Fairford Turntable page2
Continued description of building the turntable
The motor to drive the turntable is a 24volt unit from a drinks dispenser. It was envisaged that only about 2-3 volts would be needed to rotate the bridge at a reasonably slow speed. A "Powermite" controller was used to supply power to the motor and had it set on the third small marking which rotated the bridge about 25 seconds per revolution.
To connect the shaft to the motor I used a length of 6mm square tube and drilled a hole through the tube and shaft into which split pin was placed.
Mark I MarkII
Mark I only lasted 15minutes of operation as the H beams caught on the corners of the plastic base plate that had lifted slightly and the sprue shaft snapped. Mark II had a metal rod as the shaft which was a great improvement but the phosphorous bronze wipers were not maintaining contact on the brass rail even after having skids soldered on to help cross the gap at opposite side of the well. The problem of reliability needed a re-think so I went back to Terry Sutton, a member of our group of modellers here in Nelson who is a whizz on electrical things as well as photography. He devised a unit using a drumhead from an old VCR and a turned brass plate with some copper backed PCB glued to the underside and the bridge screwed on top. There are two wipers that contact on the boss at the base of the drumhead body as well there is a disc with a notch for two micro switches spaced 180degrees apart to stop the turntable with accurate track alignment. This is now Mark III and it is almost 100percent reliable.
VCR drumhead with brass plate attached. Bottom showing the square shaft and power connection.
In place in the well ready for the bridge to be attached. Mark III bridge in place.
Underside of bridge showing the power pick-up system. All wired up minus the DCC macro unit.
Terry also pulse extended the start button to make the "rotation start" reliable.
Photos by Ian McEwan