Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length.

[Backerther]

Thank you for your highly technical explanation and addition to what I posted, DereK !!
You are a specialist in this field too, aren't you ?   with stunningly awesome knowledge..


Kiyo

[derekwarner]

No, not a specialist Kiyo......just from experience years ago, with a 12v windscreen motor that by placement of the motor in a paddle wheeler hull created a question

During bench test trials, with constant voltage to the motor......resulted in varying audible hum, and recordable variation in output shaft speed  , however when applying reverse polarity [astern paddle shaft rotation] resulted with constant hum, and absolutely rock solid output shaft speed

Preferred direction of motor rotation confirmed with the thrust ball being engaged

Derek

PS...now I am not suggesting you conduct such a test, however I am absolutely confident that if you swapped the 2 motors in your vessel Kiyo, that the motors would confirmed alternate speeds so that the STDB would still confirm 20K shaft speed, with the PORT motor still at 19K shaft speed

So the location of the motor by the need for shaft direction determines the actual shaft speed and such variences etc.....

[Allen A]

Morning gentlemen ... interesting details and very valid of course, and thank you, however if I may refer back to the beginning of this topic and remind you this isa rescue, rebuild, refurbish of an already (and badly ) started second hand build and in that respect to a degree I was stuck with what I got ... had I bought this an an un-started new project I would have approached it differently and in never having built or sojourned into RC boats before, as it is I have done the best I could with what I didn't have to put it a slightly different way.

Having leant a very great deal from re building both of these boats and the wealth of information imparted on the forum as I have, I do want to buy an unopened version of this to build the 'perfect' version of it.

Common sense I think dictates that everything has to be in line and I did my best to achieve that, however when and where fixed couplings are used then it is of course paramount that it is all exact, but when and where universal couplings are not only sold, but made for models, then to a point if there was a slight mis-alignment, as in the case of this boat, then the use of u/j would help alleviate that .... if you look at the picture of the coupling (before I raised it) I would assess it as less than a 5 degree angle, something a u/j more than capable of handling, as such then I feel too it is not actually 'causing' the over heat problem

I have in fact manage to raise it all about 4mm and it is now nearly there, but with respect to these builds, short of cutting a hole in the under side of the top deck area (and possibly weakening it too) there is not a lot I can do, the boat does run and smoothly too, there is no 'rattle' to the motor noise and it does not wallow, I have it in mind to buy a smaller motor in order that I can align it perfectly with the prop shaft but also want to balance that with the power and performance the current motor gives me.

Ian, re the water ingress, I have checked the decking seal and there was a couple of places where the glue had failed somewhat leaving gaps, this has all been resealed, however in going back to the (bad) initial build of this I have noticed the prop shaft area was 'sealed' using fibreglass and I can see minor cracks in it so maybe a problem there too? ... I will look forward to seeing you and Stan next Sunday for a hands on view and further advice.

[Colin Bishop]

I have just got around to reading more of the August 2024 issue of Model Boats magazine and there is an excellent article by Richard Simpson about managing propeller thrust in both full size vessels and our model boats as the principles are the same. It is very useful in understanding the forces involved and where the source of problems might lie. Worth a read as Richard is a marine engineer.

Colin

[Allen A]

Hello again gents .. hope this isn't getting tiresome for some ... As I said above I have taken on board all that has been advised, however I have also had to put it into the context of the build of this boat and try to adapt where I can the advice given ...  a couple of pictures for reference in the hope it will clarify part of the problem ..


I don't think angle as it was had a definitive bearing on the over heating as such and as said it has been raised more inline by about 3 or 4mm, but then this gives rise to the other problem ie; space as can be seen from the other two pics, the steel ruler being across the deck as a whole while the plastic material is across the lower inset area where the upper deck sits .. and perhaps this lack of space is what is contributing to the over heating, which I don't know if it is still happening since cleaning and de-greasing the prop shaft, as I haven't sailed it again yet.

[JimG]

I would think that much of the high temperature of the  motor is due to the fact that it is a racing motor intended for a 7.2V NiCd or NiMh pack. These are intended to be high revving and need a high current which produces a lot of heat. You are running it at a higher voltage so the current will be even higher for the same prop and even more heat produced. It's normal use in a buggy would probably give around 5 to 10 minute runs maximum so running it in aq boat with longer runs will produce yet more heat. I used to use motors like yours in a fast electric on a 2 blade P35 prop, it would give a 5 minute run on a 2500mAh nicad and be hot at the end of the run (batteries as well). It might be a good idea to get hold of a Watt Meter to check the actual current in use, you could then try reducing prop size or pitch to reduce the load on the motor and the current. Alternatively replace the motor with one intended for a more scale model. A higher number of turns will help reduce the current taken by the motor and probably give more running time.

Jim

[Allen A]

Hi Jim, as ever thanks for the input .... yes I have realised that in being new to this I have been at the mercy of the dealers somewhat ..
The boat had an Mtronics Viper Marine 15 when I got it, I burnt that out trying a maiden voyage on a fish pond, clogged the prop with weeds ... I was sold an Aeronaut Race 620 Navy by Model Shop Leeds but I found that slow and it was/is large too still, ..?? 
I then went to ModelSport in Otley and they sold me the motor I have in it now, as you say and as I mentioned before they sold me it seems a fast motor more in line with what they specialise in ... fast cars and trucks and so here we are with your analysis of the overheating problem, hitting the nail on the head I think ?


I have been using it with an 11.1 volt Lipo which wont help from what you say, I do have a 7.4 v Lipo and may try that in the boat to see if it helps with getting hot ... however ultimately as I have said I do want to get a smaller motor so I can bring the bring it all inline more.  I have found a Dynamite Tazer 390 22T motor, which is 8mm shorter and 10mm narrower than the current one and so will help with space, but am wondering if it will have the power and performance I have at present which while causing problems is .. n i c e ..    ... the problem with the Tazer 390 being that it is either marked as discontinued or not in stock ,, anyway I am open  to suggestions on a suitable motor that will give the performance associated with a fast PT Boat before I order a Tazer 390 from the one shop I have found with one in stock.

[Backerther]

First of all, I did not know that you had been using 3S lipo for this motor!!..though I do not know the specifications of the motor.
I have ever burnt  my Mabuchi 540 RS with 3S lipo installed in my Jupiter P-550 and thence I have switched the battery to 2S lipo for 540 class motor up to today. My PT-109 is using 2S lipo.
Apart from the above, here are my setup of the successful example of my PT-109 just for your information.


1;Motors...Mabuchi 540 low cost motors( around less than USD 10?) Yours looks expensive and gorgeous from its appearance.??!!
2;Battery...2S lipo 5000mAh
3;ESC ..nearly the same as yours
4;Props..plastic-made 3 bladed 35mm dia.which is sooo lightweight and cheap against your gorgeous brass prop.   See the pic below.
5;Prop shaft , stern tube...as per the kit original.
6:Couplings ..so called engineering plastics-made which is tough and calm as heard ? in the video posted a few days ago.
7:Alignment between two shafts of motor and prop is nearly perfect.
8;Water-cooling was properly done which I think is so important even if proprely done in every aspect of setting.
   Without this water-cooling, my PT boat will possibly result in the over heat or stop on the water after/during continuous high speed run as in the video and pic4.
Needless to say, a slow moving PTB and/or scale ships does not possibly need such a system at all.!!
9;Grease was filled in the stern tubes fully in the beginning through the filling posts of stern tubes.


Pic1;Props used in my boat.... so low cost like the motor which will do sufficiently for this class of pla-model boat.!!
Pics 2/3...clearance between the motor and deck is narrow as the same as yours.
Pic4;Under high speed silent steering to port !

[Allen A]

I have made the comment that I had realised that its not that simple to just buy/build an RC boat and sail it, there is a degree of skill and control needed and that I am (hopefully) learning slowly, like wise I am realising too that in building a boat it is important to marry the correct motor to it and in turn then marry the correct battery to that motor in order to get a successful build.


I took the boats out today again, reduced the battery to a 7.4 2s on the No 1 boat but the motor still gets quite hot so definitely a more appropriate one needed there and smaller too for air space around it and possibly a cooling coil if the problem persists plus of course the opportunity to bring the motor and prop shaft fully inline from the (very) slight angle it has at present.
It ran well all the same but as I'm hopefully sailing at the weekend at Batley, I may try swapping out the brass prop for a plastic one on a comparison basis to see if that helps, it still ships a little water but It seems to be from where the fibre glass .. (why. ??) .. was used to 'seal' the prop shaft area, so maybe a strip down and rebuild over the winter.?


Having reconfigured the motors layout on the No 2 boat it too sailed well, not as fast as the No 1 but more sedate as I say and sails dry too.


Pics attached from todays runs then, annoyed with myself for not checking the camera as I had it on 'Program' from a previous static shoot and some otherwise excellent motion shots were lost due to slow shutter .. stupid (amateur) mistake on my part ... c'est la vie .. !!

[Allen A]

Hopefully sorted the overheating problem as I have acquired a new motor today, a Core RC CR711 core 21 with built in fan, Ok so its still a 540 and Ive still got the slight angle on the prop shaft but it fits Ok and on a test run this afternoon worked well, only getting slightly warm as against red hot as the other motor did... also swapped out the brass prop for a plastic one as a bench test and it seemed smoother in all honesty, so left it on as it crossed my mind that perhaps the brass prop is a little unbalanced ??


A further couple of pics then from today with new motor and plastic prop, it handled well on the test run, and I felt I had more control, however a question if I may ... I noticed on a previous run that it stopped suddenly, no response to the tx .. then would go for a little bit on command but stop again and after initial panic it occurred to me the battery was getting low ... same thing happened today so wondering if its standard to do that or can it be set to travel at low speed for recovery when a battery gets low ... have to confess I simply placed the ESC in the boat to get power etc, read about 'failsafe' but not exactly sure what it is or how to set it ...  anyone please ... ??

[Backerther]

From my experience....
Sudden stop on the water and repeated soon again....may come from an apparent low battery phenomenon or over-heat
of ESC and/or motors, a kind of heat protection function worked in ESC properly..???as in my experience..


The motor with a built-in fan is much much better than nothing against heat problem.
But water-cooled system is much better than air-cooled system in fully sealed hull where warm/hot air is only circulated and
used to cool and/or sometimes "warm" the motor...???                                                                                          
Difference of its effect between water-cooled and air-cooled systems possibly and typically may take place at continuous fast sailing at longer time run.
One of the most famous WW2 fighters, Supermarine Spitfire, a heroic plane of the Battle of Britain must have been equipped with..
a water- cooled Merlin engine fully covered with a cowling....mustn't it...??  In spite of its high speed capability in the (cold)air....water-cooled...

[JimG]

Sounds like normal behaviour for an esc setup for LiPo cells. These have a low voltage cut off to the motor to protect the cells from being over discharged. During running the voltage of the cells under load will drop below the cutoff voltage and the motor will cut.This allows the cell voltage to rise over the cutoff voltage and the motor will start but the load will drop the voltage again cutting the motor. this sets up the cycle of stop/start you are getting. If you cut power when the motor initially cuts and let it sit for a couple of minutes the battery will partially recover enough to allow you to run at slow and bring the boat back to you. Best to time how long a run you get before the motor cuts and actually tun for at least a minute less than this, if you have a timer on your transmitter set this up to warn yourself.
Jim

[Backerther]

If your PTB had been a bit larger, it could have installed an emergency small battery for secure recovery to the shore without
any anxiety, as my Najade that have been saved several times by this small battery in the pic below.
Even this small battery could give her over 3mitutes or so to sail at moderate speed.   

[Allen A]

Hello gents .. thanks for the info re; low battery issue, the secret being then to let it sit/drift for a short time and then guide it inshore ... raises a question for me then, are Lipos best for boats or RC as a whole or it it better to use other types of battery ?
It seems strange that a 7.4v for example will start to cut out are around 6 volts or thereabouts, an understandable safety feature but not a great margin there in reality, I like the idea of a spare low volt battery as standby for such an event but wouldn't know how to wire one in frankly ... due to sail both boats tomorrow at Batley, give them both a good try out, all batteries charged, so here's hoping for a successful day.

[Colin Bishop]

The 7.2 NiMH pack is not cutting out. It is the speed controller that is doing that. The cut out is needed for LiPo batteries because if you discharge them below a certain voltage per cell it damages them beyond recovery. The cut out voltage can usually be set on the controller or turned off altogether. If you do that, then when the NiMH pack is running low the boat will slow down noticeably but will not stop and you will have several minutes juice left to bring it in safely. It should not harm the NiMH pack if you recharge it as soon as possible (when you get home for example).

Colin

[Allen A]

Hi Colin, thanks for that, where I'm lost I think is in setting or turning off the cut off on the ESC, there is a jumper on it I have set for Lipo batteries, is it as simple as removing that while remembering of course not to run a Lipo down too low as I am aware that to do so can deep six them ...... also are you suggesting then I should switch from Lipo to NIMH batteries ..??

[JimG]

No need to switch to NiMh cells in fact plenty of reasons not too. One is that to get the same capacity the NiMh pack will be much heavier reducing the performance of the boat. All you need to do is keep an check on your running time so as not to reach the low voltage cut off on the esc. You can buy a voltage checker for LiPo packs that plugs into the balance connector and gives an audible alarm when the voltage gets too low. This can be set to go off before the esc will cut power to the motor.
Jim

[Colin Bishop]

TBH Allen, I'm not sure what you are doing! If you are using LiPos then you do need the cutoff if not then you don't.

If you are using LiPos then you could fit an audible alarm which will warn you when the voltage is getting low. However, the best thing is to measure the current consumption of your boat at full revs and work out how long it will run at that speed before running out of power with the fitted battery capacity then bring it in before the cut off operates. If the calculated time is 20 minutes then maybe bring it it at 15 if you have been running it flat out.

You wouldn't run a car until the tank runs dry so best not to do it with a boat. The battery voltage can be measured with a wattmeter or voltmeter if you are in doubt.

just seen Jim's post above - good advice.

Colin

[Backerther]

My style of low batter/operating time control is as follows;
Before setting out to sail....voltmeter checking as in the pic1 and cooking timer set to a definite time.
               I normally make it a practise to set around 5 minutes for a fast boat which requires me a bit tension.
During the sailing...cooking timer alarm around my neck that I used to do the same in RC airplanes that needed the severe tension by the fast flying. Generally speaking, a man is apt to forget the time when he is absorbed in something seriously.   Oh, don't say "so primitive like your radio" but simple, easy and secure to control a safe sailing on the time and low battery.
It should seem that the length of time under tension is reasonable to set within about 5 minutes or so for me...
Over that time, the tension will possibly be released/loosened leading to the mishap of the model boats/airplanes.

[Allen A]

TBH Allen, I'm not sure what you are doing! If you are using LiPos then you do need the cutoff if not then you don't.

just seen Jim's post above - good advice.

Colin

TBH honest Colin Im not sure what Im doing either,    .. seriously, its just that I like thing to work and work right and its all a learning curve but I am getting there thanks to replies here and as you say Jims advice does make sense too. Sadly didn't get to sail yesterday as ended up in hospital for the day, double whammy really as it would have been a chance for hands on advice from the more experienced guys there too.

I will get a voltage checker and run the tests to see what the timings are, will also look into a spare recovery battery as Backerther suggests, an optional back up if I glitch it ??

[Allen A]

Having time on my hands and it being a nice day I decided to try and ascertain how long the battery would last by running the boat on the canal .. I will though as advised buy a voltage checker I think ?


Essentially I spent 35 minutes sailing it on and off, I say on and off as I had to occasionally remove weeds from the prop, wanted to check on the motor, and I could probably have got longer but the experiment served to give me an idea and satisfy myself that I would have plenty of sailing time from the batteries, and anyway I will I think always carry a spare for the boat as I do for the TX.
The new fan cooled motor still got warm of course initially (but not as bad as the other motor) but I could tell from the motor noise when some weed had caught the prop and towards the end the motor did get hotter to touch, a combination perhaps of the enclosed below deck area and having to work harder when the prop got a little clogged ... suffice to say I cleared it straight away every time that happened, .. it still ships a little water but I'm more satisfied that is from spill onto the deck and then seepage between the deck joints but still have it in mind as a winter project to perhaps try and remove the deck and re-engineer and re-seal the prop shaft assembly.


So (probably dumb) questions if I may, or should I say opinions please, bearing in mind I'm using a 35mm prop, (scale size should be about 22mm in reality), what is best, brass or plastic, does a bigger prop give more power, what is the more efficient, 2, 3, or 4 blades  ??

[Colin Bishop]

Just out of interest, are you now running with or without grease stuffed prop tubes?

Colin

[Allen A]

Hi Colin ... no  I degreased it a while back when I fitted a new shaft ... Im guessing you're referring back to the heating up of the motor ... swapped out the prop from the brass one to a plastic one at the same time, haven't really noticed much difference in the performance though.

[Colin Bishop]

I think the length of the tube makes a difference. It was long one on my boat. Still, it sound like things are getting better.

Colin

[Allen A]

Im hoping so ... yes, the prop shaft itself is 11 inches long and rotates freely when not connected to the motor, to my inexperienced eye though I think it is at a bit of an acute angle maybe, that part of it being just about the only thing I haven't improved/modified or worked on.


There is even less room now with the new motor and with it being longer there is no gap between it and the upper deck, not that there was much more before if you look back at the previous picture, they touch but the deck doesn't bulge up out of line, thankfully too there is no heat transfer from the motor to the underneath of the upper decking.


Pictures show a somewhat crowded layout perhaps, wondering if maybe I can fit a small cooling fan in there somewhere ??