Seal and UJoint Advice

[mwb]

You won't have to worry about preload unless you intend to have reverse. My drawing is not the complete assembly, I am currently working out dimensions of various components and fitting them to close-to-stock steel. I have a small lathe but I would like a design that does not require significant machining (I like to post designs like this and use the KISS principle to make it easy for others to build also).

At the ball bearing end I would install a belleville washer and nylock nut to remove slack from the assembly but preload would be near zero.

My tapered bearing is a standard trailer bearing (3/4"), the seals are a standard trailer axle seal.

My design is nowhere near complete, I have been sidetracked designing a backhoe for my tractor - it's about 90% complete (the design is, not the build).

 

[Sherweld]

My 2 cents if this might help .......
Years ago, I did some extensive bearing seal testing for a military swamp vehicle design, that was to operate in the most extreme submerged conditions. At the time the clear winner was a Fafnir Tri-Ply bearing.

The bearing test candidates were mounted to the face of a small pressurized box which contained a mixture of fine abrasive, and dyed water. The inside test pressure was maintained at about 5 psi as I recall and the shaft and mounted bearing rotated at about 50-60 rpm for 48 hours, or until leaking occurred, whichever came first.

Despite some pretty wild claims from various vendors, the only one to reach and even far exceed the 48 hour goal was the tri-ply. Some supposedly well sealed bearings didn't even make an hour.

The tested bearings were for the "tires" on this rolligon.

http://s2.e-monsite.com/2009/12/08/09/resize_550_550//17a---Airoll-XM-759-photo-US-Army-1962.jpg

 

[Redneck in training]

Have you considred front wheel drive shaft assembly. I am guessing that it is sealed, has all the bearings, can take much sharper angle than cardan and you can get it cheap at field tested autoparts aka junk yard.

 

[DuckHunterJon]

MWB - I agree wholeheartedly on the KISS approach. In this case, I'm shooting for KICASS (keep it cheap and simple...) - but I am still thinking the preload will be needed to prevent ball skid. Ball skid will take out a bearing faster than most any other failure mode, and the tapered roller bearings are succeptible to it if there is any chatter/loosness in the assembly. I haven't found good references on what the preload force needs to be - other than to set it to run at a certain free running temperature. That said, your spring washer may very well provide all the preload nessecary. I'm going to look into this some more and see if I can figure a way to apply it to the long tail design.

SherWeld - thanks for the tips on the seals, I'll be looking them up.

Redneckintraining - I agree, a simple approach would be to use a front wheel drive assembly - my issue is that the driveshaft and housing needs to be approximately 62" long. I suppose one could cut a halfshaft, weld in a longer piece - but I'd still need to come up with a housing to enclose it within. Thanks for the idea though - I'm all for recycling other deisgns/parts when I can.

 

[mwb]

My thought is that the propeller will provide all the preload (unless the prop is out of the water). I don't think a relatively low use device would be that hard on bearings (because of no preload) - and the bearings are really cheap to replace anyway. You wouldn't normally run it long with the prop out of the water. I think seal leakage and lubricant failure, or exceeding axial load specs would cause failure long before the bearing would fail due to no preload.

My suggestions are geared more for the short shaft, belt drive. things are a little different for the long-tail.

I considered using CV type joints - shafts from a car or atv but they are expensive and making the connection to the propeller, etc might be a problem unless the CV shaft is available with keyways, etc (i.e. non-splined).

 

[pat32rf]

In the past couple of years I've replaced universals (and half shafts) on an ATV, tractor PTO snowblower, FWD import and a domestic van. Turns out they were ALL made by the same company and used the same trunion kits (except for size) IE the same fabricating tolerances. Can't figure out why the ATV was twice the price of the FWD import sedan though....they were both about the same size