Hacking old 51/4" floppy drive servo (spindle) moto

[Raydel]

Does anyone know how to modify old floppy "disk" drive motors to make the speed variable? These motors usually run at 300 RPM, I would like to be able to infinitely vary the speed between say 150 and 300 RPM. Can this be done without building complex circuitry? If you have done this, what make of drive is the easiest to modify?
Any and all help is much appreciated.<p>Cheers,
Raydel

[Dean Huster]

Raydel,<p>A lot of those drives, depending on the brand, especially the older ones from the 1980's, had a skinny board on the rear of the drive that was the spindle motor controller. They usually had a pot on them that would adjust the spindle speed, although I don't know if it had the range you need. The control circuitry was based around the LM2917 F-V converter. Hunt around the board(s) for an LM2917 and if there's one there, likely there's a pot nearby you can tweak that'll do the trick. You should be able to reverse-engineer that part of the circuit so that you can modify it to radically change the spindle speed.<p>Dean

[Raydel]

Hi Dean:<p>Thanks for the tip. I'll take a look and see what I've got to work with.<p>Cheers,
Raydel

[Donald S. Lambert]

I have tweaked the Tandon TM-100-2A and 1A floppie drives to get the speed ust below 300 RPM which is the best speed for the obsolete T/S 2068 computer equiped with vender disk interfaces.<p>The pot is located on the rear of the drive and if you look straight down from the top the adjustment screw faces you. I never tried to adjust for any other speed so I don't know what range of RPM the adjustment will give you. And I don't knoiw how to turn on the drive's stepper motor to check the drive for speed. HTH Greybie<p>P.S. The difference bewtween the 2A and 1A is that the 2A is double sided and the 1A is single sided. Otherwise the drives are identical, one has two heads and one has one head.