When off-the-shelf servoamps more than meet project needs, custom-designed amps might still be the better choice.
Form, fit, and function
Custom servoamplifiers were usually used in areas requiring specific form, fit, and function. Today, limiting costs by removing unwanted or unnecessary features plays a bigger role in determining the choice of amplifier.
Form: The packaging and dimensions Fit: The fit of how the product fits into the overall machine system. A prime example is communications: Does the product have communications capabilities that enable it to merge easily into the system?
Function: What activity the product performs. Some examples are the control structures employed in the product, or the protection and diagnostic functions offered.