I don't think the oil slowing down the motor may be that much of an issue. I would use the Shell Diala as it is$27 for 5 gallons and it has the proper inhibitors in it. If the stator is fixed and the permanent magnets are the rotating element, then the curved magnets may have pieces of plastic inserted between them. The combination of the magnets and plastic would make a continuos disk. This "disk" would be mounted on the prop shaft between two Delrin bushings (self lubricating in the water). I have seen some of the "supermagnets" made from ceramics/rare earth sold on ebay pretty cheap. They are recycled from computer disk drives and other electronics. There is even a web page where a gentleman in Colorado built a brushless wind generator turbine from them. The majority of the friction would be from the laminar fluid flow but negligable on performance due to the low rpm and the case of the u/w robot being shaped around the disk assembly. I've got a book written by a Alfred T. Forbes in new zealand called "the homebuilt dynamo" that uses one of these designs. The NeFeB magnets have flux lines that extend longer than traditional magnets and should extend through the case between the magnets and the fixed stator windings. The u/w robot case could have a molded section for the bushing to be pressed into it and molded threaded holes that don't penetrate through the case. The second delrin bushing could be then pressed into a crossarm, slid over the shaft and secured into the threaded holes. As I own a few fiberglass boat molds, my first choice for the case would be fiberglass. The part of the case that forms the barrier between the rotor magnet disc and the fixed stator windings would have to be a different material that is thinner and attached with a compression o-ring to the main case, probably the real reason for the incompressible fluid inside the case as it allows for the thinner material between the fixed stator and rotor disk containing the magnets. The larger the diameter of the disk the lower the rpm and higher the torque. A dead spot causing stalling is non-existant. Check out Hugh Piggot's web sites out of Scotland for brake drum wind generators. Everything down to his xerox machine runs off of power from his homebuilt designs. You have to be careful about the oil. For example, I have used the dummy load oil to cool ferrite baluns before that have teflon dielectric windings. The oil won't bother ferrites or teflon, but will permeate powdered iron cores and change their properties. Also, you have to be certain that the correct potting compounds and such are used. I've seen mineral oil cause rubber insulated wires turn "spongy" over time in sonar stuffing tubes for transmitters and cause shorting. I would even be tempted to look into encapsulating all my circuit boards in potting compound. If you don't have a vacuum machine to pull the bubbles out of the epoxy potting compound, possibly a circuit board potted with a spin casting machine? Spin casting is some pretty cool stuff and can be done in a garage setup. All said, I wonder if the disk could be mounted 90degrees apposed to allow a better hydrodynamic shape? Then, it would require a delrin worm gear? Regards, Mike ----- Original Message ----- From: "David VanHorn" To: Sent: Wednesday, August 01, 2001 6:10 PM Subject: Re: [OT]: Underwater robots > > > >However, I think that large size steppers could be promoted to submarine > >thrusters. They have the necessary parts in them and the stator could be > >potted. They could be oil filled as above or open to the sea. > > The rotors are also smooth, so they wouldn't suffer as much from the oil drag. > -- > Dave's Engineering Page: http://www.dvanhorn.org > > I would have a link to http://www.findu.com/cgi-bin/find.cgi?KC6ETE-9 here > in my signature line, but due to the inability of sysadmins at TELOCITY to > differentiate a signature line from the text of an email, I am forbidden to > have it. > > -- > http://www.piclist.com hint: The list server can filter out subtopics > (like ads or off topics) for you. See http://www.piclist.com/#topics > > -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics