Running at 1,000,000 RPM

There is a possibility to dynamically balance at any speed it costs a lot but is efficient. This can be done using electromagnetic-dynamic bearings.

The controls of the bearings are such that if an eccentricity occurs the electromagnetic fields are modified to maintain the rotor in the center of the stator. An un balance will generate a radial force which has to be compensated in order to maintain concentric.

This force can be measured via the used currents in the field generators. Since the polar angle can also be determined it is possible to compute where and how much has to be added or taken away for the lowest dis-balance.

Since each bearing is controlled independently the approach can be used for any kind of rotor geometry, short or long.

The higher the speed the higher will be the friction with surrounding air. This method would be an extension of the high speed morots used in machine tools for high revolutions motors (over 50.000 rpm).

Technology is avalable can be used is money is available as well.

At those sorts of angular velocities, the ability of the rotor to hold itself together starts to become more important than the bearing method. And a rotor doing that sort of rate will take a lot of slowing down prior to the corners the slot car has to pass around.

No rotor spinning in air is "frictionless".

<...in the real world we unfortunately have to deal with reality...>

Quite.

Hello route89,

That is a whole lot of speed! I am sure someone will tell me there is a need for such a speed but I can't think of one. Angular momentum I think it's called technically.

I think you would need to put the rotor or whatever was moving in a vacuum to get a truly friction free bearing.

It was a while ago now but, I did hear of a very small magnet which went over 100,000 rpm. It would be interesting to find the 'world record' for a device like that.

Take care, bb

The medical device used to break up plaque in veins and arteries, a roto rooter if you will, turned at 100,000 RPM's. I don't recall the power source, whether pneumatic or electric.

Hello Jaguar,

Hope you are well? And do not have any need for the use of this gruesome sounding device on yourself!............

Wow! 100,000 rpm sounds a bit OTT? I thought that was what the OP had mentioned until I read it several times as I was writing my post.

Have you any other details about this device please?

bb

This was in a trade magazine feature in the late '90's, I thought Design News or Machine Design but couldn't locate it at either but it is there somewhere, and was describing the technological hurdles of its development, magnetic bearings to eliminate as much damaging heat as possible, turbine blade design advances to prevent cavitation and the destruction of blood cells, all a part of the focus of the article, finite element analysis and CAD programs.

I did find something about a dental tool though:

http://www.designnews.com/article/3241-This_won_t_hurt_a_bit.php?text=100%2C000+rpm

I'm sure the physical size is MUCH greater than the rooter.

Found it.

http://www.designnews.com/article/2233-Engineering_News.php?text=plaque

Look for "Bearings help surgical instrument do more for less" about a quarter of the way down.

I guess my memory of the specifics of the article is a bit flawed but at least I did remember it.

Hi Jaguar,

I must say a big thank you for your efforts in finding what I asked about!

I was about to search and the line to my ISP dropped out. Something which is getting more regular by the day! I will be changing soon, and not soon enough for my liking! I am in a situation where the ISP blames BT, whom it rents the line from, and BT does the opposite. The only way to alter things is to use cable or sky.

Take care, bb

Thanks for all the comments - very informative and helpful. I found some neodymium magnets on ebay for $1.00 , so I'm going to just do it and see what happens. Maybe I'll put up a post to show the results. These magnets are pretty amazing:

Neodymium bearing supporting 40 lbs

Rheometer

Two chickens breaking up a fight between two rabbits

I have the feeling that you did not understand the problem.

The bearings in the "show" are axial bearings and work on whole frontal area. For rotation I hope you noticed that a rod/shaft is used to "center" the discs. As the film shows the centrifugal forces bend the shaft and the radial movement is not so small since it is easily noticed.

If you want to "BALANCE" a high speed running disc you MUST maintain the rotation axis with GREAT precision in order to measure the dis-balance and know what you have to correct.

Think again and try first to understand before you make an error and break something.

I see your point. In the end, it seems like magnetic bearings might be better at determining how perfectly balanced an armature is, rather than using it to actually balance it, or run the motor with magnetic bearings. Balance it with a computer, and then suspend it in the neodymium bearings and film both ends of the armature shaft at super speed to see how they wobble. My brother knows Stewart Koford personally, one of the leading slot car motor manufacturers in the world, and if he might be able to offer a super-balancing service to customers. Has anyone heard of using an object's resonance to measure the amount of imbalance?

Again some unclear concepts.

"Balance it with a computer, and then suspend it in the neodymium bearings and film both ends of the armature shaft at super speed to see how they wobble."

How do you imagine the CAB ? And how do you imagine the suspension of the rotor at super speed? If it is balanced the right way why does it wobble?

I am sorry but I further on think that not all is clear for you.

Well, I've seen a lot of super high speed videos that point out oscillations and vibrations unseen by the human eye at normal speed, like this one: Bow and arrow. My idea is that conventional ball bearings hold the armature shaft solid and don't allow the shaft to fluctuate even if it is out of balance. However, a neodymium magnetic bearing suspends the ends of the armature shaft in air, and if the armature is unbalanced, this would allow the ends of the armature shaft to wobble as the motor is running at various RPM. Filming it at high speed would allow these wobbles, caused by imbalance, to be seen more clearly. The whole point is to identify and eliminate points of imbalance to achieve higher RPM with less vibration by balancing the armature as finely as possible.

Route 89 --

Go back and reread my posts and Nickname's posts. He understands this subject and knows what he's talking about. I wish I could lead you to a website with a decent explanation; but after an hour of looking at Google search results all I found was some pretty poor stuff on manufacturer's web sites.

Go ahead and try your high speed camera idea. Don't forget you'll need degree markings that rotate with the wheel showing in the picture. You'll also need a stationary frame of reference close by the rotor so you can tell when the wheel surface is at it's maximum and minimum displacement off axis (in a few thousandths at most) and at what degree reading. You'll also have to be able to sort out the visible influence of precession and any other external influences like low level vibration from cars and trucks going by outside.

When you are ready to try and build a real balancing machine with flexible bearings, motion transducers, an angle sensing scheme and all the electronics needed to tell you where to put the weight and how much........ Well go check out the small Hoffman lab balancers.

Then after you've recovered from choking on the balancer price go experiment with simple wheel truing like I described in my last post. If your problem is runout that can be measured with a $25 dial indicator setup and fixed with some simple machining (remember you can grind rubber and trim many synthetic elastomer with a correctly sharpened lathe tool then why mess with balancing?

If that turns out to be not good enough take a look closer look at how balancers are made with their flexible support bearing mounts, drive motors, angle sensing methods and computational electronics. Also look at accelerometers or capacitive displacement sensors:

http://www.lionprecision.com/tech-library/technotes/tech-pdfs/cap-0020-cap-theory.pdf

If you can get use of a dual channel oscilloscope with a trigger input for the angle you can cobble up an experimental rig. Read the displacements in two known planes from the transducer signals and a little algebra will tell you how much weight to add or remove (as the case might be) at the plane where you can most conveniently make the alteration. It may not be all that accurate; but you'll have to find that out by experimentation. I'd borrow the scope and the transducers rather than buy them.

Bit of a story here -- Seventy some years ago an old circle track racer named Pappy Hough built his own crankshaft balancer out of an engine lathe in his Gasoline Alley, Patterson, NJ, shop. He built some large modified pillow block bearings with spring mounts on the lathe bed. He could tell by watching the movement of the pillow blocks while the crankshaft was being rotated by its coupling to the lathe headstock where to drill the crank counterweights. Pappy Hough's machining skills were as legendary as his skills at the wheel of a sprint car. Some years later after one of his business neighbors at the "Alley" Dick Simonek bought a real production balancer and took away the engine balancing business he was still using the old lathe to balance driveshafts and make bucks with it.

Point here is that just because an expensive balancing machine doesn't fit your program doesn't mean that your own invention won't do the job you need done.

Ed Weldon

What about a variation on this theme?

http://www.fluidampr.com/