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MAKING A SCALE 45FT TURNTABLE

  FOR   FAIRFORD  BRANCNCH  LINE.

 

 The turntable is an old 12 inch Airfix/Dapol kit that I had not built, cut down to a 7 inch long bridge and motorised with a 24-volt unit from a dispensing machine controlled by a “Powermite” controller. It was considered to be a fairly straightforward kit bash - just take a 2½ inch section from each end and strengthen the joints with two lengths of plastic H-beam, but it turned up some curly reliability problems, which took about 18 months to solve.

 First of all I made up the full length bridge as I needed both ends and of course, the centre piece. I turned it over and carefully measured out the pieces to be removed and then made the cuts with a razor saw then rejoined with the H beam. Thus, we now have a scale 45-foot turntable bridge.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 The unused bridge sides were cut down to make the sides of the road overbridge at the Lechlade Station. Above  photos show the finished length and the rails glued down with phosphorous bronze pick-up strip attached  and 2mm scored card to represent the timber top as above.

 

 

 

 

 

 

 

 

 

 

 

   Cutting a 7 3/16th diameter hole through the “Pinex” top formed the well as in above right.

 

 

 

 

 

 

 

 

 

 

 

 

            Mark I with the plastic sprue that can be seen extended out from the aluminum square section in the driving motor.

I first tried super-gluing a 3 inch long 5mm diameter plastic sprue to the centre spigot on the bridge which passed through the base plate and then was sheathed in a 6mm aluminum square section which fitted into the 24-volt motor drive unit that came from a drinks dispensing machine. This method did not last too long (about 15 minutes of operation) as the sprue snapped because the H-beams were catching on the corners of the base plate. The corners tended to rise up a little when the base plate was glued down to the sub base of 9mm MDF board. So a metal shaft was turned up and screwed to the centre of the bridge and the base plate corners were filed down. This was an improvement,  but we found that the electrical contact for the bridge rails was intermittent, caused by the phosphorous bronze strips not maintaining their tension on the electrified pick-up rail.

 

 

 

 

 

 

 

 

 

 

 

                          Mark II  with metal rod as the shaft  and in action at the 2006 Big Train Show in Christchurch. 

 

 

 

 

 

 

 

 

 

 

 

 

 

      Terry Sutton, another member of our group of modellers, devised a unit using a drumhead assembly from an old VCR, and a turned brass plate with copper backed PC board glued to the underside to which the bridge is screwed(as above Photos). There are two wiper contacts on a boss at the base of the drumhead body, as well as a disc with a notch for two micro switches, spaced 180deg apart, to stop the turntable with accurate track alignment.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

         Mark III showing the underneath workings of motor set up and the new power pickup for the bridge and finally in place ready to go. 

This last version is excellent as the bridge is far more stable and the power to the track is reliable. A relay wired across the motor, with its contacts in series with the bridge rails, ensures that the power to the bridge is off when rotating. At the last show and subsequent shows it has performed faultlessly working approximately every 10-12 minutes each day.

I was looking at the possibility of using a DCC chip instead of the Powermite to control it but Terry has engineered it to draw power from the DCC buss. He also pulse extended the start button to make the “rotation start” reliable. This also removed the need for a long power cord to power just one item, as the control system is situated at the centre of the layout. 

 

  The final and successful upgrade in operation as the pannier has uncoupled the two coal wagons at the coaling stage.