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as a novice I am not to familiar with how to setup props and shafts so please correct me if I have anything wrong with my setup. I will be drilling a holes in the hull into which I will put brass tubing and cement into the hull. I will then put a shaft through the brass tubing and on the outside of the hull I will bolt a propon the shaft. on the inside I will put a collar on the shaft to keep it from falling out. I will then put a coupler with a dogbone to connect to the motors. I am hoping that the tention of the motor and dogbone will hold the shaft in against the collar that is inside the hull. I will also be lubing the shaft with silicone oil. is this the correct way or not?
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Pictures would help me get a handle of your particular installation. Is this a single or double-shaft arrangement? You need an Oilite bearing between the propeller shaft and hull, not just a brass tube. And thrust washers between forward face of the propeller hub and Oilite bearing.
Pictures!
David,Who is John Galt? -
OK,
Probably this is as good a place as any to discuss bearings...
On the main shaft, the Wizard recommends Oilite bearings. A quick trip to Wikipedia offers some useful background: http://en.wikipedia.org/wiki/Oilite
Having read that information, I assume the desired property is the impregnated lubrication and that subs need the bronze alloy for corrosion resistance. On the surface of it, looks like Oilite Plus is the better choice, but Wikipedia doesn't include pricing information.
Axle bearings... (Wait, subs don't have axles. But they do have control surfaces that pivot around solid connecting rods that pierce through the hull.) I've always been curious why rudder posts and the like didn't pass through a bearing, but rather used the polystyrene or GRP skin of the hull as bearings. In an aircraft or in a heli, thin skinned as they are, I would expect to see a bearing anchored to the skin. I assume the lack of such surfaces is due to the expectation of light loads and a desire for simplicity. If one did use such a bearing, would it be Oilite again, or a sealed bearing as are used in aircraft? (I assume Oilite is preferable, since sealed doesn't mean "watertight.")
Standing by to receive wisdom...Last edited by Outrider; 04-08-2010, 10:32 PM.Comment
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Stand By For Wisdom!....
We don't bother with proper control surface operating shaft bearings just for the reasons you observed, Jim: light loads, and limited rotation rates.
And the self-lubricating properties are the main reason we use them in r/c subs; their simplicity and the zero corrosion problems are big virtues in a vehicle operating in a sometimes wet environment. I should also mention that we employ the shaft Oilite bears to take both transverse (journal bearings do this), ahead, and astern loads -- it's the shaft bearing that transmits all propeller loads, through the propeller shaft, the the vessels structure, with the minimum friction losses at the contact points (bore, and forward and after face of the bearing). You simply don't get that utility out of dedicated roller and ball bearings.
But it is the impregnating oil within the porous Bronze matrix that also gives us the biggest head-ache when using Oilite type bearings: the oil will leach out of the bearing into adjoining structures and will, if it gets onto the surface of the model, prevent proper sticking of primer and paints. This will happen if the bearing(s) are installed too soon in the assembly. For this reason I defer installation of the shaft Oilite bearings till after the model is primed and painted.
David,Who is John Galt?Comment
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Hmm... Sounds like Oilite is a consumable part then--no more oil leaching = no more lubricating properties, at least at some point.
I was looking at the D&E Kilo Fittings kit and it appears that the prop shaft bearings are white metal castings. I'm assuming that Oilite either isn't neccesary for these small boats or that it's tough (or cost prohibitive) to get Oilite bearings for this application. (From the wiki page, it appears that Oilite is somewhat difficult to drill in such a way that the hole bore is kept porous enough to retain the desired lubricative (is that a word?) properties. From the Caswell site, the Oilite bearings look plenty affordable in stock sizes (just $.35 each) http://www.caswellplating.com/models/oiltite.html but the stock sizes may not be of much use in small boat applications.Comment
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may I please see a picture of what a proper setup looks like. like I said my idea was for a shaft going through a brass tube held in place not by a thrust washer but by a collar on the shaft. I would like to see how a proper setup is done.Comment
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Neither Mike nor I have been able to secure a source that sells Oilite type bearings in bore sizes smaller than 1/8" diameter -- that's why I went with the white-metal bearing for the KILO fittings kit. In that application the end-user has to provide a drop of oil to lube up that bearing.
David,Who is John Galt?Comment
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Your wish is my command:
Below are shots showing how I installed the running gear (propeller, propeller shaft, Oilite bearings, thrust washers, and Dumas type universal coupler) into this 1/72 ALFA kit. Rose is showing off the primed, operational model.
It's my practice to make the propeller shaft as short as possible, sometimes so short I can get away with using only one Oilite journal-thrust bearing. But, in this case, because of the very tight taper of the stern, I was compelled to make the propeller shaft long enough to require two Oilite bearings, one at each end -- thus forming a forward, astern thrust bearing and an after, ahead thrust bearing. The ahead load presents to the after bearing through the after thrust washer pushed forward by the forward face of the propeller hub. The astern load presents to the forward bearing through the forward thrust washer pushed aft by the after face of the coupler.
Note that I first drew the proposed running gear onto the model's stern itself -- this immediately resolves fit and interference issues. Once happy with the arrangement, I cut out the shaft from 3/16" diameter stainless steel and milled flats to each end -- the after flat to accept the set-screw of the propeller, and the forward flat to accept the Dumas coupler set-screw. In foreground is the actual assembled ALFA running gear. Note the bearings and a thrust washers against each flanged end.
The two bearings had to fit into a centered hole at the stern, so I built up this foundation from West System epoxy resin poured into the up-ended model. A weep-hole (seen in the above photo) insured that the forward face of the epoxy foundation plug would terminate at the hole, later putted over. A brass rod of appropriate diameter was waxed and temporarily centered in the hull and the catalyzed resin poured in. This rod becoming a bore forming mandrel.
Later, after the resin cured hard, the rod was pulled out and the two Oilite bearings installed. The Dumas type coupler was made up to one end of the propeller shaft and the astern thrust washer. Then the propeller shaft was slide through the Oilite bearings from the inside. And, from the stern the ahead thrust washers, and propeller were installed.
Done! No big deal.
Damn! ... I'm good!
Attached FilesLast edited by Outrider; 04-08-2010, 10:36 PM.Who is John Galt?Comment
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I got it now I am trying to to figure how to apply your technique to my situation which is a little different then you setup.
I guess I could mount a transverse cross member inside the hull near the sd to drill and mount some bearings for forward support. maybe drill and mount a bearing going through the hull but will I be ok with letting the end of the shaft go through that brass bar in the stern for support?Comment
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