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>> Home > Tags > vibration

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Exciters/transducers by pmdevlin Fleet Admiral!   Posted: 10 days ago
Im not on here that much, so a little late picking this up. Are you talking about TT25 transducers like the ones Mrrcsound sell/ I suppose they all work the same, I've used these a lot, in planes mostly, and experimented with boats, so can offer some hands on advice. Firstly, you don't cut any holes to let sound out, as this isn't how they work. Its all about the vibrations. The centre ring is epoxied (that's the best way, they have to be permanent, but with some teasing they can be removed it required, rather than cyno) to the surface, which obviously needs to be flat. The thinner the material, the more sound, but its marginal, as the thinner you go, the less bass, or deeper tones. With planes, the best material by far is the epo foam, so when mounting into a ply or balsa plane they work best going to foam, then the ply, and the same will apply for a boat. 2-3mm is generally the optimum thickness. Remember, the area is going to vibrate, so use an area that can do this, the sides of a hull are ideal. The back of the transducers get hot, so don't cover the back, the heat has to dissipate and once secure, make sure the unit can move in and out, its easy to drip glue in the wrong place and the whole thing gets stuck, it wont vibrate now, so won't do the job. Also, its worth epoxying the transducer to 2mm foam, epo that the ready to fly planes works best, its close density, the stuff that packs white goods is poor as its a more open density and falls apart. Once you have this, you can move it around by just holding it against the hull to see where the best sound is. All this is relevant to the Mrrcsound transducers, I use a number of his sound units, so cant really comment on what you are using as I cant find that info on this thread (did a man read!) Here are a couple of my models to give you an idea👍 so these are all Mrrcsound units, and both have two tt25 transducers either side ogf the hull and fuselage. With the Mrrcsound systems, you can use two tt25, if you want an additional two, then an aux amp is required hope that helps! Paul

54" long Cervia tug. by tysonyoung Petty Officer   Posted: 18 days ago
My Cervia was ready built. I have replaced the Electric motor with a large servo motor (Brushed) .Direct drive and being heavy helps with ballasting. lead acid gel cells are power source. Motor rated voltage24 v but run it on 12v . low rev high torque no load current 1 amp. Shaft diameter 0.5 in. Gives some idea of power out. Being servo motor (ex computer drive 30 years old) well balanced no vibration. Photo near shore shows power of motor.

BRAVE BORDERER by RHBaker Fleet Admiral!   Posted: 1 month ago
Blog 4 update – Adjustable transom flap using metallic tape did not work. Think the vibration caused flexing and fatigue, so it finally split. Fortunately had established the correct angle, so reproduced the flap arrangement with a fixed thin alloy plate. Much more robust. Have installed the new brushless motors and ESCs. The current layout is brushless motors on the outer propellers and brushed on the centre, all powered by a single 3S Li-Po battery and Rx. Am hoping to commence water trails this week, but have found an issue which was also present with the original brushless motors. When either brushless motor is powered up it operates nicely, however, as soon as the second motor is started either motor “stutters” and a pronounced “squeal” can be heard. The brushed motor is unaffected. Have now tried several ESCs but to no avail, the issue remains. It can be cured though by powering each brushless motor with it's own battery. When this is done everything powers up cleanly and quietly. The obvious solution is to use two Li-Po batteries and abandon the single battery approach. Am reluctant to do this as the model weight will increase yet again. Has anybody experienced this when using twin brushless motors and, if so, how was it resolved?

Exciters/transducers by onetenor Fleet Admiral!   Posted: 2 months ago
I would have thought you need the thinnest part of the hull for best vibration?👍

Hull Pt2: Motorisation - Come What May!! by RNinMunich Fleet Admiral!   Posted: 2 months ago
Hi again Mike, forgot to mention the false floor bit! Sorry, no pics - shipyard design secret! 😁 No, haven't got that far yet. Still have to make the gear end plates so I can get the shaft spacing / gear meshing right, i.e. height of the motor above the prop shaft. Plan is to fix an ally plate into the hull with captive 4mm domed nyloc nuts fixed in it. The Taycol has right angled brass mounting brackets for vertical fixing so I shall mount it using 4mm bolts with compression springs between the brackets and the ally plate. The nyloc nuts SHOULD hold things in position! That way I should be able to adjust the motor height and tilt in any direction (well, pitch and roll anyway!) to get the two shafts parallel in the vertical plane and optimum meshing of the gears and minimum vibration. That's the theory anyway 😉 Then I only have to worry about getting the shafts aligned in the horizontal plane, the 'Yaw'. Which should be relatively easy with careful fitting of the ally plate. Minor yaw adjustment could be accommodated by opening out the bracket holes to curved slots with a diamond file. Objective is max power transfer with minimum noise and friction. Not to mention easier mounting than fiddling about with shims! And I don't have to worry about not getting the angle of the ally plate in the hull dead right 😊 Accurate measurements inside this sloppily built hull are virtually impossible! There are no right angles or straight lines or even symmetry where you would normally expect them 😲 So no true reference points or datum lines. We'll see. Cheers, Doug 😎 Ooops! Somehow my response to the motor conversion 'secrets' slipped into the previous Update!? See below in 'A Messy Business'.

Hull Pt2: Motorisation - Come What May!! by RNinMunich Fleet Admiral!   Posted: 2 months ago
As promised (or threatened?😁) stage two of the hull work and thoughts on motorisation. The hull was sprayed with two coats of grey primer/filler. Pic1. As usual this showed up the remaining imperfections (pics 2 & 3), but I'm not going to worry about them until I've got prop shaft tube and rudder stock sorted out and permanently fitted 😉 After my attempts to make and thread a 3mm prop shaft went awry Martin (Westway the Mechanicals Master👍) stepped in and made me a decent one complete with a bushed stuffing tube 👍 Vielen Dank Meister😊 I did however manage to make a 4mm to 3mm reducer so that I could fit a Rabeosch 35mm prop as seen in pics 2 & 3. The tube and shaft from Martin, arrived Saturday an' he only made it on Monday😊, have been dry fitted so that I can start setting up the gears, necessary to bring the drive down to the prop shaft fitted very low down in the hull, and motor mount. Pic 4. Motorisation: (Remember folks - this kit was designed and built as a static model!) I want to use the old 1950s Taycol Target motor which my Dad originally fitted in the Sea Scout which I have renovated and upgraded to brushless. See Build blog 'Sea Scout - Jessica' Many of you will know that the Taycol motors were field coil motors, meaning that they have no permanent magnet around the rotor coil, and thus reversing the battery connections to the brushes had no effect on the direction of rotation, as this simply reversed the magnetic fields of both stator and rotor coils🤔 To counteract this so that the motor could be used in both forward and reverse with a conventional brushed ESC I modified the motor slightly (separated the two coils) and built a simple converter board to connect it to the ESC. Again see the Sea Scout blog for the details of the conversion. Basically; once the field coil and brush-gear (rotor coil) have been separated a simple diode bridge can be used to apply the output of the ESC to the motor. This enables the reversal of EITHER field OR rotor coil polarity, depending on how you connect the converter to the motor. Thus reversing the direction of rotation of the motor. Beneficial side effect is that the diodes also suppress the commutator sparking😊 In my case, with the Taycol Target, I also cleaned, flattened and polished the commutator. Thus significantly reducing the potential for spark generation in the first place! A peculiarity of the Taycol motors is that they all use metal brushes, pressed phosphor bronze strip, so they need oiling! DO NOT oil conventional brushed motors with carbon brushes unless the brushes are exchangeable or you want to have to buy a new motor!!!!! Pics 5 & 6 show the proposed position of the Taycol in Gina 2 and pic 7 the prototype converter board I knocked up to test the motor, together with a Graupner Navy V30R Marine Brushed ESC. Details and results in the Sea Scout blog, including video of the sparks and oscilloscope pics of the drive waveforms before and after conversion! The latter showing the spark suppression effect of the converter😊 Some samples attached - last 3 pics. Pic 8 pic shows a more compact version of the converter, one of a few types I'm doing for Martin's various Taycols as a trade for the prop shaft he made for me and some useful material he sent. Thanks mate👍 Next steps will be 1) mounting the gears correctly on the shafts, requiring the manufacture of a 3/32" to 4mm adaptor and a 1/8" to 4mm adaptor, and keying them to the shafts - Hooray for mini milling machines 😉 2) manufacturing bushed end plates to hold the gears in place, 3) fitting the motor mounting platform. I'll probably borrow from my experiences of real shipbuilding and do this as a suspended 'false floor', i.e. mounted on stiff springs to enable adjustments to optimise the gearing mesh! On real naval ships this is done to improve shock resistance and to minimise engine noise / vibration conduction to the hull, thus significantly reducing the acoustic signature of the ship. Not that I'm tooo worried about being torpedoed 😁 Worth a try😉 Pic 9 shows the cleaned up and renovated Taycol Target motor. Pic 10 shows the drive waveform complete with sparks before modification.🤔 Pic 11 the cleaned 'forward' waveform with the converter board. Pic 12 the cleaned 'reverse' waveform, no suppression capacitors needed 😉 More soon folks, Cheers, Doug 😎 PS Along the way a new keel was fitted as can be seen in pics 1 to 3. The original builder had 'buried' the keel in the hull planking! 😲

Sea Queen prop shaft by RNinMunich Fleet Admiral!   Posted: 5 months ago
Heartily agree Rex 👍 Two such couplings in series is a guarantee for misalignment and high vibration potential 🤔 which wouldn't do the 'posh' bearings much good! 😡 I would move the motor. Bon chance, Doug 😎

Sea Queen prop shaft by Rex3644 Lieutenant   Posted: 5 months ago
What is the KV of your motor and how many volts do you intend to use? The theory is that this is how it should be done and in practice I Have done this setup with Huco type couplings which turned over very smoothly but they could not handle the high revs ie14.000 The Radio Active couplings are first class but again I have experienced some balance issues and vibration with them. I worry slightly that the length of 2 couplings together is somewhat long but I may be totally wrong. All you can do is to try it I shall follow with interest

Too Powerful Brushless ? by BOATSHED Fleet Admiral!   Posted: 7 months ago
That sound better with a 5 mm shaft. But still be sure to support the shaft under the boat and if possible also under the shaft inside the boat. This way you shouldn't have any trouble with vibration though the shaft to loosen it.

Too Powerful Brushless ? by Dave M Fleet Admiral!   Posted: 8 months ago
Hi Graham Now we can see the actual prop shaft and motor it is clear that the shaft is not supported inside the hull close to the coupling. At the high revs your motor achieves I am not surprised you have had problems. I do agree with all the comments and help you have been offered and agree a 5mm shaft would help as well as a different motor. I use 3 blade brass props with brushless and have no problems but do keep the prop size to a diameter no greater than the motor diameter, as Mark advises. It's difficult to see how much space is in the hull to allow the motor coupling and shaft to be closer, but if you are replacing the shaft it may be a good time to reposition the motor and the shaft with the prop attached to a slightly different angle. This will mean opening the slot and perhaps enlarging the outside skeg but you can easily repair any damage with plastic padding to make good. Even if you keep the existing arrangement I suggest you provide support for the prop shaft close to the bearing as I suspect this is where you have experienced the problem with the vibration. A simple 2" block of wood attached to the keel and shaft would suffice. Model looks very good and I look forward to seeing some on water shots.

Too Powerful Brushless ? by jarvo Fleet Admiral!   Posted: 8 months ago
HI Graham. Every picture tells a story!!! The motor is definitely wrong, its designed for racing, low torque, mega revs, not for scale boats. What diameter is the shaft tube??? looks thin??? did the prop shear in the water?? would explain the vibration and damage to the shaft mountings, try a Raboesch shaft, with a ballrace at the motor end, great quality, also they do a huge range of props, google the name there site will come up. Mark

Too Powerful Brushless ? by onetenor Fleet Admiral!   Posted: 8 months ago
By the way the Araldite is very good glue but is brittle and as you have found cracks off with vibration. The other glues mentioned all have flexibility so will absorb any vibration.

Too Powerful Brushless ? by rmwall107 Lieutenant   Posted: 8 months ago
Hi traiderman I am no expert. dont forget, as pmdent highlights, you you multiply the KV by the volts of the supply to get the RPM of the prop. so you can play with the volts supplied or the Kv of the motor or both. regarding the vibration, have you supported the outer end of the shaft? if the shaft leaves the hull and has a good amount of unsupported shaft the end of the shaft effectively will scribe a circle. At the speed the shaft is turning and with the pressure on the prop this may cause your vibration. Richard

Too Powerful Brushless ? by pmdent Chief Petty Officer   Posted: 8 months ago
Traderman - whilst I am not an expert ( I am currently trying to decide what brushless combo to fit to a 34" RAF Crash tender) - clearly your motor is turing your prop shaft way to fast. With your motor spec of 3180 kV and a 14.7 V Lipo - your motor will be trying to turn your shaft at a speed of somewhere in the order of 45,000 RPM !! Firstly your prop shaft may not be rated for anything like this speed and secondly any slight mis alignment will likely be generating significant vibration - enough to cause your problem- have you noticed any? As to motor power - the motor may not be too powerful - but certainly dropping to a lower kV motor say 1100 and reducing the Lipo voltage to a 11 or even 7 volt system might be the right answer......but as I am finding its all a bit suck it and see... Peter

RE ads90's Vosper Firefloat by ads90 Commander   Posted: 8 months ago
Many thanks Dave and all. The reason I think it was a kit is because of the superstructure and deck detailing which you cannot see on my photos. All of the window frames have raised rivets around them and the deck has deck raised deck strips. As a modeller I know that these can be recreated but they look too perfectly spaced, etc. Many thanks for looking through your back catalogues Dave. Terry was very helpful and sent me quite a bit of information - he is a font of knowledge. My boat is well used at our pond at Eastrop, Basingstoke where I am the Secretary and Treasurer of the model boat club. Every couple of years I do have to give the hull a rub down and re-spray as being made from balsa and when running fast, the vibration does tend to crack the hull along the panel joint lines, but it is an easy fix and I try not to abuse it as it is precious to me.