How to move a turntable?
Now let's look under the module - how is the turntable-bridge powered to spin?
I show the equipement of the SP "Taylor" turntable.
I realized this project years ago - so I can tell you that this instalation is really working!
I use a DC-motor with a installed reduction gear.
What we need is torque with a low speed.
So the reduction gear has to have a high reduction ratio.
The motor turns a small rubber wheel - you can see it on the foto as a small black cylinder allocated at the right hand side of the big propulsion-wheel.
The big propulsion-wheel is installed on the axle of the turntable - so the torque is transmitted to the turntable-bridge, that is located on the other side of the wooden plate that forms the turntable-pit.
I first tried with a synchronous motor - that failed because the motor didn't have enough torque.
So I replaced this synchronous motor by a DC-motor and I got the propulsion I wanted.
The turntable-bridge is slowly moving - even with a big steam-locomotive moved onto the bridge it makes the turn.
The foto shows on the right hand side the motor with its attached reduction gear.
The power-axle of this unit is arranged in a perpendicular direction - the rubber-wheel is fixed on it.
The big propulsion-wheel then turns the bridge.
How to control the turntable?
When moving the turntable-bridge you have to align the rails of the bridge with the rails of the track you want to move a locomotive to.
I decided for a manual control without automatic indexing.
This is like the prototype - the operator at the controls moves the bridge to the desired track.
I use my eyes view to finally check the propre location of the rails.
I correct the position of the bridge until the rails are in line - back and forth (sometimes more than one approach 😏 ).
To do this I need a good position to clearly whatch the rails.
The modules of the engine-terminal are designed to allow the access of the operator close to the turntable - so the operator can watch the position of the table.
The operating controls are quite simple: It is a small handheld box with 1) a selector to chose the moving direction and 2) a push-buttom to activate the turntable-bridge movement.
The operator selects the direction and then presses the buttom as long as he want to move the bridge.
When the buttom is released the bridge stops.
The operator can look at the alignment of the rails.
A short touch of the buttom moves the bridge a little foreward - after changing the direction with the selector he can inch the bridge back to the desired position.
With some experience the operator can move the turnpable very efficiently.
I think this is like the real thing - I prefer to work so.
When ever you have watched an original turntable in operation, then you know - on the original thing its all manually done and thus it takes time and sometimes several attempts!
For me this is O-Scale operation - it is not automated, it is maually operated on site.
And you are the guy doing the job!
The foto shows my control box.
The operator takes it in his hand, with the long cable he can take the good position to watch the propre rail-alignement.
The silver selector changes the moving direction of the bridge and the red push-buttom controls the movement of the bridge.
How to feed electrical power to the rails of the turntable-bridge?
Before I start explaining the solution that I applied to the turntable, I have to describe the elecrtical system I use to power my locomotives.
To move my locomotives I use either analogue DC-power or digital DCC-power. Only a part of my fleet is actually digitalized.
To move a locomotive to and from the turntable-bridge, we need to supply the electrical power to the rails of the turntable-bridge.
Well, the bridge is movable and can be turned several times around itself in the same direction.
So it is clear, we can not feed the electrical power directly over two wires to the rails on the bridge.
We need electrical sliding contacts.
But that is not all about requirements - when the turntable-bridge is moved 180 degrees the polarity has to be changed to be compatible with the polarity of the fixed tracks.
This is needed to make the movement of the locomotive from the turntable to the fixed track possible.
This is how I realized the change of the polarity in the electrical feed:
I fixed two seperate copper-plates onto the propulsion-disc (see explanations of the posts about "how to move the turntable").
I placed a thin plastic sheet in between to keep the copper-plates electrically isolated.
A soldered wire connects one copper-plate with one rail of the bridge - this is repeated for the other plate and the other rail.
Two electrical sliding-contacts connect the power station with the two copper-plates.
The location of the sliding-contacts makes shure that the change of the polarity takes place in a sector without fixed tracks reaching the bridge.
It sounds a bit complicated to read - but it is not so difficult to install, when you have understood the principle.
The foto shows one sliding contact - the second-one is located on the other side of the axle.
So this are the electrical principles I use to operate my turntable in "Taylor".
It works well for many year now.
I will install a similar system for the new turntable in "Redondo".
Detailing the turntable-bridge (1)
OK - the construction of the turntable is well advanced.
Let us talk about the prototypical view of the turntable.
A typical equipment of a turntable is the arch located at the center of the turntable-bridge.
In reality it carries the power cables, bringing the electricity to the bridge to power the motors that will turn the bridge.
On my model turntable the arch is only an optical gadget. It is built with standard profiles matched together to become the arch.
See the foto that shows the construction details of the arch.
Detailing the turntable-bridge (2)
The real thing is typically hold together with rivets.
Depending of the age of the bridge the number of rivets can vary widely.
Some bridges even were extended during their life to handle larger locomotives - additional sections were riveted to the existing bridge.
I did not spend too much time to locate the propre position of the rivets.......
Do not try it - you never can count them!
I used decals to simulate rows of rivets.
Decals for large scale-models provide rivet-heads with a good dimension.
The foto shows the impression you get with this simulated rivets in different areas.
The bridge still has be aged to show the wear of use - that will change the look of the rivet-rows.
Detailing the turntable-bridge (3)
To lift-off the whole bridge from the pit, it has four lifting-points each located at the outher section of the bridge on both sides and both ends.
The foto shows such a lifting-point.
"Redondo" locomotive terminal - how it looks today
That is an overal view of the the turntable, in the background you see the frontwall of the main shop.
This is the actual status of my work - I plan to continue soon.
Juerg - Orange Empire