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Question About Cooling motors

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Question About Cooling motors

Postby Darksheer » Mon Aug 31, 2009 2:41 pm

I recently changed my robbe U47 over to 12 volt operation using graupner 500e motors and when i had the sub out yesturday the motors for lack of better words over heated very badly after a run of about 25 mins
they were so hot that they warped the motor mounts and burned someones hands when they touched them. The linkages and prop shafts were freely turning and nothing was fouled in the props

I am looking at installling a set of these cooling jackets and setting the intakes up at the stern of the sub it would require me to drill 2 small intake lines and a single larger exhaust pipe hole in the WTC

http://www.cornwallmodelboats.co.uk/acatalog/water_cooling.html

will these work in a submarine model
or will need to install a water pump on top of these for proper cooling ?

or should i just abandon the idea of these 12 volt motors and go back to the stock robbe ones

any help would be appreciated
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Re: Hot Tamales !

Postby Darksheer » Mon Aug 31, 2009 3:35 pm

sunworksco wrote:Are you direct driving the motor ?
Something is wrong if it is overheating.
I would start by testing the motor under load with a watt meter hooked up.You may consider using a sensored brushless motor direct drive.Novak #3420 motors operate at 0-11,000 rpm and do very well at low speeds,have high torque to move large props,run very cool,have no noise feedback to esc/receiver,have oversized ballbearings and are the equivilant to a 540 brushed can motor.

yes they are direct drive and are turning counter rotating 35 size brass props
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Re: Props

Postby Darksheer » Mon Aug 31, 2009 4:21 pm

sunworksco wrote:35 mm?


yes 35mm props same size as waht comes with the kit but made of brass
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Postby Skip Asay » Mon Aug 31, 2009 5:16 pm

Throw those motors away!! If you're generating that much heat, you're pulling too many amps. I would recommend a couple of Speed 400 motors geared at least 3:1. You'll be amazed at how much power you'll have as well as a tremendous increase in run time and decrease in heat.

Anytime watercooling is necessary indicates faulty drive train engineering.

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Postby tsenecal » Mon Aug 31, 2009 6:45 pm

Original design for the u47 is as a dynamic diver, which is why it needs 500 size motors. It needs to go much faster than scale speed to drive itself below the surface.

Most people drop the original 500 size motors for the u47 because they drain batteries rather quickly, but at the same time, they upgrade to a static diver. this is what allows them to drop to a geared 400 size motor.

for what reason did you drop the original 6 volt design for the 12 volt?

have you kept it as a dynamic diver?

If you have kept it as a dynamic diver, you may be stuck with the original motors and 6 volt operation.

I can't imagine how much amperage the 12 volt setup must have used, even compared to the original setup, that is way overkill.
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Postby RickNelson » Mon Aug 31, 2009 7:04 pm

If you kept the same motors (it wasn't clear in your post) and just doubled the voltage here is what happened. By doubling the voltage (I'm assuming that you were running a 6v system before) you doubled the amount of power the motors had to dissipate. The current would have stayed the same since the motors didn't change. The equation P = I * E (Power = Icurrent * Evolts) is what got your motors hot. By going to 12 v you changed the equation to 2P = I * 2E. The motors were not designed to dissipate twice the power.

This would be like changing your TV voltage from 110v to 220v without doing anything else. You would fry you TV.

You have to change the motors to take advantage of the additional power available. And keep in mind that the power dissipated will be higher so you may have to provide cooling. You don't get something for nothing.
Last edited by RickNelson on Mon Aug 31, 2009 7:12 pm, edited 1 time in total.
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motors

Postby fgroza » Mon Aug 31, 2009 7:05 pm

Skip hit the ideal setup. I run speed 400 motors with 3-1 Great Planes ball bearing gearboxes on 6v. You can series the 6v motors and run 12v through them as each motor will see 6v. However if one motor/shaft gets bound or stuck, all 12v will go through the free motor. I can run as fast as I need to dynamic dive my U-47 even though it is converted to RCABS. The run time will increase with the 400 motors also. And yes I am running 35mm brass props.
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Postby Darksheer » Mon Aug 31, 2009 11:22 pm

tsenecal wrote:Original design for the u47 is as a dynamic diver, which is why it needs 500 size motors. It needs to go much faster than scale speed to drive itself below the surface.

Most people drop the original 500 size motors for the u47 because they drain batteries rather quickly, but at the same time, they upgrade to a static diver. this is what allows them to drop to a geared 400 size motor.

for what reason did you drop the original 6 volt design for the 12 volt?

have you kept it as a dynamic diver?

If you have kept it as a dynamic diver, you may be stuck with the original motors and 6 volt operation.

I can't imagine how much amperage the 12 volt setup must have used, even compared to the original setup, that is way overkill.



first off thank you for all the replies everyone

I did alot of research and it seemed that the graupner speed 500e motors were the motors of choice on various forums here included so i ordered a set and changed them around it was a simple change over and just required me to switch the batteries from series to parrallel and drop them in

The sub is still a dynamic diver and i was unable to get the boat to submerge with these new motors fitted I was eventually planning on fitting the engel tank to it but after the ease of diving dynamically i decided to just change the motors over to more efficiant 12 volt ones or so i was told

Altho with the old 6 volt setup i could submerge with ease

I spoke with one of the techs at work and explained the problem to him his first question was if i got the props out of the water while attempting to dive the boat which it did a good dozen times and after a second or 2 of them being in the air they would hit the water again

he seems to think thats what caused the over heating as he could find nothing wrong with the set up on the bench every read normal and according to him having the props come out of the water and drop back in would put enormouse stress and load on the motors causing alot of heat


I will probably switch the system back to 6 volt and put the original motors back in as I cannot seem to find a decent efficient set of 500 size motors in 6 volts and the speed 500e do not provide alot of thrust at 6 volts
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Postby Skip Asay » Tue Sep 01, 2009 12:33 am

"he seems to think thats what caused the over heating as he could find nothing wrong with the set up on the bench every read normal and according to him having the props come out of the water and drop back in would put enormouse stress and load on the motors causing alot of heat"

Sorry, I'm quite sure your tech is very knowledgeable in his field but this isn't it. Heat in an electric motor is caused by the amperage going through it, usually caused by too much load. In his scenario, if anything, the motors should run a little cooler since with the props out of the water the load is reduced substantially thereby reducing the amperage being drawn. Here's how you can prove it: run the boat in your test tank (you do have one, right?) for that same 25 minutes but don't let the props come out of the water. They're still super hot, right? Now spend the time and effort and get a pair of Speed 400 motors with 3:1 gearboxes and do the same test again. Much less heat, right? And you have the added benefit of substantially more run time, as well.

Too many people feel that big boat=big motors. This is just so wrong. But don't take my word for it. Try it yourself.

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Postby Sub culture » Tue Sep 01, 2009 2:30 am

The point that puzzles me, is that you're having problems with Speed 500e's. These motors should work those props easily without any gearing.

You're quite sure you have 500e's and not another 500 variant?
'Why are you staring at an empty pond?'

Want to dive your boat in crystal clear water? Then you had better Dive-in- http://www.diveintomodelsubmarines.co.uk
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Postby Darksheer » Tue Sep 01, 2009 7:33 am

Sub culture wrote:The point that puzzles me, is that you're having problems with Speed 500e's. These motors should work those props easily without any gearing.

You're quite sure you have 500e's and not another 500 variant?


the box and the motors both read "graupner speed 500e" and the shafts turn with almost no resistance
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Postby TMSmalley » Tue Sep 01, 2009 7:44 am

Are you sure you are getting 12 volts from the batts?
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Postby Darksheer » Tue Sep 01, 2009 8:34 am

TMSmalley wrote:Are you sure you are getting 12 volts from the batts?


postive 2x 6 volt batteries running parralel

volt meter reads 12 volts
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Postby Robert F. » Tue Sep 01, 2009 10:13 am

Running batteries parallel doubles the total of Amperes available, NOT the Voltage. If you want to double the voltage, hook them up "in series". I.e. connect the + of one battery to the - of the other.......... that's really basic knowledge of electricity. I can only hope you did the right thing but used the wrong term naming it.


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Postby Darksheer » Tue Sep 01, 2009 10:49 am

yes your correct sorry it was early when i replied they are in series plus to minus around the batteries wiring is right term was wrong

tech guy also suggested i reprogram my speed control again and see if that helps ?
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