[h3ndrix]

Hey all,

I just saw some cheap stepper motors and it got me thinking about something that I had thought about in the past but never asked about ( I decided to use servo motors so I just forgot about it) :

If the step of a motor is 1.8 degrees, then, in my understanding that would make 200 steps for a single turn of the motor. Assuming thats correct, a 5 TPI ( ~5mm lead ) ballscrew requires a single turn for 5mm movement, so if I want to find out what the smallest step of the motor would me in axial movement, I would divide 5mm by 200 (?) and that would give me 0,025 mm which is roughly 0,001 inches.

If this is all correct, then is it true that the smallest step of a stepper motor is 0,001 and in return the finest precision I can get of a piece that is being made is 0,001 inches?

Help me out in this one

Thx

[KTP]

true except...

Most step motor drives will at least do half stepping, which would be .9 degrees per step, or 400 steps/rev, and a lot of step motor drives will do microstepping, like 10 microsteps per full step, or 2000 steps/rev.

Of course sometimes the microsteps are not exactly the same as each other, so you might not *really* have .0001 accuracy/precision.

[mcpltd]

microsteps are not linear so if you want it accuate, i would work in full step and use a ratio like 3:1 or a finer thread, but then you will loose out on speed.

[CJL5585]

Example:
stepping motor 200 steps per revolution X 10 microstep drive X 8 turns per inch leadscrew = 16,000 steps per inch.

1 inch divided by 16,000 = 0.0000625 inch or 0.0015875 mm per step.

So, if the steps are off a VERY small amount, I think it is accurate enough for most hobbiests.

Jerry

[H500]

Unless the load is VERY light, relative to the size of the motor, the system would never approach the theoretical microstepping resolution.

Microstepping is like pulling on a spring. The smaller the increment, the less force generated. It will often take the accumulation of several microsteps before enough force is generated to turn the screw.