I bought a dozen types of stepper motors with rated voltages ranging from 4v to 12v and currents from 2A to 0.3A. I am unable to get anywhere near the rated torque on all motors except those with rated voltages 10v and higher. My setup:
Power supply: Agilent E3610A set to output 12V (current limited to 2A)
MCU: Teensy 3.1
Stepper Driver: Pololu A4988 (Cant provide link due to low reputation)
Now, for steppers like this one with rated voltage of 4.2v and current 2A - no matter what I do with current limiting pot on the surface of the driver - I simply cant get the motors draw more than a fraction of their rated currents. Its a single turn pot - so I fall off the adjustment space before current (measured at power source AND motor coil) reaches any appreciable amount (usually it maxes out around 0.1-0.2A). Torque too is very low, naturally. I tried voltages 8-17V (the range limited by the driver board and my power supply) - but still, cant get the motors produce more torque.
All 4 wire steppres are in bi-polar config.
Interestingly, it is not a problem with steppers rated 10-12v, for instance CanaKit stepper (cant provide link due to low reputation) rated at 0.33A and 12v - I can get them draw more current, although even in that case - there is a huge mismatch between the current they ought to draw based on VREF pin reading, and what the actually draw. For instance, measuring the VREF (~1v)and applying the formula - I should have gotten 2.5A (or slightly less due to 70% energization) - but I really measure only 0.29A on the coils.
Everywhere I read, it looks like I should not have this problem. I.e. read the threads on SE (cant provide links due to low reputation) What am I missing? All is wired up together on a breadboard. Wiring is solid, but could this be a problem? Should I consider a different driver?
Appreciate any tips!