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Old Feb 14, 2013, 04:46 PM
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I think I have found a solution to the 2855 2100 melting the CS shrouds. First the exit cooling hole is only 7mm and should be opened up to equal the 6 5mm exit holes on the inside of the bell. I figure a little over 12mm is about right. Second I added some gasket material between the motor and shroud, and gasket washers under the motor mounting screws. This is to help isolate the heat from the plastic. In a trial run, the motor with the larger exit ran at least 10 degrees F cooler than the stock opening motor. I only ran at 1700 Watts (combined for both fans) so the motors were not very stressed. I believe if they get pushed harder the temperature difference might be greater. Hoped to find fiber washers, but the automotive gasket seems to work quite well.

PS edited.... temperature difference with larger exit is at least 10F. My first reading was false as I had inadvertently reduced the gap behind the fan when the motor was spaced father aft with the gasket material.
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Old Feb 14, 2013, 05:00 PM
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My L2855-2100kv didn't even get that hot to seem to matter.
I run 2300kv's in the CS10, and they were under too much duress in the CS12 so I changed to 2100kv. Sustained WOT at that now is 'too low' KV and meant less power and less heat anyway.
I usually test with an infrared temp gauge after test runs, but I grab it by fingers first.... and if I go "ouch" that means "50degC to 60degC" range most likely and then I will test it by temp meter. And I never went "ouch", so that meant it wasn't even 50degC so no need to check accurately.

I was not very happy with the CS12 results at all....
Same power draw (Amps) as the CS10, but less thrust. In both the 2100kv and 2300kv (2300kv being overly hot afterwards though).
So you are forced to use the 2100kv..... get less thrust than the CS10 with a 2300kv, but uses the same Power (Amps) anyway! And doesn't sound any better either.

At that power level the better housing is irrelevant.... so there is just no point in using it over the CS10.
But I will be trying the Lander10 rotor in the CS12 housings, as they will fit it exactly as per the 12 blade rotor (same diameter), and will hopefully be more efficient.

I don't know what I will do with the 12 blade rotors.... I will test them with much better motors (2200kv 5S & 6S with a 2960 motor) just IN CASE they miraculously work more efficiently at the higher RPM areas that would be.
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Old Feb 14, 2013, 05:11 PM
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Peter I am running 6S. That is why I'm running the lowest KV version of the 2855. At WOT it will burn up so I have to limit the current (as posted earlier). I can't speak for the thrust or sound in the air (10 blade vs. 12 blade) as I haven't flown the combination yet. On the bench it is hard to see any difference other than the higher draw of the 12 blade.
Cheers
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Old Feb 14, 2013, 05:17 PM
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Lander 10-blade rotors; direction of cool air in the motor

I don't know, the Lander 10-blade rotors I have are smaller even than the CS 10-blade rotors, and they have a LOT of clearance in the Freewing or CS 12 shrouds.

Regarding the exit holes on the L-2855 motors, that is interesting that there would be such a difference. I would like to know where the air is actually flowing. For the Wemo Minifan I know (from WeMoTec) that the air is actually sucked from the rear to the front of the motor, driven by the low pressure in the gap between the rotor and the motor "housing" (fast air over the gap sucking stronger there than the pull at the rear of the motor). BTW they know because the dirt from the brushes in the old days went through the motors and out in the front, to be blown back in the main airstream...
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Old Feb 14, 2013, 05:41 PM
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Oh, derr, LOL.... I was automatically thinking 5S. Seeing I would never run them on 6S in these CS10/12.
But a decent 2200kv (2960) I will run 6S.
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Old Feb 14, 2013, 06:21 PM
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Anyone have the edfhobby 2500kv 5s 90mm motor to try only 40ish dollars?
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Old Feb 14, 2013, 08:01 PM
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Picture of modified cooling exit on Turnigy L2855...
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Old Feb 14, 2013, 10:09 PM
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Did you use the motor as a "lathe"?? LOL

How did you do it?
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Old Feb 15, 2013, 02:09 AM
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Peter,

I did a number of them for special projects and EDFs, by laying them on thier side in an "almost closed" drill vise, then rotated the fairing by hand while cutting with a Carbide, cutoff disc in a Dremel tool.
Then cleaned up the edge by hand "lapping" on a piece of 400 grit wet-n-dry sandpaper.

Hope that helps.
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Old Feb 15, 2013, 02:33 AM
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Quote:
Originally Posted by mopetista View Post
For the Wemo Minifan I know (from WeMoTec) that the air is actually sucked from the rear to the front of the motor, driven by the low pressure in the gap between the rotor and the motor "housing" (fast air over the gap sucking stronger there than the pull at the rear of the motor). BTW they know because the dirt from the brushes in the old days went through the motors and out in the front, to be blown back in the main airstream...
Should be true for any fan. Stu has made the same comment. It's caused by the pressure difference between the air at the back of the stators and the gap in front of the stators. If the motor is entirely behind, on a standoff, it should just keep going backwards.

Of course, the carbon dust must have been blown forward by something other than pressure rise, as many people here will scream blue murder if you insinuate EDFs raise pressure
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Old Feb 15, 2013, 05:36 AM
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Quote:
Originally Posted by Odysis View Post
Should be true for any fan. Stu has made the same comment. It's caused by the pressure difference between the air at the back of the stators and the gap in front of the stators. If the motor is entirely behind, on a standoff, it should just keep going backwards.

Of course, the carbon dust must have been blown forward by something other than pressure rise, as many people here will scream blue murder if you insinuate EDFs raise pressure
And of course this kind of talk would open another can of worms and a new kind of bench testing. ie: size of gap vs amount of pressure vs amount of cooling through the motor...
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Old Feb 15, 2013, 06:39 AM
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no, I am not interested in initiating just another pseudo-scientific EDF "knowledge" contest.
I just found it interesting to note that what is usually considered an "air exit hole" at the rear of the motor is in fact a air inlet since the air is going back-to-front inside the motor. Not sure if that calls for bigger or smaller rear holes, that should in fact depend on the holes in the front of the motor mount - I'll stop here for fear of the can-o-worms :-)
I guess that measurements are still the best way to progress in that complicated matter, and if the motor stays cooler with a bigger rear hole then that then is the way to go where superior cooling is needed
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Old Feb 15, 2013, 06:47 AM
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The exit was simply ground down on my bench mounted belt sander. The alloy is pretty thin and grinds away fast. The bell was first removed from the motor and was full of alloy dust after the process. I now have three others to shorten now that I know it works.
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Old Feb 15, 2013, 07:10 AM
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Eric,

I like the gasket material idea.

About enlarging the cooling hole, wouldn't it better to remove the cone altogether even if it reduces the heat radiation surface?

Andrew
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Old Feb 15, 2013, 08:09 AM
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Hi Andrew,
I think it is good to have the streamlining effect from the cone and only have the opening just as large as the 6 air openings just behind the motor. Any larger and the air will become more turbulent as it passes the sharp edge of the flat motor end (assuming the cone is removed). I always add a cone to my inrunners for the same reason.
I still don't know how the cone is secured to the motor bell. It must be threaded or pressed on very well. I know it is separate as there is a set screw in the traditional place to hold the motor shaft to the bell.
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