Stepper-motor drive modes and torque at moderate speeds Evaluate the statement: “The wave-drive sequence of a stepper motor has more torque and operates more smoothly than the full-step sequence at moderate speeds.”

Introduction / Context:
Stepper motors can be driven using several phase-energizing patterns: wave drive (one phase ON), full-step (two phases ON in many motors), half-step (alternating one and two phases), and microstepping (sinusoidal current shaping). Torque output and smoothness depend on how many windings are energized and how current is shared between them.

Given Data / Assumptions:

• Wave drive energizes a single phase at a time.
• Full-step commonly energizes two phases simultaneously in hybrid and PM steppers.
• Moderate speed region means operation well below resonance issues but above creep.
• No current limiting or advanced current profiling beyond the named modes is assumed.

Concept / Approach:
Electromagnetic torque in a stepper is proportional to the vector sum of phase currents and the motor’s torque constant. When two phases are driven at the same magnitude, the resultant torque vector is larger than when only one phase is energized. Additionally, having two phases ON provides better detent against load disturbance, improving positional stiffness and reducing vibration compared with single-phase excitation.

Step-by-Step Solution:

Verification / Alternative check:
Practical datasheets and application notes consistently show full-step torque curves above wave-drive curves. Microstepping can be smoother than both, but that is not the comparison being made here.

Why Other Options Are Wrong:
“Correct” reverses the well-known torque relationship. “True only with microstepping drivers” mixes modes; microstepping is a different approach. “Applies only to variable-reluctance motors” misattributes a general torque principle to a subset of motors.

Common Pitfalls:
Confusing smoothness improvements from microstepping with wave drive. Assuming less electrical power (one phase) somehow yields more torque.

Final Answer:
Incorrect