Stepper Motors

[Anonymous]

I was pageing thru an electronics catalog ( that makes about as much sense to me as trying to read the Koran in Arabic) and I came across some DC Stepper motors. My questions are;

1. What is a stepper motor?

2. Can they be AC powered as well as DC powered?

3. Are there any practical applications for stepper motors in model
railroading?

Any enlightenment would be appreciated

Joe

[BR60103]

Joe:
A stepper motor is one that moves from one position to another and stops.
It is tempting to say they would be useful for a turntable because it would have built in indexing, but the motion is too abrupt and it would be jerky.
I don't know the answers to 2 and 3. Check the search facility -- they were talked about her a while back.

[Adelie]

Stepper motors were used on computer disk drives, even older (like almost 20 years older) hard drives because they can "step" from track to track to put the heads where they needed to be.

I can't think of anything in model railroading that benefits from that sort of motion. I could probably hook one up to an automobile somehow and model my wife's driving. [(-D]

I've seen some locomotives that ran like they had stepper motors, but that was a coincidence, I'm sure.

[mlehman]

Actually, stepper motors have a very specific modeling application -- for turntable drives. The New York Railway Supply (www.nyrs.com) turntable drive is a very precise stepper motor with a sophisticated control.

The trick is finding a stepper motor with small increments and then designing your own control to hold it in the exact spot to line up with your TT leads. I have a little electronics training, but decided to just let NYRS do all the design and fabrication for me. However, the cheap prices of surplus stepper motors will be tempting to many and may work out. Anyone who can design an adequate control for a suitable one for TTs and write it up in the model press will certainly be famous.
Mike Lehman
Urbana, IL

[bgrossman]

These motors are used for precise positioning drives, and they are frequently found in scientific instruments. The control is digital and pulses are "counted" either to move something a very definite amount or to measure the amount of movement. Each pulse moves the shaft a very small amount. The rate of pulsing also controls the speed that the motor turns. It's unlikely that the signal to the motor is AC because of this, but I could be wrong.

Bernie

[davekelly]

In an earlier thread concerning stepper motors I included a url for an internet store that sells stepper motor controllers. I haven't tried one yet, but was thinking of the possibility of using it for turntable control. You might want to try a search.

[Anonymous]

Thanks for the input. I have a much better understanding of what a stepper moter is. When you were talking about turn table control the first thing that I thought of was opening and closeing a bridge.

For the DCC folks would a decoder be a better option than a stepper motor for precise position control of turntables, bridges,etc.?

Joe

[rrinker]

This one gets the 'weasel' answer... it depends. If the turntable is up front where you can clearly see the table and tracks, then a regualr DC motor controlled by a DCC decoder is FAR less expensive than a computerized controller and stepper motor drive. You cna program the DCC decoder so that it ALWAYS runs slow no matter what speed step, and if it's all up front you cna move it into alignment fairly easily.
But if the turntable is more tot he back where you can;t clearly see the tracks to line up the bridge, you're going to have a heck of a time getting things to line up so the locos don't end up in the pit. In tht case, you might be better off with a good solid indexing system. That NYRS system is quite impressive, but it costs more than my DCC system.

--Randy