Greetings.
I've facing following problem: i have a few stepper motors (Mineba 17pu-k303, hybrid 5 wire 8 coils stepper). I am able to control this stepper using stepper motor shield (DK Electronics, i've used 4 wires, common wire ignored), but the torque is exetremely low: its possible to stop the motor with just your fingers. And at the same time, the motor produces a really high holding torque while being connected directly to 5v power supply: it's impossible to rotate the shaft. I've also tried to connect external 12v power - the difference was very tiny.
Could you please suggest me something to increase engine's torque?
5 wire steppers are unipolar only, you cannot ignore the 5th wire as it shorts the centre-taps
of both windings together.
"DK Electronics" only throws up an agricultural electronics company, can you
provide a link or datasheet for the actual shield you refer to please...
Hi, if you have good holding torque, then you may be stepping with too small a pulse, try making the pulses longer for each step/half step.
Also if they are 12V steppers then a 12V rather than 5V supply will improve things.
Tom..... 
http://cnc25.free.fr/documentation/moteurs%20pap/pap_nmb.pdf
This is a link to the catalogue and a very good explanation of how steppers work and how to get the best out of them.