General Stepper Motor - Encoder Question

Hi,

I've just seen that Sparkfun.com sells some nice Stepper Motors and also Motor drivers for those:
Motor: http://www.sparkfun.com/commerce/product_info.php?products_id=9238
Driver: EasyDriver - Stepper Motor Driver - ROB-12779 - SparkFun Electronics

After googling some, I found that there are nice tutorials showing how to run a stepper motor with Arduino:

http://lusorobotica.com/index.php/topic,106.0.html

I've wanted to do a project with these motors for a while now. The only question that I couldnt answer is: Do they also need an encoder to ensure the right position of the motor? Or does the stepper motor move exactly the steps as told to the driver, whatever torque is on the motor?
The Driver datasheet says:

By simply inputting one pulse on the STEP input the motor will take one step (full, half, quarter, or eighth depending on two logic inputs).

But I dont quite understand if the motor does that anyway, like ensures to do that, even if it was blocked - would it try to move the step anyway until it was moved?

My idea is to create a table with a XY carriage to shape thin lumber and maybe aluminium. I'd build in a reduction gear to raise the step-resolution of the motor and also the torque. But would I need like a rotational counter to check if the stepper motor does exactly the amount of rotations whch I tell to the driver?

Thanks!

The coils inside a stepping motor can be sequenced either by an hardware encode or by a logic sequence generated by the computer. If all you have is a step and direction then the hardware is generating the sequence. See:-
http://www.thebox.myzen.co.uk/Workshop/Motors_3.html
and
http://www.thebox.myzen.co.uk/Workshop/Motors_4.html

even if it was blocked - would it try to move the step anyway until it was moved?

No it would twitch but not actually move a step.

My idea is to create a table with a XY carriage to shape thin lumber and maybe aluminium.

Have you seen the RepRap project (Google it)

But would I need like a rotational counter to check if the stepper motor

Not if you keep the motor steps within the maximum speed for your setup.

Thanks for the answer!
I've seen RepRap and also PhlatBoyz CNC machine.
The "Not if you keep the motor steps within the maximum speed for your setup. " is not exactly clear to me. Can I run it faster than the maximum speed? Does the motor also block at a certain position, when I tell it not to move? I mean, when I want it to hold a position, does it correct errors from outer influences?

Nevermind. Your posted links about Motors explained everything, I just didnt read n the right place first :slight_smile:
thanks