Keith, I've read the various posts on this thread - here's my take based on what's been said - If, as suggested, the motor consists of 6 pairs of coils 60 degrees apart and with opposite airs connected then the motor seems to be a 3 pole brushless DC motor. The centre is the common of all coils does not need to be connected to anything else (but can be if desired - see below). The motor is rotated by successively applying voltages which attract or repel adjacent magnets on the rotor. For mechanical reasons there are liable to be X North-South pairs of permanent magnets on the rotor where X is NOT a multiple of 3. Because all coils are commoned you must apply voltage to 2 coils at once to cause current to flow. When you do this one coil will produce a N pole and the other a S (as current goes into one and out of the other using consistent descriptions of in and out. After applying power to 2 leads for a certain time the motor will have rotated to its stable position (one rotor N will have been attracted to and aligned with a stator S (or vice versa) and the other rotor pole will be repelled and now be mid-way between two same sign stator poles). Power must now be applied to one of the previously activated leads (but with opposite polarity) and to the previously unactivated lead. This process continues indefinitely and the rotor rotates :-). Position may be detected by 2 sensors (almost always hall effect sensors) which determine when the stator inputs should be changed by determining rotor alignment. Alternatively, if the system is designed to run at a single speed as it is here) the system may be synchronous, run at a single speed with the rotor locked to the rotating field by virtue of the magnetic attraction being substantially greater than the forces which attempt to cause dropout. Using sinusoidal voltages rather than square waves will assist this process. If your coils etc are overheating they are being overdriven. IF this is indeed a brushless motor as above then it will also have upper and lower drivers for each lead and you should be able to drive these rather than driving the coils directly. If you must drive it without original drivers and power doesn't have to be maximised then you may be able to drive it "half wave". This is very easy using square waves. The centre is now connected to eg V+ and up to 2 leads are taken low at any time via driver transistors, FETs or whatever. Lends itself nicely to PIC control and no high side drivers needed. Keith - if this sounds like its along the right lines you could contact me directly for some more directed comment. Russell McMahon _____________________________ >From another world - www.easttimor.com What can one man* do? Help the hungry at no cost to yourself! at http://www.thehungersite.com/ (* - or woman, child or internet enabled intelligent entity :-)) From: Keith Causey >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. >