Why I Water cool
04-20-2011, 04:11 PM
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Why I Water cool
Its been a while since I have posted but this one is to say the least very interesting.
Before I could only guess at just what temperature the drive motors on my Robbe Type XXI a 73 inch monster was running at after a long run and long I meanwalking some 2800 steps round trip,what that averages out to I do not know yet,but its a big lake with walkways allthe way around.
Usually Imake the missionfor 3 round trips around the lake with a 2 to 3 rest stops and to practice docking and sub pen maneuvers in the underground pens (culverts) they make perfect pens foreven 2 subsas long as the water level is adequate which is most of the time now with the rains very cool.
Well as one can imagine thats allot of distance and ruining time and with Lipos its so easy to go the distance but one has to watch out for the enemy of electric motors and that is heat,you wonder how much you won't believe how hot they get and that does not account for the air space that also gets heated up and expands inside of the casing,so much that a seal or plastic wall could burst causing a catastrophic failure of the casing and consequent flooding ,one day I will make a pressure reading of it at peak temperature.
After running the sub on the surface for some 1000 paces the reading on the Telemetry screen read 123 F on the port motor and 128 F on the starboard motor,no water cooling at all except for the motor coming into contact with the casing which is plastic ,not the best conductor of heat but some dissipation does occur.
Then the same run and distance but submerged, it gets even hotter as the motors must work harder to go at the same speed as more serf ace area of the sub is in direct contact with the oncoming water stream.
The temp reached 145 F on the starboard and 142 F on the port .
The air temp was a 85 F and the water in the 70's.
Imagine how much hotter it will get in the peak of summer!
So now we know just how hot it gets inside of a normally set up sub of this size.
The motors are 2Mabuchi 550 can motors on11.1 Lipos and 2 3.5 to 1 ball bearing geared boxes and 2 motronics ESCs turning the stock 3 bladed props with very little friction on the hole drive,so its set upvery well .
So that is why I water cool all my subs and have done so for many years now no regrets just good long runs.
Now comes the fun part of installing water cooling to this sub as it was not done for this test and will be challenge in that the casing is 3 inches in diameter and those 2 motors side by side and with the offset of the gearboxes it gets too tight with the cooling coils ,so I have to figure out a different approach ,maybe a epoxy that conducts heat ,placed around the motor and then a screw or brass shaft exiting the casing at the rear into the water just might do it.
Anyway I have to figure out something that will extract that heat and keep them cool as already there is afaint smell of hot windings and that I do not like.
If one goes for any descent distance and run times on there sub no mater the size to me it would be a good idea to keep them cool.
I know I brought this up before but now I have some hard evidenceand thoughtI would share it.FYI.
Dave Amur Sub Yard
Before I could only guess at just what temperature the drive motors on my Robbe Type XXI a 73 inch monster was running at after a long run and long I meanwalking some 2800 steps round trip,what that averages out to I do not know yet,but its a big lake with walkways allthe way around.
Usually Imake the missionfor 3 round trips around the lake with a 2 to 3 rest stops and to practice docking and sub pen maneuvers in the underground pens (culverts) they make perfect pens foreven 2 subsas long as the water level is adequate which is most of the time now with the rains very cool.
Well as one can imagine thats allot of distance and ruining time and with Lipos its so easy to go the distance but one has to watch out for the enemy of electric motors and that is heat,you wonder how much you won't believe how hot they get and that does not account for the air space that also gets heated up and expands inside of the casing,so much that a seal or plastic wall could burst causing a catastrophic failure of the casing and consequent flooding ,one day I will make a pressure reading of it at peak temperature.
After running the sub on the surface for some 1000 paces the reading on the Telemetry screen read 123 F on the port motor and 128 F on the starboard motor,no water cooling at all except for the motor coming into contact with the casing which is plastic ,not the best conductor of heat but some dissipation does occur.
Then the same run and distance but submerged, it gets even hotter as the motors must work harder to go at the same speed as more serf ace area of the sub is in direct contact with the oncoming water stream.
The temp reached 145 F on the starboard and 142 F on the port .
The air temp was a 85 F and the water in the 70's.
Imagine how much hotter it will get in the peak of summer!
So now we know just how hot it gets inside of a normally set up sub of this size.
The motors are 2Mabuchi 550 can motors on11.1 Lipos and 2 3.5 to 1 ball bearing geared boxes and 2 motronics ESCs turning the stock 3 bladed props with very little friction on the hole drive,so its set upvery well .
So that is why I water cool all my subs and have done so for many years now no regrets just good long runs.
Now comes the fun part of installing water cooling to this sub as it was not done for this test and will be challenge in that the casing is 3 inches in diameter and those 2 motors side by side and with the offset of the gearboxes it gets too tight with the cooling coils ,so I have to figure out a different approach ,maybe a epoxy that conducts heat ,placed around the motor and then a screw or brass shaft exiting the casing at the rear into the water just might do it.
Anyway I have to figure out something that will extract that heat and keep them cool as already there is afaint smell of hot windings and that I do not like.
If one goes for any descent distance and run times on there sub no mater the size to me it would be a good idea to keep them cool.
I know I brought this up before but now I have some hard evidenceand thoughtI would share it.FYI.
Dave Amur Sub Yard
04-23-2011, 01:55 PM
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RE: Why I Water cool
I know I brought this up before but now I have some hard evidenceand thoughtI would share it.FYI.
Dave Amur Sub Yard
Dave Amur Sub Yard
I have answered that before too.
http://www.rcuniverse.com/forum/m_98...anchor/tm.htm#
ORIGINAL: Tony Fitzpatrick
Dave,I have shown you are a country mile out when you imply it is beneficial to water cool motors in model subs.You can stop hyperlinking to or copy/pasting irrelevant rubbish.
Dave,I have shown you are a country mile out when you imply it is beneficial to water cool motors in model subs.You can stop hyperlinking to or copy/pasting irrelevant rubbish.
04-23-2011, 07:10 PM
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RE: Why I Water cool
I do not see your evidence from a actual RC sub ,a bit different from your engineering hyperlinks,I would sugest that you take some measurements of your subs motors in real time ,like engineers do with Telemitry ,till then there simply is no comparison,wheather good or not it does not hurt anything to keep them cool,does it?
This is FYI only amigo.
This is FYI only amigo.
04-24-2011, 04:10 AM
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RE: Why I Water cool
Your temperature measurements against the material lifetime charts actually demonstrate the futility of cooling that motor in that fashion.You provided the hard evidence indeed.The finite lifetime of the brushes is the limiting factor there.
And FYI,I'm not going to enter any game of personalising this issue but I will not allow you to misrepresent my past statements without comeback.
And FYI,I'm not going to enter any game of personalising this issue but I will not allow you to misrepresent my past statements without comeback.
04-24-2011, 06:04 PM
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RE: Why I Water cool
You should tell that to the RC Boat folks ,do you think they will stop water cooling ,I do not think so ,sure they go allot faster but still get quite hot ,imagine if they sealed them up with no air flow,very very hot.
We go much slower but we are sealed up tight and with big subs comes big loads on the motors and double heat sources ,it gets even hotter.
Tell me how would you cool the subs motor ,do your charts show us how ,no they can not because no one has made one,will the materials take the heat of course I do not argue that ,all I am saying is that to keep it cool aids in efficiency ,longevity and keeps internal air temps down so that expansion is kept down safely preventing leaks.
If any one is misrepresenting another's statements it is you,I do not demonstrate "rubbish" as you have no counter evidence to prove me incorrect.
It is simple physics taking place hear not any games no sir I am serious in these facts.
Later I will show the pressure build up inside of the casing as heat expands the surrounding air.No games just facts ,that is all intuitive people want to see.FYI
We go much slower but we are sealed up tight and with big subs comes big loads on the motors and double heat sources ,it gets even hotter.
Tell me how would you cool the subs motor ,do your charts show us how ,no they can not because no one has made one,will the materials take the heat of course I do not argue that ,all I am saying is that to keep it cool aids in efficiency ,longevity and keeps internal air temps down so that expansion is kept down safely preventing leaks.
If any one is misrepresenting another's statements it is you,I do not demonstrate "rubbish" as you have no counter evidence to prove me incorrect.
It is simple physics taking place hear not any games no sir I am serious in these facts.
Later I will show the pressure build up inside of the casing as heat expands the surrounding air.No games just facts ,that is all intuitive people want to see.FYI
ORIGINAL: Tony Fitzpatrick
Your temperature measurements against the material lifetime charts actually demonstrate the futility of cooling that motor in that fashion.You provided the hard evidence indeed.The finite lifetime of the brushes is the limiting factor there.
And FYI,I'm not going to enter any game of personalizing this issue but I will not allow you to misrepresent my past statements without comeback.
Your temperature measurements against the material lifetime charts actually demonstrate the futility of cooling that motor in that fashion.You provided the hard evidence indeed.The finite lifetime of the brushes is the limiting factor there.
And FYI,I'm not going to enter any game of personalizing this issue but I will not allow you to misrepresent my past statements without comeback.
04-25-2011, 03:46 AM
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RE: Why I Water cool
I use 2 $10 Graupner 500E motors on 12v direct drive. Fitted them when I built the XXI 6 years ago (Robbe motors are 6v). Runs forever (never managed to exhaust the battery) and have not needed to replace or service anything. No additional cooling or heatsinks.
I dont think your motor/gear box was designed for continous running or this application. Just use some cheap hobby grade motors and save yourself a headache.
I dont think your motor/gear box was designed for continous running or this application. Just use some cheap hobby grade motors and save yourself a headache.
04-25-2011, 04:29 AM
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RE: Why I Water cool
Yes I used those original Robbe motors and they do stay nice and cool but they have no performance compared to a regular 12v 550 can motor the difference is nominal without a hole lot of power usage either.
By gearing them down one gets even better power higher torque and longer run times ,this drive setup I have used for years, why because it works, it cost more but is very well worth it as it never has failed not once in over 30 years since the very first one installed in my first RC boat.
I do not see where you have concerns about headaches,I like to have a sub that is swift in just still water but also in a river ,not a torpedo though but a nice normal walk.
As I mentioned above I take my subs for long walks so that it and I can get some good exercise and 2 to 3 times around the lake does the job however it would not be possible at a fast walking speed if I used the Robbie motor setup they just do not have the speed even at 12 volts.
Dave
By gearing them down one gets even better power higher torque and longer run times ,this drive setup I have used for years, why because it works, it cost more but is very well worth it as it never has failed not once in over 30 years since the very first one installed in my first RC boat.
I do not see where you have concerns about headaches,I like to have a sub that is swift in just still water but also in a river ,not a torpedo though but a nice normal walk.
As I mentioned above I take my subs for long walks so that it and I can get some good exercise and 2 to 3 times around the lake does the job however it would not be possible at a fast walking speed if I used the Robbie motor setup they just do not have the speed even at 12 volts.
Dave
