Hello Adam, upon disassembly of the motor I observed 6 stationary coils under the plate-like permanent magnet that is attached to the movable spindle. Opposite coils (those 180 deg. apart) are wired in opposite polarity. In effect what you have are 3 coils that are 120 degrees apart. In order to get the permanent magnet to move, a pattern of moving magnetic fields must be applied to the coils. Here is how I arrived at that conclusion. Since the field on the permanent magnet, as measured from a stationary point on the motor, will vary sinusoidally from north to south as the spindle is spun by hand I reasoned that a set of three sines in (hexature? triduture? :o) - derived from the word quadrature) would turn the plate. Indeed it does but the whole thing (my totem-pole drivers with the 2N3904 - 2N3906 combo) generates far too much heat. The resistance through each coil is 4.6 ohms and I am having trouble driving it. My question is more specific than the theory of operation of the device which I believe (until convinced otherwise) I understand. I need some information on the nature of the drive circuit that feeds the coils. I'm having trouble generating high-current low-voltage waveforms. I'm a digital guy that needs help from an analog guy. The motors that you mention I have seen before. I believe that the second set of wires are, as you surmised, a tachometer that allows the motor to be used as a closed loop servo. I havn't seen that type in floppies though, just VCR's. > Keith > Aren't these DC motors? It sounds like you are trying to drive them with > AC? I have several of these that I scavenged from full height 5 1/4" > floppy drives and it was my understanding that of the 4 lines coming out > of the motor, 2 were used to drive the motor (DC voltage and ground) and > 2 were used as feedback to the controller board for speed control. > > I had a related question about these motors: How do you measure motor > speed (RPM) via these two extra wires? From experimenting (IIRC, it's > been awhile since I did this) you could drive the motor from a battery > pack by applying V+ and ground to either pair of the wires. That would > lead me to believe that if you spun the motor, both pairs of wires would > generate voltage dependent on how fast the motor was spun. Read the > voltage generated with an A/D and you can then figure out the motor RPM. > > My thought was to use one of these motors to build a wind speed indicator > for our R/C flying field (with a PIC in it of course). Mounted > vertically with the 4 cup arrangement attached to the shaft, it should be > possible to get an accurate enough indication of wind speed. Any > thoughts on whether or not this motor would generate enough juice to > power this circuit (PIC 16F84, A/D, plus 5 to 8 LEDs for wind speed > indication)? > > On Mon, 8 Nov 1999 20:40:01 -0700 Keith Causey > writes: > > Hello all, I am attempting to drive a spindle motor (the type used in > > floppy > > drives) with 3 duty-cycle generated sine waves 120 degrees apart. > > The SX > > generates these signals from a look-up table. These logic-level > > outputs are > > converted to +- voltages with a comparator. This bi-polar output is > > then fed > > into 3 totem pole amplifiers consisting of 2N3904's and 2N3906's. > > The > > resistance of each of each coil is 4.6 ohms. It barely works. > > Voltages above > > +-3 smoke everything and the positive side of the drivers gets > > distressingly > > hot. Also I couldn't find a ground return for the 3 coils so I just > > made one > > (they were connected - just not routed anywhere) What am I missing > > about the > > way these motors are controlled? Thanks - Keith Causey. > > Adam Bryant (age 0x23) > adamdb@juno.com > Parker, CO, USA > Robotics, RC Airplanes, anything using a PIC > > ___________________________________________________________________ > Get the Internet just the way you want it. > Free software, free e-mail, and free Internet access for a month! > Try Juno Web: http://dl.www.juno.com/dynoget/tagj.