On Thursday 04 April 2013 09:23:01 Gregg Eshelman did opine: > --- On Thu, 4/4/13, John Stewart <alex.stew...@crc.ca> wrote: > > I'm looking for ideas here. > > > > A Unimat SL1000, MK1 landed on my desk last Saturday. It's > > mine if I want it. Have been thinking of taking some of my > > CNC parts kicking around home and using them, but I don't > > think using a 5i25 + 7i76 + Nema 34 steppers is great. > > > > So, with a little lathe like this, if I go with NEMA 17 "3D > > Printer" steppers (think Reprap or one of the Thingverse > > machines), what would be the best, least expensive way of > > driving these steppers from a LinuxCNC setup? > > Even 17's would dwarf that Unimat. I'd try some motors from printers or > old 5.25" full height floppy drives. I just happen to have a pair of > Tandon single sided 5.25" drives I've been trying to give away for a > while. ;) Had them on a TI-99/4A years ago before upgrading to double > sided drives. > > The drive motors for spinning the disks might also be useful for micro > CNC with encoders added. I think they have tachometers built in. > They would probably be pretty puny for x-z drives even on that small a lathe. They were normally belted to the spindle, and belt slippage on the lathe would destroy any accuracy unless you also put scales on it. The 17 class steppers might be overkill. but at least you can microstep them.
> Even cooler would be using the motor control boards from the drives. > They do step and direction for the head steppers and on/off for the > drive motors. 'Course they have rather poor resolution with only 40 > normally accessible steps, though that's not a hard limit, there was > software for increasing the number of tracks on disks for some > computers. Steps available are virtually unlimited. The driver SW in the computer usually steps them outward, either until it hits a mechanical limit & sits there hammering the stop till enough steps have been issued that the computer knows it has to be at track zero ( racket you hear at bios bootup from any pc with a floppy in it, or if fancy driver, the track zero switch closes to indicate its at track zero. Stepping the other way is limited in the drive by the head carriage hitting the spindle mechanics but if that limit is removed, there is not any other limit. The biggest problem will be the low voltage it runs on. The disk drives board will fail at the voltages we commonly use for steppers, even the toy stuff we generally use is 24 volts, and that is enough to cook the floppy board because they do not chop for current control, they power up, do the step and shut the current off 40 milliseconds or so later if no more steps come in since there is not any torque pushing on them, the normal steppers cogging is sufficient holding power. The next problem is the speed they can step. At the voltages they do run at, and at no more mass than they have to move, the maximum step rate is nominally 6 ms per step. Mechanically geared down for accuracy, that is not going to be very fast at all. Synopsis: Look for a small chinese stepper board that can microstep with chopper controlled current, and hit the surplus places looking for 4 wire, not more than 12 volt, probably $12 or so, steppers. I have a few, rated at 24 volts, which means they'd be pretty slow on 24 volts, but I didn't buy them for motors, but as generators, turned by hand they output a nice pulse for a jog pendent. But my round tuit came up missing. :) Those head steppers out of the old tandon's that drive the head carriage via the thin steel tape, can be made to put out considerably more torque, and faster by 5x or so, if driven by a xylotex board and a 24 volt supply. But the xylotex board doesn't do idle current reduction, just on & off via the enable pins, so the motor temps need to be watched. Getting that alu tape drum off the shaft so you can fit something else is a problem, they are pressed on, interference fitted. Interesting what if problem. :) > I wonder if it'd be possible to hack the control board (which is > separate from and much smaller than the data read/write board) to work > as a more general purpose one? Microstepping might be a bit much to > add. Not practical at all. > There was a site that showed using the boards and motors from a pair of > floppy drives to build a robot, but it vanished. No wheels there that we can't reinvent if needed. :) 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) My web page: <http://coyoteden.dyndns-free.com:85/gene> is up! My views <http://www.armchairpatriot.com/What%20Has%20America%20Become.shtml> ... My pants just went on a wild rampage through a Long Island Bowling Alley!! A pen in the hand of this president is far more dangerous than a gun in the hands of 200 million law-abiding citizens. ------------------------------------------------------------------------------ Minimize network downtime and maximize team effectiveness. Reduce network management and security costs.Learn how to hire the most talented Cisco Certified professionals. Visit the Employer Resources Portal http://www.cisco.com/web/learning/employer_resources/index.html _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
