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[shadysadie]

Today, I took my recently completed Aeronaut " Victoria " for its first trial run. 545 motor, 15amp speed controller, 5000ma 7.2V power pack and 45mm. two bladed prop.. I was initially very pleased with the performance as the boat was fast enough to get up "on the plane" without being too fast to handle comfortably and the steering was excellent. After about 25mins. fairly fast running, the boat seemed to slow down so I brought it to shore suspecting a low battery, only to discover a VERY hot and smoking motor. Seems that I switched off just in time to prevent a serious fire. Have just examined the boat back at home and found no tight spots on the entire drive train - only a badly cooked motor.




I have been making and sailing model boats with brushed motors for quite a few years now without any problems but either this was a faulty motor (doubtful) or I have made a silly mistake (probable). Only factor I can think of is prop. size so is this the problem? Please put me out of my misery.

[raflaunches]

I think they recommend that you don't fit a propeller that has a bigger diameter than your motor for this reason. Everything else you've fitted sounds right.

[Tug Fanatic]

I suspect that the answer comes in several parts.
1. The prop is at the very large end of what the motor will handle.
2. 25mins of fairly fast running is a long time
3. Probably not much cooling - not enough anyway!


It all adds up to a motor that is producing more heat than it can dissipate on a battery & controller that can provide more than enough to achieve it.

[CGAux26]

My Springer ran OK for years on its 600 motor, 40 mm prop, and 6 VDC SLA batteries.  No overheating while living and running in NW Washington, where the weather is cool and the water is cold.  Then I moved to Texas, where weather and water are warm to hot, and the motor and ESC got warm enough to cut off occasionally.


The boat's hull was built totally sealed, no air circulation.  Now I have added 2 air scoops and the problem has abated.

[shadysadie]

Thanks folks. When I get down from the naughty step I'll order a speed 600 motor and try again with various smaller props. and also check the motor temperature more often during trial runs.

[CGAux26]

What I was implying is not to change the motor, but to add some air circulation around it.

[John W E]

hi there

had a very similar problem when I built the Fairy Swordsman for beginners - I was running this model on a 40 mm diameter twin blade prop and that was also cooking a 550 motor.   I ended up dropping the prop diameter down to a 35 mm 2 blader; and adding a cooling coil bought from Ebay for a couple of pounds.   Never had any problems since./

Funny enough similar speed due to the fact the motor is allowed to rev at its true rpm on 7.2 NiCads.

John

[shadysadie]

Thanks CGAux26, I'm only changing the motor because the existing one is well and truly cooked! Your air scoop idea is good and I'll incorporate if necessary.


Thanks bluebird, please tell me more about the cooling oil.

[malcolmfrary]

Thanks CGAux26, I'm only changing the motor because the existing one is well and truly cooked! Your air scoop idea is good and I'll incorporate if necessary.


Thanks bluebird, please tell me more about the cooling oil.

It's a "cooling coil" - a pipe that wraps closely round the body of the motor and is connected to a scoop at one end and an outlet at the other.  Cold water is picked up by the scoop, passes through piping to the coil, gets warmed by the motor, passes on to the outside world via more piping and the outlet.

[John W E]

Boat-Motor-Water-Cooling-Coil   

Thanks bluebird, please tell me more about the cooling oil.
[/quote]

http://www.ebay.co.uk/itm/RC-Boat-Motor-Water-Cooling-Coil-540-550-560-Size-36mm-Brushless-Nitro-Radio-/262849589864?hash=item3d330e7268:g:ZB0AAOSwBahU7zYs

[John W E]

hi there

Here are a couple of pics of the internals of an RAF Launch which I built a while ago.   As you can see both the motors have cooling coils fitted.  The pickups are behind the props taking the thrust of water from the props to drive the water around the cooling coils and then it exits out the side of the model.   The motors are Vision 600s high performance motors.   The speed controller on this model has been especially modified by myself.   Its an Electronize 30 amp speed controller which has had the output transistors 'beefed up' to take higher loads which are generated by these motors.

[red181]

your motor will have a specific max amp draw, with graupner its usually on the box, or easy to find on the net.


Take all this guess work away, and use one of these


http://www.4-max.co.uk/wattmeter-budget.htm


You then start with a small prop (they are only a quid or two anyway, and you can always keep them for spares) and work up, over say 3 different sizes, or borrow from clubmates. This way, you know the exact max volts, amps, and watts, no more guess work. Another motor may not be the answer,  your relatively low amp esc didn't cut out,


all this "sounds right, feels right, looks right", feeling how hot or cold the motor feels is just guessing, just the same as it looks faster, and so on

[unbuiltnautilus]

Prop size all the way. Look for a prop between 32mm and 36mm for the 600 motor. They have a bit more torque than the 545 motor ( I have never encountered a good high speed 545. I tried one twenty years ago, it ran hot, it didn't like a 2 blade 35mm prop. Everyone rated them for years..I tried another one about ten years ago, glitchy as hell, no longer a fan   ). 600s are usually decent motors, it should tide you over till the pull of brushless tempts you!

[Ron Rees]

From my experience most 540 sized motors seem happy running a 35mm two bladed prop, You can push it a bit by moving up to a 35X with a greater pitch. My cousin in Holland and I built a Swordsman from the Dave Milbourne plan (2000), fitted a 545 and a 35mm prop on a 7.2 NiMh.


The model went very well at my club lake. After taking it back to Holland he wanted more speed....and then more speed!, increased the prop to 40mm, then 45mm and lo and behold, his boat really did catch fire. No water cooling or anything else. If you need to drive a bigger prop you will have to go up to a bigger motor, but they all like to turn at speed so testing different sizes is common sense.


Personally, I only tend to use brushless now which I find amazing, and a 35mm diameter outrunner will perform much better than the 545, but it will still only need a 30 to 35mm prop!!! to do it. If you want faster..then up the battery voltage instead.


Ron.

[shadysadie]

Many thanks to all of you for reminding me of the basic rules, some of which I seem to have forgotten over the last few years! It was indeed a silly mistake regarding prop. size but now I can do the job properly thanks to this invaluable forum.