Bearing drag

I'm constructing a homebrew anemometer and on my first try used a new sealed bearing. Unfortunately there seems to be too much drag for accurate readings, the bearing does not rotate freely enough. Can anyone knowledgable about bearings tell me, is it the bearing seals or the 'lifetime' lubrication that is causing most of the drag? Or some of each? I was wondering whether I should just look for another kind of bearing; try to purge the factory lube out with a solvent while leaving the seals intact; or pry the seals out. The poor thing does have to live up on top of a pole in all weathers. I was thinking of replacing the factory lube with snowmobile grease which doesn't stiffen up at low temperatures.

Reply to
John Ings
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If the bearing is sealed rather than shielded, the seals will introduce quite a lot of drag. Shields won't cause any drag, but the standard grease is likely too thick even at normal temps, and the shields will make it difficult to flush and replace the grease.

I think you really need to buy open bearings and wash out the factory grease and relube the bearings with a very light oil. ATF would probably be as good as anything without getting into synthetics. Then you need to protect the bearings with labyrinth seals. The shields in a shielded bearing are a type of labyrinth seal. For an anemometer I would think an upside-down can attached to the shaft that sheds rain and with minimum clearance around the bearing housing to exclude dust would be adequate.

For something fancier, you might want to look at "Nilos Rings", but you'll still need something positive to shed the rain. There are both contact and labyrinth Nilos rings, the labyrinths are obviously the ones to look for.

I've got a CAD model of a prototype I designed and built for a customer that had some of your requirements. I can post a few images if you think it might be helpful.

Sensors magazine had an interesting article on anemometers several years ago. Much of the article was about the author's experience building experimental instruments to survive the conditions on the summit of Mt Washington.

Ned Simmons

Reply to
Ned Simmons

The one I am using is a standard sealed bearing.

How about just prying the seals out of the existing bearing?

That's what I've constructed. The 'can' is 2 1/2" diameter aluminum and the 1 1/2" diameter bearing is well up inside.

This sort of thing?

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I don't think the intended environment is too severe as long as I lower the mast occasionally and squirt some lube in. It's a desert environment.

Thanks for your advice.

Reply to
John Ings

You might be able to rig a small lube reservior and a wick, but getting the parameters right (the wick flow slow enough, but still delivering a little bit of oil) would take some experimentation. I'd guess dust will be more of a problem than rain in the desert, and dust loves excess lube.

Reply to
Ecnerwal

Do like Ned says. Pry out the seals and lube with a light oil. At the very low loads this bearing sees it will need hardly any oil. A labyrinth seal will keep all the dust and rain out.

Reply to
Eric R Snow

You can try, but often not easy to do without damaging the bearing.

No, those are contact seals. The LSTO seal on this page is the Nilos labyrinth seal. They're sized to match the ID and OD of standard bearings.

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Ned Simmons

Reply to
Ned Simmons

Interesting coincidence. I am at the reading and design stage for one and would appreciate some details on yours if you would be so kind.

Please remove the stuff between the E and the @ to get a valid address.

Ted

Reply to
Ted Edwards

INCH and a HALF diameter bearing? That is a substantial bearing for that kind of application! I'd rather go with a magnetic bearing to support the shaft as the resistance to movement will be a lot less than with a contact bearing of any kind. Smaller diameter bearings will produce less impedance to motion than larger ones will in addition. Unless you're doing something odd, the weight of the rotating mass can be handled with a little 1/4" OD bearing without any problems. Any friction (like the sealing surfaces of a sealed bearing) will make for errors in the reading and unfortunately, the errors won't be constant which will make for even more problems.

-- Bob May Losing weight is easy! If you ever want to lose weight, eat and drink less. Works evevery time it is tried!

Reply to
Bob May

Simple and crude. I machined an aluminum 'can' that sits atop a 1/2 inch shaft with a single bearing. The crosspieces are 1/4" rods with

3" dia metal tea strainers welded to the ends. The strainer meshes are filled in with pvc cement so they are wind tight. The readout is the speedometer from a bicycle made by Cateye.
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work off their own little internal asprin-tablet size battery and employ a reed switch. On a bike the reed switch is attached to the front forks and a small magnet is attached to a wheel spoke. In my application the magnet is crazyglued to the 'can' and the reed switch mounted to a proximate bracket with a wire lead to the unit inside the house . If you wanted an recording anemometer, the same reed switch pickup could be used to feed a signal to a computer serial port, and a Visual Basic program to monitor, record and graph windspeed would be easy to write.
Reply to
John Ings

I was in the surplus business for 25 years and used to get in all kinds of weird things. One was an idler for for 2" wide video tape. These were 1/4" ID ball bearings with flanges and shields. I tried to use one set with a follower arm to unwind small diameter wire. With a 1/4" shaft and a 7 or 8" arm the thing would go forever. I had to put a brake on it. As these idlers were not one off items I am sure the Mfr did not degrease them himself. If you talk to a bearing Mfg I am sure they can give you a correct PN which would include a "light" lub. To protect it from the weather just put an inverted cup on the shaft to cover the bearing and seal it to the shaft.

Chuck Pilgrim

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Reply to
Pilgrim

John Ings wrote in news: snipped-for-privacy@4ax.com:

a true 'sealed' bearing will have significant drag from the seals in such a light load situation. You would probably be better off with a 'shielded' bearing. These have a metal plate that does not contact the inner race. This very slight gap eliminates drag from the seal. You are also on the right track with the lube. You would probably be better off with a very light low-temp grease. You most likely do not need any real load handling ability, or high-speed tack, or anything else really related to a grease. Sounds like you only need corrosion protection. You may acutally get by with something like 'break-free' or one of the other silicone/teflon spray lubricants.

Reply to
Anthony

I was over at my friend's company a few weeks ago. They build weather stations for the FAA. They had a pair of anemometer/ direction sensors sitting on a bench and I fiddled around with them for a minute.

They *felt* like they had tiny unshielded, unsealed ballbearing races in them and they looked like they might have been weatherproofed with a non-contact labyrinth of some sort.

Reply to
Jim Stewart

I sorta took the lead here, but turned a top cap out of 2" aluminium, the arms out of fiberblass arrow shaft, and the cups out of the quarter machine at the grocery store. For the bearings, I salvaged a plastic case fan(REALLY free spinning, unsealed, etc) , removed the extraneous bits that didnt look like an anemometer and turned it to fit in some 1

1/2" aluminum tube, the cap is about 2" tall, and overlaps the tube by about an 1 1/2", and 0.010" clearence, its been up about a month and thru a couple good wind storms and still seems fine.

mark

John > I'm constructing a homebrew anemometer and on my first try used a new

Reply to
mark

Take a browse at mcmaster.com, they have some choices of ceramic and other low drag, non-lubricated, corrosion resistant bearings. Seems like a better choice than depending on steel bearings to stay free.

Reply to
Toolbert

Where are you? I'm in SW BC Canada with associated temperature range.

You might want to try Reid Tool at

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pg 353 of my 2002 catalog, they list ball bearings with a delrin shell and 316 Stainless Steel balls. They state that these need no lubrication. This is likely the way to go.

The catalog shows these at under $4 for a likely size.

Ted

Reply to
Ted Edwards

Seals can be contact or non-contact (seal either does or does not make contact with the inner race). For example NTN LLB series seals are non-contact and provide better water exclusion than shields (but not as good as the LLU series which is full contact but does not create any resistance..

Can be done (and often is) and if done carefully, can be replaced although most often you will destroy them. Just be careful to not damage the retainer. Assuming you use a non-contact seal can you remove one and flush the grease then install with the remaining seal on top? Are you only building one or is this going to be a production item? If quantities are involved, you can get bearings made with minimal friction lubricants and seals but it is difficult for just one.

Reply to
Tom

Well, my life is not bearings, but, it seems to me that this is a situation where the forces will be low enough that minimizing friction is vital. I would suggest this: use two glass ball-bearings in contact as a bearing. Get a couple of tubes, one a slip fit in the other. Get a marble that is a press-fit in each tube. Press one marble in at the end of each tube. Attach the arms on the marble end of the larger tube, and slide them together. That should provide you with a fairly accurate, low friction bearing. You can put a cap over the top of the outer tube to seal it and keep the dust and rain out. The glass will be very resistant to wear, and, should last essentially forever. You can pick up the rotation of the anemometer by an optical pickup, looking at a pattern on the outside tube. To protect it from weather, you could put the pattern on the INSIDE of the outer tube, and mount the sensor inside the support tube. By the by...in my opinion, direction is important too, and you can use the same techniques to create a wind vane.

Regards Dave Mundt

Reply to
Dave Mundt

Searching Google for Anemometer Bearing brings up some really interesting stuff. There are sapphire bearings, several Teflon bearings, and one made out of table-tennis balls.

Interestingly, there are several companies that make torque-testing instruments specifically for measuring the drag of anemometer bearings.

'Makes you appreciate how many niches there must be out there in industry...

Ed Huntress

Reply to
Ed Huntress

How about two rare earth magnets at opposite ends of the shaft? There is a propeller balancer used by modelers that has this and it is essentially frictionless. That one is a horizontal shaft but it should work vertical as well or maybe better. I would use plastic spoons for the cups as they should be pretty close in weight.

Reply to
dann mann

There was a pretty good discussion here a few years ago on bearings for gyroscopes.........Dave

Reply to
Dave

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