John, Dennis, et al...
Thanks much for the notes, they are a great help. I am no machinist or engineer but I do like to learn as much as I can and this project is certainly a help!
Dennis, based on your suggestions I did read about the bearings on the SKF site, and I looked at bearings for sale through a half dozen distributors willing to sell at the single-unit level (McMaster-Carr, Grainger, thebigbarningstore.com, Baldor, etc.).
At first I let myself be surprised that no bearing recommendation has emerged on this site, since a thrust bearing seems to me to be as important to the conversion project as motor/controller/batteries.
But then it occurred to me that there isn't any consensus on motor/controller/batteries either. ;-)
I suppose in a direct electric drive system, no bearing is necessary since the mounting hardware that holds the motor down transfers the thrust to the hull. But since many electric conversions require reduction to be efficient, from what I have learned they all require a bearing.
The variety is by no means bewildering, but it hasn't seemed like a simple choice to me so far! A great many of them are not manufactured for the corrosive environment of a boat, so that makes the first step easy; but then there is the choice of flange or pillow block; and I was also able to find some which have a bore to accommodate my 1in shaft, but which are not rated to handle the 1600+rpm I expect to demand. The stainless steel ones seem to vary in price from $60something to $200something.
My ICE (an Atomic 4) doesn't have anything that I would call a "thrust bearing," but that's probably because I am just learning the names for these things. As far as I can tell, the tailshaft emerging from the engine is connected mechanically to the pistons via the crankshaft and some other magic that makes reverse happen...in any case what is on the aft side of the engine is just a flange, called perhaps an output flange, which bolts directly to the prop shaft flange. I suppose technically there must be a bearing where the tailshaft exits the engine, but the two applications are quite different in my mind since the tailshaft is really part of the engine, whereas the pulleys and belts I will end up installing as part of the electric drive system are not part of the electric motor.
...put another way, the tailshaft is not tabbed to the hull,but the flange mounting plate will be.
Has anyone been particularly happy or unhappy with the bearing they selected?
Thanks, Paul
-- In electricboats@yahoogroups.com, "John Green" <v_2jgree@...> wrote:
>
>
> Paul, Dennis has it nailed in my opinion.
> From a mechanical point of view, in some dry land applications, some bearings that might be mounted in the same manner as a cutlass bearing might be of a design to take thrust as well as rotation loads, and it would be easy to assume, as you have done, that the prop hub or boss face provides the thrust, but that is not the case.
> In a boat setup, the ICE transmission will no doubt have a thrust bearing on the output shaft. This will likely be in the form of a dual purpose bearing, that can take thrust as well as regular loads.
> This, combined with the fixed transmission mounts, will prevent the shaft moving forwards to enable the prop to rub on the tube.
> So there should be clearance between the prop and cutlass bearing.
> No doubt that in reverse, the same transmission bearing is designed to take a thrust load in that direction as well.
> So you should be replicating that, I think. I have never seen details of which bearings electric boats use, but it should take forward and reverse thrust, as well as supporting the shaft as a regular bearing.
> If you look at car cam belt setups, most have a separate disc like a large washer that is assembled right next to the toothed crank pulley. It has a 'curved-away' edge to prevent belt rub at the outer edge, but will effectively stop the belt sliding off the pulley, and some installations have one on both sides of the pulley, others have it only one side, but have a similar shaped, 'curved-away'(but larger diameter) part on the other side. But this in no way means that this is meant to take thrust, presumably merely to guide the belt. Only one pulley in the drive train has this feature, the camshaft pulleys have open sides.
> The amount of play in a suitable typical industrial bearing would be just a few thousandths. Perhaps other group members who actually have bearings in use can give the make and parts number, so that the specs can be looked at.
> Sorry if I confused things in my original response post where I had incorrectly assumed that there was a top bearing in the tube. From the descriptions of other members, it is simpler than that.
> Hope this helps,
> John
>
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