Once you have the bridge track aligning with all of the tracks that are serviced by the turntable without creating a short upon entry or exit, then a locomotive can successfully operate in either direction because the rails control the polarity.
Rich
There’s a split ring pickup powerign the bridge, so if you turn 180 degrees, the polarity on the rails is flipped. That turn of 180 degrees MUST include one end of the bridge passing the “no track here” zone though, or the bridge track will not reverse polarity. It’s nearly impossible to install it in such a way that this wouldn’t happen, but I suppose if you planned it out just right…
Not so much a design flaw as it’s really an issue with ANY split ring pickup system - There needs to be a gap wide enough so that the pickup wipers or wheels do not bridge both halves of the ring (instant short again), and the gap has to be SOMEWHERE. Let’s say that because of the gap, ‘half’ of the table isn’t 180 degrees, it’s maybe 170 degrees. If ALL stall tracks are in one 170 degree segment, and all lead in tracks are in the other 170 degree segment, all is fine. Split the stall and/or lead tracks on both sides of one of those dead areas though and you will have a possible problem. This would happen with any split rail pickup turntable (there may be some fancy pants way to build it so there is no actual gap). Personally, I’d prefer if it WASN’T split ring which then REQUIRES an autoreverser on the bridge rails. Mianly because unless all of your locos have a keep alive installed, that dead section will cause the sound to cut out. An autoreverse will flip fast enough so that doesn’t happen - plus it only has to reverse when you actually start moving on or off the bridge. Modifying the Walthers turntable would seem rather difficult especially since there are already a bunch of wipers on the bridge shaft because everything realted to moving the table is located within the bridge. The old Walther KIT turntable which is mostly the same outsode of the electronics, I believe that one use wipers on the shaft to transfer power to the bridge, and thus would need an autoreverser module.
Properly wired, the split ring bridge will do exactly that. Also, there is no worry about which direction the bridge is facing. That’s taken care of, too.
But there is one and only one way to correctly wire each stall track. You haven’t done that. Take all the stall tracks that are shorting, disconnect them from the bus and reverse the two feeders to those tracks. This will solve your problem. You don’t need the cost and complexity of an autoreverser to make this work.
It will on the same side of the split as the lead, Mr. B. If you have them all wired so that there is no conflict on the one side of the split, but reverse the bridge to get an engine onto one of those radials, you’ll have an immediate conflict because, on that same side, you’ve just reversed the wire feeders effectively.
It is worth noting that the NO TRACK dead zone divides the turntable into two zones of opposite polarity, permitting the split ring to work effectively.
All of the entry/exit tracks to the turntable on one side of the NO TRACK dead zone must be wired the same way so that the polarities all match.
All of the entry/exit tracks to the turntable on the other side of the NO TRACK dead zone must be wired the opposite way of the entry/exit tracks on the other side of the NO TRACK dead zone.
Any entry/exit track that is stub ended (e.g., a roundhouse stall track or a service track) will not need to be gapped and no auto-reverser will be required.
However, if multiple approach tracks from the mainline enter/exit the turntable from the same side of the NO TRACK dead zone, any mismatched polarity will require that approach track to be gapped and an auto-reverser will need to be added to prevent a dead short.
That was the situation that occurred on my layout where approach tracks from the mainline reached the turntable from opposite directions but on the same side of the NO TRACK dead zone.
Rich
My Atlas turntable is electrically the same, although as a deck turntable it uses copper circles and wipers instead of a ring.
A split ring actually breaks and re-makes the circuit twice each time around. That’s why the direction of the bridge does not matter. The polarity will always be the same as that of the stall track when wired correctly.
Yes Rich, what you had was a Wye, just with a turntable in it instead of the third turnout. That, like any other reversing section, required some form of reversing the polarity.
I’m trying to draw a picture but making half a circle one color and the other half a different color is a sticking point. It’s really not hard to understand. If the gap in the split ring is at the 12 o’clock position, and the left half is the rail a, and the right half is rail b, if the bridge is from 10 o’clock to 4 o’clock, the left side of the bridhe will be rail a, and the right side will be rail b. If you not turn the bridge clockwise to the 2 o’clock to 8 o’clock position, the left side of the bridge will now be rail b and the right half rail a. Now, extend stall tracks out at the 10 o’clock posistion and the 2 o’clock position. It’s fairly obvious that the left rail of the 10 o’clock track has to be rail a and the right rail has to be rail b to match the bridge polarity. Likewise, it’s pretty obvious that for the track at the 2 o’clock position, the left rail has to be rail b to match the bridge, and the right rail has to be rail a.
That is what happened with the OP for this thread. The location of where the polarity change of the bridge takes place is completely arbitrary, but you need to know where it is when laying track around the turntable to avoid this problem. Walthers makes it obvious where this spot is because it HAS to be a completely dead, so if you put a stall track exactly over the gap, there would be no power to move a loco on and off the bridge. The real key bit of information is that as the bridge passes the point in rotation, the polarity of the rails change. It’s not complicated or magic, it’s liek any other segment of track, in that the polarity of all tracks - the lead in to the bridge, and the bridge to the stall track - have to match so there is no short. In the case where there is a lead directly across from
The NO TRACK dead zone is clearly marked on the underside of the turntable.
Another way to locate the NO TRACK dead zone is to find the “zero point”, the opening in the wall of the pit that houses the optical sensor. The optical sensor sits perpendicular to the NO TRACK dead zone.
Rich
I have followed this topic and other similar ones which refer to auto reversers as my installation had no such problems and there was no need for a reverser. My install is quite simple as the two approach tracks are on one side of the dead zone and the stall tracks are on the other side and are only connected to the rest of the layout through the turntable.
So, tonight I made a change to the track plan by connecting one of the stall tracks back to the main so a loco can proceed from the main, through the yard, over the turntable and back on to the main.
I was half expecting a short based on the above but all was fine. Therefore I am somewhat baffled as to why others should have problems.
As a by the by, I note the OP has used position 1 as a stall track. While that is fine, P1 is not programmable which means that there is no choice as to where the dead zone is. I installed with the dead zone midway between the approach tracks and the stall tracks. My install therefore doesn’t use P 1 & 2. I wonder if this is part of the OP’s problem?
Bill
Bill, the OP solved his problem by flipping the feeders on the stall tracks (12-17) that were shorting. In his initial post, the OP mentioned that all of the radial tracks were wired the same way all the way around. That was the problem in his particular situation.
The split ring design is not an auto-reverser. The Walthers turntable does not detect mismatched polarities and corrrect them. The split ring expects the connecting tracks to match the polarity of the split ring which changes as the bridge track rotates 180 degrees. So, the radial tracks cannot be wired identically, as to the polarity, if the radial tracks are on both sides of the NO TRACK dead zone.
In your situation, no short occurred because the stall track that you rewired was on the opposite side of the NO TRACK dead zone from the approach track. As long as the stall track that you rewired matches the polarity of the main line track that you connected it to, no short will occur.
In my situation, I had two approach tracks from the main line wired identically on the same side of the NO TRACK dead zone, but the two approach tracks converged from opposite directions, resulting in mismatched polarities on the same side of the NO TRACK dead zone.
I drew up the attached diagram to illustrate these various situations. You can see that as you move radially around the turntable, counter clockwise from the lower left approach track to the upper left stall track, the polarities are flipped on the opposite sides of the NO TRACK dead zone.
My situation is illustrated on the lower right where I was forced to isolate a small len
The wiring is still the same as originally done. What I did was I cut the bus line to the tracks on the other side of the split ring and dead zone and just connected them opposite wired to the same bus. I uses suitcase connectors and wire to do this. So everything associated with the roundhouse, the bridge, and radial tracks are all on one circuit breaker. I found the instructions for the NEW 110 Walther’s DCC turntable HAD THE INSTRRUCTIONS to do this unlike the instructions I had. Bill