kajabbi

Hi,

I am entirely new to R/C boating and i have just built a balsa 22" hull and have put
a single 540 motor, a speed controller and servo and have the rudder and prop shaft set to go. Basically at the condition it is in
i could take it to the water and it would go. Fast i hope. But i have heard all about cooling and i have none and i am curious to know if i'll most likely need it.
I have a 4200 MAh Nimh battery. The motor is capable of 22,000 rpm loaded. I think i might just take it to the water as is and if the engine starts getting really hot i will consider getting water cooling but i was just wondering as a newbie, how necessary the cooling actually is.

Any help would be much appreciated. Thanks

Here are some pics of the boat. By the way i got a too long prop shaft so the motor sits rather far forward. (the motor is not in the boat in the pics)
Also the hatch doesn't have anything to secure it down yet and i am working on this.

Constructive criticism expected as the boat is tacky on all levels. Not being a professional boater i just don't care to a certain extent.
Also in the pics the rudder is not secured.

P.S. I'm sorry about the paint job as i havn't properly painted it yet.

Simon.O.

First off, welcome.
Great to see a home build !
22" on a 540 with a straight shaft has potential to go fast, not 70 kmh or anything silly but it will look quick.
You can get away without cooling if you are lightly proped and keep run times down.
I would suggest you get a 35mm prop to start with if the prop is setup for surface drive.
I have a 19" home-brew hydro with a 540 on a x534 prop with no water cooling and it does not get hot, and that thing honks !!
You are on the right track to trial and see if the motor gets hot, short 1 min runs and bring it in to check.
A rough rule of thumb is if you cannot keep your finger on the shaft at the wired end for 5 seconds then it is too hot.
That hatch is going to cause some serious air resistance and looks a bit...........o.k, I'll leave that one for now.

Whereabouts are you in N.Z
I'm on the Shore.

EDIT. ooops i just rechecked the first photo and you have the shaft set for sub drive. Start with a 25-30mm prop.

pompebled

Simon said it all, but as youre going to run 4200mAh cells, your biggest concern will be the long runtime.

If the boat isn´t overpropped, it´s the runtime that will cause massive heat build up in your motor, which will either fry it after a few runs, or permanently damage the magnets due to overheating over a longer period.

Adding a simple aluminum coil the the can is the first thing to do, adding brushtab cooling is better, ast that´s closest to where the heat is generated, the commutor.

The pics show a 700 motor, but the principle is the same.

The inlet sketch shows a tube glued into the hull next to the prop, on the right side, viewed from behind, facing forward.
Sand it flush with the hull, you can do without the extra drag from things sticking out from under the hull...

The outlet can be on the side close to the motor (short lines less friction), or, better, in the bottom, facing towards the transom, creating sucktion, sanded flush like the intake.

This is a pressureless cooling loop that wil always function and cause minimal drag.
As the hull will be sealed, there´s no airflow, so cooling the ESC is always a good idea.

Let me know if you have more questions or need more pics.

Regards, Jan.

SV27dayton

Great work. I've leaned so much since buying my first boat, I can't imagine building first thing. Good start. You'll learn alot. I don't knwo alot about brushed motor cooling so I'll just say nice work.

peterpella

Hi there

what to say more...

all above is right. I used to use spiral alu pipe made by me using a battery which diameter is close to 540 class motor. You can also buy it for some bucks

This is the most simply method of cooling your brush motor. The most sophisticated question is what area should be cooled. A man can say thet all motor can is to be. But if you want to do it in right way, first there is a need to cool the brush area, then magnet area. Some magnets, specially produced in china dont have their characteristics. Usually good neodym magnet needs no cooling but this is only theory.

So, making any answer, better cool your motor using water.

A hope you know where the inlet water 'point' is. There are many methods to do it. The most useful is to make a hole in the bottom of your hull close to the edge of it, lets say 1 cm from the edge. Then your flow will be LAMINAR.

Regards

Peter



Better ugly boat than wise mother - in - low !!!

kajabbi

Hi,


Thanks so much for your advice on the matter.
If my engine does start to overheat I'll be sure to fit a aluminum coil around the motor.
Don't worry about me knowing where the inlet hole should go. I have looked this up before o the net and i found a do-it-yourself tutorial on it. This had good pictures and i will refer to it if i decide to cool it. It also just plainly showed me where the inlet hole goes so i think i'll be fine there thanks. :-)

I only decided to build this boat because a guy at my school built one for a project and me and my friend had been building stuff out of balsa for
years. Nothing professional at all, just stuff. Boats included but to know plans. Just flat bottomed ugly things that never worked. Then i went and got the plans of the guy and we built it. It is fairly basic to build. The guy's one when it was done, whent at least 20mph from what i've seen and i think he only had a cheap 540 motor in it. I have a Tamiya Super Stock TZ which is better so i am reassured that it will go fast even when you stick everything in it and it feels like it weighs a lot.

As for the prop i currently have a SAB 35SR Nylon prop. I cannot find the dimensions/ size of this on the internet and it is not written on the packaging.
I'm assuming that it is maybe 35mm as thats in the model number.
With the prop i can go smaller but not bigger as if i go any bigger it will start slicing into the hull. This is ok though because by what you guys have told me i should only have to go smaller. Will my prop be ok? I have tested in bath. It creates huge amounts of push and i couldn't test it much over minimum throttle (the least amount of power i can get the motor to spin on)

Anyway thanks for the help!

Conor, :-)

P.S. To Simon.O. I'm based in Auckland, Remuera area. :-)

pompebled

Testing in the bathtub will only get you wet...
It's no indication as to how the boat/prop/motor combo will work once it gets moving.

Standard procedure is to start with a prop that's a lot(!) smaller than required, preventing the magic smoke on your first run.
Run it for a few laps, bring the boat in, check the temperature of motor and batteries and go for the next size prop.

If things get hot, before you can run a bigger prop, install watercooling before trying that.

Keep us posted (preferably with pics)!

Regards, Jan.

Simon.O.

Conor
Remers, eh ? That's nice.
O.k back to your boat, the SAB props are just ok but there are a lot better out there for the same price or less.
I am assuming that you have the 4mm threaded shaft for the sab props, I have been here before so I know my way around the sab props.
If so then the best thing is to get a 4mm drive dog for a Kyosho or Academy boat and start uing some of thier props.
This I know as I spent a lot of time last year trying to get a home built rigger up and running with sab props......A non starter.
If you want to pm me, or txt me on 021 027 03185, I am keen to help.
Boats are fun and can take up a LOT of time setting them up properly.
Cheers, Simon.

kajabbi

Hi Simon,

Yes the prop is a 4mm thread.
I bought all the parts i have from Hobby City on Quey street Waterfront area. It is a really good model shop
but they don't specialize in boats so they have a reasonable boat selection but not huge. This means that some of their staff
don't really know how to help you. I was just wondering where you buy all your parts. I'm assuming you go to
High Performance Boats which i know is on the north shore but i have not been there yet as it is further to go than the waterfront.

So basically is a drive dog a connector that converts a 4mm shaft head into various sizes so that you can fit other props? anyway
your help. :-)

Cheers, Conor

pompebled

Sort of..., your 4mm threaded shaft will take all (Graupner) props with M4 thread, obviously.
As not all sizes come with M4 thread, you can use a drive dog to be able to use all other props, fitting that drive dog (specially the metal props are mostly drive dog).

Regards, Jan.

Simon.O.

With your 4mm shaft you have alot of props to choose from.
I hade very limited sucess with the sab props.
The academy and kyosho props are a lot better, I have yet to try the Graupners.
Now if you have enough shaft protruding from the stuff tube then you can fit a drive dog then the prop slides on and last goes the prop nut. Another alternative is to use silicone fuel hose instead of a prop nut. I have only lost one prop with the method and that was when the little hydro hit a log, it tore the prop off and bent the shaft[X(]
Hobby city do have kyosho props, HPM in Browns Bay will post stuff out. I live in Birkdale and still get them to post me stuff. The other shop I use is Ace hobby in Birkenhead.
You can use 3/16" octura props with an alloy or brass sleeve to step it down to 4mm. I do
I also have bored 1/8' props out to 4mm
Now that I am building my own shafts I make them to suit the intended prop.

WO

You seem to have a handle on cooling so mabe you can help me. I live in the Desert of CA and even when it is very hot I still like to fly or run boats. My first boat was a sv 27 and I fryed the motor in just a few minutes of fast run time. Now I am building a sk daddle and want to use a sig fuel pump to cool the motor as I don't want fryed motors this time as the motor I am using cost $200. Would this be ok? wo