sizing motors?

[Guest]

Does anyone know how to work out the correct size motor for a 1/12th scale cabin cruiser?

this hobby is new to me, and I'm trying to learn as I go along.

I have been told by one shop that I should have 2 x electronise 545/12 motors, but I have no way of knowing if thats true or not. I want it to have a realistic speed, but not plod, or go so fast that it aquaplanes:thinking:.

the boat is an heirloom, made by my dad 40 years ago, but never finished. its a mahogany planked cabin cruiser with twin props, and its 40" (1 metre) long x 12" (300mm) wide. The propellors are 3 bladed and have a diameter of 2" 950mm)

any / all help appreciated.

[Guest]

that sounds about right, the electronise speed ctr are some of the best I have used, and would recomend them over any other. the motors if you look on the electonise site they have a graph for motors and sizeing.

peter

Electronize Quality Electronic Controllers

[Guest]

ok, thanks. When your new to a hobby, its hard to tell if a shop is being honest, or just trying to offload its junk.

So far, this one seems to be checking out well.

One more question please, If I want to have a servo to move the rudders, as far as I can see, i will need to have the servo at half way travel, so that the rudders are dead ahead, then it will go left or right on command.

Is that usual? will the servo stay exactly where I set it?

(I did say I was new to this, didnt I?):grinball2:

bob

[Guest]

You should set the servo to it's mid position, ideally by using the transmitter with the trim switches in the mid position as well but if you don't have a transmitter available you will have to rotate the servo by hand fully anti clockwise and then fully clockwise to identify the mid point.

When you have the mid point the servo arm should be set on the splines at a 90 degree position and the horns on the rudders should be set at 90 degrees. You then have the lengths of the linkages you need.

I would use use ball and socket joints on the linkages to ensure that all linkage lengths can be adjusted to give the perfect mid position of the rudders when you have finished.

If you have got all the neutral points in the mid positions you will always be sure that the travel will be correct port and starboard.

Here is a link to a two rudder set up using one servo. I didn't use ball and socket joints for this because it is such a small model and I wanted to keep everything small and light. I did pay the price though and ended up with the rudders not perfectly aligned.

http://www.scale-models.co.uk/under-construction/2410-revell-1-72nd-type-vii-u-boat.html

[Guest]

That sub set-up has made me rethink the whole rudder assembly. great way of keeping moving parts to a minimum. I was going to over-engineer by a factor of four, I think. I have one servo at present, and have just checked its travel. It will move a 180 degrees, so thats even better than I thought I had.

Bob

[Guest]

Glad I could help Bob, keep us updated as you progress.

[Guest]

Hear is a two ruder set I did for my fire boat , it may give you an idea , I try and keep all linkages square and ajustable so as to get equal throw , I mock mine up at an earley stage so I can be shure that when the decks are on and bits are coverd I know I have nice direct links that are smooth.

Peter

[Guest]

forgot the picture

Peter

[ATTACH]15958.IPB[/ATTACH]

[Guest]

Hello Sunnybob, you can use individial speed controllers if you want separate control over each motor or can use a single a single controler to control both, I run a 42" Riva Aquarama using 'Motors Direct' 11 pole 5000rpm motors pulling 10amps each via and Electronize 30 amp controller, with three blade 65mm racing props with no problem, without knowing the boat weight and the space in the motor compartment and battery compartment it is difficult to be precise, try Alistair at Motors direct (link on Stourbridge Model Boat Club site) or Electronize they are both more than helpful, regards, Aquarama.:thinking::dancing1:

[Guest]

very interesting, thats closer to what I had originally planned, but i like the simplicity of the sub set up. I think I'll start off with that one, and see how it goes.

[Guest]

I've been advised against seperate speed controllers, I am told that if one one engine is cut while the other is running, the cut engine will still turn from the prop, and generate a back feed and hurt the battery and controller. Is that true? At this stage I'm trying hard to learn who to trust for advice.

The boat has loads of room inside, Space is not an issue, so I will most likely go with twin engines (once I am sure of the size I need) and a single controller, as

I'm also trying not to spend huge amounts on this boat. Its a 50 year old project that I want to see completed, but I just cant afford another big time hobby (lol).

[Guest]

A single controller will be easier to set up, just make sure you get one that will handle the stall current of two motors.

Damage to batteries/ controllers? the controller will be effected by any stalled prop on a two controller system, the battery should escape any problem. With the modern controllers i would guess that they would be protected from any damage, but i cannot say i have tested them out.

J.

[Guest]

well, I've just ordered the motors and controller, so its just a case of waiting now, and getting on with painting the hull

[Guest]

Co-incidentally we had a tutorial the other night in the Club on ESC's and here, to the best of my recollection, is what was said:

There is really no difference between motors and generators. If you rotate the stator of a motor you will generate a voltage at the terminals.

ESC's work by feeding pulses of power to the motor.

In between the power pulse the motor is still turning and so it generates what is termed a back EMF.

ESC's don't like back EMF's and so are protected by the installation of a suitable size diode at the design stage.

So I guess, having an prop drive the motor would not be a problem and should certainly not damage the ESC. If the back EMF can't get through the ESC it can't reach the battery so allus gud so to speak.

Any more and I've got to see the man that knows :emo4:

[Guest]

Thanks Ian, yes thats right regarding a motor being a generator, but I did not know that the esc was protected from back emf. I have some electrical and electronic knowledge, but this radio control stuff is completely new to me, so I'm on a huge learning curve (G).