On Saturday 03 January 2009, Jon Elson wrote: >Gene Heskett wrote: >> On Saturday 03 January 2009, Dean Hedin wrote: >>> Take this one for example: >>> >>> http://www.hobby-lobby.com/brushless-gazaur.htm >>> >>> The R/C motors are rated with "Kv". Which means rpms per volt with no >>> load. The above motor is rated at 4100kv and can go up to 12volts. >>> So that would be 49200 rpm. >> >> That link says up to 14.8 volts, which would be nearly 61k rpms. >> >> But surely a motor of that size cannot be rated for CCS service. 450 watts >> of input (30+ amps at 14.8 volts) would fry it in 2 or 3 minutes even if >> it was pumping its own cooling air. Or at least I'd think so. And this >> is the sort of info I'd need. Bearings aren't mentioned either, and even >> torrington needles have limits of around 150k rpms for their teeny >> cartridges needles. > >Well, the ultimate motors for this are Westwind air bearing spindles or >Rockwell/Precise high speed spindles. >The Westwinds are really designed for drilling, but can be used for >light routing, too. You have to be real careful to keep the radial >loads down to avoid crashing the air film in the bearing.
Interesting. The length of the radial portion of the bearing must be fairly short then? Or the recommended air pressure to the bearing is too low. Back when we (tv stations) all had the 2" quadruplex vcr's, I often noted that turning a headwheel by hand with the air off was both difficult, and draggy like it was full of sandpaper. Bring up the compressor and it would turn freely even with 15 or 20 pounds of push on the rim of the 2" diameter wheel, and would sometimes turn slowly for minutes if it was given a push. Air pressure to those bearings was in the 40-55 psi range, and used maybe .5 scfm at that pressure. Guide posts also were air powered so the tape floated on an air film. They generally used more air in the venturi vacuum if the compressor wasn't double ended to make vacuum too. That could keep a 4 cylinder 2 horse oil-less Gast fairly busy. The vacuum was used in the shoe that held the tape in the curved shape as it was pulled past the spinning head, otherwise the head would have simply sawed the tape in two. >These are >about 2" diameter and 6" long. The motor rotor is about .7" diameter >all the way, just a plain cylinder with a "hat" on the end for a thrust >bearing. It will produce at least half a HP, and can go up to 80,000 >RPM. It runs great on a VFD, although my VFD only goes to 400 Hz, so >you get 24,000 RPM max. So it's not an air motor, just air bearings. How fast could it be brought to speed? Toward the end of the 2" vcr run, Ampex had a couple of machines that could give a locked picture in 400 milliseconds from a stopped wheel. Needless to say, the amps were about 100x overkill for cruising operation. The last 1200 I had at WDTV took about 2 secs to hit speed, and another 1.5 to 2 to achieve phase lock and output video that was airable. But it took a recalbration of all the servo stuff a couple of times a week to stay inside of 5 seconds, the standard pre-roll for those things. >I also have a Rockwell/Precise spindle that will go to 45,000 RPM, and >is rated at 3/4 Hp. It uses a 2-phase motor, so i don't have a proper >system to run it yet. I did fire it up on a Gecko stepper drive, >however, and it did run. I'm not sure it would develop rated power on that. >The oldest Precise spindles have universal motors, and can be run on a >Variac. Something us hobby types would gravitate to because of the cost. :) -- Cheers, Gene "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) If you think before you speak the other guy gets his joke in first. ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
