I have a scratchbuilt 100 foot turntable on my N scale switching layout and I just finished automating it, using a stepper motor from an old computer printer. The stepper motor is driven by an Arduino, so I have complete control over its speed. I have it set to rotate the turntable at 1 RPM, which looks OK based on some prototype videos I’ve seen, but it seems “too slow” when I’m operating.
Does anyone have any information regarding the proper rotational speed for a turntable?
Walt
1 full RPM, 360 degrees in 60 seconds, is actually quite past compared to prototypes. Most seem to be about 1/3 of that. Standing next to a moving turntable, it seems to be moving way faster than that, but if you do the math and convert to linear velocity (what you see watching the end of the table sweep past), consider you are 50 feet (for a 100 foot table) from the center. A 100 foot table turning at 1 RPM is sweeping past at over 5 feet per second. A 120 foot table - over 6 feet per second. That’s quite fast. Over 4 miles per hour. It’s one of those things though, that kind of looks right since the trains are relatively small and your eyes are relatively far away, it’s not like you are actually standing pitside. I wouldn’t go any faster though. If you aren’t indexing it, the real thing usually had 2 speeds, a travel speed and a slower jog speed to line things up.
–Randy
My HO scale CMR 135’ turntable turns at ½ RPM and that seems too fast for me. Remember it could have a half to one million pound locomotive perched on the rails. In my case a 1,048,000 pound SP Cab Forward.
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.
Youtube shows a CSX loco spinning on a pretty generic turntable. It took about a minute to turn end-for-end. Thus .5 RPM. And it looked like it was spinning pretty briskly.
Ed
Thanks everyone. I guess I’ll slow it down and learn some patience. Yes, I do have a jog speed, currently set at about half of full speed, and I was thinking of slowing that down too. Phase two, if I ever get to it, will be auto-indexing so I don’t have to stand there with my finger on the button for a (very long) minute. Still puzzling out how to do the position sensors for the indexing. Thanks all! Walt
Walt,
I have a New York Railway Supply TT drive, which is a stepper motor and available with various number of positions able to be programmed into the drive depending on what you choose as the control. No external sensors at all. That’s all internal to the stepper motor drive, so it should be more of a mod to the Arduino’s programming than external inputs.
Walt,
Just wire around the pushbutton with a toggle switch. Use it for the “high-speed” spinning, and use the PB for the slow.
It’s not like anything bad will happen if you “forget” to throw the toggle off. Except the guys in the roundhouse will be ribbing you for a few days.
Ed
Actually, it would be no problem to put a 30 second +/- delay in the program so it would stop “near” 180 degrees and I could then use the jog button. I’ll think about that. I could actually put different timing parameters in there to “encode” all of the possible exit tracks, without having to use sensors at all. Just get the bridge close to its target and then use the jog button for the final alignment. Thanks for the idea! Walt
I’ve witnessed a geep on a real turntable which was turning so fast that when it stopped, the locomotive rocked from side-to-side very visibly. I don’t know if the table was malfunctioning or what, but I wouldn’t have believed it had I not seen it.
I’d guess that 2 rpm would be better suited for a model version (not of the fast one which I saw), as any slower might be the model railroad version of watching paint dry.
I have a Walthers 90’ turntable which I’ve motorise because it’s such a lightweight and therefore unreliable to spot accurately when operated manually. I still have to figure out how to wire the motor, though, to get both the full rotational movement and to have the ability to jog it into final position with momentary contact buttons.
Wayne
Last night I changed the Arduino sketch so that the Turntable roates at 1/2 RPM, and put a loop in the program so that touching a button starts the bridge turning and stops it after exactly 180 degrees. Ironically, 10100 pulses equates to 180 degrees exactly; the tracks line up perfectly every time. Incredible considering the totally random ratio of the drive pulleys on the turntable bridge.
Wayne, if you are using a straight DC motor to drive your turntable, you can also control it with an Arduino, although not as accurately as a stepper motor. The PWM (Pulse Width Modulation) output gives better control over the motor speed than pure DC. I’ll help with the wiring and coding if you like.
Walt
Wayne I’m glad someone else has seen that. I was on a railfan trip from Cumberland to Frostburg. They put the steam engine on a turntable and spun it faster and faster round and round like a carnival ride. It was easily 5 rpm maybe more. I couldn’t believe a turntable would be geared to go so fast. In the end, they backed the engine off and it backed it’s way back to Cumberland. [*-)]
Thanks for the offer, Walt. My walkaround throttle is a PWM one, and works very nicely with any of my DC-powered locos. I also did a test run of the turntable using jumper cables from the track and control is very nice. I’ve used a DC motor from a VHS player, as it has a fairly nice gear train, and am powering it with a 3 volt wall wart. I think it needs to be a bit slower, but I also need to do something about the out-of-round wheels supplied with the Walthers turntable, as the table doesn’t ride very smoothly as it rotates.
Wayne
The stepper motor is driven by an Arduino
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Walt
What Arduino product are you referring to?
Thanks,
Ed
I’m using a DC Boarduino from Adafruit:
https://www.adafruit.com/products/72
With a SparkFun Stepper motor driver
https://www.sparkfun.com/products/12779
The Boarduino programs like a Duemilanove but any basic Arduino board like the Uno would work fine. I have put a photo of the controller on my Dropbox account at
https://dl.dropboxusercontent.com/u/89301118/Controller-small.jpg
There is a basic sketch on Dropbox too:
https://dl.dropboxusercontent.com/u/89301118/Turntable1.ino
This just uses 4 buttons to control high/low speed, CW and CCW rotation. I’m working on some more features - a 180 degree rotation, and a routine to rotate a fixed number of degrees; eventually I would like to have each track automatically selectable, but without the need for sensors installed at each track position. If you’re interested, let me know and I’ll post progress reports.
A picture of the completed drive assembly is at
https://dl.dropboxusercontent.com/u/89301118/Complete%20Assembly%20small.jpg
Walt
Yes would be nice to have more infos’ about your drivre system.
Sure a stepper motor is the best we can use to drive precisely a turntable.
If a cheap driver whith arduino could do the job, this open many possibility to drive many thinghs for model railroader.
Waiting for your news.
Marc
OK Marc, you’ve got me off “Dead Center” 
I’ve been meaning to write this up for the forum for a couple of weeks, so now I’ll really do it. I’ll post a link here in the next day or so.
Walt
Two hours later…
There is a description of the build on dropbox:
https://dl.dropboxusercontent.com/u/89301118/Building%20Turntable.pdf
This is by no means the quality of what you’d expect from Model Railroader magazine, but I think there’s enough info that you could adapt the design to your layout.
Some years ago I was on an NMRA national convention tour to Stevens Point WI and we toured the Wisconsin Central (former Soo Line, now CN) roundhouse and engine facility. They put us all on the turntable and gave it a spin. It seemed we were moving at a fairly good clip, perhaps at a brisk walking pace or even a little faster. There was a considerable “momentum” effect when stopping and starting. Unless you can capture that momentum effect I’d pick a slow speed, because I think the main goal is to give the impression of weight and heft.
Dave Nelson
This is interest because it looks like an Atlas turntable (it’s indoors) and it looks like it is human powered. I know they turn SF cable cars by hand at the end of the line, but this is a steam engine, not a wooden cable car.