris
Hi Pilot, first of all welcome to the forum. Do you have any modeling experience?? Which kit or plan are you using??? I would recommend an outrunner look for one with about 700 - 800 watt output, 3s or 4s rated with an ESC rated at least 100 - 150 amps, as a start with a 40 - 45mm brass prop. Kit or plan, reduce the angle of the propshaft to about 15 - 20 degrees electric motors can lie lower in the hull which was designed for I/C motors with their flywheel hanging below the motor, needing extra clearance. Suppliers. Have a look at the hobbyking site, for motor and esc, once you have the basic build underway, decide on the batteries you are going to use. Hope this helps as a starter, look round the web sites get more info and we can direct you further as to your requirements Regards Mark
Hi, thanks for the info👍 I'm new to BLs, but learning fast, and your experience confirms my growing suspicions that outrunners not only deliver more torque than inrunners (size for size) but that they are also more reliable and seldom need water cooling. Your new motor seems to be a larger diameter 58mm?, as opposed to 31mm for the old one, so I begin to wonder if the old ones were simply overloaded by a big prop causing them to draw more and more current and hence cook! 😡😭 Check out this test drive (Italian)of your new type motor!! https://www.youtube.com/watch?v=4_dlcLbFehw cheers Doug 😎 PS Caption says that with more than 3/4 throttle the boat becomes unstable! Then it flips 🤔
Hi Neil, yes, very similar. Could be regarded to as a first step before applying Eze-Kote to give it a harder, knock and almost everything else resistant surface. Hammerite then sticks to it like the proverbial to the blanket and you have a super clean 'engine compartment' dead easy to keep clean. 😊 80 quid for a brushless !!! Do you want it gold plated or what? My Propdrive 2830 cost less than 20 knicker from Hobbyking and was delivered almost before I ordered it! Just make sure it comes from the UK or EU (still!?🤔) warehouse and not USA or Global. otherwise you might get stuck for import tax 😡 For the motor mount / shaft alignment: no one said it was easy, but Nothing's Impossible', maybe that's why I drive Toyota!!😁 back end is determined by the diameter of the prop you want to fit, which in the case of brushless motor should be roughly the same diameter as the brushless (outrunner). In my case 28mm motor and 30mm prop. This defines how far you can lift the aft end of the shaft, leave at least 1cm between the prop tip and the hull! This reduces unwanted interaction between the vortex from the prop and the lamina flow along the hull, result; more forward thrust and better rudder effect. (Didn't spend 30 odd years talking to shipyards for nowt😉) If you have plan (or at least a sketch - take some measurements if you don't have one of these and make a sketch) of the keel and existing motor mount; project back from the newly determined exit point of the shaft. Check how far forward you need to go to be able to comfortably fit the motor mount with good alignment and purchase a shaft of appropriate length. Cut a wood block to fit around the keel as the basic mount and 'fiddle' with it until your motor and mounting (e.g. the Robbe / Romarin 400 mount) aligns with the shaft line. Alignment is checked by running the motor at a fixed low speed with an ammeter showing the current it draws. Shim the motor mount up / down, and shift slowly from side to side until the current reading is a minimum. Then glue and screw everything in place quick before anything moves! Takes almost longer to describe than to do😉 The coupling type shown in my photo is called a 'Steg' coupling here in Germany (don't know the English🤔) and available from Krick Modellbau, for various motor shaft / prop shaft diameters, here the link to their English page- http://www.krickshop.de/?shop=krick_e Part number for the 3.17mm (1/8") to 4.0mm version I used is 63902. part number for the motor mount I used for my 28mm brushless is 42117. Advantages (to me at least!) they are not as long as the traditional UJ and Cardan types, they are resilient but don't flop about like the UJ types so are much easier to fit and align. Cos they are shorter you can use 'em for mountings in confined spaces. And they don't make no noise!! 😉 One final tip (may not be so useful on hard plywood built boats!). When I had this problem with my destroyer I sharpened the end of an 8mm alu tube (same as the shaft tube dia) and used it to bore back from the hull exit to the last bulkhead before the motor mounts. the bulkheads though were 1/4" balsa! Nice and soft man 😉 Hope this helps more than confuses, but it all worked for me! Cheers and happy fiddling, Doug 😎