Floppy drive speed

Floppy drive speed

Post by William Manchester Shube » Fri, 02 Nov 1990 16:36:00



        Somebody I know wanted to know how you alter the speed on your floppy
drive (to set it to the proper 300 rpm, or whatever it should be.)  They've
gotten theirs open, found what they call a "meter" of sorts, but now cannot
figure out how to uncover the actual speed that their drive is running at.
Can anybody help?

 
 
 

Floppy drive speed

Post by Phil Hugh » Fri, 02 Nov 1990 02:01:00



Quote:

>    Somebody I know wanted to know how you alter the speed on your floppy
> drive (to set it to the proper 300 rpm, or whatever it should be.)  They've
> gotten theirs open, found what they call a "meter" of sorts, but now cannot
> figure out how to uncover the actual speed that their drive is running at.
> Can anybody help?

Most floppy drives have a strobe disk on the motor drive.  To check the
speed you need to strobe it with 60HZ.  A neon bulb will do the trick.
Either get an NE-2 and resistor and plug it in or get one of those
$.49 elcetrical testers which is a neon bulb in a plasicc case, plug
it in tio the ac line and hold it next to the strobe disk.
--
Phil Hughes, SSC, Inc. P.O. Box 55549,
Seattle, WA 98155  (206)FOR-UNIX or 527-3385
    ...!uw-beaver!tikal!ssc!fyl

 
 
 

Floppy drive speed

Post by Michael Schust » Fri, 02 Nov 1990 18:29:00




>>        Somebody I know wanted to know how you alter the speed on your floppy
>> drive (to set it to the proper 300 rpm

>Most floppy drives have a strobe disk on the motor drive.  To check the
>speed you need to strobe it with 60HZ.  A neon bulb will do the trick.

I heartily agree. Recently I had some problems with extended formats and
interchange of disks with friends, so I decided to look at this in detail.

Ever check your drive speed using the only (to my knowledge) public domain
speed checker? It's called DSPEED.TOS and was written by Mike Curry a long
time ago. It seemed strange that most (hmmm, come to think of it - ALL)
of the disk drives I tried it on ran a little fast - from 302-304 rpm.

Well recently a friend, who has been using IBM-vintage 3.5" drives on his ST,
told me an interesting story. He said that he tweaked his drive speed to
300.030 using DSPEED.TOS, and then connected the drive mechanism to his
IBM. Using an MS-DOS disk speed program he got 297 rpm!!!!

The solution, as suggested, is to use a strobe disk. Trouble is, not many
ST drives have one. I stole one off an old dead Tandon mechanism and
put it on my SF314's flywheel. Lo and behold, DSPEED.TOS reads 303.54
when the strobe is exactly stationary.

Conclusions:
1. If you can get one, adjust your disk drives with a strobe disk.
2. Beware of DSPEED.TOS; 303-304 rpm by it's reckoning may very well be
   right on the mark!

-----

--
l\  /l'   _  Mike Schuster          {sun!hoptoad,cmcl2!phri}!dasys1!schuster

l    lll\(_  New York, NY USA       DELPHI,GEnie:MSCHUSTER  CIS:70346,1745

 
 
 

Floppy drive speed

Post by 8706.. » Fri, 02 Nov 1990 09:48:00


Please correct me if I am wrong, but isn't the drive speed on the ST
drives controlled by the strobe only, I had a look at one at the shop
and it looked as if there were no adjustments???
later
Barry
 
 
 

Floppy drive speed

Post by Ross Alexand » Fri, 02 Nov 1990 11:43:00


Muke Schuster and others have written about setting drive speeds, et
c., and the fact that strobe wheels are a a good deal more accurate
than DSPEED.TOS or whatever.  Fine.  But there has been an unspoken
assumption all along, and that is:  You want your drive to be going
_exactly_ 300 RPM.  I question this.  Yes, that's the specification
alright, but there is a good reason to run your drives a little bit
SLOWER (say, 297 RPM or so).

The reason is thusly:  if you are using one of those clever
formatters, such as DCFORMAT or any of its ilk, that can put 10
sectors on a track, the last gap (Gap #4, made out of 0x4e's) gets a
little bit shorter than normal, which is 1401 bytes; it gets trimmed
down to 780-odd bytes.  It's not a bad idea, however, to run slightly
larger than normal Gap 3's (normally 40 bytes, I like to double
this), and then Gap 4 really gets crowded.  But if you run the drive
a little slow, the effect is that to the 1770, all the tracks look a
little longer than normal, and you get your Gap 4 size back to
something reasonable.  You can check this by looking at the data
coming off the read line with an oscilliscope (take the scope sync
input from the index pulse line) and noting how close the end of the
last sector comes to the end of the track.

I have done this routinely for years and find it doesn't generate
any trouble if you are only 1 or 2% slow; the PLL in the data
separator can handle this kind of an error with it's eyes closed,
and the added security of the longer gaps helps to overcome all
kinds of write-skew and drive wow-and-flutter problems.


alberta!auvax!rwa

 
 
 

1. Blood Money and floppy drive speed

Hello all,

    I read on the net that drive speed can have an effect on Blood Money,
the real version, not the magazine version.  Using QuickIndex 15, I noticed
that my RPM was constantly at 301.  Surely Blood Money couldn't be thrown
by THAT?!
    Well, it was.  I took the drive apart and tried to lower the rpm with
the potentiometer inside of the drive but Blood Money seemed to not
notice anything.  I checked the drive's speed qith QuickIndex15 again.
Drive rpm still hovered at 301.  I guess the pot has a VERY limited
range.
    To test things further, I temporarily replaced the drive (Mega computer,
by the way) with an old wheezing Epson mechansim (rattles, bangs, and
thrashes).  Weeeeelll, it booted up Blood Money just fine.
    I returned the original drive and decided to fool around with the
idea of placing some sort of weight on the flywheel.  Using SuperGlue and
a dime, I glued the dime to one side of the flywheel's center.  After only
a few minutes of potentiometer adjustment, I was able to get the drive
down to 300rpm!!!  For confirmation, I snapped the dime back off and
tried to adjust again.  Nope, I never was able to get the rpm rating down
to 300.  Regluing the dime onto the flywheel restored the 300rpm speed.
    Blood Money now boots fine.
    Ok, well, that is fine and good, but I'd have preferred an 'electronic'
method.  If anyone can suggest another means of correction that is less of
a hack, let me know.  Also, can the dime's weight cause undue wear on the
flywheel?


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