In addition to axial construction, pancake stepper motors have two other unique features: an ironless core and lack of a commutator. These construction principles give pancake motors several performance advantages over conventional cylindrical motors. First, because the armature contains no iron, there is no cogging effect, which is traditionally caused by the magnets in the stator attempting to align themselves with the iron in the rotor. Cogging makes it nearly impossible for conventional motors to achieve smooth motion, and pancake motors are the only motor type with no cogging or torque ripple.
Also, no iron means minimal inductance and no stored energy to be dissipated during commutation, so there’s no arcing of the brushes. Brush wear is a significant drawback to traditional brushed motors, but with no arcing, brush wear is greatly reduced and brush life is improved in pancake motors.
The low inductance of pancake designs also means that they have low electrical time constants, allowing current to flow very quickly into the armature for virtually instant torque production. Peak torque production is also higher in pancake motors due to their lack of iron. In conventional iron core motors, the magnetic field of the armature can demagnetize the permanent magnets, so peak current (and, therefore, peak torque) is limited to just 2 to 3 times the continuous rating. Pancake motors, without iron in the armature and with an axial magnetic field, can withstand peak current up to 10 times the continuous rating, for higher peak torque.
The second unique feature of pancake motors is that in addition to the copper conductors, the commutator is also printed on the armature. This design allows the brushes to run directly on the armature surface. The lack of a separate commutator ring, in conjunction with the flat overall design, make pancake motors very compact, especially when compared to conventional cylindrical motors. Their thin design, along with a low inertia (due to the absence of iron) allows pancake motors to achieve extremely fast acceleration and deceleration.
Pancake motors such as (nema 6 motor or nema 8)were originally designed to drive the capstans on tape machines, where a very compact footprint was required, along with the ability to start and stop rapidly. Their uses have expanded, but pancake motors are still found primarily in applications that require a slim profile, smooth motion with no torque ripple, extremely fast acceleration and deceleration, or high peak torque.
Nema23 vs Nema17 Stepper Motor for the engineering challenged
