CERVIA FIXTURES AND FITTINGS
A new day; fresh start; fresh problems to solve ::)
A lot of fixtures and fittings can be bought off the shelf and there is nothing wrong with purchasing fixtures and fittings for model boats.
Some, though, we may wish to make ourselves; this is entirely up to the person and is your own choice. I like to make my own fittings sometimes, but, occasionally I do buy some.
For the Cervia, we are going to try and make as many fittings as possible and where I am commencing is going back to the Freeing ports in the bulwarks.
The Electrical side of things :D
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Before we go too far down the road, building fittings and attaching them to the model, we have to pause for thought for a minute.
Although we have the motor and gearbox installed and we have a rough idea of what size battery we are going to put into our model; we need now, to look in depth at the type of speed controller we are going to fit, where we are going to fit the TX receiver for the radio and are we going to fit any working functions in the model such as lights, water pumps etc.
The main thing on our list at the moment is:
What size speed controller to do we need? When we say what size? What we mean is – how many amps do we need and how many volts?
Now the motor I have installed into this model is a 550 motor. When we tested it ‘free running’ coupled to nothing, the motor was sitting on the bench and we ran it at 6 volt. According to the book we have and the information sheet, for this particular motor, at 6 volt; she should draw between 0.4 and 0.5 of an amp and she should rotate in the region of between 15000 and 16000 rpm.
This motor is going to drive through a 2-1 ratio belt drive gear box. So, we will say, she is turning at 15000 rpm connected to the gearbox at the output end of the gearbox, she should be turning or will be turning in the region of 7500 rpm. At the end of the output shaft, we are going to connect to the propeller shaft, via a Dyco coupling unit; and then onto the propeller shaft and on the end of the propeller shaft; we have the propeller :) in my case it’s a 50 mm three blade brass prop. Now, with all of this connected up; sitting on the bench in the tug; the first stage is to connect the electric motor up directly to a 6 volt battery and let it run for at least an hour (aye you have to sweet-talk/make the Mrs a cuppa O0 ) as it can be on the aggravating side for those who don’t know what is going on :) What is actually happening is – we are RUNNING THE MOTOR IN and the PROPELLER SHAFT and we are constantly checking for ‘hot-spots’ – is the end of prop shaft running hot WATCH YOUR FINGERS!!!! IT DOES HURT!!!! :'( When we have ran the motor for about an hour with no load on; disconnect one lead off the battery – preferably the positive lead. In between the wire from your motor and the battery; connect an amp meter up. Make sure the amp meter can handle at least 10-20 amps.
Now once we have connected the amp meter between the motor and the battery; check the reading on the amp meter.
When the motor was free running on the bench, we knew that it was drawing no more than 0.5 of an amp. So, in theory, with the coupling and propeller shaft and propeller all connected up to the motor through the gearbox; it should be no more than ¾ of an amp to 1 amp. If this reading is higher; we have some friction somewhere and something must be preventing the propeller shaft from turning freely.
If we have a hotspot or we are pulling in the region of more than 1 amp – or maybe more we have to start to looking for problems in misalignment in between the gearbox and the propeller shaft. Problems with the gearbox and we must have these problems sorted out before we advance any further.
As soon as we are happy {-) and we have the motor running between ½ - ¾ of an amp we can go and get the model’s ‘bum’ wet – aye, the big test tank – stick the model in the test tank – apart from checking for leaks, first job is to place the battery in the position in the hull; and, then ballast it down to its waterline with your chosen set of weights. I am lucky; I have a bit lead left over from the Church roof down the street 8) so, we ballast the hull down to waterline level. Sometimes it is adviseable here to have two pieces of cable to make up an extension. This is because multi-meters or amp meters do not like being dropped in water :-\ yes I have done that myself, balanced the amp meter on the model and its fallen straight off into the water.
Anyway, we need to take the reading now – of how many amps the motor is actually drawing whilst under full load.
So, just with the amp meter connected; in circuit with the battery and the motor; this will give us the total amps at full power - the motor is consuming, driving this propeller and in my case it was 5.8 amps. For those who like it spot on, we will just say – what we have to take into consideration (although the motor is using 5.8 amps) when she is actually running free and moving and not being held, the amperage will drop slightly; only slightly though. So, we have a reading now of 5.8 amps.
We are going to round the 5.8 amps off to say 6 amps. Its back to the worktable once again, we need something now between the battery and the motor to control the speed.
In olden days and still today sometimes we used to use:-
• Bob’s boards –
• the fixed resistance type boards (where you had a series of resistors of different values giving you different speeds);
• Resistant wire controllers, which looked like the old fashioned bar-type electric fire (those ones with the elements showing);
These types are semi-mechanical – where you require a servo to adjust them; through a mechanical linkage.
Today though the norm is to use a purely electrical speed controller, and, for those who wish to have an easy description of how these work – they work on switching the electrical power supply ON and OFF lots of times per second. So, if the switch is switched on all of the time; the motor is running at full belt – flat out – with full power from battery. But, as you commence decreasing the speed, what happens is the speed controller begins switching ON and OFF – the more times it’s being switched OFF in a given set time, the slower the motor is going to go.
So that is an ‘easy’ description of how an electronic speed controller works.
What we need to do is to determine what size (as in how many amps) speed controller we require. Now, maximum amps free running the tug is going to use 6 amps. So, that was with me holding the tug stationary in the test tank, allowing the motor to thrash round at full belt. So, if I am towing something that stops the tug dead in the water; I know it is not going to pull more than 6 amps. In theory then what we require is a speed controller to handle double 6 amps i.e. 12 amps. The reason I have doubled the amps that I require for my speed controller (and also a lot of other people do that too) is for a safety margin. The unforeseen – a plastic bag floating in the water which gets wrapped around the propeller; the occasional lump of weed; and that dreaded swan feather; all get mangled around the prop. Insufficient enough to stop the propeller dead, but sufficient enough to take the motor into what is called the ‘Stall amperage’. The stall amperage is where the motor has been stopped physically whilst still under load. In the case of the 550 it’s in the terrifying region of between 45 and 50 amps – these are the amps the motor stops at.
If we are to physically hold the motor stationary whilst the power was still being supplied, we would start to see smoke either from the wiring, or the motor, or worse case you would see your batteries EXPLODE and the WIRING BURSTING INTO FLAMES so, to prevent this, we could, if we required, fit a speed controller which is capable of handling 50 amps. To be honest though, a bit of unnecessary expense and a bit overkill, for this particular model anyway. What we do the safeguard this is add a fuse in line between the battery and the speed controller. Now, our speed controller I am going to use a 10 amp one – protected by a 10 amp fuse, So if the situation does arise where the propeller is stalled and stopped, before it does any damage the fuse WILL POP. A 20 pence fuse is a good deal cheaper than a £30 speed controller or in the worse scenario watching your model BURST INTO FLAMES.
Electric Speed controllers then – there are literally dozens on the market today; and, as they say THE CHOICE IS YOURS. But, before you go away handing out money – a couple of pointers which have taken me a long way:-
Although today’s trend is to ‘Purchase the cheapest we can because if it goes wrong, we can throw it away’ because that is the way a lot of cheap imported speed controllers are built nowadays; it is a bit of a heartache when you know – you have fried the speed controller yourself by a silly mistake – by getting the wires mixed up and when you read the small print – you are not covered under the warranty for that and, I do not think there is not a modeller on this earth who can put his hand on his heart and say – “I have never made an error by mistakenly picking the wrong wire and connecting it up”. :angel: This is one of the reasons I try to purchase from our ‘home-grown’ industry. Because, as some will tell you on this forum, there have been one or two occasions where I have picked up the telephone and spoken to the manufacturer and said “Hands up – I have dropped a clanger – can you help me?” . Once or twice I have had the reply “BLOOBS – A FULL TEAM OF DOCTORS AND NURSES COULDN’T HELP YOU MY SON!!!!” ::) But, it will cost you the postage and the replacement is always there for the next morning. O0 You try and find that response from one or two Companies from abroad.
So, I do like to build ‘kit’ speed controllers and, the particular one for this model I chose P79/79S CONDOR 10/2 SPEED CONTROLLER. Kit build, I am going to include a couple of photographs because there are on this Forum kit building speed controllers and switches – so you could follow those threads if you wish.
Now, last but not least; the wiring side of things:
• The motor has been what is known as ‘suppressed’ and for anyone requiring further information on suppression the subject is well-covered on other threads.
• The supply wires from the speed controller to the motor are led and fed down one side of the hull; well away from any signal carrying wires. This is what is commonly known as ‘The dirty side of the hull’.
• On the opposite side of the hull there are the ‘clean wires’ and these are the wires that carry the power supply and signals to your servo and your speed controller and also extra units which you may wish to add in – such as switchers for lights and radar working. These lead to your RX radio receiver which is on the clean side of the hull.
Following this practice helps to eliminate SOME OF THE electrical interference which can be troublesome at times.
One picture will show the layout of the speed controller along with the RX mounted at the front (bow) of the hull. The other pictures show you what you will find when you purchase a kit speed controller – from YOU-KNOW-WHO ;) and you can see these are the basic tools I used to assemble the kit and lastly the assembled kit, but, without the casing – JUST SO YOU CAN SEE WHAT THE INTERNALS are like. O0
Aye
John e
Bluebird