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STEPPER MOTORS FAQ
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.