I am considering building a turntable for my LGB trains, utilizing an
old (record) turntable as a rotating platform. I plan on motorizing
the turntable usng a small DC motor, some gear reduction and a couple
I am looking for ideas on how to electronically control/index the
turntable so I could simply move a selector switch and have the table
rotate to the appropriate position.
This is a good move - you're guaranteed a smoothly turning turntable.
Try using a rubber sleeve on the motor shaft running on the outside edge
of the record turntable.
Mount the motor on a pivoted arm sprung lightly against the disk. (no
gears to grind and whirr)
Cams screwed to the top edge of the disk operating micro switches.
From my experience, I would recommend separate cams and switches for each
direction to avoid the need to make the complex adjustment of both
position and throw for single cams.
IR diodes and IR detectors - turn on the IR diode aligned with the
required track - detector turns off motor.
The problem then arises as to how much momentum remains in the drive :-)
1. If you enjoy playing with microcontrollers/microprocessors -- or have a
(good) friend who does -- you can work this problem by having a "getting
close" detector before the position detector.
2. Rather than using continuous motors, you can get steppers with very small
incremental motion that look completely continuous but can stop on a dime.
"Complete book of Model Railway Electronics" Roger Amos ISBN 1-85260-288-0
It's simpler than you might think - An Infra-red LED and matching sensor from a
electronics shop and a sensing circuit, perhaps a 555. The LED shining on the
sensor alters the
resistance of the sensor which flip/flops the 555 and drives a relay or
transistor or TTL logic
I've never seen a published circuit devised for a turntable but all you would be
interupting current to the driving motor with the cams and micro-switches and
electronic switches so that only the one IR lighted TT track end electrons
switch is "off".
The mechanical problem then is that the electronic on/off is on the revolving
bridge and all the
other control circuitry is on the baseboard.
BTW, I prefer the drive mechanisim on the baseboard rather than on the TT bridge
as it's much
easier to quieten the mechanisim and everything can be built to blacksmiths
than microsurgery standards. :-)
switch is "off".
There's at least one detailed description of an opto-electronic
indexing system on the web, just do a bit of searching. The links page
at is a good place to start, look under
'Model Railway Electronics.
Make friends in the hobby.
Garratt photos for the big steam lovers.
Paul, years ago "floppy drives" for computers were powered by "Step Motors".
If you have an old computer laying around check to see if the floppy drive
does indeed have this type of drive and the electronics to go with it. You
should be able to adapt this to your needs. Glenn