Mag Lev Telescope

[mattermanator]

Hi all,

I have this idea for a telescope's rotating axis to levitate on magnets and have no mechanical contact. In my mind this seems like it would work, but because of my lack of knowledge with magnets I was hoping for some help.

http://www.geocities.com/matermanator/magnet-scope/

I made those pictures to help demonstrate my idea. In Mag1, the telescope (dobsonian) rotates on that cylinder. Normally these telescopes use roller bearings or teflon pads and have the cylinder rest on the bearing surface and rotate on that.

My idea was to take some neodymium magnets of whatever size it took to get enough force and situate them in a circular pattern around the cylinder without ever touching the cylinder. I figured the cylinder would need to have some sort of steel plating (or the whole shaft be steel) and have the magnets all pull on the shaft evenly. The telescope tube could be done out of composite or wood or with thin aluminum poles, anything to reduce weight.

I mainly want to see if it could work, doesn't really matter if it worked well just if I could experiment enough to make it work.

I will start with tests and so fourth to get a rough grasp. My main questions are whether or not it will work at all, and what kind of calculations I could do to figure out what sized magnets (or their pound rating) and what weight limits I would have for the telescope and so on.

I hope this isn't to off topic or just plain stupid. I got kicked off a yahoo groups forum for physics, they said "don't pollute my boards with nonsense".


Thanks
-Matt

P.S.
I wanted to use electromagnets to build this but I just don't know much about them either (except how to make one out of a nail and some wire). My hope is to have the telescope driven like a mag lev train, using varying amounts of magnetic force to move the telescope around it's axis in precise amounts.

[nkt]

Why? It will cost a lot in magnets, and then you will have issues with it not being very stable as it moves in the wind, or the temperature changes. Also, don't think that it will be easy to keep "balanced" - there are no stable systems, so you will need some clever force feedback to stop it moving to one side or the other and then slamming together!

[mattermanator]

Originally Posted by nkt

Why? It will cost a lot in magnets, and then you will have issues with it not being very stable as it moves in the wind, or the temperature changes. Also, don't think that it will be easy to keep "balanced" - there are no stable systems, so you will need some clever force feedback to stop it moving to one side or the other and then slamming together!

"Why?" Well really only to see if I could come close to seeing if I could get a usable system. There are alot of good systems for telescopes out there already, but if I could figure something good out maybe it could be used for something else?

With the force feedback system, would that be a system used with electromagnets to vary the power? Would that be hard to build, even on a small scale?


Thanks
-Matt

[C1ay]

If you're looking for a cheap option for a homemade scope use chrome plated trunnions in teflon lined, sleeve type bearings. Put split sleeves in split housings you can adjust the clamp force on to adjust the friction that holds the scope steady.

If you're going to spend some dough on it use tapered bearings on the trunnions and worm gears to drive the axes.

Magnets will drain your pockets and provide no real benefit.

[UncleAl]

I have this idea for a telescope's rotating axis to levitate on magnets and have no mechanical contact.

You will get uneven grab unless the field is uniform around the entire periphery, bearing and sleeve.

http://www.sti.nasa.gov/tto/spinoff1996/62.html
http://www.miti.cc/magnetic-backup-hybrid-bearings.html

http://www.grc.nasa.gov/WWW/spacemec...2/mag-brg.html
http://www.amsat.org/amsat/sats/phase3d/wheels/

Halbach arrays are used for permanent magnetic levitation. BTW, newly constructed ships are traditionally launched from dry dock using slabs of the ultrasophisticated high pressure lubricant... bacon grease.

http://www.matchrockets.com/ether/halbach.html
http://www.gaussboys.com/halbach.php
http://www.ian.org/Magnetics/Halbach_Arrays.html

http://www.unitednuclear.com/magnets.htm
Last on page. The BIG KAHUNA of small magnets

[CraigD]

It wouldn’t be hard to build the bearing you describe at all.

A couple of flat, washer-shaped permanent magnets will work. You can get these online or at a science store – a small pair like these will support about 7 lbs, and cost $5.

You can get larger magnets in a variety of sizes from commercial sources. Most will sell small quantities at decent prices – these companies seem to like hobbyist experimenters.

Such bearings aren’t dynamically stable, so there needs to be slight mechanical contact to keep it together, such a dowel through center of the floating magnet. Surprisingly, it is possible to levitate a magnet without mechanical contact by spinning it – the Levatron toy is an easy-to-find, though impractically small and at $30-100, depending on the extras, pricey example. Note: the word “anti-gravity” used to describe these toys involves only the usual sort – lifting an abject in opposition to the force of gravity – nothing more exotic.

Bearings that use attraction, rather than repulsion, are difficult to control, requiring high-speed computer-controlled switching systems. The Transrapid monorail is a well-known example of such a system.

I don’t think telescope mounts are a very good application for magnetic bearings – they’re usually used for high-speed, low friction applications like motors and flywheels – but you can have fun experimenting, none the less.

Halbach arrays, by the way, are very cool, but don't produce lift unless they're moving, so won't be much good in the application you describe. Any king of conductive wire, some hotwheel track, and some rectangular permanent magnets can make a cool model of an “Inductrack” train.

[nkt]

The other thing that is often forgotten is that the thrust rating for magnetic non-contact bearings is normally really, really poor. Any real force will overwhelm the system, and cause problems.

Now, if we could just get these magnetic monopoles sorted out...
I keep ordering them, but they always send me two stuck together... ;-(