Tuesday, June 16, 2015

New Turntable at Stockton Wharf

The Stockton Wharf turntable serves two tracks plus the lead. A small figure at one end of the table acts as a reference market for alignment. The two bright metal T-nuts support the motor assembly. This entire area will eventually be scenicked as a marsh.
The turntable at Stockton Wharf is fairly far away from the view of the operator and, as such, the rails have been difficult to align. A step stool and a mirror have been the best tools so far and those are a bit crude. The best solution would have been an indexing system like that made by New York Railway Supply but I thought that was a bit pricey for just three tracks to the turntable. Finally, I have found a lower cost system which seems to solve the problem.
A stepper motor is supported by a piece of aluminum and two lengths of all-thread rod hung by the T-nuts in the photo above. A machined coupling connects the turntable shaft with the motor shaft. The long rod extending from the coupling is an index to zero the table's initial position with the sensor at the left of the support bar.
 Last year I found a video on the internet which showed a small system being developed by a Scottish electronics company. I followed up with the company who then produced a circuit board kit which can be programmed by the user. The product is limited in that only six positions can be programmed. This means that two positions are used just to turn an engine (one for each end of the table). It's only good for those end-of-the-line turning situations with few or no tracks. I only used four positions for the Stockton table to serve a lead and two roundhouse tracks. 
A simple controller handles the position. The button and knobs along the bottom
are for programming. 
A system was duly bought and assembled (it's a kit), the additional parts (motor, switches, etc.) purchased and the mechanical end designed and built. Once it is installed, it is easy to program and can be reprogrammed just as easily. The motor used is a stepper motor which means that the hardware retains the motor's position so it always returns to the same place. The nice part is that it works. My only criticism is that the table's lowest rotational speed is too fast for my taste. I've spoken to the company and they said they would lower the speed. I'm now awaiting a new board to see how that works.