I'm only familiar with a gas powered generator that I use at home when the power is out. But I'm designing a contraption that will be able to spin a generator with considerable torque. But the RPM will not be consistent. I can limit the upper end but it will often be below max RPM. Am I correct in assuming that lower RPM will affect the 60 Hz frequency generation? If so, are there ways to maintain 60 Hz with a varying input RPM?