Floating element in a spinning cylinder

The way it tends to go with spun liquids is like this: slow speed: surface a little tilted. high speed: a continuous layer around the circumference.

Brian Whatcott Altus OK

John, The lowest amount of friction you can get without a lot of work will be an air bearing. Next on the list is magnetic bearings, but they require sophisticated electronics, since it is a feedback controlled system.

?? What is RPM, and size of things? Dave

snipped-for-privacy@googlemail.com wrote in news:a02ef120-3e73-46f5-860b-4c02fd9b3420 @e23g2000prf.googlegroups.com:

If I understand this correctly, you want to have an stationary electronic device floating in a fluid that fills the interstitial space between it and the ID of a rotating cylinder. Above some minimum rotational velocity, the rotating cylinder will cause the fluid to rotate. The rotating fluid will then cause the electronics device to rotate, absent some moment resisting force on the package. The force that causes the rotation is surface drag which goes up as the square of fluid velocity. The first thing that comes to mind is inertial stabilization. Without knowing things like the rotation speed, the fluid, the size of the electronics device and the cylinder, whether the cylinder needs a top and whether the top needs to rotate, and other similar design details it is hard to go much further.

Strangely enough, I just finished a project measuring the forces transferred to a stationary cylinder from a coaxial rotating cylinder through an interstitial fluid.

Dear qing3000:

You have received some good responses.

Would you consider also rotating the electronics, and delivering power and receiveing data wirelessly?

David A. Smith

I believe that, because all fluids have viscosity, any fluid will couple the device to the cylinder and rotate it. Can you magnetically levitate the device in a vacuum? Unfortunately, much more expensive and prone to problems than floating in a fluid.

Mitch

Air is a fluid. Use an air bearing.

The OP is going to have to have a mandrel of some sort going down the bore of the tube. BTW is it an oil rig, a washing machine, or a uranium enrichment centrifuge?

Cheers,

Phil Hobbs

Many thanks for all the responses. This forum is really useful. I should have consulted here earlier. After reading the comments from all you guys, a stationary solution seems to be complicated and expensive to implement. How would a wireless channel work in a long tube environment and possibly nearby places? We want to transfer the signal from the bottom of the long tube to the other end and possibly further beyond.

There have been no interesting posts in in a long time. You happened to get a bunch of good responses from mostly-bored individuals. Ultimately, you get what you pay for.

It will have difficulties either way. Lots of things to learn.

Lets pretend you were not building centrifuges for separating uranium, since you will not say what you are trying to do. One end could have a "board" that picks up and receives signals from sensors, and outputs a serial data stream along "wires". The wires could be flexible circuitry that travel to an end where the interface board would be located. The interface board will accept / regulate power induced by an alternating electric / magnetic field, and house an infrared LED emitter/detector for transmitting the serial data stream out of the rotating environment. Think "TV remote control".

David A. Smith