Bearings

[lukevanoort]

What sort of bearings have your teams used? Has anybody used synthetic sapphire? Or, some of those crazy high rpm air bearings?

[Tristan Lall]

Originally Posted by lukevanoort

What sort of bearings have your teams used? Has anybody used synthetic sapphire? Or, some of those crazy high rpm air bearings?

No need for stuff that fancy. Conventional ball bearings will easily handle anything that a FIRST robot is likely to throw at them in terms of radial load; ABEC-3 precision ought to be more than enough. Also, consider conventional sleeve bearings for slow-running or low-precision mechanisms.

Though an air bearing might work, you'd want to be wary of the pneumatic system rules; it's very possible that those won't be allowed, since they're difficult to define as a "pneumatic fitting". In any case, they're not a good solution given the limited air capacity of the robots.

[sanddrag]

MY personal favorites for FRC are Small Parts p/n BRF-06 and BRF-08.

[Rod]

We have in the past used Boston Gear Plain Sleeve Bearings. They are small, light weight,and cheep.

[Al Skierkiewicz]

There is really nothing on the robot that would be capable of the saphire bearings. Although they work really well in certain applications, something with the kind of vibration in the robot would likely fracture them. They are hard but brittle.

[lukevanoort]

I think we're thinking about different air bearings. The ones I'm thinking about don't need air supplied to them. They are fully enclosed, using air instead of balls, oil, etc. They are very low friction, but need insane rpms to work.

[Tristan Lall]

Originally Posted by lukevanoort

I think we're thinking about different air bearings. The ones I'm thinking about don't need air supplied to them. They are fully enclosed, using air instead of balls, oil, etc. They are very low friction, but need insane rpms to work.

I'm thinking of air cushion bearings, which use jets of air to support the rotating portion.

[Al Skierkiewicz]

The original quad video tape recorders used from the fifties through the seventies used air bearings on the video heads and occasionally in other places. The head motor (about 10" long and close to 10lbs. of metal) required 12-15 PSI (I am trying to remember what the low side regulator was set for) to run the video head motor. There was a bearing surface at each and and a thrust bearing behind the head wheel. (the rotating disk that held the video heads) The pressure had to be applied first before power to the motor was allowed to be turned on. (the motor wouldn't even turn without air on it.) The motor ran at 15,000 RPM and was speed and phase controlled to record and playback video. Each of four video heads recorded one line of video across a two inch tape. (Unlike the helical scan machines today that scan almost lengthwise on the tape.) The only friction involved was the friction with a jewel tipped screw which set the stop for the motor shaft and the drag encountered by the head wheel turning so fast in the air. In addition the tape had to run in a vacuum "shoe" to keep it from getting eaten by the video heads. If you lost vacuum there was a distinctive high pitched squeel just before your tape got cut in two and little particles of mylar and iron powder erupted into the air.

[EricH]

Originally Posted by lukevanoort

The ones I'm thinking about don't need air supplied to them. They are fully enclosed, using air instead of balls, oil, etc. They are very low friction, but need insane rpms to work.

Define insane RPM. I think the CIM is the motor with the fastest free speed. It's about 5500 RPM (I think). Unless your definition of insane is insanely low, or you gear a CIM (or any other motor) up, you won't be going anywhere near fast enough to be able to use one on a robot.

[KenWittlief]

The only common place I have seen self sustaining air bearings is on the laser spinner on high end laser printers.

the mirror head may spin up to 30 or 50,000 RPM, and it rides on an air bearing

typically air bearings or mag-lev bearings are for 50,000+ rpm applications, where an object needs to be spun with no wobble or vibration, but there is no real side load or end load on the shaft being spun.

[lukevanoort]

I'm thinking about foil bearings. The reason I asked is that I have no idea of the operating speed. It sounds like the only motor that could even get close to using, or needing them (doubtful) are the Fisher-Prices without gearboxes.
EricH, I'm looking at the 2005 spec sheets now and the CIM is 5310 rpm give or take 10% (irritaing number) and the gearboxless FP is 24000 rpm.