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Dec 09, 2019, 06:43 AM
kry
kry1001's Avatar
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Why are the propeller shaft tubes heated?


Hello!
I found a problem at my submarine and I want to ask for your advice, or if you had this problem too.
I have a Type XXI 1:40 scale submarine from Robbe that I converted into static dive with ballast tank from Engel.
  Aft tube with propeller shaft with bronze brushes from the kit are still used. In the tube I inserted grease to prevent it from entering the water and for lubrication. I found that the ends of the rods (both in the propellers and in the coupling of the motors) are very hot, from the area of the bronze bushes. Basically burn!
Has any of you happened the same? Do you think the water will cool enough to function normally? If the shaft port will cool (it is 95% outside, basically only 3cm are in WTC), do you think it will cool inside?
Why are the propeller shaft tubes heated?
Thank you for help!
Last edited by kry1001; Dec 09, 2019 at 06:48 AM.
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Dec 09, 2019, 08:43 AM
Registered User
tchalfant's Avatar
Are your shafts brass or stainless steel? I ask because I have found brass expands a little more than stainless steel. However, water will help cool. The heat is friction and a light sanding of the shaft in that area might reduce the rubbing using 1200 grit or higher sandpaper.
Another thought, what RPM are you running at?
Dec 09, 2019, 08:51 AM
kry
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The tube is made of brass with bronze bushes and the shaft is made of stainless steel.
I honestly don't know what RPM the engines have. I use two Engines 540, 6V engines.
Even if the engines go at full speed, even if they rotate at half the speed, after about 5 minutes, the tube, in the area of the bronze bushes, is hot, even burn!
Dec 09, 2019, 10:59 AM
Registered User
tchalfant's Avatar
Your shaft build look really good. I build them the same way.
Your prop turns easily when not connected to the motor?
With no gears to bring the RPM down, your motors are running 12,000 to 18,000 RPMs, for subs we gear them down to 2,000 to 3,000RPM. So, the friction is the issue. Try running the end of the WTC in water and see what happens (if you are at that point). Just know running in the air is not sufficient to cool down those bushings and shaft ( as a side note, a drop or less of synthetic motor oil [I use STP] might help). As things heat up they expand, meaning even more friction.
So, for right now, wait until you can test in water and do not run for 5 minutes (if you use o-rings, you can burn them up with the heat).
Dec 09, 2019, 01:25 PM
kry
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The coupling from the propeller shaft to the motor is made with navy coupling kardan. Inside the WTC, we also installed an o-ring system from Modellbau Wikinger.
Dec 09, 2019, 01:28 PM
kry
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A few photos
Dec 09, 2019, 03:48 PM
Registered User
tchalfant's Avatar
Very good seals. Just be careful running it dry (again from heat). I like what you have going there.
Dec 09, 2019, 05:53 PM
Latitudes vs Attitudes
Bob Gaito's Avatar
Sure sounds like too much friction. There should be a little end play between the props and the shaft logs-especially under load...also end play between all hubs, like the universal and the end of the stuffing tube and the universal to where the drive shafts exits the WTC. It was asked quickly earlier, can you easily turn the props by hand? The cause is usually where the heat is..
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Dec 10, 2019, 09:17 AM
kry
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Hello!
I also have a submarine from Robbe type VII. I did the test on him. The tubes of the propeller shafts are not heated at all, and when rotated by hand, they move very easily.
I also did the type XXI test. When rotating the propeller shaft, without mounting the couplings to the motors, they move slightly (but harder than in type VII). It seems to move harder than the Type VII because of the Modellbau Wikinger's O-ring system, or there would be too much grease in the tube (although in the tube I didn't put too much grease, just a little at the ends of the tube, and in the tube mounted perpendicular to grease supply). It does not seem to move any harder because the bushes would tighten the propeller shaft.
Dec 10, 2019, 11:23 AM
Latitudes vs Attitudes
Bob Gaito's Avatar
What about end play-there should be a little movement fore and aft on all shafts (a few thousandths of an inch)
Latest blog entry: Mark V Navy Seal SOC
Dec 10, 2019, 03:11 PM
kry
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There is an axial and diametric clearance of the propeller shaft in the tube. I ordered a new set of propeller shafts from Krick. I also removed the o-ring system from Modellbau Wikinger (the o-ring support is made of aluminum and has a portion of about 3mm in contact with the bronze bush and which is in contact with the shaft. I think the expansion of these materials is different : bronze-steel - aluminum). When I get the new axles I will mount them and see how it will work. Until then I will change engines. I'll put engines without brushes.
Dec 11, 2019, 11:35 AM
Modeler/ Historian
Stephen Vick's Avatar
I had a Robbe Type XXI , which I modified with an Engle Tank. I used the stock Robbe tech rack and screw joiner too. I found that once I had the boat buttoned up, the tension on the rack would miss-align the shafts and they would bind.. a rebuild with a stronger tech rack solved the problem .
Dec 11, 2019, 02:33 PM
kry
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Hello Ștefan
The type XXI of the Robbe I used Rack of the Modellbau Wikinger

https://www.rcgroups.com/forums/show...I#post37074736
Dec 11, 2019, 02:36 PM
kry
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Thread OP
Type xxi
Dec 11, 2019, 04:43 PM
Modeler/ Historian
Stephen Vick's Avatar
The Wikinger tech rack is a great piece of gear. I'm using one in a Robbe Type VII.


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