Jump to content

Bearings for home-built gyroscope?


THX-1138
 Share

Recommended Posts

One of the projects on my back burner array is making a gyroscope out of an old 6" ball bearing race. One of the things I need to figure out is how to mount the spindle in the frame.

 

Given the mass of the thing, the mounting needs to be robust in order to resist the effects of precession. My first thought was to use a needle bearing:

 

GyroscopeBearings-needle.png

 

but that would require a seriously hardened spindle tip and equally wear-resistant fitting. And precession thrusts would probably do neither much good.

 

Next I considered a simple ball-bearing:

 

GyroscopeBearings-ballbearing.png

 

and that's the best I've been able to come up with. Shoulder bearings such as used in 'jewel' watches would require the fitting to be adamantine and refractory. and there'd need to be at least a tiny bit of play. One's hard to come by, and the other's not something I want in a fairly massive device spinning at thousands of RPM.

 

Any thoughts or suggestions on a solution suitable to construction in a home shop?

 

Thanks!

Link to comment
Share on other sites

Graphite or Graphalloy Bearings are really good for high speeds, and are more easily adapted to smaller applications as they are solid as opposed to being made of small balls. You will probably have to shop around for something in your size, or you could probably have something custom made.

Link to comment
Share on other sites

You don't say what your intended application is but...

 

An air bearing might be fun to build.

 

The application is a fairly massive gyroscope (I'm guessing the rotor is about 1kg) spinning at whatever RPM I can safely manage. The bearings are to mount the spindle in the inner gimbal, so they need to be able to support the axial thrust and provide low-friction support of the spindle rotation. And be strong enough to support the precession forces if the gimbal is locked and an attitude change is attempted.

 

The Graphalloy stuff looks like it would work very well:

 

GyroscopeBearings-graphalloy.png

 

provided the flange can support the axial load and act as a keeper.

 

Unfortunately, I haven't heard back from the Graphalloy people..

Edited by THX-1138
Link to comment
Share on other sites

Google 'high speed angular contact ball bearings'. They'll accommodate combined loads, i.e. simultaneously acting radial and axial loads. You can get ultra/super precision grade from some manufacturers which will accommodate high speeds as well. Timken, Fafnir and NSK are some that come to mind that I've used before in screw type air compressors and blowers where multi-axis loads at super high speeds are common.

 

P.S.

 

The application is a fairly massive gyroscope (I'm guessing the rotor is about 1kg)....

 

Typical rotor weights on the screw compressors I've used these in is 50kg+ so massive to you is lightweight to me...

Edited by doG
Link to comment
Share on other sites

I'm not sure I understand what your shaft size is, but anyway:

 

http://mechanicalcarbon.metcar.com/category/s-flange-blocks-w-metcar-self-lubricating-bearings

 

http://www.hightempbearings.com/4bolt-HT750.aspx

 

http://www.randallbearings.com/page17.php Ctlg. pg 12

 

these could be anywhere from $50 - $200+ depending . . . . . I have worked with them on high speed applications, including high speed vacuum pumps and high speed steel brush finishing wheels . . . . the point is that they are durable! The brush was a 20kg mass spinning at between 2500 an 5000 RPM, and the pumps ran up to 10000 RPM.

 

or what doG said . . . I like NSK!

Link to comment
Share on other sites

Well, the Graphalloy folks finally got back to me. They do sell small quantities retail -- at US$100 apiece. That's too dear for me, so I'm checking the other suggestions. (Single-threading due to mental resources.)

 

Personally, I've always been rather fond of Fafnir. :)

 

I frequently see bearing dimensions specified as 'NNmm × NNmm × NNmm,' but I haven't been able to figure out which dimensions those numbers specify. I'm guessing ID, OD, and width (thickness/bore depth), but that's just a guess -- and I don't know in which order they'd be listed, anyway. For a bearing supporting axial loads, somewhere in there I'd expect the diameter of the load-bearing inner-race flange.

 

This is probably in Machinery's Handbook somewhere, but my copy is at home and buried. :-/

Link to comment
Share on other sites

I frequently see bearing dimensions specified as 'NNmm × NNmm × NNmm,' but I haven't been able to figure out which dimensions those numbers specify. I'm guessing ID, OD, and width (thickness/bore depth), but that's just a guess -- and I don't know in which order they'd be listed, anyway. For a bearing supporting axial loads, somewhere in there I'd expect the diameter of the load-bearing inner-race flange.

Generally so. I've seen many angular contact ball bearings that don't have a flange though. Mainly in screw compressor applications where the inner race bottoms against a shoulder on the through shaft. Many of these also have double row type bearings that support axial loads in both directions so they are not unidirectional in their mounting configuration because they are effectively back to back single row assemblies in one common race.

Link to comment
Share on other sites

Generally so. I've seen many angular contact ball bearings that don't have a flange though. Mainly in screw compressor applications where the inner race bottoms against a shoulder on the through shaft.

 

That (inner race against shoulder on the spindle) is my current plan for axial support. (See my diagram for the Graphalloy solution.)

 

I can't lay my hands on the rotor at the moment, but here's a drawing I made of it; also attached to this reply. (Careful examination might reveal that it is, in fact, itself the outer race of a Fafnir ball bearing that never made it to the assembly stage. :rolleyes: ) From the drawing it should be possible to calculate the part's volume and hence its approximate mass, but I lack the geometry skills to do that. Although I might try modeling it in SketchUp and seeing if that can tell me the volume. :lol:

 

A tapered roller bearing would probably suffice for the radial and axial loads -- but I don't think it would be too happy doing so at 20_000 RPM. :blink:

 

Thanks!

BearingRaceGyroscope.pdf

Link to comment
Share on other sites

A tapered roller bearing would probably suffice for the radial and axial loads -- but I don't think it would be too happy doing so at 20_000 RPM.

The tapered bearing will have a little more rolling friction than a similarly rated angular contact ball bearing generally. More important though is that you have the means to get the rotating assembly balanced. 1 kg spinning that fast could be quite dangerous if it comes apart.

Link to comment
Share on other sites

... A tapered roller bearing would probably suffice for the radial and axial loads -- but I don't think it would be too happy doing so at 20_000 RPM. ...

We used matched-pair angular contact ball bearings in superchargers spinning >35000 rpm. That was more than twenty years ago, and I don't have any of the engineering data, but I know the lateral shaft load was significant (using "multi-v" belt drive).

 

When you get all of your data together, just call the technical department at one of the bearing manufacturers. They will help you determine the best solution.

Link to comment
Share on other sites

The tapered bearing will have a little more rolling friction than a similarly rated angular contact ball bearing generally. More important though is that you have the means to get the rotating assembly balanced. 1 kg spinning that fast could be quite dangerous if it comes apart.

 

Absolutely! Are you saying that one style of bearing is better than the other for that? How about a Wingqvist bearing?

 

Thanks!

Link to comment
Share on other sites

With the specs you are suggesting your per bearing price is still going to be greater than $100 for angular contact ball bearings. The weight and frequency of rotation are well into precision engineering requirements and your project is very dangerous. You might want to add to your list the cost of some high quality grease, which can also go for upwards of $100/tube (sometimes small tubes.)

 

Kluberquiet BQ 74-73 N ~$150/400g tube

Link to comment
Share on other sites

With the specs you are suggesting your per bearing price is still going to be greater than $100 for angular contact ball bearings....

Yep, it is not uncommon for me to spend $1500-$2000 for 4 bearings to go in a high volume blower. Then again, I get about $5000-$6000 for a rebuild on one of those so it's really not coming out of my pocket :D

Link to comment
Share on other sites

One of the projects on my back burner array is making a gyroscope out of an old 6" ball bearing race. One of the things I need to figure out is how to mount the spindle in the frame.

 

Given the mass of the thing, the mounting needs to be robust in order to resist the effects of precession. My first thought was to use a needle bearing:

 

GyroscopeBearings-needle.png

 

but that would require a seriously hardened spindle tip and equally wear-resistant fitting. And precession thrusts would probably do neither much good.

 

Next I considered a simple ball-bearing:

 

GyroscopeBearings-ballbearing.png

 

and that's the best I've been able to come up with. Shoulder bearings such as used in 'jewel' watches would require the fitting to be adamantine and refractory. and there'd need to be at least a tiny bit of play. One's hard to come by, and the other's not something I want in a fairly massive device spinning at thousands of RPM.

 

Any thoughts or suggestions on a solution suitable to construction in a home shop?

 

Thanks!

 

This is what I have done some time back. And it is cheep along with doing in you home shop.

 

post-66453-0-49197900-1336319922_thumb.jpg

Edited by Amateur -1
Link to comment
Share on other sites

I know wiki isn't God but according to this

http://en.wikipedia.org/wiki/Magnetic_bearing

"It is difficult to build a magnetic bearing using permanent magnets due to the limitations described by Earnshaw's theorem, and techniques using diamagnetic materials are relatively undeveloped."

so I rather doubt the bearing Amateur described would work at all. If it could cope with the axial load then I suspect that

it would deal with the radial load about as well as a block of cheese.

Link to comment
Share on other sites

How well does that handle radial loads?

 

 

Amateur -1

 

Well the one that I made was made from a 9" flywheel off a out board motor and was about 3.5Lb.

And I can assure you the that ½ in. By 3/8th. thick button magnets are strong enough that you can not

 

 

pull the apart & for sure that you and a friend would be able push them together.

 

 

Edited by Amateur -1
Link to comment
Share on other sites

"And I can assure you the that ½ in. By 3/8th. thick button magnets are strong enough that you can not pull the apart"

 

The same would be true for a couple of bits of metal covered with epoxy cement, but I wouldn't use them as a bearing.

 

What did you use as the bearing with that flywheel?

Did you use magnetic bearings and if so how?

 

(BTW, I'm not too fussy about Earnshaw's theorem. I have a small magnet floating in mid air and if you blow on it you can set it spinning. But it's horribly unstable and has almost no resistance to radial forces.)

Edited by John Cuthber
Link to comment
Share on other sites

"And I can assure you the that ½ in. By 3/8th. thick button magnets are strong enough that you can not pull the apart"

 

The same would be true for a couple of bits of metal covered with epoxy cement, but I wouldn't use them as a bearing.

 

What did you use as the bearing with that flywheel?

Did you use magnetic bearings and if so how?

 

(BTW, I'm not too fussy about Earnshaw's theorem. I have a small magnet floating in mid air and if you blow on it you can set it spinning. But it's horribly unstable and has almost no resistance to radial forces.)

 

Dear John Cuthber;

 

I have one of thouse toys also, but do you understand that in Germany & Japan they are working on high-speed trains

 

that totally float on magnets fields. Also they are very coustly but you can get on the market Magnetic floating barring.

 

 

 

 

post-66453-0-64620100-1336489703_thumb.jpg

Edited by Amateur -1
Link to comment
Share on other sites

Yes I know they have magnetically levitated trains.

I know they are expensive.

They are expensive because they are complicated.

If you could make them work without being complicated they would be cheaper.

The people who buy trains do not want them any more expensive than they need to be.

So the people who make them complicated do that because that can not make them simple.

If your idea for a bearing worked then it would be simple and cheap and so people would use it. They don't.

So your idea does not work.

Magnetic bearings do work, but they are much more complicated than your idea.

Edited by John Cuthber
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.