Cooling the motors?

[john_h]

This is a model of the 1890s semi-submersible steam ram, USS Katahdin. It is to be equipped with two 5-pole motors -- Johnson 545's, which are comparable to Mabuchi 545s. There will be no gearbox. Here is a link to a photo of the boat, empty machinery compartment, etc.

http://www.grovestreet.com/servlet/View?pid=487559&cd=226

The model is designed to use differential prop steering electronically mixed with rudder steering.

These motors are going to be pretty much buried inside the finished model, and working a lot. My question is, would it be good practice to use water cooling coils? What do you do on your subs?

Many thanks for your insights.

[john_h]

Link didn't work for some

Link didn't work for some reason. Let's try this one.

http://www.grovestreet.com/jsp/onepic.jsp?id=487559

[safrole]

Great model!

I have the same

Great model!

I have the same question. My motors get pretty toasty, especially if I run them at capacity. Too hot to touch firmly for more than about two seconds. They don't seem to have suffered for it, but I have contemplated a contrivance of brass tube and airplane fuel line to draw water around the motors. I figured if one end dumped out by the props, the Venturi effect would change the water. Maybe it wouldn't flow continuously, but I don't think that's critical.

I think there are solutions to be borrowed from the electric racing guys, too.

[safrole]

Check this out.

http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXT036&P=7

Check this out.

http://www2.towerhobbies.com/cgi-bin...?&I=LXT036&P=7

[rpm]

You should have a gearbox.

[color=#000000]You should have a gearbox. Not using one is a good way to turn your battery capacity into heat]

[john_h]

You are probably right. I

You are probably right. I am a novice at this and feeling my way into it. However, here is the supplier's commentary re high rpm vs high torque motors. A similar choice must be made in selecting motors for aircraft, so it seems to square with experience.

http://www.eaelec.com/motors.htm#john

Pandan in the UK has lots of cooling coils, and also a heat exchanger from Robbe that looks simpler to install -- tho a lot less elegant than those gorgeous chromium plated Kyosho coils

A problem with any of these cooling system is the requirement for holes in the hull or hulls.

[Guest]

Err, sorry but I have

Err, sorry but I have to disagree with you there RPM. Using direct drive is the MOST efficent means of drive , provided the motor is well matched to the propeller.

Unfortunately this is often difficult to achieve, either through availability of appropriate motors or insufficient space to mount a large diameter armature motor.

Therefore it's often necessary to reduce the motors RPM using either gears or belt drive. Both impart an efficency loss of at least 5-10%.

I've found the best source of marine motors to be my local breakers yard. Look at heater blower fan motors, electric window motors, windscreen wiper motors, radiator fan motors.

These are extremely efficient, very high quality, and will barely work up a sweat in our models, plus they work in a good RPM band, generally 2000-5000 RPM.

I never pay more than fiver for a motor.

For smaller models (3 foot and under), try and look out for surplus Buhler and Maxon motors- these are excellent, but it can be difficultto find the right model.

Andy

[john_h]

Here is the Pandan link.

Here is the Pandan link. If you scroll down not quite 3/4 of the page, you can find heat exchangers, coils, and hull scoop/exit fittings. All this stuff seems intended for the fast electric enthusiasts, and it looks nicely made.

[john_h]

Nuts. Forgot the link]http://cgi.ddkeo.force9.co.uk/acatalo....89.html

Nuts. Forgot the link]http://cgi.ddkeo.force9.co.uk/acatalo....89.html[/url]

[Guest]

Overkill, IMHO.

What size of prop

Overkill, IMHO.

What size of prop are you spinning?

If it's less than about 1.25", I shouldn't worry too much about gearing.

As for cooling, remember that although the motors are in an enclosed space, the air inside is cooled by the surrounding water in a submarine boat. Admittedly this is no competition for direct watercooling, but it is in 99% of cases, more than adequate.

Fast electric boats are a different kettle of fish. The motors in those boats are required to work very hard for a short period of time, plus they spend most of their time out of the water with the motor being hermetically sealed in a small (usually) plastic hull.

Clearly in that scenario the motor is going to get very hot, very quickly, so watercooling makes some sense.

[john_h]

Well, there is often something

Well, there is often something to be said for overkill.

Here is a stern view of the boat, and the props. It will run semi-submerged to the level of the painted waterline.

http://www.grovestreet.com/jsp/onepic.jsp?id=487556

The ship displaces a lot of water. I have some passive cooling through the smokestack. (1892 tech) but the ventilators are all dummies.

Anyway, I gather no one is using water cooling?

[rcher]

I agree with Sub-Culture. On

I agree with Sub-Culture. On my sub, I'm planning on bolting the motor to an aluminum end plate which will be exposed to water on the outside of the WTC. Simple watercooling without the plumbing.

In anycase, I believe that I read that the WTC depends on positive pressure on the outside of the WTC to achieve a good seal. I think that if you're going to use a cooling coil inside your WTC, that it might be a good idea to use hard plumbing and avoid the use of rubber(silicone) lines inside the WTC. ( else the silicone lines may balloon and pop off.)

[bigdave]

I am running water cooling

I am running water cooling in my Disney Nautilus. The rear motor WTC is small and was getting a little warm during a run. I have a 540 with a 6/1 gear ratio. The prop is very efficent even though it looks antique. I ran two 1/4 inch copper tubes in through the end cap. They go up and over the motor and are connected to it with brass straps. Each tube has an input and output in the end cap. I connected the inputs to the water inlet scoops that were on the hull already with plastic tubing. I just made them functional. I know it is working because after I run for a while the water that drains from the tubes is warm. Dave.

[Guest]

I agree with Sub-Culture. On

I agree with Sub-Culture. On my sub, I'm planning on bolting the motor to an aluminum end plate which will be exposed to water on the outside of the WTC. Simple watercooling without the plumbing.

In anycase, I believe that I read that the WTC depends on positive pressure on the outside of the WTC to achieve a good seal. I think that if you're going to use a cooling coil inside your WTC, that it might be a good idea to use hard plumbing and avoid the use of rubber(silicone) lines inside the WTC. ( else the silicone lines may balloon and pop off.)

Fair point, but as this boat doesn't fully submerge, water pressure isn't going to be a concern.

Looking at those props, they look fairly sizeable, and quite coarse in pitch, so you may find the boat runs a little fast. There some reduction in the motors RPM may be necessary.

You can do this by gearing, or by reducing the voltage to the motors. The latter will give a corresponding reduction in motor torque, but they may already have more than enough to spin the props.

Suck and see.

Andy

[rpm]

Of course it depends on

[color=#000000]Of course it depends on the motors you use, Most of our suitable hobby motors should have reduction drive, or a very small speedboat type prop. If you need water cooling you are either loading the motor too much, or you are using too high a voltage. This is fine in a speedboat and preferable.
I am talking about motors like 380-550 size.

It is just a mis-matched setup to have a scale sub with little Octura type props you NEED to avoid over loading the screaming direct drive motors. It's like putting a Ferrari engine in a tractor.

I guarantee you will measure a higher amp with direct drive vs reduction, and reduced run times, more heat etc.
It will work but it is not really the way to go.

The way to do direct drive is to use a lot bigger motor and lower voltage, but again most motors need to spin like 7000 rpm to not be over loaded. But Why? nice 3]