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>> Home > Tags > propeller

H.M.S BRAVE BORDERER by RHBaker Fleet Admiral!   Posted: 13 hours ago
Looks like everything is set for the first open water test. Sun is shining, ice has gone and water smooth. Intention is to start the open water test program with a repeat of the pool test, except this time with everything wired correctly; the load cell positioned so the “pull” is more horizontal and ballast available to hold the propellers underwater if necessary. Hope these improvements help reading stability. To modify the “pull” arrangements, wrapped a light cord around the propeller shaft struts and fed the loose end above the transom shelf and out over the stern. The load cell was hooked into this and then tied to a fixed grating on the pond side. Started by measuring the electrical requirements for each of the three motors and the propeller bollard pull, using the 2 S battery. Found the bollard pull was up slightly at almost 3 lbs per propeller. Probably because they were now held at a greater depth in the water. Also blew several 20A fuses, so fitted 30, which seem to work. A series of runs showed adequate performance with plenty of spray, although the bow did not lift much onto the plane. The forefoot did raise almost above the water surface. Then tried a 3S battery. Although this was much heavier, the performance improved dramatically. The bollard pull was up to almost 18 lbs per shaft. The bow still did not lift much to a plane, although the forefoot was almost clear of the water at full speed. The battery was located just back from the bow, so it is suspected that it held the bow down. The impact of the transom flap down angle could also hold the bow down, but have decided to leave as is for the time being and avoid the temptation of making too many adjustment at once. Whilst it is still too early to draw definite conclusions, it seems as if a 3S battery will be required. The model sustained some slight damage due to the test arrangements, so will repair that and also fit the 2 bladed Hi Speed propellers. Will then repeat the program and report. Should be able to draw some definite conclusions then on the best power train. Neither of the batteries used, neither the 2 S nor the 3S are ones I would choose for this model. As a result the capacities and weights are not ideal. That must also be remembered in future deliberations.

H.M.S. BRAVE BORDERER by RHBaker Fleet Admiral!   Posted: 23 days ago
From the brief pool test, had decided that the motors could be susceptible to overheating, so connected up the water jacket cooling system and powered it with a small pump. Did not leave enough space to fit a scoop behind a propeller anyway, but prefer the positive action of a pump though. From feeling the ESCs, was also concerned they could overheat within a confined space such as the hull. Mounted a couple of small fans in a bridge structure above the ESCs, along with the ESC switches. Not sure either of these cooling modifications are really required, but erred on the side of caution. Final weight of the hull, with all electrics (apart from battery) comes to 5.05 lbs. Looks like will not achieve the target weight of 6 lbs, but am hopeful will be able to get close to it.. Built the deck up with gun mount bases and a removable decking over the engine area. This limits access to the internals; so will not fit it permanently until the test program is complete and all modifications incorporated. Have now reached a point where any further work will be to start finishing the model, unless drivetrain modifications are required. Have thus decided to leave it until after the first open water test date. This will be in late May as am away until then.

Rudders and propeller by Donnieboy Fleet Admiral!   Posted: 24 days ago
Wonderful craftmanship.I had a schnellboot just a little bit larger.I used 3 speed 400's.Had no problem with them.The boat moved at a scale speed.That's one option to try.

Rudders and propeller by teejay Lieutenant   Posted: 24 days ago
Hi all for the second blog report on the schenllboot I am going to go over the rudder an propeller shaft assembly in more detail. The first stage was to make the rudders which were made of brass ,and having taken note of what has been said about the increase in size needed for the kit by other members I have increased the size of the rudders by 50% so that they have more effect and hopefully the boat will be more agile .I fitted 3mm treaded rod on to the rudder and in a 4mm flanged tube to reinforce the brass rod. The second stage was to make and fit 5mm flanged tube in the location for the rudders in the boat , these were made to be above the water line and will be sealed in place to reduce the possibility of leaks. These were fitted to a rudder platform inside the boat which was fitted to the kit moulding for the rubbing strip that runs the length on the boat and secured by making resin blocks which were fitted with computer extension nuts .which were then superglue in place to secure the rudder platform. The rudders were then fitted in place and held in position with the tiller collars which were made from 8mm rod and fitted the tiller arms and locked in place with 3mm computer screws and ni-lock nuts, a connecting plate was then fitted to connect the three tillers together, I also fitted rubberised washers to seal the rudder tubes. The third stage was to make the propeller supports. The centre support was a direct copy of the kit part made of brass and fitted to the kit with a plate and screws (this plate and the rudder plate were made from galvanised steel)and will sealed with resin after the I test the boat for leaks. The port and starboard supports were made by taking the kit parts and cutting them in have along the joint line or mould seam this gave me a template ,which I used to make cross-section segments but I did alter the template by increasing the boss diameter to 10mm and extending the support legs so that the finished support could be fitted through the hull (the picture of these show the mk1 version where I forgot to allow for the 4mm prop shaft which has a 6mm tube) any way the boss of these segments were drilled out with a 7mm drill and a length of 7mm brass tube fitted through the boss to assemble the segments, all of which were coated in soldering flux at this stage of the assembly which were riveted at both ends to hold it all together during soldering, after soldering the supports were then filed to the size and shape to resemble the kit parts as close as possible and fitted to the hull using a superglue and talcum power mix and then I cast resin around the extensions to secure the prop supports in place. The forth stage is the propeller shaft housing for the centre propeller housing I place a brass rod in a plastic straw and place in position in hull and using resin I sealed the hull with the rod in place this gave me a pilot hole for the centre prop shaft after I removed the brass rod. For the port and starboard shafts I used the kit parts which had hole place when assembled, this when I reinforced the housings ,the centre housing I glue 2mm of plasticard on each side and for the port and starboard I made a brass tube shroud which covered the housings which left gaps between the kit part and the brass which was filled by casting resin in the gap this increased the diameter to 10 mm so that there were little chance of breaking throw with the drill and finished these off by fill-in the outside with body filler and sanded to shape and finish . I then drilled through the pilot hole in the housings using very long extended drills and a wheel brace ( if I had use a power drill the heat would have melted the plastic of the kit and may have caused problems) I drill the shaft housings out 6mm them filed them out with 6mm file so that I could insert a length of 6mm brass tube. After all this was done I fitted a flanged bush made from 7mm tube and 2mm brass plate turned to 11mm to the ends or the propeller shaft housings. And now it is time I have to ask for some help could any one advise me on the length of propeller shafts , I know I can use a 300mm shaft for the centre shaft but port and starboard will have to be longer . and I also need advice on selecting the motors , I want to use 4mm prop shaft with 35mm propellers. Any opinions welcome.

PROPELLERS by RHBaker Fleet Admiral!   Posted: 25 days ago
Thanks Doug. Always thought, my old mathematics text books would come in useful! Was hoping for was a simple chart of speed vs thrust, recognizing there are many factors that influence them. Even a max speed and efficiency rating would help. R

PROPELLERS by RNinMunich Fleet Admiral!   Posted: 25 days ago
Evenin' Rowen, not surprised they don't publish charts, it ain't so easy! Here's the theory and maths! 😲 happy integrating! Maybe when you're done you can sell them the charts😉 Cheers Doug 😎

PROPELLERS by RHBaker Fleet Admiral!   Posted: 25 days ago
Does anybody have any performance charts or operating information for Raboesch propellers? Am looking for the rpm vs thrust relationship for the under 45m/m 3 blade sizes particularly, but anything would help. My traditional supplier cannot help and neither does the web site. Am trying to plan a future models and would like to be rather more scientific than the "if it fits it will work" approach or just using the motor O.D. as a guide to the propeller diameter.

H.M.S. BRAVE BORDERER by RHBaker Fleet Admiral!   Posted: 25 days ago
An unexpected opportunity arose to try the unfinished hull in a small pool. Whilst the performance envelope could not be explored, was able to try and measure operating parameters and get a “feel” for the model. Used an electronic scale and a combination voltmeter/ammeter/wattmeter to measure propeller thrust /bollard pull and motor power requirements. If it is necessary to fit different drivetrain components, or a 3S cell this will serve as the baseline. The model floated levelly and well above the waterline. At about 8 volts the motors drew around 20 amps each at full speed; so only about 35% of the potential output capacity was being used. Tested each motor individually and measured the bollard pull at just over 2 lbs. A considerable amount of spray and wash was created making stable readings difficult. For further testing, will add ballast at the stern to hold the propellers further underwater. Should help reading stability. Currently using 20 A fuses; which as one failed seem marginal. For sustained use think 25 or 30 Amp better. With these high-speed, low torque motors establishing the “dry” propeller rotation is deceptive. Found one motor to be reversed! Nevertheless, the model accelerates quickly and is sensitive to engine speed movements. Left the pool with a list of modifications to make before assessing the installation properly on an adequate body of water. Some conclusions can be made though. If it is necessary to add a second cell this needs to be located around midships, not in the bow or stern. Still hoping a 3S cell will not be necessary and that 2S may be adequate. The suggestion to do testing using the bare hull with a minimum of detail was a good one. For a models with a sophisticated power train think this is a good approach. Nothing worse that finishing a boat just to find the performance disappointing, then have to to rip it apart to make major modifications or adjustments!

H.M.S. BRAVE BORDERER by reilly4 Captain   Posted: 1 month ago
Hi Rowen, I have had water cooling on all my patrol boats running at 12Volts, whether brushed or now brushless. For the brushed motors I have used aluminium tube coils with water pickups between the propellers and rudders. I did try water jackets a couple of times but found too much friction loss and therefore lack of flow. For the newer brushless outrunners I use a brass tube soldered to a brass plate across the front of the motor fitted between it and motor mounting bracket. I agree with Doug with regards to the disconnection of the red wires on the ESC's. This is now common practice, especially if you have an external receiver battery.

H.M.S. BRAVE BORDERER by RHBaker Fleet Admiral!   Posted: 1 month ago
Once the rudder, propeller and shafts were installed, the position of the motors could be established. A light aluminium bracket to hold all three was fabricated and bonded to the hull. Due to the high speed capability of the brushless motors, particular attention was paid to alignment. Also kept to the shortest prop. shafts that could be fitted to avoid whipping. Although the motor type might change, whatever is best will require a sound electrical installation as the current requirements for each brushless motor could reach 50 Amps. Wired each motor and ESC separately with its own dedicated fuse to give the maximum system protection. There is an extra fuse section allocated for auxiliary circuits, such as a cooling water pump and lights. Will try the original planned layout of 3 x 2835 motors with 30mm propellers and a 2S Li-Po battery first. Am hoping the reduced voltage will also make these motors more tractable. For the test program the three ESCs will be each controlled from an individual Rx channel. Once the final layout is determined, a more sophisticated and flexible control system can be installed. To minimize ballast, particularly around the stern, the battery will be housed as far into the bow as possible. After the test runs the final battery type, size and location can be established. To assess performance, hope to try both 2 and 3S Li-Po batteries. Planning to reduce heat build up by fitting cooling water jackets to the motors, these are easiest to instal at this stage so the wiring or mounts are not disturbed in the future. Have not decided the layout for the water circuit yet, but this easily can be added later. All that is needed now is the ice to melt off our local lakes so tests can commence.

Choose a brushless motor by CB90 Commander   Posted: 1 month ago
1. Added strakes to bow used a rectangle section of styrene as more flexible. 2. Brought a motor mount (cooled) but may also add a jacket. 3. Painted cabin will need to redo as paint cover was poor. 4. Looking to find the best brushless motor for the job, remembering these boat race on 7.4v 3300mah batteries fo 5-6 mins. That gives a ruff consumption of 33 Amps which means the motor need to be able to handle about 250Watts. I have pick out 4 to test 1. 2850 2650 kv, 800W, max 19v, max 52A. 2. 2860 4050 kv, 1300W,max 12v, max 108A. 3. 3650 3930 kv, 800W, max 13v, max 60A. 4. 2845 3100 kv, 800W, max 17v, max 47A. On paper it should be between 1. and 3., 3 being the most suited ???. So on paper motor 3. running 7.4v will give 450 watts max at (60A max current at 13v) so 7.4v should have a max a round 30A (unless stalled). giving 222W 244.2 watts target at 7.4v = 33A max for 6 mins on a 3.3ah battery if battery function is good. 33A drain will depend on the propeller size 32mm- 45mm ! A safety margin may be 30A when moving and 33A in bath. 7.4v x 3930kv = 29,082 rpm perfect for hydro, not for sub drive.

H.M.S. BRAVE BORDERER by RHBaker Fleet Admiral!   Posted: 1 month ago
Just to clarify. Shipping was only 7 days to Canada, manufacture slightly longer. Examined the hull closely and was pleased. It is dimensionally accurate and robust, but light. It had also been reinforced in strategic areas and trimmed to the correct deck line. My many questions to Christian Sheppard – Capurro of MTBHulls were quickly and knowledgeably answered. A company I would recommend others. Reviewing the build blogs and U Tube videos of the both the Brave and Perkasa models, shows most use either single or twin screws. The original vessel had a triple screw contra - rotating layout. Experience from others suggests the third screw just adds weight and complexity, but little to the performance. Nevertheless, it was how the Braves were built, so that was how it would be. Christian gave several suggestions for other modelers who have built this vessel. Contacted them and was readily provided with information and advice. The finished weight of this model is important and a target of around 6 lbs recommended for a 1:32 scale version. This is to achieve the potential performance. Plans for drivetrain are 3 x 2835 4500kVa brushless motors, direct driving 3 x scale 3 blade 30mm screws. Decided use a single Li-Po battery for the best performance with minimum weight. It was suggested three batteries, each powering a single motor would be the best layout. After some research, concluded this would introduce a weight penalty and was discounted. There are various ideas for the best drivetrain. Unfortunately none for triple screws. Decided the best approach would be to fit the bare hull out as planned, then try it. Leaving all the finishing features for later. A contact in Australia had already done this using a single screw layout and kindly sent pictures of his hull layout and then under test. Very informative. The positions of the rudders, propellers and shafts are established by the scale dimensions and were permanently installed. Everything else was to be temporarily fitted, so it could be moved or replaced if necessary.

Propeller for brushless by canabus Fleet Admiral!   Posted: 2 months ago
Hi CB90 I totally agree with you on that, they like to rev !!! Canabus

Propeller for brushless by CB90 Commander   Posted: 2 months ago
Thanks Cannabis, for the information I have noticed that brushless motors seem to run better on smaller propellers. than brushed direct drive.

Propeller for brushless by canabus Fleet Admiral!   Posted: 2 months ago
Hi A 2 blade 32mm x 1.4 pitch would be closer to the mark. That's what my Hobbyking outboard has with a 3000kv motor, but, it's now running on 3S 2650mah. Canabus