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This page is to show the development of my scratch-built turntable.
I am in the process of building a turntable with a stepper motor.  I have taken apart a couple of 5 1/4 inch floppy drives.  These yield a stepper motor and a platter with a good ball bearing race.  I am going to drive this with the stepper motor.  Has I have an incredibly restricted space, I am constructing the TT bridge out of an Atlas Plate Girder bridge.

As to indexing, I also liberated a LED/photodiode pair from the floppy drives,  I will use this as a fixed detent position, or home.  I plan to use a PIC to drive the stepper.

To calibrate, the PIC will drive around clockwise to the detent, then anti-clockwise to the dent, those learning the number of steps required for 360 degree.  Tracks will be n steps relative to the detent.  Every time the table passes the detent, it will recalibrate (so maybe a good place for the detent would be between track positions).

To control it I have several options:
                 1. manual drive: push button left, right, you're on your own bud;
                 2. manual drive with auto-stop: two buttons, right and left, auto stops at
                 next track;
                 3. DCC, mimicking a series of turnouts, so each pair of tracks would be a
                 virtual turnout;
                 4. DCC, mimicking a locomotive: speed, direction controlled with handset;
                 5. DCC, where the speed setting is the track number, so max. 14, 28, or 128,
                 depending on the setting.

Of course, there has to be a way to program in the track positions as well.  Also thought it might be nice to be able to set acceleration, max rotation speed.

So far, I have accumulated some parts from 5 1/4 inch floppy drives.  These are a veritable treasure trove of parts.  The most useful are the platter motor which gives an excellent rotor, the stepper motor, and opto-interupter.

Progress is being made, as can be seen below.

Floppy drive parts Selected Floppy drive parts
Here is a selection of platter motors and stepper motors from the 5 1/4 inch floppy drives.  The two platters on the left are identical but the one in the foreground is flipped.   You can see the magnet 
material in the interior of the one in the foreground.  Also there are two different kinds of stepper motors, some with two and some with four coils.  (click to expand)
Here is the one I selected - it has useful mounting tabs, and you can see the rubber band I placed around it for traction.  The motor has some teeth which allows good traction on the platter.  (click to expand)
Opto interrupterBack of interrupter Building TT base
This is an opto interupter that I got from the floppy drive.  It consists of a LED and photo-transistor, with a handy 3-wire cable. On the right is the back.  It is labelled:   A=anode, K=kathode :-) (of diode)  E=emitter, C=collector (of transistor)   G=ground, A=anode, C=cathode. Here is the base for my turntable with the track applied.  It is being held down while the glue sets.  The flex track does not like being contorted to this extent!
Completed TT base TT with bridge
Here is released base with track glued down.   Here is how the bridge sits on the circle of track - pivot is not attached.
View1 of bottom View2 of bottom
Two views of the stepper motor applied to the table with a tensioning spring and high-tech adjustment.  Note the pale coloured rubber band applied around
the platter.