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Motor, Indexing and Drive Systems


Diamond Scale Products has developed a motor kit specifically designed to operate our turntables by connecting to the 3/16 inch diameter worm shaft supplied with the turntable kit.  It uses  a very smooth running, medium rpm, low current, reversible DC motor and a reduction gear box.

A double pole double throw (dpdt) switch is included to change motor direction.  A universal joint is supplied to correct for any slight shaft  misalignment between the motor and the worm shaft. 

Construction consists of assembling the gear box and gears, attaching the unit to the underside of the turntable with plastic hinges, connecting the universal joint, and attaching electrical wires between the motor and controls.  Attaching the motor unit to the turntable is more easily accomplished while the pit is on your workbench prior to installation into your layout.

[Photo of Motor Unit]


Voltage Limiting Potentiometer – MK-122

Our DC motor must be operated with no more than 10 volts DC to avoid ruining the motor.  We offer a 3 Watt 250 Ohm potentiometer which can be used in series with the motor to prevent accidental conditions of over-voltage from a variable power supply.

Motor Jog Control – MK-125

We offer a normally open push-button switch which can be placed in series with the motor, after the direction control switch, which will cause  the motor to run only when the switch is pressed.  Turntable operation is thereby controlled by this switch, and the bridge can be “jogged” into final alignment with stall and approach tracks.


An indexing kit is required to control the motor if total automatic operation of the turntable is desired.  Our indexing kit is designed to stop the bridge rotation in correct rail alignment at any track selected.  The system uses mechanical sensors and electronic control circuitry.

The operator selects the track, determines the direction of bridge rotation, and then actuates the indexing system with a push-button.  The bridge will rotate until an initial contact with the selected track sensor.  The bridge will slow, and then stop when the final track alignment is obtained.  Because of the slow speed of rotation, frictional drag of the bridge and worm gear drive, the bridge will not drift out of position.  Accuracy of 1/50 inch at rail ends can be achieved.  The kit includes a led to indicate that the track is in alignment.

There is no pre-set index spacing, and track sensors can be mounted anywhere around the turntable circle.  A sensor is mounted wherever you desire the bridge to stop.  If tracks are aligned directly opposite each other, one sensor can be used for both tracks, otherwise you will need one sensor for each stall or approach track.  You can add as many tracks as you can squeeze in around the edge of your turntable.  The kit comes with six track sensors, a track sensor selection rotor, a 12 position single pole rotary switch, a round 12 position dial plate, a rotary switch knob, a pre-wired solid state circuit board, and miscellaneous hardware.

Construction of the kit consists of mounting the sensors to the underside of the pit, installing the silver rotor sensors, mounting the rotor, the selector switch, and wiring the system components.  Note that wiring is not supplied in the kit due to the unlimited and variable choices unique to each layout.  Attaching the indexing to the turntable is more easily accomplished while the pit is on your workbench prior to installation into your layout.

HO-scale 51 to 105 foot turntables, and all N-scale and Sn3-scale turntables use kit LK-110.

HO-scale 115 to 135 foot turntables, and all O-scale turntables use kit LK-114.

Additional sensors, LK-1151, are available as required.

[Photo of Indexing System from underside of the pit]


Rotary Switches

The index kits come with a single pole 12 position rotary switch which provides 11 switching positions to control the index unit.  If you desire to switch power to the selected track as well as to control the index unit, you will need a two pole rotary switch with as many positions as you have approach and storage tracks.  We offer both a 12 and 24 position rotary switch which will provide 11 and 23 positions respectively.

If you wish to control only the index unit for more than 11 stops you can order and use the 24 position two pole switch since a single pole 24 position switch is no longer available.  Rotary switch knobs are available separately.

12 Position Dial Plate

An aluminum dial plate numbered 1 through 12, suitable for a rotary switch, is available, allowing for maximum flexibility in control panel mounting.  This dial-plate is included in our index kits.

Index Display Panel, 24 positions

We offer a silk-screened 0.050 inch thick rectangular aluminum panel as an option.  The panel is pre-drilled to receive the push-buttons, direction switch, rotary switch and indicator led furnished with the index kits.  The 12 position dial plate can be used with this display panel by placing it over and covering the 24 position indicator.

Conductor Cable

Electrical hook-up wire is not included with either the motor or index kits.  We have available, as an option, both a 15 conductor and a 25 conductor cable with color coded 24 AWG stranded wire, sold by the linear foot.

[Photo of DP-12]

[Photo of DP-74]


All of our turntables come with a worm and gear drive reduction system and can be easily equipped with a manual hand-crank.  We offer all the parts necessary for you to fabricate your own hand-crank system as well as a standard hand-crank kit.  The parts are described individually in the Parts and Miscellaneous section of our web-site.

Our standard manual hand-crank system includes a 3-1/2 inch diameter phenolic hand-wheel with knob, a 3/16 x 1/4 inch ID single universal joint, a 1/4 inch ID oil-filled bronze flange bushing, a 1/4 inch ID shaft collar, a hanging-mount self-aligning (pillow block) bearing, and instructions.  These parts can be combined with a length of 1/4 inch cold rolled steel to construct the hand-crank system.  The 1/4 inch diameter shaft is directly coupled to our turntable’s 3/16 inch diameter worm gear shaft using the single universal joint provided.

We offer a three foot length of 1/4 inch diameter cold rolled steel suitable for the hand-crank system.  This length shaft requires a special shipping container and consequently an additional shipping charge.  1/4 inch diameter cold rolled steel shaft is readily available at DIY stores such as Home Depot nationwide.

[Photo of Hand-wheel]


Copyright Diamond Scale, all rights reserved
Last updated August 23, 2007