Complex sentence: The motor, mounted separately and tethered to a spring, was allowed limited rotation about its own axis; because the load varied with groove modulations, the increases in drag would thus be dampened by the spring-loaded motor, and the platter acceleration mitigated.
Split into simpler sentences: The motor, mounted separately and tethered to a spring, would be allowed limited rotation about its own axis. And as the load varied with groove modulations, the increases in drag would thus be damped by the spring-loaded motor, and platter acceleration mitigated.