New approach to Turntable gearing/stepping

[Fergmiester]

OK guys/gals time to "Brain Storm". As some of you are aware I'm building my own motorized turntable.

Originally and what is fitted right now is a 3 pole 1.5 mm "Amplifier" plug fitted at the fulcrum (Pivot point and power to rails). The pedestal will be fitted with a large gear and a smaller gear fitted on a spindle mounted to a motor under the well. Positioning would be hit and miss but the motor I have is High torque and very slow.

This concept is still problematic.

After looking in a RC Plane/Boat catalogue the solution (I think) came to me.

Get rid of the plug and mount a Sail servo (High Torque and has a 360 degree rotation) at the fulcrum.

Run light wire across the top and down Wire wont twist, as rotation never exceeds 360. Another option is to run the wire to the top of the mast where a very small receptacle is located (I'm thinking ear phone size). The plug will fit into the receptacle and will rotate so the wire won't twist.

The only problem I foresee is the control of the Sail Servo, as I really don't want to use a RC transmitter to control the servo. I have to figure a way to hook up the dial directly to the servo so I can operate it simply.

Any thoughts?


Regards

Fergie

[Anonymous]

Good Morning Capt. Fergie:

WHAT'S THE PROBLEM?

Are we working on getting the power to the turntable rails or hooking up a motor drive?

Bob

[Anonymous]

My Bowser turntable is very simple. I do not have indexing and although this would be nice, it isn't necessary if you can visually align the tracks. The turntable pivot is telescopes through brass tubing. The pivot from the turntable bridge, runs through the brass tube bearing. Below the pit, and mounted to the pivot is a plywood disk almost the size of the turntable. Making contact with the edge of this disk through spring pressure, is the drive motor with gear reduction. The drive wheel is an aluminum spool with rubber o-rings for tires.

I have a center off toggle switch which controls power to the turntable. In the up position, the tracks on the turntable bridge receive track power. In the center position both track and turntable motor are off, in the down position, the motor receives track power and the rotation direction and speed of the turntable spin is controlled with my hand held DC throttle.

I will eventually be converting the turntable to DCC, however, I haven't doped all that out yet.

[Anonymous]

QUOTE: Originally posted by deschane

My Bowser turntable is very simple. I do not have indexing and although this would be nice, it isn't necessary if you can visually align the tracks. The turntable pivot is telescopes through brass tubing. The pivot from the turntable bridge, runs through the brass tube bearing. Below the pit, and mounted to the pivot is a plywood disk almost the size of the turntable. Making contact with the edge of this disk through spring pressure, is the drive motor with gear reduction. The drive wheel is an aluminum spool with rubber o-rings for tires.

Good Morning:
For me this is a whole new idea.
Is that the Bowser method for turning the turntable? How much slippage do you get between the motor and the plywood disk? What about the disk being out of round?

Have a blessed day and remember SANTA FE ALL THE WAY
Bob

[Anonymous]

I always thought that a neat way to turn a turntable was to use a stepper motor, but I didn't have a clue on how to control such a motor. I was surfing the other night for optical detectors and stumbled upon Hobbytron.com. (optical detector pairs were $10.00, I think they can used to run a relay which would in turn . ... .oops - off topic). Hobbytron has some stepper motor controls available. I've never played with the motors myself, but it is my understanding that a stepper motor moves in steps, each step being a set amount of degrees. It seems that by using a stepper motor you get turning plus indexing.

[Anonymous]

I had built a Turn Table following a design in one of the magazines that had the track power routed through the rail that the Turn Table was supported by and rotated on. The ring of rail was divided into 4 sections. 2 Large sections transfered power while 2 small sections were unpowered to provide an electrical gap to prevent shorting as the electrical pickups on the ends of the table crossed from one large section to the other.
The polarity of the rails was automatic with this design eliminating the need for a reverse switch to control the direction of the locomotive on the table.
A stepper motor sounds like a good way to go. A drive/indexing circuit would need designed as well as a positive reduction free of backlash. Possibly a toothed belt arrangement.
I would be interested to know how to build a stepper motor drive/indexing circuit.

[Anonymous]

Ray,

I remember such an article several or more years ago in Model Railroader. I'm sure the magazine index would quickly find the article. If I remember, the author built a really neat looking turntable.

I also remember seeing an article where photo-resistors were used for automatic indexing. It would seem that this could get quite complicated. I've also seen articles where the modeler uses two speeds to drive the turntable. Regular speed to get it close and a slower speed to do the final alignment.

I am thinking that with a stepper motor, an indexing circuit would not be needed as the motor takes defined steps (I've seen motors listed at 3.5 degrees per step up to 10 degrees per step). Of course the operator would have to energize the motor for each step which might be a pain to do a 180 turn, but if doing so cuts down on the electronics involved it might be worth it. Depending on the torque of the motor, a drive system might not be needed with the turntable attached directly to the motor shaft.

I haven't fully explored this yet as I am quite aways away from buildling my turntable. The stepper driver is listed on Hobbytron.com's website. It looks relatively inexpensive. If you decide to play with the thing, please post your results/opinions and I will do so also, although this project is probably a year or two away for me.

Also. I believe the new Walthers turntable comes complete with a driver and indexing thing. I don't believe I will go this way as the table is too long for what I model and my available space and the price is a little out of reach for me (although I'm thinking that all my tinkering will come out to be the same price lol it seems it always works that way for me, although I do derive a high level of personal satisfaction in figuring things out and doing it myself).

Dave

[Fergmiester]

I like the outer rail concept, something that didn't occur to me before (Duh). I talked to my LHS people this morning and becoming more convinced the Sail Servo is viable and can be easily done for under $100. I'll keep you posted

[robengland]

I don't like the idea of being limited to a 360deg turn. Prototype turntables don't go all the way back the other way when they reach a limit. they go endlessly in either direction. stepping motors, plywood wheels, basic geared drives, handpushed ones like some prototypes - they've all been made to work. I just read about using an Atlas turntable mounted underneath as the control mechanism - there's another idea....

[nfmisso]

QUOTE: Originally posted by Fergmiester

I like the outer rail concept, something that didn't occur to me before (Duh). I talked to my LHS people this morning and becoming more convinced the Sail Servo is viable and can be easily done for under $100. I'll keep you posted

You should be able to do a stepper motor based turntable for way less than one half of that.....
http://www.allelectronics.com/cgi-bin/category.cgi?category=400600&item=SMT-72&type=store

[BR60103]

I saw the stepper motor proposed before. The objection was that the rotation was close to instantaneous and both didn't look realistic and might leave the locomotive where it started.

[Anonymous]

I don't think a stepper motor would work. The rails must align probably within .015 to keep from derailing when going aboard or leaving the bridge. As well as my Bowser TT, I built a Diamond Scale TT with indexing for a club I belonged to. I left the club before they ever got the indexing up and running. However the system operated with a geard down motor. An indexing arm was attached to the pivot and below the TT and had three contacts. When the appropriate track was arrived at one of the two outside contacts slowed the motor down. Once the center contact was reached, the motor was stopped. I was doubtfull about the workings of this system, due to the accuracy needed to stop the bridge tracks aligned with what ever track was chosen. I have seen other indexing systems for $300.00 which use electric eyes or LED sensors. Aligning by eye is a viable alternative. I'm surprised more turntable builders haven't put in their tw cents here.

[Anonymous]

Has anyone tried a TV antenna rotor system for a turntable drive?

[Anonymous]

Teffy, With the o-ring tires, there is no slipage. Also, my Bowser uses the ring rail divided into two parts, so that no reversing unit is needed.

Having spent 20 years flying R/C airplanes, I can tell you Fergie that a sail servo does not have the required accuracy to do what you want it to do. Servos are subject to the jitters which at the very least will cause problems. I don't know if they are capable of turning 180 degrees, which is absolutely necessary.

The problem with turntables is they need to be as accurate as a Swiss watch! This goes for the mechanism as well as the ring rail, pit and turntable bridge. Alignment with the approach tracks and stall tracks must be precise, not only in left to right but in up and down. My bridge is higher on one side than the other. I have two stall tracks that are directly aligned with the two approach tracks. However, when the bridge is turned 180 degrees, the tracks don't exactly line up. There are many ways from Sunday these things need to be tweeked. It's all do able, you just need to be precise.

Again, I wonder why some really knowledgable craftsman doesn't chime in here! Could it be that the true crafstmen of this hobby have already passed away?

[Fergmiester]

Thanks Mark

I'm up from the basement waiting for the kids to get home for lunch and am contemplating what youi said for the simple reason I spent the 30 minutes doing alignments on the Turntable Bridge. And yes I have some serious concerns with centering. As working with bearings and angles I realize this kind of stuff has to be dead on with no room for cocked hats.

I'm thinking Nigel's step motor is also a good option. I'll have to take more pics to document this as if it works, others maybe interested.

As always

Fergie

[jwmurrayjr]

I'm not expert modeler but I do know that you can get the Walthers and Heljan turntables to work well. So I reckon that almost any other TT is fair game since these two can be troublesome. Careful assembly is required.

The key is to provide a drive that is both smooth (no jerking) and has very good slow-speed control. Real turntables are not indexed and models don't need indexing either. Of course you need to be able to see the tracks to visually align them with a slow-speed motor.

A reasonably good DC pack or a DCC decoder will provide good slow-speed control to most motors, even the Walthers motor. I use a DH123 decoder set to address "99".

The photo below shows a simple mount that will allow all manner of vertical and angular adjustment to the TT pit/bridge assembly. The adjusting screws are just deck screws with a smooth shoulder at the head which allows the screw to turn freely in the 1/2" plywood mount. The threaded end of the screws move the mount, and pit, with respect to the layout surface.

Once adjusted the pit rim can be blended into the scenery with flexible caulk. This will allow re-adjustment if your layout is subject to "shifting".



With all that said I don't pretend to have the perfect implementation. I still get some jerky movement occasionally which I think is due to leaving too much slack (slop?) in the bridge-shaft/pit assembly when I assembled the bridge to the shaft. I didn't take time to think it through and I need to redo that part someday.[B)]

[Anonymous]

Jim,

Way cool pic. It gives a better description than anything written!! The ability to make adjustments without tearing the whole thing down is excellent! Would love to see the topside pic too!

[jwmurrayjr]

QUOTE: Originally posted by dkelly

Jim,

Way cool pic. It gives a better description than anything written!! The ability to make adjustments without tearing the whole thing down is excellent! Would love to see the topside pic too!

Here are a couple of photos from the topside at various stages:


TT in place. You can see a little of the flexible caulk around the pit. (The white beaded foam around the engine service facilities has been replaced with blue extruded foam and painted tan. The white foam was a mistake!)


Later, with "yard ballast" and a bit of ground cover in place.

[Anonymous]

Looks great!

[Fergmiester]

Well I'm inspired those are nice pictures. I just came up from the basement after putting the railyard on hold realizing the track couldn't get laid until the pivot point was established.

I've scrapped the servo idea and am going back to a high torque geared motor. I'm using gears from an RC car, which I bought last month. I've centred the main gear with styrene shims and the glue is drying (fingers crossed). This time Sunday I believe I will have a working Turntable. Pictures to follow

As Always

Fergie

[Fergmiester]

I've made some headway this weekend as I have fitted a new gear wheel to the base of the turntable. The external gears are from a manufacturer who makes parts for RC Cars/trucks.The geared motor came from Princess Auto and was originally made in Germany.

A picture of this can be seen on page 6 of my Webshots MESS file. Short cut is on my signature.