In the last months we see a lot of post about turntable and especialy the Walthers turntable.
If a turntable look great in his box or on pictures what about the reality when you operate it; in fact when you index a track
“FRUSTRATION !!!”
You need very precise alignement whit the brigde rail and the adjacent track; as small is the scale as precise the index need to be.
Some have said the index is fine, other said not; I have seen a Nscale Walthers turntable and the index it’s not precise because two small millimeters are enough to get a derailment. The other turntable manufacturer have the same problems…for years. My turntable is a CMR one.
A lot of device have been tried to index precisely turntable bridge from eye looking, hard mechanicals one,opto sensored one to electronics one, but all in all we must admit it’s hard to accomplish and the results are far beyond what we expected.
Because I am looking for a near zero frustration level when operating my layout I always look for top level system and easy to use I make the choice of the " New York Railway Supply indexing device" and place an order to it tomorrow.
This device exist since a few years; it was reviewed in MR by Mister Sperandeo and show in the Kalmbach book " Locomotive Servicing Terminals".
www.nyrs.com is quite expensive but if you want an accurate positionning system which is reliable and time life and non frustrating that’s what you need. All in all it does’nt cost much than a articulated steam loco.
It’s easy to install, to programming and install. It fits all brand of turntable already in use or new one.
NYRS make a special device and bracket to use with the Walthers turn
Turntables have been a thing of mine for years. Having built a CMR unit several Diamond Scale turntables and a few others you could not be more correct. Indexing has always been the Achilles heal of turntables. I presently have two Walthers turntables and even though the indexing is set up I some times prepare to just line up the tracks by line of sight. There are a few guys out there who have figured out how to install a stationary decoder in concert with the standard Walthers control box o you can operate it from your throttle if you wish. The only thing that makes the transition a little easier is of course filing a beveled edge on the lead in tracks so you don’t have that sharp 90 degree end. I have often wondered about positioning a photocell hooked to a timer circuit in front of each lead in track so when the bridge comes to the exact spot where it is lined up with the lead in track the power to the bridge drive motor is cut for a preset amount of time.lets say 2 or 3 seconds. If it’s not the track you want you simply keep the button depressed until you get to the one you want where you lift off the button stopping the bridge.This is sort of the way it’s done electronically when you index the Walthers unit but in my O/P not as accurate. I would say the reliability of the Walthers t/t hitting the right spot every time is some where around 90% a far cry from the old Diamond scale days.
I have the Walthers HO scale 130’ TT and I haven’t been able to get it to index reliably. All you can count on is getting it close, then making the adjustment by eye. For that reason, I have removed all indexing and just do it by eye. The TT now just stops at the track where I want it. Sometimes I have to make a final adjustment to get perfect allignment but I am guessing that is the way the prototype worked as well.
I have the Walthers HO 90’ ‘auto indexing’ turntable. Getting all of the tracks(8) mechanically aligned was a pain. I marked out the center ‘lead’ track and the radial track opposite the lead and installed the turntable. I had to adjust the roundhouse a little to get everything ‘square’ for each of the radial tracks. I ‘beveled’ each of the radial track rails as well.
The indexing appear to work well - it ‘overshoots’ the radial track and backs up to alignment. Our club has the 130’ turntable with over 20+ radial tracks. Twice in the past two years it seems to have ‘lost’ it’s indexing and has had to be re-programmed. I suspect either ‘user error’ or maybe a surge from the cheap train set power pack that powers it may be the issue.
I have had some minor glitches with my 90’ indexed version from Walthers, but usually a power-down and then power-up restores the good will. Other than that, I would have to give mine very high marks for both accuracy and reliability. I have never once had to reprogramme the indexing. Now, nearing three years of use with mine, I count myself fortunate to have this very nice appliance.
If I ever again have a turntable on a layout (I’ve got a Diamond Scale tucked away), it will be within inches of the front of the layout, and it will NOT have indexing. I will operate that turntable just like the real ones–by eye and hand co-ordination. And I’ll watch those locos spin on their little “display” track nice and up-close.
I did once have a great big Wilson turntable. It had a stack of reduction spur gears, so there was an ENORMOUS amount of backlash in the system. If you overshot the track, you could almost have a cup of coffee before you could swing that bridge back. So, there will be no backlash in whatever drive I use–haven’t checked the Diamond yet, but it won’t go in until there’s no backlash.
Ed, I’ve been looking into a manual solution as well, with the goal of reducing the backlash you describe. From one of my other interests, I’ve become aware of spring loaded split spur gears. Honda has built motorcycle’s transmissions with a primary gear that is “split” (think two halves of a hamburger bun). The tooth count is the same, but one half of the gear wheel is slightly offset from the other via spring loading. In this implementation, the goal is to reduce noise, as well as removing some backlash. When the split gear engages a normal gearwheel, the teeth are forced into alignment (against the spring pressure), with the result being a tighter, quieter gear mesh. An already long story short, I’m looking for gearboxes that may have this feature (on a much smaller scale) to keep the slop out of a manual turntable drive. Perhaps there’s a similar, but better idea out there somewhere. Matt Goodman
Another looking to a manual solution is the use of a crank belt like the ones in or car motors.
The only drawback it’s the need of an heavy tension to the belt so it did’nt have any blacklash.
The idea is to mount a mechanism with the belt apart from the shaft of the turntable so we don’t give any tension to the turntable, The turntable shaft could be attached to one of the wheels of the belt.
This kind of belt could be found in a lot of dimensions, so you will be able to find which one you need for your purposes.
May be using old wheels from cars already mounted on rollerbearing would be a n ice solution. The drawback is the size of the mechanism and the need of a very rigid frame to allow the tension to the crank belt.
For the ones using the new Walthers turntable NYRS (see my post above for the link) mke a conversion kit to use their control system.
I think the flaw with the Wilson turntable design (that should perhaps be “one of the flaws”) is that it uses a stack of spur gears–the backlash just keeps multiplying along with the reduction. While anti-backlash (the “official” name) spur gears will make a dramatic, or even complete, improvement, there’s the cost. Another approach to cutting backlash is to use a worm gear reduction. It won’t get rid of all the backlash, but it would have eliminated maybe 98% of what I was observing. And the expense is relatively low. Precision Scale offers a worm drive gearbox with a 27:1 ratio. Two of these cascaded would give a reduction of 729 to 1. They’re about $13 each. I might also mention that there exist anti-backlash worm gears. Now, there’s a neat solution. And undoubtedly SO affordable.
But, Marc suggests another route–a belt drive. And I recall still another option–installing a big disk below the table and putting a small driven rubber wheel on the edge. Both of these ideas have been used in the other kind of turntables (record). Young folks may call and make appointments to look in awe at my old AR. Funny, it was cutting edge when I bought it.
Thought I’d mention a couple of GOOD things about the Wilson turntable: It was affordable! It had an enormous table span (for it’s time)! It had a very sturdy turntable pit (steel)!
Since you ask, the negatives: pretty funky and too wide bridge, no track in the turntable pit, and, of course, backlash. I also think PERHAPS that you had to get power to the bridge track on your own (with overhead wires), but I emphasize that “perhaps”.
I’ve thought about this, but have also wondered whether they would have the torque capacity for a longer turntable with a heavy locomotive on it. Thoughts?
I’m less familiar with belt drives in general; that’s worth a look. Marc’s point about the tension causing binding in the tables bearings would seem to be a valid one. My speculation (and it’s just that!) is that it could be reduced by using a toothed belt and cog. I saw this just today on a site that is advertising O scale tables.
I think the design of the table should be such that NO weight from the bridge is borne by the gearbox bearings. Then the only load on those bearings is the mass of the bridge and the locomotive. If the motor speed is brought up “slowly”, there should be minimal load on the gearbox bearings. There would be a much greater load if the motor was supplied with full voltage right away (F=ma).
Toothed belt might be better, but you’ll still need tension. Best bet with either a flat, V, or toothed is to pick a bearing and mounting that can take the tension load–shouldn’t be too hard to find. Build–that may be a bit more work.
7j43k, I have set up a Diamond sccale TT for our local club. The one we haad used a contaact system and aan electronic control board to sort things out.The indexing was avccomplished by means of contact tabs under the table. Backlash was not a problem as the contacts controlled the indexing. While initially a pain to set up it worked well without a lot of adjustment,and this in a club environment. The TT was controlled by a mutiposition switch indicating the track one wished to move to. The TT advanced til within 1/2" or so then slowed and stopped exactly where the contacts were.The instructions are long and thorough and requieres several readings then placed under your pillow for a few nights then rereading and you will get how its laid out. Involved installation but worrth a try. BILL
I doubt real turntable operators used indexing but I could be wrong. I am sure they watched what they were doing or lost their job. If that happened in MRR clubs, many clubs would go out of existance fpr lack of memebers or there would be really good MRR operators. Prototype Practice.
Same thing with operating locos, operators did not normally go off for a cup of coffee or spend time jawing with another operator while running their loco.
Well with cell phones, I guess that is changing. MRR clubs just do not kill passengers is the only difference between modeling and prototype railroads.