Thanks for the comments! I've passed them on to the mechanical engineer. Harold > > > --- Harold Hallikainen wrote: > >> We are looking at having the magnet inside the coil and having the >> magnet >> move (like a loudspeaker with the coil stationary and the magnet >> moving). >> The magnet will slide within a cylinder with the coil wrapped around >> the >> cylinder. The cylinder could be magnetic or not, whichever works >> better. >> We could use a spring for return, or reverse the current through the >> coil. >> We could end up with a motor of some sort on a lead screw, or a rack >> and >> pinion, or something else. The voice coil is just so simple though, >> it'd >> be nice if it worked. >> >> Thanks for the ideas! >> >> Harold >> > heat will be your killer problem. Also it requires a uniform magnetic > field to operate correctly. The type of magnets you need are > DANGEROUS, just telling you now before you actually hurt yourself, they > can break bones etc. they are so strong. They require VERY careful > handling precautions. You should think very carefully about assembly > before you even touch the magnets in sumamry. If you just want end to > end movement you can put in stops and sensors for end of travel > information. Then banging it from one end to the other is no big deal. > > If you wish the magnet to move, that complicates things a lot. As I > mentioned before you need a uniform magnetic field. This is a complete > magnetic circuit so you have a core magnet and steal cup shaped pole > piece extending around the coil facing the other side of the coil. > Since you only seem to need 5lbs thrust force and not continuously you > can set it to have a thrust current and holding current. A current > limited driver in this case will work just fine. Peek current would be > in movement blah blah. I'm sure you understand all that :D > > You do need something for the actuator to roll against to keep it > straight unless you already have a linear bearing system in mind. > Since you do not require a real voice coil action you do not need a > spring to return it (as the magnetic field should be adequate to move > it and you don't need seem to need galvonometer type movement). You > might be able to use hall effect sensors to find the end of travel > (that makes it fast and simple). You should have cushioned stops (IE > elastic such as rubber and the like) for end of travel, shock is VERY > bad for any kind of magnet (and rare earth ones tend to break easily). > > Here is a link to assorted high power rare earth magnets. > http://engconcepts.net/List_Of_Disc_Magnets.asp > http://engconcepts.net/List_Of_Cylinder_Magnets.asp > http://engconcepts.net/List_Of_Ring_Magnets.asp > http://engconcepts.net/List_Of_Motor_Magnets.asp > > I repeat these are very dangerous, as you CAN get seriously hurt if you > aren't careful this is why you see them with those 'handy' plastic > spacers on the web site. > > It's preferable if you plan on cycling this thing a lot too use N40 > material as it can handle higher temperatures. Cooling should be > considered a very important aspect of such a system. Hehehehe. Steel > is a lousy thermal conductor, copper is better than that of aluminium. > > You will not need 4700 AMP turns, you can compute how much current you > need based on the magnetic field strength of the magnets. Since the > magnetic field needs to be between the magnetic core and the steel pole > (cup shaped) outside (IE it's field needs to be perpendicular to the > coil's magnetic lines of force) you should read through all the magnet > information on the site and take that into consideration. > The magnets listed for use in motors may be the best suited. > > Stephen > > Stephen R. Phillips was here > Please be advised what was said may be absolutely wrong, and hereby this > disclaimer follows. I reserve the right to be wrong and admit it in front > of the entire world. > > __________________________________________________ > Do You Yahoo!? > Tired of spam? Yahoo! Mail has the best spam protection around > http://mail.yahoo.com > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- FCC Rules Updated Daily at http://www.hallikainen.com -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist