To have a variable speed on the output shaft of a pair of gears,
you can use a pair of elliptical gears.
The graphic representation of the movement of this variation is a sine wave.
If the sine wave does not satisfy the operational requirement, you can vary the profiles of the pitch diameters of the two gears, resulting in many varied and non-regular forms, e.g. triangular, hexagonal, etc.
Of course the two pitch forms must match perfectly in order to transmit a regular motion.
If you have any questions, please do not hesitate to contact us.