Is Axial Gap (pancake) motor better for servo drive applications?
One advantage i can think of is that the low inductance of axial-flux motors means that they have low electrical time constants, allowing current to flow very quickly into the armature for virtually instant torque production , which should translate to fast acceleration and deceleration which maybe desirable for high performance servo control..

BUT:

However they are not widely used probably because of their higher price and manufacturing challenges explained in magnax motors white paper : WP- High Efficiency Axial Flux Machines - whitepaper v1.7

The pancake motor also might suffer from several problems:

1-High interia due to their shape which might not be desirable for rapid movments.



more details in :motor-sizing-calculations (source:orientalmotor.com)

2-low inductance cause problems in torque loop:

motor-inductance-effects-on-servo-drives (source is doc.ingeniamc.com)

Quote1: "Motor inductance, or more appropriately electrical time constant value affect the servo drives in many ways. While high inductance values may limit the system bandwidth, low inductance values can lead to control loop instabilities, inaccuracies in current readings, increased power losses and other problems. These issues are especially critical in high speed brushed motors with very low friction and fast dynamics.The problem is more notorious with brushed DC motors"

Since The current ripple can be expressed as :


Quote 2: "At low loads, positive motor currents can be read as negative due to current ripple. This leads to unstable current loops that become uncontrollable!"