Re: Magnets allowed?¿?
 

Fun thread. Too bad that the Neodymium magnets would probably shatter if they were allowed to slam in to a bar rapidly when used as a guide. Even magnets that are tougher can have their magnetic strength reduced by shock. In the trade it's called "thumping" and is a crude way to adjust the magnetic level downward if you don't have a magnetreater (sort of a controlled degausser). Just tap it with a little hammer.

Ever see what it takes to charge up some of these magnets? Check out the 110,000 Joule charger: http://www.maginst.com/capacitive.html. I used to work at a company that made some of these same chargers (up to 20 KiloJoule). The techs called them "widow makers". You didn't want to get hold of a huge bank of capacitors charged up to 2000-3000 volts DC!

Re: Magnets allowed?¿?
 

Soo thats why all my magnets eventually get weaker: impact forces as they stick to things.


Mmm... 110,000J capacitor bank. That would do wonders for a railgun. :)

To prevent Neodymium magnets from shattering, why couldn't they we cubered by a thin plate of something stronger. Por additional impact resistance, the plate could even be dipped in that tool handle coating stuff.

Re: Magnets allowed?¿?
 

James,
On a Trinitron tube the phosphors are stripes rather than dots. So it is unpredictable as to what the outcome would really be. The best test is turn the monitor on and get something displayed. Then while it is on turn it 90 degrees. The change in orientation to the earth's mag field will change the display. If it makes the vertical lines worse then degaussing may be the answer. If it goofs up the color but doesn't change the vertical lines then you may have cashed the CRT. Ask around at school, there may be a coil in the repair shop or at the district office they may let you use for a few days. Building one is dangerous and reguires some materials you may not have access to. Good Luck!

Re: Magnets allowed?¿?
 

Shock is not the only way to reduce the field. Here's the word from Roger at Magnetic Instrumentation: "You got the term thumping of a magnet right. The thumping shock does tend to throw a certain number of particles off the magnetized orientation and then you have north polarities and south polarities negating each other and producing less energy out of the magnet. To get the maximum energy out of a magnet you want all the particles aligned in the same direction, to get less energy you need realign some of the particles “Off axis” by mechanical or temperature (typically heating) shock or by applying a reverse polarity DC or an alternating AC field." In addition, you've probably seen horeshoe magnets with a little steel plate stuck on. I haven't exactly researched the phenomenon, but this is known a "keeper" to keep the magnet from weakening. It effectively closes the loop between the North and South fields. I'll see if I can find out any more about it.

And by the way, I've heard about people using one of those big Weller-type soldering guns (the ones with the wire loop) being used as degaussers. Search on "soldering gun degausser" and you'll see. If the monitor is really big, maybe you could use one of the coils that they use to degauss battleships (yes, they do that - don't want to set off magnetic mines).

Re: Magnets allowed?¿?
 

This is actually another mentor on the Team 236 design/build team, Jim. I cannot figure out how to log in under another name using the school computer system, so I am using Jon236's profile. If this causes a problem, let Jon236 know and I will figure out how to get my own profile.

I have been watching this thread with interest and have not seen whether the original question was answered. Are magnets going to be allowed?

As for some of the other topics, I was part of a team that developed permanent magnet motors for US Navy applications, using Neodymium-Iron-Boron "rare earth" magnets in the rotors. A major concern with these magnets was the well known susceptibility to damage from shock. To address this we selected commercially available grades of NdFeB magnets from over a decade ago that were particularly resistant to demagnetization by shock. This is actually not an unusual characteristic of NdFeB magnets. These magnets, however, were still susceptible to cracking and fragmenting due to their relatively poor mechanical properties, especially in tension and bending.

To overcome this characteristic we "broke" the magnets into smaller near cube shapes (good geometry for a magnet to resist tensile and bending loads), and then packaged them so they were unable to turn, flip or otherwise change their orientation in the motor rotor. This concept has been tested in shock tests to over 200g's at over 80*C without any degradation.

Today there are many more, significantly improved grades of NdFeB magnets, and, considering the application you have in mind, it should not be difficult to select a suitable magnet for under $30, with a few spares. The question at hand is does the use of a magnet violate the FIRST rules for 2004? Has this been posed in the Question and Answer area yet?

Thanks, Jim

Re: Magnets allowed?¿?
 

It really isn't a matter of FIRST allowing magnets. The issue is that using magnets strong enough to hold up a robot would be safe. Personally I really do not see how it can be done. Especially reading about how it can affect people with medical devices.