Newsgroups: comp.robotics
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From: roger034@gold.tc.umn.edu (Brynn Rogers)
Subject: Re: Motors found in 3.5-inch floppy disk drives
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References: <30hq19$e87@gazette.bcm.tmc.edu>
Date: Wed, 20 Jul 1994 03:20:33 GMT
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In article <30hq19$e87@gazette.bcm.tmc.edu> you write:
>I just got a bunch of small floppy drives, and after taking one apart,
>I found what _looks_ like a stepper motor, but it is attached to a PC
>board, with no apparent means of removal.  This is the main drive motor,
>and it also seems to have a RPM sensor in the form of a magnet-coil
>arrangement with the magnet attached to the outer rim of the moving
>portion.  There is a 5-wire cable leading from the whole assembly,
>which includes not only the freely-spining rotor, but an attached PC
>board with a bunch of components, including chips, SMT resistors, the
>aforementioned coil, and other stuff.

  It sounds like you are describing the motor that spins the disk, and
not the stepper motor that moves the head.
  If so, this is probably a brushless DC motor that is optimized for
constant speed and a light load.  This probably isn't real usefull for
driving a robot,  but if you want to spin a sensor around at a constant rate
it might be handy.  Driving it is a pain compared to a brushed DC motor.


>
>Has anyone used one of these motors on a robot?  Any ideas on how they
>work?  If I knew what the rotocol used by the cable to make the thing spin
>up that would be  a start!

  They work because voltage is applied to the three stationary coils in a
sequence, and the rotor (which is a permanent magnet) spins inside this moving
magnetic field.  The coils are usually connected as a delta or Y configuration,
like this:   
                            wire a\         /wire b               
             | wire A              \\     //                      
             |                coil A\\   //coil B                 
            / \                      \\ //                        
     coil1 // \\ coil2                \ /                         
          //   \\                      |                          
         /       \                    ||          Y configuration 
wire B-----=====-----wire C     coil C||                  
           coil3                      ||                          
                                       |                          
                ^                    wire c                       
         Delta  |                                                 

 
The other two wires would be going to the Hall effect sensor that might
look like a turned on transistor when the magnet is adjacent to it, and
a transisitor that is off when no magnet is around.

>
>Thanks for any help!
>

Brynn


--
Brynn Rogers     roger034@gold.tc.umn.edu

