CMR 90 foot Turntable

[BigDaddy]

I bought one off Ebay. http://www.custommodelrailroads.com/turntables-3.aspx

The seller was the kit builders son.  It has some modifications that aren't in  the directions and CMR may have later added a wiper to replace the power pickup from the bearings. 

Regardless of bearing vs wiper, one end of the turntable supplies power from the turntable rail (which is split) to one rail.  The other side to the other rail.

When one wheel of one end crosses the gap, it looks to me like it's a dead short between the two wheels and a reversing circuit isn't going to help until the second wheel crosses over the split.

I've talked to RR Mel about the modification he made on his turntable.  He found the electical pickup from the wheels a bit dodgy and made elaborate modifications in how electricity is supplied to the turntable.  Mel has posted this link before.

http://melvineperry.blogspot.com/p/135-foot-turntable-project.html

As designed, I don't see how it could possibly work which might mean I am missing something very obvious and having a Doh Homer Simpson moment.

I will be using DCC.  My only other TT experience was,  oh my, 30 years ago, I used a center off DPDT switch. 

Edit I had was indeed having a Homer moment.  There are 4 cuts in the rail   I need to examine the wiring closer.  There are 2 long rails and 2 short rails.  According to the directions from CMR the short rails are powered through a reverser.  I need to think about this.

 

 

[RR_Mel]

Henry

 

Your picture brings back memories for me, I haven’t seen the bearings (pit rail wheels) on my turntable for ten years.

 

 

EDIT:

 

The Dayton 12 volt .5 RPM 2L003 gear motor is what makes the CMR turntables work so well.  Warning to anyone using the 2L003 gear motor, it has 50 in-lbs of torque, use a slip coupling, if something stops or jams the bridge you will be very sorry if the shaft doesn’t slip.  It could put one of your best locomotives on the floor across the room.

 

 

Mel

 

Modeling the early to mid 1950s SP in HO scale since 1951

 

 

My Model Railroad   

http://melvineperry.blogspot.com/

 

Bakersfield, California

 

I'm beginning to realize that aging is not for wimps.

 

[7j43k]

I think the reason for having the turntable ring rail split is to provide "automatic" polarity correction for DC locomotives on the table.

With DCC, you don't need that.  I do wonder about making the entire ring rail all the same polarity (that is, tieing all the 4 pieces together electrically), and then using the center bearing and shaft for the other electrical feed.  Then there's no electrical switching needed or provided.

A few more seconds of thought on that matter reveals that you will need, I think, one of those automatic polarity reversers as used on loop tracks and such.  I suppose you could place it in the feed for the turntable track supply.

 

Ed

[rrinker]

 That is the BEST way to do it, skip the split ring pickup with DCC. Because there is a certain "wheelbase" of the pickup wheels/shoes on the table, there needs to be a large enough dead section, not a simple gap in the pit rail. Preceisle to prevent the two wheels on one side from spanning both sides of the split ring, which indeed would be a short. OK for DC, and for DCC locos without sound, but when you ht that dead spot with a simmering steamer on the bridge, all sounds will stop and then restart. Using a solid ring plus the center post so there is no break does require an autoreverser on the feed to the bridge rails, but there would be no sound interruptions. Or two wipers on the drive shaft, leaving the pit rail just for show.

                                      --Randy