Mystery stepper...help with finding number of steps

My son and I are hacking an old (1980s?) Dahlgren engraving machine that is driven by 3 steppers. The nameplate on the motors has voltage and current listed but nothing about steps, and Google doesn't turn anything up based on model, serial, manufacturer etc.

I tried to 'feel' the number of steps by rotating the shaft...can I assume that each detent (i.e. stop) represents one step?

We hooked up one of the steppers to a power supply and Arduino with an L298N-based motor shield, but can only seem to get it to twitch, vibrate and shudder no matter what we choose for the STEPS and SPEED arguments. We tried switching one set of leads in case we had the polarity backwards, but nothing different.

Is there a standard process for figuring out the number of steps?

I took a picture but can't figure out how to post it here (what do I put in between the tags?). They are pretty robust-looking motors and we didn't see an obvious way to get them open without harm to them or us.

I'd set it for 100 steps per revolution and 6 RPM. Then run it for one 'revolution' and see how far it has traveled.

First you have to get your wiring right. How many wires does the motor have? What is the resistance across each pair of wires?

Disassembling a stepper motor is a bad idea as it apparently causes permanent damage to the motor.

To upload an image, when composing a reply, look near the bottom left of the composition window where it says "Additional Options". Click it and it will expand to a menu that will allow you to upload an image.

Here is a pic of the stepper.

It has 4 wires and we measured the resistance to get the pairs right. It is still possible to get one set of coils ‘backwards’ relative to the other, correct? We switched one set to check and it didn’t make a difference.

IMG-20130204-00018.jpg

According to this cross reference (http://www.anaheimautomation.com/products/crossref/cr.php?crID=88&pt=i&sID=33&tID=74&cID=19), your motor is equivalent to the Anaheim Automation model 23W102S
http://www.anaheimautomation.com/manuals/stepper/L010214%20-%2023W%20Series%20Spec%20Sheet.pdf

It supposedly has a 1.8 degree step angle, which is 200 steps. it does say this one has 8 leads, though.

Thanks that is very helpful. The second page of the spec sheet seems to indicate that there is a 4-wire configuration, which would match what we have. I believe we tried as high as 200 steps but now that I know it is in that range we at least have a good starting point.

Perhaps that 1.8 degree resolution requires microstepping? I am definitely not a stepper expert.

200 steps / 1.8 degree is standard and most likely what you have. I have seen steppers with 0.9 degree and 7.2 degree steps, but those are the smaller "pancake" type of steppers.