Subject: PM Servo Motor (9Tk Tape drive)
Sent: 31 Jul 99

I picked up at a ham swap, two low speed Servo Motors that controlled a tape 
reel, used in an old 9 track 2400 ft reel to reel .5 inch wide computer tape 
drive.  They say "permanent magnetic servo motor" and have two wires coming out 
of each motor.  

The way to check the efficiency and whether these things are still operational 
is to electrically hook them together.  If one hooks the black wire on one unit 
to the black on the other unit and the red to red.  Then, if one turns by hand 
back and forth one shaft on one unit, the shaft on the other unit will rotate 
and do the same motion at the same time.  What this is saying is the one unit 
being turned by hand is generating enough current, as a generator, to turn the 
other one as a DC motor.  One can then do this motion slower until slippage 
occurs due to not being able to over come the friction of the barrings.  In this 
way one can get a pertly good idea of the efficiency of these units as a slow 
speed generator and motor.   These passed the test.

The units are extremely sturdy built being 5.75" long and 4" in diameter and 
have a .65" diameter shaft with ball barrings each end. They have 4 separate 
brushes in each unit. They have a heavy duty flange with 4 holes for mounting. 
They came with the hub that clamps onto a Reel to reel type tape still on the 
shaft.  This is not the capstan motor this the one that drives the tape reels.  
I plan to use the inside aluminum ring out of an old Tape Reel to clamp-mount it 
on the hub. Then mount this hub-ring unit in contact with a exercise bicycle 
wheel.  The result will charge one 12 Volt battery or possibly two in series. I 
was told they were designed to be operated at 28 volts.  At this time I am not 
sure how much power can be generated without causing a problem.  My cost was $15 
for both.  This vendor didn't have any more available.  

If these units were planned to be used outside in a small windmill then the 
hosing and ball barrings would need to be made water proofed in some fashion. 

Model: E722 
The company that made them is:
Electro-Craft
Corporation
1600 Second St. So. Hopkins, MN 55343.

I think other Reel to reel tape drive hub servo motors independent of brand 
should also work.  Just check them out as noted above before you purchase.



