Q: Why is motor sizing so important? Can’t I just choose a larger motor?

A:  If the motor’s own rotor inertia is most of the load, resonance tends to increase

     and pose problems. It should also be taken into account that larger rotors require more

     time to accelerate.

Q: Why do stepper motors lose torque as they increase in speed?

A: Stepper motors are current driven, not voltage driven like servos. Full torque is only  

     produced when all of the motor’s rated current has saturated the coil being charged.

     As speed increases, the amount of time allowed for the current to shift from coil to

     coil decreases. This is why stepper motors are rated for holding torque.

Q: If stepper motors are not voltage driven, why then does increasing the voltage increase

     the torque?

A: Think of voltage as the force that pushes current into the coil. Increase the voltage,

     and the pressure on the current to enter the coil increases. This means more current

     saturates the coil in the allowed time. The result is that less torque is lost as speed

     increases.

Q: How hot is too hot to run a stepper?

A: Stepper motors are designed to run hot. Most have class B insulation which means

     they can sustain temperatures up to 90 C without thermal breakdown occurring. This

     breakdown comes in the forms of insulation and winding failure.

Q: Is it true that I can get more torque by running the motor at double the rated current?

A: Increasing the current will produce more torque but there is a cost. The motor will not

     run as smoothly since increasing the current hinders the motor’s linearity.

Q: Why do some motors have six and eight leads when yours have only four?

A: Stepper motors can be run in parallel or series modes. Six lead motors can only be run  

     series while four lead motors can only run parallel. Eight lead motors can run in

     either mode. In most applications we encounter, more torque is needed at the higher

     speeds. This is where the lower inductance four wire motor prevails over the others.