Watercooling a brushless outrunner motor.

[785boats]

Although this motor is in a fast electric boat I thought I'd post the cooling setup here because brushless outrunners are now suited to scale models with all the Kv ratings and hi-torque motors available, from 400kv to 5000kv plus.
Cooling may still be required if the prop size is loading the motor to near it's max amp draw.
I won't know if this works until the weekend as I'm still putting the boat together.
I searched the forum to see if there was any info on this but could'nt find any so this is how I'm cooling a 2700kv outrunner. It may be of interest to some.
Cheers.
Paul.

[pompebled]

Nice adaptation of the commercial available version!
Well done.

How effective is it?

Regards, Jan.

[Hoghappy]

Let us know how that works...I'm thinking about going brushless in one of my Crackerbox boats. Why aluminum plate and not brass or copper to solder the tube to?

Capt. Crash

[pkboo]

Paul, it works, somewhat! I´ve got almost the same setup for a cracker I´m buildin´ out of a 1/32 PT Hull. Score so far one almost to a chrisp burnt :eek: TowerPro, but not because it doesn´t work. The TowerPro although Kv1750 can only handle 12A, I´m in wait of a bigger capacity outrunner (Kv3650) at the moment. My setup is a brass plate with brass tubing soldered, this is a more direct way to keep the plate cool. If you can do the same with the ESC. I´ll post a pic or two later today. Boo

[Shaun Hendricks]

Aluminum would be lighter for racers, for scale or play it probably wouldn't matter. There are also hollow shaft outrunners that would let you pass water directly through the core if you wanted to put in the right setup. That would allow you to cool your bell and magnets somewhat. I wouldn't do it in a racer but something slower would probably benefit from it.

[pkboo]

2 pics of my setup. It's difficult to measure if it works and how much effect it has but following the logic it should help, somewhat, in the cooling. Besides cooling it with water I also have a prop mounted on the inside to aircool it too :) Even with the amount of cooling couldn't help burning the TowerPro motor, it still turns though :eek: at full speed but the next time it get's a bit hot it might be just too much. Boo

[Hoghappy]

Awesome idea the fan on the shaft next to the motor...what are the out tubes on the transom...water or air?

Capt. Crash

[pkboo]

That's where the water for the cooling comes out CC, kinda fake tailpipes :D It leaves a nice even double trail in the wake of the boat! If I wasn't amazed at the speed the boat had with this motor I could have caught it time not to have it burned. Although turning up to complete rev it's useless now :( the magic puff has already left! Boo

[Hoghappy]

Ok...2 more questions....is that Silicone sealer your using to glue down the motor mount with?

And what is the coil looking thing the wires are wrapped around in the upper center part of the photo....a magnet?

Capt. Crash

[pkboo]

Yes, silicone not also holds everything together well, it also dampens noise, takes up vibration, is waterproof, etc. etc. and it also is as easily removable. Do not forget there's one for every application (important!). The wires going to the ESC are wound around a ferrite bead to supress RFI. Contrary to brushed motors it is the ESC that causes most of the RFI with brushless. I would usually put the bead around the wires coming out of the ESC going to the motor(s) if I used brushed. Good eyes CC :) Boo

[Hoghappy]

Thanks...I'm soaking it all in today! ;)

Capt. Crash

[785boats]

Hi guys.
I was sure someone else would have done something similar. Thanks for proving me right. Never seen a comercial one though.
Capt Crash
The reason I use aluminium is because I believe that it transfers & dissapates heat faster & more efficiently than brass or copper.
pkboo
Those windings have lost their shine have'nt they? I like the little prop as a cooling fan. I might give that a go too. It must do something to help cool the motor.
Shaun
This is the motor that came with the boat so I'm going to give it a good try before I decide whether or not to change it. A hollow shaft motor. I've not seen one of them. Sounds interesting.
All the best.
Paul.

[pkboo]

LOL, definitely Paul :D It does help cause you can really feel the prop pushing air, so one way or another your moving the air around! But I'm as sure that the watercooling must work also! Don't forget to take pics and showing us and a movie would be nice when ready :) Eugène

[785boats]

Sure will. It should be this weekend
regards.
Paul.

[retoabcr]

Cooling in place, how about a 3" square fan sucking the cool air thru motor as you have the space in the yellow boat for such a system. Only a suggestion!

[pompebled]

I was sure someone else would have done something similar. Thanks for proving me right. Never seen a comercial one though.
Paul.

The boat in the Jolly Motor has a commercial watercooling installed, can't find the thread at the moment...

It's an aluminum block with water running through it, similar to ESC coolings, but with a hole in the middle where the shaft passes through.

Regards, Jan.

[785boats]

Hi there.
I've done a bit of a test result thing over in the fast electric forum if anyone's
interested. A few pics & a video.Cheers .
Paul.
http://www.rcgroups.com/forums/showthread.php?t=896251

[nick_75au]

Aluminium (205) about 1.5 times better than brass(109-125), copper(386) nearly 2 times better than aluminium. If you can afford it, :D diamond(1000 impure to 2500 pure), water (0.6) air (0.026). Im not exactly sure of what the numbers mean but the higher the better.

Info out of Wikipedia

It looks to me that a fairly high surface area is required to dissipate heat to both air and water?

[785boats]

Well there you go. I based my theory on the fact that Aluminium seems to cool down quicker than brass or copper after you heat them up. Looks like I'll try copper next time. Thanks Nick.
Did I see somewhere that you are having another night sail? I might try & make it down. If that's OK. The last one was great fun.
Cheers.
Paul.

[nick_75au]

Hi Paul,
The Night sail is going to be on the 2nd of August, we are thinking about having one a month.
Regards
Nick

[Hoghappy]

Aluminium (205) about 1.5 times better than brass(109-125), copper(386) nearly 2 times better than aluminium. If you can afford it, :D diamond(1000 impure to 2500 pure), water (0.6) air (0.026). Im not exactly sure of what the numbers mean but the higher the better.

Info out of Wikipedia

It looks to me that a fairly high surface area is required to dissipate heat to both air and water?


According to this copper works better at cooling than Aluminum? And whats up with water and air....wouldn't ambient water/air temps make those numbers change?

Capt. Crash

[nick_75au]

Yup copper is better as a heatsink ( it can be smaller for the same effect), the numbers only quantify the materials ability to transfer heat, I.e. hotter part of material to colder part of material, it has nothing to do with ambient temp. Aluminium is still a good heat conductor and has some properties that are desirable, such as weight :D
Regards
Nick

[E-Challenged]

It's my uneducated guess that ducted fan cooling would be more effective and similar to a motor enclosed in a model plane cowling. A small fan, attached to the motor shaft and running inside a piece of ABS tubing that loosely encloses the motor should blast the motor with cool air and exhaust warm air. It would be good to provide a cool air inlet and hot air exhaust outlet perhaps with removable hatches or lightly spring loaded hatches that open with air pressure. Low KV rating, proper choice of props and conservative operating voltages should also help keep motor heat down. Scorpion outrunner motors from Innov8tive Designs are supposed to be able to handle heat better than some other brands, they are supposed to have more heat resistant magnet material and windings. A high amperage/larger than normal speed control should be able to run cool enough. A phase reversing toggle switch, operated by a servo , for two of the three brushless motor wires should allow use of standard/less expensive airplane type esc's.

(Switch diagram attached)

[Shaun Hendricks]

Problem with air cooling in a boat is that frequently you can't exhaust the air without jeopardizing water intrusion integrity.

Water is a much better thermal transmission mass than air, (.6 vs .026 according to the previous post). The issue is what actually get's hot on an outrunner, and that is likely the stator, not the bell and magnets. If you can cool the stator, you've probably got most of the issue under control.

[pkboo]

Problem with air cooling in a boat is that frequently you can't exhaust the air without jeopardizing water intrusion integrity.

Water is a much better thermal transmission mass than air, (.6 vs .026 according to the previous post). The issue is what actually get's hot on an outrunner, and that is likely the stator, not the bell and magnets. If you can cool the stator, you've probably got most of the issue under control.

And because the stator is the static and to be mounted part in an outrunner this setup should be able to cool it somewhat better than air cooled ;) Of course a concentrated blast of air should also do a rather good job :D Boo

[E-Challenged]

I have read that the magnets in outrunner motors can get hot and lose their magnetism, that results in runaway current draw and sudden heat buildup, resulting in fried windings. I'll ask Lucien Miller, Innov8tive Designs/Scorpion guru, about the efficacy of water cooled stators vs ducted fan cooling in boats. He has a running thread in the E-Zone Power Systems forum.

[Shaun Hendricks]

Magnets in brushed inrunners get hot as well. In both cases the magnets are on the outside case. In the case of a brushless inrunner, the magnets are on the armature and don't get as hot. I think heat has a lot to do on whether the magnets are moving or not.

A drawback to the Neo magnets is this problem, they lose magnetism at a much lower temperature. Samarium Cobalt magnets aren't as 'strong' as the Neo's but the motor would come apart from heat before they'd lose magnetism.

You'll notice a lot of new outrunner designs actually 'bevel' the air intake holes to act as a fan to move air through the motor. Clearly, the moving bell cools the outside of it. You could attach a small fan to the armature but I don't know if this would have any significant affect in a sealed boat hull, which is why water cooling is so popular. You are dumping the heat outside the boat and not building it up inside.

[pkboo]

Shaun logic and theory says that it should make a difference if and when you ventilate the hull in an adequate way, ie. have enough openings so to let the natural effect (heat rises!) take place besides moving the air around with that little prop. You´ld still have to deal with the best thermal transmission coefficient, I still believe that water is more adequate than air in Paul´s setup, but it will help.......somewhat more next to the watercooling. As we say here, "every little bit helps". Boo

[Hoghappy]

I got one of those little electric fans last night and will be giving it a try....can't hurt except it does add more weight. Blowing any air on the brushes is better than nothing. I feel moving inside air is going to help some as it will also be moving and cooling the air as it contacts the hull and other parts that are cooler than the ambient air. Is it better than cool outside air?...no but here the outside air/water is not that cool in the summer.

Has anyone figured out a good way to move air in and out of the hull and NOT allow water to intrude in a rollover?

Capt. Crash

[Shaun Hendricks]

Pkboo- I'd agree but depending on the application. For scale or situations where weight and performance don't matter much, adding a fan to the armature is probably just fine if you ventilate the hull right. It's certainly better than nothing if you are getting the motor too hot to begin with (wrong motor choice for application).

For racing and such, you need to be certain you can deal with the additional weight, performance loss and sealing factors. Those fans don't spin themselves and pull power from the motor when they are attached to the motor.

So, traditional water cooling is probably not going away and you'll probably find more outrunners designed to move some air through the motor as it runs, but just not in high velocity factors.

I'm not against air cooling, but how you choose to cool a motor really depends on the application. I am using air cooling to cool my conversion boat. If the cobalts get too hot, I'll introduce a form of water cooling to them.

[Hoghappy]

...I duplicated your fan application on a Crackerbox while also opening up the motor mount to allow air to flow through the armature out the other end of the can. This is a Titan 12turn brushed and already has a built in fan on the brush end. I will see if this thing will cool this motor as it swings a Octura X632. I also added heat sink paste under those heat sinks (you can see it oozing out). I test in the morning.

I thought about the slight loss of revs due to the drag of the fan...but just don't think it will be that noticeable...we shall see.

Capt. Crash

[pkboo]

Shaun, agree in some cases you apply if and when needed and of course FE is like a racing horse, the jockey needs to be as light as possible :D

CC great! Like I said it would definitely not hurt and with the heatsink, hey I just built something similar for the outrunner a few days ago (pics will follow), is a little bit more help to keep the heat down. GL with it and of course we are all very curious of the outcome. Boo

[pkboo]

I'm still waiting for the motor, it should be coming in next week, actually it should have been here already but the carrier went to France and then back to China :eek: It's either gonna be a 3650Kv or a bell shaped 1600Kv (those are extra because I've got two BL ESC's without motors!) but the mounting "sled", another of my favourites, is ready.....and you beat me to it :) with what you came up with :cool: Boo

[pkboo]

I got two TowerPro like motors I ordered, Turnigy's 1600 Kv bells, in yesterday and after the measuring, drilling, setting up and cementing I got two runs in today :cool: I am now in the process of fabricating trimtabs :eek: for the d :censored: mn thing :confused:

It not only runs cooler, the motor seems a little more powerful and is faster or overcomes the water resistant better than the 1750Kv TowerPro. I've also changed the u-joint setup, I'm using a smaller single joint instead of the big heavy raboesch's double joint and all these little changes seem to have contributed to a way faster PT hull. To my surprise with the same kind of motor I burned to a crisp before.

I'm building up the top of it to to be a pirate/smuggler like launch, after it's built up I'm making a movie. I'm not so sure if I'm putting the 3650 Kv motor, I ordered from China, into this hull ;) I might be rebuilding the PT 357 with it instead, I'm not sure if the hull is up to a direct drive 3650 Kv :D Boo

[pkboo]

As it's already semi scale and I thought I'ld experiment a little further I installed the trim tabs and had a run with it ;) Wow :eek: , I retract my words on not being able to control the boat and 'fraid of putting a faster motor into that hull, what a difference a day makes :cool: Can't wait for the arrival of the motor now, it ran straight as an arrow, it didn't sink in the back, it stuck it's nose a tad up, just so that the sideboards coming up the bow would be picking the waves underneath it, what a sight! I'm amazed at the change, the power of trim tabs wow, only 20x15mm big! Boo

[Hoghappy]

I love that water cooled motor mount! Very nice! :cool: I may try to do something similar.

Capt. Crash

[785boats]

Brilliant piece of work pkboo. A water cooled heat sink. Good thinking. I realy like the adjustable aspects of the motor mount too.
Best regards.
Paul.

[pkboo]

Thanx guys, it seems to work, I got my third 20 min. run in this afternoon without any incidence while using the same kinda motor, I'm a happy camper :D Boo

[nick_75au]

Hi pkboo,
those tabs completely transformed the crash boat hull as well, and the balsa square stopped it from completely digging in on the turns, enough that when I build a super structure I wont need to tape down the deck like I have been doing in the past.
Regards
Nick

[pkboo]

Hi Nick, ain´t life sometimes great with simple solutions!? I´ve seen the transformation in turns as well and yes mine used to put the deck into the water as well but mine is siliconed shut :) Eugène