On Thu, 11 Sep 2014 07:23:47 -0700, "William Sommerwerck"
wrote:
Mythbusters, anyone?
Sounds like fun. Let's run some fans at Mach 2 in a wind tunnel and
watch them fly apart. (Anything worth doing is worth overdoing).
To the best of my knowledge, there is nothing in any motor that
//mechanically// favors rotation in one direction. "Forwards" and "backwards"
are determined electromagnetically, not mechanically.
The maximum speed before the bearings are damaged depends on the bearing
quality, I assume. The only damage I can image is knocking the shaft
off-kilter.
Oh-oh. I think you may have hit on a potential problem. As long as
the pressure is equal on all the rotor blades, the rotor shaft remains
centered in the middle of the bushing. However, with an air hose, one
could apply all the pressure on one side of the frame, producing an
asymmetrical side load on the rotor shaft. In other words, I'm
producing a bearing load condition for which it was not designed. If
the rotor shaft were dry and the lube gone, the high speed rotation of
the rotor shaft might put a gouge into the edge of the bushing. A
ball bearing would be unaffected.
I've seen a variation of the above potential problem with bushing type
fans, as in ATX type power supplies. The components inside the power
supply are not uniformly distributed around the fan intake area. The
result is that the pressure drop at different points around the fan is
not uniform. This produces an asymmetrical fan load which results in
a side load on the bushing. If lube were present and functioning, no
damage would be done. However, if the rotor shaft were mounted
vertically, and all the oil drips to one end of the shaft, the
potential for damage is quite real.
I guess the proper cleaning technique with bushing type fans is to
move the air hose nozzle rapidly around the circumference of the duct,
thus preventing bushing wear at any one spot.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558